3236 PART 12 Endocrinology and Metabolism

hepatic transaminase levels, aminoaciduria, and hemolytic anemia.

Incorporation of radiolabeled 64Cu into serum ceruloplasmin, measured as the appearance of copper in the serum after an oral load, is a

highly specific diagnostic test; patients with Wilson’s disease incorporate very little 64Cu into ceruloplasmin.

Increased urinary excretion of copper (>100 μg/24 h) is an easily performed and important diagnostic test for Wilson’s disease.

Acid-washed (copper-free) collection containers should be used.

The penicillamine challenge is a variation using serial urine copper

measurements in which 500 mg of penicillamine are administered

orally after collecting a baseline 24-h urine. The penicillamine dose is

repeated after 12 h, the midpoint of the second 24-h urine collection.

A severalfold increase in copper excretion in the second collection is

suggestive of the diagnosis.

Although invasive, percutaneous needle liver biopsy for measurement of hepatic copper remains a gold standard technique for Wilson’s

disease diagnosis. Hepatic copper values >200 μg per gram of dry

weight (normal 20–50 μg) are characteristic of Wilson’s disease. Inductively coupled plasma mass spectrometry and atomic absorption spectrometry are preferred quantitative methods; histochemical staining

for copper in liver biopsy specimens is unreliable.

■ MOLECULAR

Wilson’s disease is caused by loss-of-function variants in ATP7B.

Despite similar genomic structures, large deletions are much less

common in ATP7B than in ATP7A, the closely related X-linked gene

responsible for Menkes disease. Several ATP7B missense variants are

common (H1069Q, M645R, and R778L), with various allelic frequencies reflecting geographic, racial, and/or ethnic differences. Major

ATP7B databases list >650 pathogenic or likely pathogenic variants.

Population-based and genomic-based estimates of prevalence range

from 1 in 7000 to 1 in 30,000, with genome-based ascertainments supporting the higher prevalence. This disparity may reflect incomplete

penetrance, although there is little doubt that some affected individuals

unfortunately escape medical attention.

DIAGNOSIS

The formal diagnosis of Wilson’s disease relies on a combination of

clinical, biochemical, and molecular features (Table 415-1). A scoring

system (Leipzig) that weights and collates various signs and symptoms

was produced by an international expert group in 2001 and remains a

valuable guide to diagnosis endorsed by the European Association for

the Study of the Liver (EASL).

TREATMENT

Wilson’s Disease

COPPER CHELATION

The era of successful treatment of Wilson’s disease began with

the use of British anti-lewisite (BAL) by a defined regimen of

intramuscular injections. An orally administered alternative was

d-penicillamine (Cuprimine), a free thiol that binds copper. This

chelating drug does not formally correct the basic defect of impaired

copper excretion in the bile. However, it greatly enhances urinary

excretion of copper and thereby corrects and prevents copper overload and its effects. Pyridoxine (vitamin B6

) is usually prescribed

concomitantly to counter the tendency for deficiency of this vitamin to develop during chronic penicillamine administration.

Certain individuals are intolerant of penicillamine, however,

encountering significant side effects that include nephrotoxicity,

hematologic abnormalities, and a distinctive rash, elastosis perforans

serpiginosa (usually involving the neck and axillae). Furthermore, in

some Wilson’s disease patients with neurologic presentations, penicillamine treatment induces paradoxical worsening of neurologic

status. Triethylenetetramine dihydrochloride (trientine hydrochloride [Syprine]) is a suitable alternative chelating agent with a somewhat less extensive side effect profile.

Tetrathiomolybdate (TM) is another molecule in the Wilson’s

disease therapeutic armamentarium. TM forms stable tripartite

FIGURE 415-1 Kayser-Fleischer ring in Wilson’s disease, representing copper

deposition in Descemet membrane of the cornea. (Image courtesy of Tjaard U.

Hoogenraad MD, PhD, Department of Neurology, University Medical Centre Utrecht,

Utrecht, The Netherlands.)

disorder. The neurologic signs and symptoms reflect the predilection

for basal ganglia (e.g., caudate, putamen) involvement in the brains of

affected persons. Parkinson disease or other movement disorders may

be mistakenly diagnosed.

Psychiatric Presentation In psychiatric presentations, changes

in personality (irritability, anger, poor self-control), depression, and

anxiety are common symptoms. Typically, patients presenting in this

fashion are in their late teens or early twenties, a period during which

substance abuse is also a diagnostic consideration. Wilson’s disease

should be formally excluded in all teenagers and young adults with

new-onset psychiatric signs.

Ocular Manifestations The eye is a primary site of copper

deposition in Wilson’s disease, producing a pathognomonic sign, the

Kayser-Fleischer ring (Fig. 415-1), a golden to greenish-brown band in

the peripheral cornea. This important diagnostic sign first appears as a

superior crescent and then develops inferiorly and ultimately becomes

circumferential. Slit-lamp or optical coherent tomography examinations are required to detect rings in their early stage of formation.

Copper can also accumulate in the lens and produce “sunflower” cataracts. Approximately 95% of Wilson’s disease patients with neurologic

signs manifest the Kayser-Fleischer ring compared to ~65% of those

with hepatic presentations. Copper chelation therapy causes fading and

eventual disappearance of corneal copper.

Other Clinical Manifestations Secondary endocrine effects of

Wilson-associated liver disease may include delayed puberty or amenorrhea. Renal tubular dysfunction in Wilson’s disease leads to abnormal

losses of amino acids, electrolytes, calcium, phosphorus, and glucose.

Presumably, this effect is related to copper toxicity. High copper levels

have been noted previously in the kidneys of patients with Wilson’s

disease. Treatment with copper chelation often improves the renal disturbances. There can also be skeletal effects of Wilson’s disease, including

osteoporosis and rickets, and these may be attributable to renal losses of

calcium and phosphorus. Osteoarthritis primarily affecting the knees and

wrists may involve excess copper deposition in the bone and cartilage.

Hemolytic anemia due to the direct toxic effects of copper on red

blood cell membranes is usually associated with release of massive

quantities of hepatic copper into the circulation, a phenomenon that

can be sudden and catastrophic.

■ BIOCHEMICAL

Laboratory findings that support the diagnosis of Wilson’s disease

include low levels of serum copper and serum ceruloplasmin, elevated

3237The Porphyrias CHAPTER 416

TABLE 415-1 Main Diagnostic Features of Wilson’s Disease

CLINICAL SIGNS/SYMPTOMS

BIOCHEMICAL/

LABORATORY

FINDINGS MOLECULAR FINDINGS

Hepatic:

Jaundice

Anorexia

Vomiting

Ascites and/or edema

Splenomegaly

Neurologic:

Dysarthria

 Facial grimace (risus

sardonicus)

Drooling

Dysphagia

Dysgraphia

Dystonia

Tremor (“wing beating”)

Ataxia

Seizures (rare)

Ocular:

Kayser-Fleischer ring

Sunflower cataract (rare)

Psychiatric:

Decline in school

Personality change

Mood disorder

Schizophrenia

Low serum copper

Low serum

ceruloplasmin

Increased urinary

copper excretion

Elevated liver

enzymes

Hypoalbuminemia

Increased liver

copper level

Fatty liver

Cirrhotic liver

Hemolytic anemia

Renal Fanconi

syndrome

Variants in ATP7B on

both chromosomes

Variants or

polymorphisms in other

genes (CAT, SOD2,

MTHFR) may influence

clinical expression of

Wilson’s disease in some

individuals

complexes among albumin, copper, and itself. This drug functions

both to decrease copper absorption and to reduce circulating free

copper. It is fast acting and can restore normal copper balance

within several weeks compared to the several months required

with other copper chelators or with zinc. This drug is the subject of

recent clinical trials and may one day be an approved treatment for

advanced breast cancer as well as Wilson’s disease.

Copper Chelation Treatment During Pregnancy Spontaneous miscarriage is increased in women with untreated Wilson’s disease.

From a benefit/risk perspective, it is important to maintain copper

chelation treatment during pregnancy to prevent hepatic or neurologic relapse, as well as to lower risk of pregnancy loss. Some

academic centers favor copper chelator dose reduction during

pregnancy, although if zinc monotherapy (see below) is in place

at the time of conception, evidence suggests it is safe to maintain

the usual daily dose. Since all anticopper medications enter breast

milk, breast-feeding is not recommended for mothers with Wilson’s

disease.

REDUCTION OF COPPER ABSORPTION

Zinc acetate (Galzin) has proven highly effective for treatment

of Wilson’s disease. The mechanism involves induction of metallothionein synthesis in intestinal epithelial cells; increased metallothionein synthesis results in greater binding of dietary copper

and thus decreased absorption. Zinc therapy has particular value in

(1) young, presymptomatic patients; (2) patients who are pregnant,

given the possible fetal teratogenic effects of other compounds;

and (3) as maintenance therapy for patients after their initial

“de-coppering” is accomplished. Zinc acetate has minimal side

effects. The only drawback to its use is the relatively long time

(4–6 months) needed for restoration of proper copper balance

when used as monotherapy in the initial stages of treatment.

LIVER TRANSPLANTATION

Liver transplantation is a consideration for Wilson’s disease in

advanced stages and/or when the condition is unresponsive to

medical therapy. This is generally necessary only in cases where

delayed diagnosis or poor compliance results in irreversible hepatic

damage. A recently proposed alternative for this circumstance is

methanobactin, a bacterial peptide that binds copper avidly and

dramatically improves mitochondrial copper overload and restores

normal mitochondrial morphology in a preclinical (rat) model.

GENE THERAPY

In a different preclinical (mouse) model of Wilson, proof of principle that adeno-associated virus-mediated ATP7B addition to hepatocytes can be effective was recently demonstrated. Transduction

of only 20% of hepatocytes was sufficient to normalize copper

homeostasis in the animal model. These results potentially pave the

way for clinical trials of gene therapy in Wilson’s disease patients.

FUTURE OUTLOOK

Wilson’s disease is arguably one of the best-characterized human

inborn errors of metabolism from combined clinical, biochemical,

and molecular perspectives, related to the detailed attention devoted

to this condition. As noted, novel copper chelators are still being evaluated, and generic formulations of established drugs are contributing

to increased affordability for patients and their families. Viral gene

therapy to provide working versions of ATP7B to the liver, kidney, and

brain or that delivers gene-editing molecules to correct specific mutant

alleles is now an emerging prospect. In addition, advances in newborn

screening technology may eventually enable wider population-based

screening for Wilson’s disease, which could help address lingering

questions about clinical penetrance. Such future progress in newborn

screening would also avert the tragedy that missed diagnoses of this

eminently treatable disorder of copper transport represent.

■ FURTHER READING

Bandmann O et al: Wilson’s disease and other neurological copper

disorders. Lancet Neurol 14:103, 2015.

European Association for Study of Liver: EASL Clinical Practice

Guidelines: Wilson’s disease. J Hepatol 56:671, 2012.

Gao J et al: The global prevalence of Wilson disease from nextgeneration sequencing data. Genet Med 21:1155, 2019.

Kumar M et al: WilsonGen: A comprehensive clinically annotated

genomic variant resource for Wilson’s disease. Sci Rep 10:9037, 2020.

Murillo O et al: Liver expression of a MiniATP7B gene results in

long-term restoration of copper homeostasis in a Wilson disease

model in mice. Hepatology 70:108, 2019.

Sandahl TD et al: The prevalence of Wilson’s disease: An update.

Hepatology 71:722, 2020.

Wallace DF, Dooley JS: ATP7B variant penetrance explains differences between genetic and clinical prevalence estimates for Wilson

disease. Hum Genet 139:1065, 2020.

THE PORPHYRIAS: INTRODUCTION

The porphyrias are metabolic disorders, each resulting from the

deficiency or increased activity of a specific enzyme in the heme

biosynthetic pathway (Fig. 416-1 and Table 416-1). These enzyme

disorders are inherited as autosomal dominant, autosomal recessive, or

X-linked traits, with the exception of porphyria cutanea tarda (PCT),

which is usually sporadic (Table 416-1). The porphyrias are classified

as either hepatic or erythropoietic, depending on the primary site of

416 The Porphyrias

Robert J. Desnick, Manisha Balwani

3238 PART 12 Endocrinology and Metabolism

Non-enzymatic

HEME

Coproporphyrinogen III

Uroporphyrinogen III Uroporphyrinogen I — Uroporphyrin I

Coproporphyrinogen I — Coproporphyrin I

Hydroxymethylbilane

Porphobilinogen

Succinyl CoA Glycine

δ-Aminolevulinic acid

Protoporphyrinogen IX

Protoporphyrin IX

ALA-synthase

ALA-dehydratase

Hydroxymethylbilane synthase

Uroporphyrinogen III synthase

Uroporphyrinogen decarboxylase

Coproporphyrinogen oxidase

Protoporphyrinogen oxidase

Ferrochelatase

X-linked protoporphyria (XLP)

X-linked sideroblastic anemia (XSLA)

ALA-dehydratase

Deficiency porphyria (ADP)

Acute intermittent porphyria

(AIP)

Congenital erythropoietic

porphyria (CEP)

Porphyria cutanea tarda (PCT)

Hepatoerythropoietic porphyria

(HEP)

Hereditary coproporphyria

(HCP)

Variegate porphyria (VP)

Erythropoietic protoporphyria

(EPP)

Negative feedback

Negative feedback

FIGURE 416-1 The human heme biosynthetic pathway indicating in linked boxes the enzyme that, when deficient or overexpressed, causes the respective porphyria.

Hepatic porphyrias are shown in yellow boxes and erythropoietic porphyrias in pink boxes.

TABLE 416-1 Human Porphyrias: Major Clinical and Laboratory Features

PORPHYRIA

DEFICIENT

ENZYME INHERITANCE

PRINCIPAL

SYMPTOMS:

NV OR CP+

ENZYME ACTIVITY

% OF NORMAL

INCREASED PORPHYRIN PRECURSORS AND/OR PORPHYRINS

ERYTHROCYTES URINE STOOL

Hepatic Porphyrias

5-ALAdehydratasedeficient porphyria

(ADP)

ALA-dehydratase AR NV ~5 Zn-protoporphyrin ALA,

coproporphyrin III

—

Acute intermittent

porphyria (AIP)

HMB-synthase AD NV ~50 — ALA, PBG,

uroporphyrin

—

Porphyria cutanea

tarda (PCT)

UROdecarboxylase

AD CP ~20 — Uroporphyrin,

7-carboxylate

porphyrin

Isocoproporphyrin

Hereditary

coproporphyria

(HCP)

COPRO-oxidase AD NV and CP ~50 — ALA, PBG,

coproporphyrin III

Coproporphyrin III

Variegate

porphyria (VP)

PROTO-oxidase AD NV and CP ~50 — ALA, PBG,

coproporphyrin III

Coproporphyrin III,

protoporphyrin

Erythropoietic Porphyrias

Congenital

erythropoietic

porphyria (CEP)

URO-synthase AR CP 1–5 Uroporphyrin I

Coproporphyrin I

Uroporphyrin Ia

Coproporphyrin Ia

Coproporphyrin I

Erythropoietic

protoporphyria

(EPP)

Ferrochelatase AR CP ~20–30 Protoporphyrin — Protoporphyrin

X-linked

protoporphyria

(XLP)

ALA-synthase 2 XL CP >100b Protoporphyrin — Protoporphyrin

a

Type I isomers. b

Increased activity due to gain-of-function mutations in ALAS2 exon 11.

Abbreviations: AD, autosomal dominant; ALA, 5-aminolevulinic acid; AR, autosomal recessive; COPRO, coproporphyrin; CP, cutaneous photosensitivity; NV, neurovisceral;

PBG, porphobilinogen; PROTO, protoporphyrin; URO, uroporphyrin; XL, X-linked.

3239The Porphyrias CHAPTER 416

overproduction and accumulation of their respective porphyrin precursors or porphyrins (Tables 416-1 and 416-2), although some have

overlapping features. For example, PCT, the most common porphyria,

is hepatic and presents with blistering cutaneous photosensitivity,

which is typically characteristic of the erythropoietic porphyrias.

The major manifestations of the acute hepatic porphyrias are

neurologic, including neuropathic abdominal pain, peripheral motor

neuropathy, and mental disturbances, with attacks often precipitated

by dieting, certain porphyrinogenic drugs, and hormonal changes.

While hepatic porphyrias are symptomatic primarily in adults, rare

homozygous variants of the autosomal dominant hepatic porphyrias

usually manifest clinically prior to puberty. In contrast, the erythropoietic porphyrias usually present at birth or in early childhood with

cutaneous photosensitivity or, in the case of congenital erythropoietic

porphyria (CEP), even in utero as nonimmune hydrops fetalis. Cutaneous sensitivity to sunlight results from excitation of excess porphyrins

in the skin by long-wave ultraviolet light, leading to cell damage, scarring, and disfigurement. Thus, the porphyrias are metabolic disorders

in which environmental, physiologic, and genetic factors interact to

cause disease.

Because many symptoms of the porphyrias are nonspecific, diagnosis is often delayed. Laboratory measurement of porphyrin precursors

(5′-aminolevulinic acid [ALA] and porphobilinogen [PBG]) in the

urine or porphyrins in the urine, plasma, erythrocytes, or feces is

required to confirm or exclude the various types of porphyria (see

below). However, a definite diagnosis requires demonstration of the

specific gene defect (Table 416-3). The genes encoding all the heme

biosynthetic enzymes have been characterized, permitting identification of the mutations causing each porphyria (Table 416-2). Molecular

genetic analyses now make it possible to provide precise heterozygote

or homozygote identification and prenatal diagnoses in families with

known mutations.

In addition to recent reviews of the porphyrias, informative and

up-to-date websites are sponsored by the American Porphyria Foundation (www.porphyriafoundation.com) and the European Porphyria

Network (https://porphyria.eu/). An extensive list of unsafe and safe

drugs for individuals with acute porphyrias is provided at the Drug

Database for Acute Porphyrias (www.drugs-porphyria.org).

GLOBAL CONSIDERATIONS

The porphyrias are panethnic metabolic diseases that affect individuals

around the globe. The acute hepatic porphyrias—acute intermittent

porphyria (AIP), hereditary coproporphyria (HCP), and variegate

porphyria (VP)—are autosomal dominant disorders. The frequency

of symptomatic AIP, the most common acute hepatic porphyria, is ~1

in 20,000 among Caucasian individuals of Western European ancestry,

and it is particularly frequent in Scandinavians, with a frequency of ~1

in 10,000 in Sweden. However, recent studies using genomic/exomic

databases showed an estimated frequency of pathogenic variants in the

HMBS gene as ~1 in 1700. Thus, the penetrance of AIP, and likely the

other acute hepatic porphyrias, is low, with ~1% of those with pathogenic mutations experiencing acute attacks (see below).

VP is particularly frequent in South Africa, where its high prevalence (>10,000 affected patients) is in part due to a genetic “founder

effect.” The autosomal recessive acute hepatic porphyria, ALA-dehydratase-deficient porphyria (ADP), is very rare, and <20 patients have

been reported worldwide.

The erythropoietic porphyrias—CEP, erythropoietic protoporphyria (EPP), and X-linked protoporphyria (XLP)—also are panethnic.

EPP is the most common porphyria in children, whereas CEP is very

rare, with ~200 reported cases worldwide. The frequency of EPP varies globally because most patients have the common low expression

ferrochelatase (FECH) mutation that varies in frequency in different

populations. The allele rarely occurs in Africans, is present in ~10%

of whites, and is frequent (~30%) in the Japanese. The reported prevalence of EPP in the Caucasian population ranges from 1 in ~75,000

to 1 in ~150,000.

The autosomal recessive porphyrias—ADP, CEP, and hepatoerythropoietic porphyria (HEP)—are more frequent in regions with high

rates of consanguineous unions. PCT, which is typically sporadic,

occurs more frequently in countries in which its predisposing risk

factors such as hepatitis C and HIV are more prevalent.

■ HEME BIOSYNTHESIS

Heme biosynthesis involves eight enzymatic steps in the conversion

of glycine and succinyl-CoA to heme (Fig. 416-2 and Table 416-2).

These eight enzymes are encoded by nine genes, as the first enzyme in

TABLE 416-2 Human HEME Biosynthetic Enzymes and Genes

ENZYME

GENE

SYMBOL

CHROMOSOMAL

LOCATION

cDNA

(bp)

GENE PROTEIN

(aa)

SUBCELLULAR

LOCATION

KNOWN

MUTATIONSb

THREE-DIMENSIONAL

STRUCTUREc SIZE (KB) EXONSa

ALA-synthase

Housekeeping ALAS1 3p21.1 2199 17 11 640 M —

Erythroid-specific ALAS2 Xp11.2 1937 22 11 587 M >30 —

ALA-dehydratase

Housekeeping ALAD 9q32 1149 15.9 12 (1A + 2 – 12) 330 C 12 Y

Erythroid-specific ALAD 9q32 1154 15.9 12 (1B + 2 – 12) 330 C —

HMB-synthase

Housekeeping HMBS 11q23.3 1086 11 15 (1 + 3 – 15) 361 C 400 E

Erythroid-specific HMBS 11q23.3 1035 11 15 (2 – 15) 344 C 10

URO-synthase

Housekeeping UROS 10q26.2 1296 34 10 (1 + 2B – 10) 265 C 45 H

Erythroid-specific UROS 10q26.2 1216 34 10 (2A + 2B – 10) 265 C 4

URO-decarboxylase UROD 1p34.1 1104 3 10 367 C 122 H

COPRO-oxidase CPOX 3q12.1 1062 14 7 354 M 70 H

PROTO-oxidase PPOX 1q23.3 1431 5.5 13 477 M 181 —

Ferrochelatase FECH 18q21.31 1269 45 11 423 M 192 B

a

Number of exons and those encoding separate housekeeping and erythroid-specific forms indicated in parentheses. b

Number of known mutations from the Human Gene

Mutation Database (www.hgmd.org). c

Crystallized from human (H), murine (M), Escherichia coli (E), Bacillus subtilis (B), or yeast (Y) purified enzyme; references in Protein

Data Bank (www.rcsb.org).

Abbreviations: ALA, 5-aminolevulinic acid; C, cytoplasm; COPRO, coproporphyrin; HMB, hydroxymethylbilane; M, mitochondria; PROTO, protoporphyrin; URO, uroporphyrin.

Source: Reproduced with permission from KE Anderson et al: Disorders of heme biosynthesis: X-linked sideroblastic anemia and the porphyrias, in Scriver CR: The

Metabolic and Molecular Bases of Inherited Diseases. New York, NY: McGraw-Hill; 2001.

3240 PART 12 Endocrinology and Metabolism

the pathway, ALA-synthase, has two genes that encode unique housekeeping (ALAS1) and erythroid-specific (ALAS2) isozymes. The first

and last three enzymes in the pathway are located in the mitochondria, whereas the other four are in the cytosol. Heme is required for a

variety of hemoproteins such as hemoglobin, myoglobin, respiratory

cytochromes, and the cytochrome P450 (CYP) enzymes. Hemoglobin

synthesis in erythroid precursor cells accounts for ~85% of daily heme

synthesis in humans. Hepatocytes account for most of the rest, primarily for the synthesis of CYPs, which are especially abundant in the liver

endoplasmic reticulum, and turn over more rapidly than many other

hemoproteins, such as the mitochondrial respiratory cytochromes. As

shown in Fig. 416-2, the pathway intermediates are the porphyrin precursors, ALA and PBG, and porphyrins (mostly in their reduced forms,

known as porphyrinogens). At least in humans, these intermediates do

not accumulate in significant amounts under normal conditions or

have important physiologic functions.

The first enzyme, ALA-synthase, catalyzes the condensation of

glycine, activated by pyridoxal phosphate and succinyl-coenzyme A,

to form ALA. In the liver, this rate-limiting enzyme can be induced

by a variety of drugs, steroids, and other chemicals. Distinct nonerythroid (e.g., housekeeping) and erythroid-specific forms of ALA-synthase are encoded by separate genes located on chromosome 3p21.1

(ALAS1) and Xp11.2 (ALAS2), respectively. Defects in the erythroid

gene ALAS2 that decrease its activity cause an X-linked sideroblastic

anemia (XLSA). Gain-of-function mutations in the last exon (11) of

ALAS2 that increase its activity cause an X-linked form of EPP, known

as XLP.

The second enzyme, ALA-dehydratase, catalyzes the condensation

of two molecules of ALA to form PBG. Hydroxymethylbilane synthase

(HMB-synthase; also known as PBG-deaminase) catalyzes the headto-tail condensation of four PBG molecules by a series of deaminations

to form the linear tetrapyrrole, HMB. Uroporphyrinogen III synthase

(URO-synthase) catalyzes the rearrangement and rapid cyclization of

HMB to form the asymmetric, physiologic, octacarboxylate porphyrinogen, uroporphyrinogen (URO’gen) III.

The fifth enzyme in the pathway, uroporphyrinogen decarboxylase

(URO-decarboxylase), catalyzes the sequential removal of the four carboxyl groups from the acetic acid side chains of URO’gen III to form

coproporphyrinogen (COPRO’gen) III, a tetracarboxylate porphyrinogen. This compound then enters the mitochondrion via a specific

transporter, where COPRO-oxidase, the sixth enzyme, catalyzes the

decarboxylation of two of the four propionic acid groups to form the

two vinyl groups of protoporphyrinogen (PROTO’gen) IX, a decarboxylate porphyrinogen. Next, PROTO-oxidase oxidizes PROTO’gen

to protoporphyrin IX by the removal of six hydrogen atoms. The

product of the reaction is a porphyrin (oxidized form), in contrast to

the preceding tetrapyrrole intermediates, which are porphyrinogens

(reduced forms). Finally, ferrous iron is inserted into protoporphyrin

IX to form heme, a reaction catalyzed by the eighth enzyme in the pathway, FECH (also known as heme synthase or protoheme ferrolyase).

TABLE 416-3 Diagnosis of Acute and Cutaneous Porphyrias

SYMPTOMS

FIRST-LINE TEST:

ABNORMALITY

POSSIBLE

PORPHYRIA

SECOND-LINE TESTING IF FIRST-LINE TESTING IS POSITIVE:

TO INCLUDE: URINE (U), PLASMA (P), AND FECAL (F)

PORPHYRINS; FOR ACUTE PORPHYRIAS, ADD RED BLOOD

CELL (RBC) HMB-SYNTHASE; FOR BLISTERING SKIN LESIONS,

ADD P AND RBC PORPHYRINS

CONFIRMATORY TEST: ENZYME ASSAY

AND/OR MUTATION ANALYSIS

Neurovisceral Spot U: ↑↑ALA and

normal PBG

ADP U porphyrins: ↑↑, mostly COPRO III

P & F porphyrins: normal or slightly ↑

RBC HMB-synthase: normal

Rule out other causes of elevated ALA;

↓↓RBC ALA-dehydratase activity (<10%);

ALA-dehydratase mutation analysis

Spot U: ↑↑PBG AIP U porphyrins: ↑↑, mostly URO and COPRO

P & F porphyrins: normal or slightly ↑

RBC HMB-synthase: usually ↓

HMB-synthase mutation analysis

“ HCP U porphyrins: ↑↑, mostly COPRO III

P porphyrins: normal or slightly ↑(↑ if skin lesions present)

F porphyrins: ↑↑, mostly COPRO III

Measure RBC HMB-synthase: normal

activity

COPRO-oxidase mutation analysis

“ VP U porphyrins: ↑↑, mostly COPRO III

P porphyrins: ↑↑(characteristic fluorescence peak at neutral

pH)

F porphyrins: ↑↑, mostly COPRO and PROTO

Measure RBC HMB-synthase: normal

activity

PROTO-oxidase mutation analysis

Blistering skin

lesions

P: ↑ porphyrins PCT and HEP U porphyrins: ↑↑, mostly URO and heptacarboxylate porphyrin

P porphyrins: ↑↑

F porphyrins: ↑↑, including increased isocoproporphyrin

RBC porphyrins: ↑↑ zinc PROTO in HEPa

RBC URO-decarboxylase activity: halfnormal in familial PCT (~20% of all PCT

cases); substantially deficient in HEP

URO-decarboxylase mutation analysis:

mutation(s) present in familial PCT

(heterozygous) and HEP (homozygous)

“ HCP and VP See HCP and VP above. Also, U ALA and PBG: may be ↑

“ CEP RBC and U porphyrins: ↑↑, mostly URO I and COPRO I

F porphyrins: ↑↑; mostly COPRO I

↓↓ RBC URO-synthase activity (<15%)

URO-synthase mutation analysis

Nonblistering

photosensitivity

P: porphyrins usually ↑ EPP RBC porphyrins: ↓↓, mostly free PROTO

U porphyrins: normal

F porphyrins: normal or ↓, mostly PROTO

FECH mutation analysis

P: porphyrins usually ↑ XLP RBC porphyrins: ↑↑, approximately equal free and zinc PROTO

U porphyrins: normal

F porphyrins: normal or ↑, mostly PROTO

ALAS2 mutation analysis

a

Nonspecific increases in zinc protoporphyrins are common in other porphyrias.

Abbreviations: ADP, 5-ALA-dehydratase-deficient porphyria; AIP, acute intermittent porphyria; ALA, 5-aminolevulinic acid; CEP, congenital erythropoietic porphyria; COPRO

I, coproporphyrin I; COPRO III, coproporphyrin III; EPP, erythropoietic protoporphyria; F, fecal; HCP, hereditary coporphyria; HEP, hepatoerythropoietic porphyria; ISOCOPRO,

isocoproporphyrin; P, plasma; PBG, porphobilinogen; PCT, porphyria cutanea tarda; PROTO, protoporphyrin IX; RBC, erythrocytes; U, urine; URO I, uroporphyrin I; URO III,

uroporphyrin III; VP, variegate porphyria; XLP, X-linked protoporphyria.

Source: Data from KE Anderson et al: Recommendations for the diagnosis and treatment of the acute porphyrias. Ann Intern Med 142:439, 2005.

3241The Porphyrias CHAPTER 416

■ REGULATION OF HEME BIOSYNTHESIS

Regulation of heme synthesis differs in the two major heme-forming

tissues, the liver and erythron. In the liver, the concentration of “free”

heme regulates the synthesis and mitochondrial translocation of the

housekeeping form of ALA-synthase 1. Heme represses the synthesis

of the ALA-synthase 1 messenger RNA (mRNA) and interferes with

the transport of the enzyme from the cytosol into mitochondria.

Hepatic ALA-synthase 1 is increased by many of the same chemicals

that induce the CYP enzymes in the endoplasmic reticulum of the

liver. Because most of the heme in the liver is used for the synthesis of

CYP enzymes, hepatic ALA-synthase 1 and the CYPs are regulated in

a coordinated fashion, and many drugs that induce hepatic ALA-synthase 1 also induce CYP gene expression. The other hepatic heme

biosynthetic enzymes are presumably expressed at constant levels,

although their relative activities and kinetic properties differ. For

example, normal individuals have high activities of ALA-dehydratase

but low activities of HMB-synthase, the latter being the second

rate-limiting step in the pathway.

In the erythron, novel regulatory mechanisms allow for the production of the very large amounts of heme needed for hemoglobin synthesis.

The response to stimuli for hemoglobin synthesis occurs during cell

differentiation, leading to an increase in cell number. In contrast, the

erythroid-specific ALA-synthase 2 is expressed at higher levels than

the housekeeping enzyme, and erythroid-specific control mechanisms

regulate other pathway enzymes as well as iron transport into erythroid

cells. Separate erythroid-specific and nonerythroid or “housekeeping”

SUCCINYL COA

COO

CH

CH2

C

CoAS O ALA-synthase

B6 CoASH CO2

COO

CH2

CH2

C=O

H-C-NH

H

δ-Aminolevulinic acid

ALA-dehydratase

COO–

CH2

CH2

COO

CH2

H

H

NH2 — CH2 N

Porphobilinogen

HMBsythase 4NH3

Pr

Pr

Pr

Pr

Ac

Ac

Ac

Ac

H

Hydroxymethylbilane

H2O UROsynthase

Pr

Pr Pr

Pr Ac

Ac

Ac

Ac

N N

N N

H H

HH

Uroporphyrinogen III

UROdecarboxylase

4H

4CO2

N N

N N

H H

H H

Pr

Pr

Pr Pr

CH3

CH3

CH3

Protoporphyrinogen IX Coproporphyrinogen III

Pr Pr

Vi

CH Vi 3

CH3

CH

CH

COPRO-oxidase

2CO2 2H

PROTO-oxidase

Protoporphyrin IX

CH3

CH3

CH3

PrPr

CH

Vi

Vi

N N

NN

H

H

N N

N N

H H

H H

Ferrochelatase

Fe2+

2H

Heme

CH3

CH3

CH3

CH3

Pr Pr

Vi

Vi

N N

NN

Fe

Feedback

repression

Glycine

H

H-C-NH2

COO

6H

H2O

CH3

N N

NN

H

H

H

H

Mitochondria Cytoplasm

FIGURE 416-2 The heme biosynthetic pathway showing the eight enzymes and their substrates and products. Four of the enzymes are localized in the mitochondria and

four in the cytosol.

3242 PART 12 Endocrinology and Metabolism

transcripts are known for the first four enzymes in the pathway. As

noted above, housekeeping- and erythroid-specific ALA-synthases

are encoded by genes on different chromosomes, but for each of the

next three genes in the pathway, both erythroid and nonerythroid

transcripts are transcribed by alternative promoters from their single

respective genes (Table 416-2).

■ CLASSIFICATION OF THE PORPHYRIAS

As mentioned above, the porphyrias can be classified as either hepatic

or erythropoietic, depending on whether the heme biosynthetic intermediates that accumulate arise initially from the liver or developing

erythrocytes, or as acute or cutaneous, based on their clinical manifestations. Table 416-1 lists the porphyrias, their principal symptoms, and

major biochemical abnormalities. Three of the five hepatic porphyrias—

AIP, HCP, and VP—usually present during adult life with acute attacks

of neurologic manifestations and elevated levels of one or both of the

porphyrin precursors, ALA and PBG, and are thus classified as acute

hepatic porphyrias. Patients with ADP have presented in infancy and

adolescence and typically have elevated ALA with normal or slightly

elevated PBG levels. The fifth hepatic disorder, PCT, presents with

blistering skin lesions. HCP and VP also may have cutaneous manifestations similar to PCT.

The erythropoietic porphyrias—CEP, EPP, and XLP—are characterized by elevations of porphyrins in bone marrow and erythrocytes

and present with cutaneous photosensitivity. The skin lesions in CEP

resemble PCT but are usually much more severe, whereas EPP and

XLP cause a more immediate, severe, painful, and nonblistering type

of photosensitivity. EPP is the most common porphyria to cause

symptoms before puberty. About 20% of EPP patients develop minor

abnormalities of liver function, with up to ~5% developing hepatic

complications that can lead to liver failure requiring liver transplantation. XLP has a clinical presentation similar to EPP causing photosensitivity and liver disease.

■ DIAGNOSIS OF PORPHYRIA

A few specific and sensitive first-line laboratory tests should be

used whenever symptoms or signs suggest the diagnosis of porphyria

(Table 416-3). If a first-line test is significantly abnormal, more comprehensive testing should follow to establish the type of porphyria,

including the specific causative gene mutation.

Acute Hepatic Porphyrias An acute hepatic porphyria should

be suspected in patients with neurovisceral symptoms after puberty.

Symptoms include acute abdominal pain, nausea, vomiting, tachycardia, hypertension, and motor neuropathy. As these symptoms are

common, other causes should be ruled out. The diagnosis is made by

measuring urinary porphyrin precursors (ALA and PBG) in a spot

sample of urine (Fig. 416-2). Urinary PBG is always increased during

acute attacks of AIP, HCP, and VP and is not substantially increased

in any other medical condition. Therefore, this measurement is both

sensitive and specific. Results from spot (single-void) urine specimens

are highly informative because very substantial increases in PBG are

expected during acute attacks of porphyria. A 24-h collection is unnecessary. The same spot urine specimen should be saved for quantitative

determination of ALA, PBG, and creatinine, in order to confirm the

qualitative PBG result and also to detect patients with ADP. Urinary

porphyrins may remain increased longer than porphyrin precursors

in HCP and VP. Therefore, it is useful to measure total urinary porphyrins in the same sample, keeping in mind that urinary porphyrin

increases are often nonspecific. Measurement of urinary porphyrins

alone should be avoided for screening, because these may be increased

in disorders other than porphyrias, such as chronic liver disease, and

misdiagnoses of porphyria can result from minimal increases in urinary porphyrins that have no diagnostic significance. Measurement of

erythrocyte HMB-synthase is not useful as a first-line test. Moreover,

the enzyme activity is not decreased in all AIP patients, a borderline

low normal value is not diagnostic, and the enzyme is not deficient in

other acute porphyrias.

More extensive testing is justified when an initial test is positive.

A substantial increase in PBG may be due to AIP, HCP, or VP. These

acute porphyrias can be distinguished by measuring urinary porphyrins (using the same spot urine sample), fecal porphyrins, and plasma

porphyrins. Assays for COPRO-oxidase or PROTO-oxidase are not

available for clinical testing. More specifically, mutation analysis by

sequencing the genes encoding HMB-synthase, COPRO-oxidase,

and PROTO-oxidase will detect almost all disease-causing mutations

and is diagnostic even when the levels of urinary ALA and PBG have

returned to normal or near normal.

Cutaneous Porphyrias Blistering skin lesions due to porphyria

are virtually always accompanied by increases in total plasma porphyrins. A fluorometric method is preferred, because the plasma

porphyrins in VP are mostly covalently linked to plasma proteins and

may be less readily detected by high-performance liquid chromatography (HPLC). The normal range for plasma porphyrins is somewhat

increased in patients with end-stage renal disease.

Although a total plasma porphyrin determination will usually detect

EPP and XLP, an erythrocyte protoporphyrin determination is more

sensitive. Increases in erythrocyte protoporphyrin occur in many

other conditions. Therefore, the diagnosis of EPP must be confirmed

by showing a predominant increase in free protoporphyrin rather

than zinc protoporphyrin. In XLP, both free and zinc protoporphyrin

are markedly increased. Interpretation of laboratory reports can be

difficult, because the term free erythrocyte protoporphyrin sometimes

actually represents zinc protoporphyrin.

The various porphyrias that cause blistering skin lesions can be differentiated by measuring porphyrins in urine, feces, and plasma. The

porphyrias should be confirmed by genetic testing and the demonstration of the causative pathogenic variant. It is often difficult to diagnose

or “rule out” porphyria in patients who have had suggestive symptoms

months or years in the past and in relatives of patients with acute porphyrias, because porphyrin precursors and porphyrins may be normal.

In those situations, detection of the specific gene mutation in the index

case can make the diagnosis and facilitate the diagnosis and genetic

counseling of at-risk relatives. With the increased access and accuracy

of genetic testing, this often precedes secondary biochemical testing in

clinical practice. Consultation with a specialist laboratory and physician will assist in selecting the heme biosynthetic gene or genes to be

sequenced.

THE HEPATIC PORPHYRIAS

Markedly elevated plasma and urinary concentrations of the porphyrin

precursors, ALA and/or PBG, which originate from the liver, are especially evident during attacks of neurologic manifestations of the four

acute porphyrias—ADP, AIP, HCP, and VP. In PCT, excess porphyrins

also accumulate initially in the liver and cause chronic blistering of

sun-exposed areas of the skin.

■ ALA-DEHYDRATASE-DEFICIENT PORPHYRIA

ADP is a rare, autosomal recessive, acute hepatic porphyria caused by a

severe deficiency of ALA-dehydratase activity. To date, there are only a

few documented cases, some in children or young adults, in which specific gene mutations have been identified. These affected homozygotes

had <10% of normal ALA-dehydratase activity in erythrocytes, but

their clinically asymptomatic parents and heterozygous relatives had

about half-normal levels of activity and did not excrete increased levels

of ALA. The frequency of ADP is unknown, but the frequency of heterozygous individuals with <50% normal ALA-dehydratase activity was

~2% in a screening study in Sweden. Because there are multiple causes

for deficient ALA-dehydratase activity, it is important to confirm the

diagnosis of ADP by mutation analysis.

Clinical Features The clinical presentation depends on the

amount of residual ALA-dehydratase activity. Four of the documented

patients were male adolescents with symptoms resembling those of

AIP, including abdominal pain and neuropathy. One patient was an

infant with more severe disease, including failure to thrive beginning

at birth. The earlier age of onset and more severe manifestations in

this patient reflect a more significant deficiency of ALA-dehydratase

activity. Another patient developed an acute motor polyneuropathy

3243The Porphyrias CHAPTER 416

at age 63 that was associated with a myeloproliferative disorder. He

was heterozygous for an δ-aminolevulinic acid dehydratase (ALAD)

mutation that presumably was present in erythroblasts that underwent

clonal expansion due to the bone marrow malignancy.

Diagnosis All patients had significantly elevated levels of plasma

and urinary ALA and urinary coproporphyrin (COPRO) III; ALAD

activities in erythrocytes were <10% of normal. Hereditary tyrosinemia

type 1 (fumarylacetoacetase deficiency) and lead intoxication should

be considered in the differential diagnosis because either succinylacetone (which accumulates in hereditary tyrosinemia and is structurally

similar to ALA) or lead can inhibit ALA-dehydratase, increase urinary

excretion of ALA and COPRO III, and cause manifestations that

resemble those of the acute porphyrias. Heterozygotes are clinically

asymptomatic and do not excrete increased levels of ALA but can

be detected by demonstration of intermediate levels of erythrocyte

ALA-dehydratase activity or a specific mutation in the ALAD gene.

To date, molecular studies of ADP patients have identified 12 pathogenic mutations, including missense mutations, splice-site mutations,

and a two-base deletion in the ALAD gene (Human Gene Mutation

Database; www.hgmd.org). The parents in each case were not consanguineous, and the index cases had inherited a different ALAD mutation

from each parent. Prenatal diagnosis of this disorder is possible by

determination of ALA-dehydratase activity and/or gene mutations in

cultured chorionic villi or amniocytes.

Treatment The treatment of ADP acute attacks is similar to that of

AIP (see below). The severely affected infant referred to above was supported by hyperalimentation and periodic blood transfusions but did

not respond to intravenous hemin and died after liver transplantation.

■ ACUTE INTERMITTENT PORPHYRIA

This hepatic porphyria is an autosomal dominant condition resulting

from the half-normal level of HMB-synthase activity. The disease is

widespread but is especially common in Scandinavia and Great Britain.

Clinical expression is highly variable, and activation of the disease is

often related to environmental or hormonal factors, such as drugs, diet,

and steroid hormones. Attacks can be prevented by avoiding known

precipitating factors. Rare homozygous dominant AIP also has been

described in children (see below).

Clinical Features Induction and increased expression of the

rate-limiting hepatic gene ALAS1 in heterozygotes who have halfnormal HMB-synthase activity is thought to underlie the acute

attacks in AIP. The disorder remains latent (or asymptomatic) in the

great majority of those who are heterozygous for pathogenic HMBS

mutations, and this is almost always the case prior to puberty. In

patients with no history of acute symptoms, porphyrin precursor

excretion is usually normal, suggesting that half-normal hepatic

HMB-synthase activity is sufficient and that hepatic ALA-synthase

activity is not increased. However, under conditions where heme

synthesis is increased in the liver, half-normal HMB-synthase activity may become limiting, and ALA, PBG, and other heme pathway

intermediates may accumulate and be excreted in the urine. Common

precipitating factors include endogenous and exogenous steroids, porphyrinogenic drugs, alcohol ingestion, and low-calorie diets, usually

instituted for weight loss.

The fact that AIP is almost always latent before puberty suggests that

adult levels of steroid hormones are important for clinical expression.

Symptoms are more common in women, suggesting a role for estrogens

or progestins. Premenstrual attacks are probably due to increasing

endogenous progesterone during the luteal phase of the menstrual

cycle. Acute porphyrias are sometimes exacerbated by exogenous

steroids, including oral contraceptive preparations containing progestins. Surprisingly, pregnancy is usually well tolerated, suggesting that

beneficial metabolic changes may ameliorate the effects of high levels

of progesterone. Extensive lists of unsafe and safe drugs are available

on websites sponsored by the American Porphyria Foundation (www

.porphyriafoundation.com) and the European Porphyria Network

(https://porphyria.eu/), and at the Drug Database for Acute Porphyrias

website (www.drugs-porphyria.org). Reduced intake of calories and carbohydrate, as may occur with illness or attempts to lose weight, can also

increase porphyrin precursor excretion and induce attacks of porphyria. Studies in a knockout AIP mouse model indicate that the hepatic

ALAS1 gene is regulated, in part, by the peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α). Hepatic PGC-1α is induced

by fasting, which in turn activates ALAS1 transcription, resulting in

increased heme biosynthesis. This finding suggests an important link

between nutritional status and the attacks in acute porphyrias. Attacks

also can be provoked by infections, surgery, and ethanol.

Because the neurovisceral symptoms rarely occur before puberty

and are often nonspecific, a high index of suspicion is required to

make the diagnosis. The disease can be disabling but is rarely fatal.

Abdominal pain, the most common symptom, is poorly localized

but may be associated with cramping, ileus, abdominal distention,

and decreased bowel sounds. However, increased bowel sounds and

diarrhea may occur. Abdominal tenderness, fever, and leukocytosis

are usually absent or mild because the symptoms are neurologic

rather than inflammatory. Nausea; vomiting; constipation; tachycardia; hypertension; mental symptoms; pain in the limbs, head, neck, or

chest; muscle weakness; sensory loss; dysuria; and urinary retention

are characteristic. Tachycardia, hypertension, restlessness, tremors, and

excess sweating are due to sympathetic overactivity.

The peripheral neuropathy is due to axonal degeneration (rather

than demyelinization) and primarily affects motor neurons. Significant

neuropathy does not occur with all acute attacks; abdominal symptoms

are usually more prominent. Motor neuropathy affects the proximal

muscles initially, more often in the shoulders and arms. The course and

degree of involvement are variable and sometimes may be focal and

involve cranial nerves. Deep tendon reflexes initially may be normal or

hyperactive but become decreased or absent as the neuropathy advances.

Sensory changes such as paresthesia and loss of sensation are less prominent. Progression to respiratory and bulbar paralysis and death occurs

especially when the diagnosis and treatment are delayed. Sudden death

may result from sympathetic overactivity and cardiac arrhythmia.

Mental symptoms such as anxiety, insomnia, depression, disorientation, hallucinations, and paranoia can occur in acute attacks. Seizures

can be due to neurologic effects or to hyponatremia. Treatment of

seizures is difficult because most antiseizure drugs can exacerbate AIP

(clonazepam may be safer than phenytoin or barbiturates). Hyponatremia results from hypothalamic involvement and inappropriate vasopressin secretion or from electrolyte depletion due to vomiting, diarrhea,

poor intake, or excess renal sodium loss. When an attack resolves,

abdominal pain may disappear within hours, and paresis begins to

improve within days and may continue to improve over several years.

Homozygous dominant AIP (HD-AIP) is a rare form of AIP in

which patients inherit HMBS mutations from each of their heterozygous parents and, therefore, have very low (<2%) enzyme activity. The

disease has been described in a Dutch girl, two young British siblings,

and a Spanish boy. In these homozygous affected patients, the disease

presented in infancy with failure to thrive, developmental delay, bilateral cataracts, and/or hepatosplenomegaly. Urinary ALA and PBG

concentrations were markedly elevated. All of these patients’ HMBS

mutations (R167W, R167Q, and R172Q) were in exon 10 within five

bases of each other. Studies of the brain magnetic resonance images

(MRIs) of children with homozygous AIP have suggested damage

primarily in white matter that was myelinated postnatally, while

tracks that myelinated prenatally were normal. Most children with

homozygous AIP die at an early age. Recently, later-onset HD-AIP was

described in an adult with leukoencephalopathy.

Diagnosis ALA and PBG levels are substantially increased in

plasma and urine, especially during acute attacks. For example, urinary PBG excretion during an attack is usually 50–200 mg/24 h (220–

880 μmol/24 h) (normal, 0–4 mg/24 h, [0–18 μmol/24 h]), and urinary ALA excretion is 20–100 mg/24 h (150–760 μmol/24 h) (normal,

1–7 mg/24 h [8–53 μmol/24 h]). Because levels often remain high

after symptoms resolve, the diagnosis of an acute attack in a patient

with biochemically proven AIP is based primarily on clinical features.

3244 PART 12 Endocrinology and Metabolism

Excretion of ALA and PBG decreases over a few days after intravenous hemin administration or treatment with givosiran (see below).

A normal urinary PBG level before hemin effectively excludes AIP as

a cause for current symptoms. Fecal porphyrins are usually normal

or minimally increased in AIP, in contrast to HCP and VP. Most AIP

heterozygotes with no history of symptoms have normal urinary excretion of ALA and PBG and are classified as latent. Patients can also have

high levels of urine PBG and ALA with no clinical symptoms. These

patients may have a previous history of an acute attack. These patients

are classified as asymptomatic high excretors (ASHE) or chronic high

excretors (CHE). Therefore, the detection of the family’s HMBS mutation will diagnose asymptomatic family members. A urinary ALA and

PBG will diagnosis CHE patients who may have a higher risk of an

attack if they experience a precipitating factor such as administration

of a porphyrinogenic drug.

Patients with HMBS mutations in the initiation of translation codon

in exon 1 and in the intron 15′-splice donor site have normal enzyme

levels in erythrocytes and deficient activity only in nonerythroid tissues. This occurs because the erythroid and housekeeping forms of

HMB-synthase are encoded by a single gene, which has two promoters.

Thus, the enzyme assay may not be diagnostic, and genetic testing

should be used to confirm the diagnosis.

More than 515 HMBS mutations have been identified in AIP,

including missense, nonsense, and splicing mutations and insertions

and deletions, with most mutations found in only one or a few families

(Human Gene Mutation Database, www.hgmd.org). The prenatal diagnosis of a fetus at risk can be made by analysis of the familial mutation

in cultured amniotic cells or chorionic villi. However, this is seldom

done because the prognosis of individuals with HMBS mutations is

generally favorable.

TREATMENT

Acute Intermittent Porphyria

During acute attacks, narcotic analgesics may be required for

abdominal pain, and phenothiazines are useful for nausea, vomiting, anxiety, and restlessness. Chloral hydrate can be given for

insomnia, and benzodiazepines are probably safe in low doses if

a minor tranquilizer is required. Carbohydrate loading, usually

with intravenous glucose (at least 300 g daily), may be effective in

milder acute attacks of porphyria (without paresis, hyponatremia,

etc.) if hemin is not available. Intravenous hemin is more effective

and should be used as first-line therapy for all acute attacks. The

standard regimen is 3–4 mg/kg of heme, in the form of lyophilized

hematin (Panhematin, Recordati Rare Diseases), heme albumin

(hematin reconstituted with human albumin), or heme arginate

(Orphan Europe), infused daily for 4 days. Heme arginate and heme

albumin are chemically stable and are less likely than hematin to

produce phlebitis or an anticoagulant effect. Recovery depends on

the degree of neuronal damage and usually is rapid if therapy is

started early. Recovery from severe motor neuropathy may require

months or years. Identification and avoidance of inciting factors

can hasten recovery from an attack and prevent future attacks.

Inciting factors are usually multiple, and removal of one or more

hastens recovery and helps prevent future attacks. Frequent attacks

that occur during the luteal phase of the menstrual cycle may be

prevented with a gonadotropin-releasing hormone analogue, which

prevents ovulation and progesterone production, or by prophylactic

hematin or givosiran administration.

Recently, a hepatic-targeted RNA interference (RNAi) therapy,

givosiran (Givlarri, Alnylam Pharmaceuticals), was approved by the

U.S. Food and Drug Administration and the European Medicines

Agency for the treatment of the acute hepatic porphyrias. Givosiran, a monthly subcutaneous injection of 2.5 mg/kg, is designed

to silence the expression of hepatic ALAS1 mRNA and was initially

shown in clinical trials to markedly reduce ALA and PBG levels in

CHE patients and in patients with recurrent attacks. In a phase 3

trial in acute hepatic porphyria patients with recurrent attacks, the

RNAi therapy significantly reduced the frequency of acute attacks,

decreased hemin utilization, and improved daily pain scores.

The long-term risk of hypertension and chronic renal disease is

increased in AIP; a number of patients have undergone successful

renal transplantation. Studies have shown that up to 59% of symptomatic AIP patients will develop chronic kidney disease. The PEPT2

receptor polymorphic genotype affects the severity and prognosis of

porphyria-associated kidney disease with the high affinity polymorphic PEPT2 *1 allele and the PEPT2 genotypes *1*1 and, to a lesser

degree, *1*2 associated with decreasing kidney function. Chronic,

low-grade abnormalities in liver function tests are common, and

the risk of hepatocellular carcinoma is increased. Hepatic imaging

is recommended at least every 6 months for early detection of these

tumors. Other long-term complications include neuropathy, fatigue,

chronic pain, nausea, depression, and/or anxiety.

Orthotopic liver transplantation (OLT) has been successful and is

curative in patients with severe, disabling, intractable attacks that are

refractory to hemin therapy. Reports from both the United Kingdom

and the United States show a marked improvement with no subsequent attacks, an improvement in the neuropathic manifestations,

and normalization of the urinary PBG and ALA levels after liver

transplantation. OLT is associated with morbidity and mortality

and should be considered a treatment of last resort in these patients.

In addition, patients who already have advanced neuropathy are

considered poor risks for transplantation. Some patients with both

recurrent attacks and end-stage renal disease have benefitted from

combined liver and kidney transplantation.

Liver-directed gene therapy has proven successful in the prevention

of drug-induced biochemical attacks in a murine model of human

AIP, and clinical trials of adeno-associated virus vector (AAV)-HMBS

gene transfer have been initiated. Although the therapy was safe, there

was essentially no biochemical evidence of its effectiveness, nor did it

prevent recurrent attacks in the treated patients.

■ PORPHYRIA CUTANEA TARDA

PCT, the most common of the porphyrias, can be either sporadic (type 1)

or familial (type 2) and can also develop after exposure to halogenated

aromatic hydrocarbons. Hepatic URO-decarboxylase is deficient in

all types of PCT, and for clinical symptoms to manifest, this enzyme

deficiency must be substantial (~20% of normal activity or less); it is

currently attributed to generation of an URO-decarboxylase inhibitor

in the liver, which forms a uroporphomethene in the presence of iron

and under conditions of oxidative stress. The majority of PCT patients

(~80%) have no UROD mutations and are said to have sporadic (type 1)

disease. PCT patients heterozygous for UROD mutations have the

familial (type 2) PCT. In these patients, inheritance of a UROD mutation from one parent results in half-normal enzyme activity in liver

and all other tissues, which is a significant predisposing factor but is

insufficient by itself to cause symptomatic PCT. As discussed below,

other genetic and environmental factors contribute to susceptibility

for both types of PCT. Because penetrance of the genetic trait is low,

many patients with familial (type 2) PCT have no family history of

the disease. HEP is an autosomal recessive form of porphyria due to

the inheritance of two pathogenic UROD mutations resulting in the

marked systemic deficiency of URO-decarboxylase activity with clinical symptoms in childhood.

Clinical Features Blistering skin lesions that appear most

commonly on the backs of the hands are the major clinical feature

(Fig. 416-3). These rupture and crust over, leaving areas of atrophy

and scarring. Lesions may also occur on the forearms, face, legs, and

feet. Skin friability and small white papules termed milia are common,

especially on the backs of the hands and fingers. Hypertrichosis and

hyperpigmentation, especially of the face, are especially troublesome

in women. Occasionally, the skin over sun-exposed areas becomes

severely thickened, with scarring and calcification that resembles systemic sclerosis. Neurologic features are absent.

A number of susceptibility factors, in addition to inherited UROD

mutations in type 2 PCT, can be recognized clinically and can affect

3245The Porphyrias CHAPTER 416

FIGURE 416-3 Typical cutaneous lesions in a patient with porphyria cutanea tarda.

Chronic, crusted lesions resulting from blistering due to photosensitivity on the

dorsum of the hand of a patient with porphyria cutanea tarda. (Used with permission

from Dr. Karl E. Anderson.)

management. These include hepatitis C, HIV, excess alcohol, elevated

iron levels, and estrogens. The importance of excess hepatic iron as a

precipitating factor is underscored by the finding that the incidence

of the common hemochromatosis-causing mutations, hemochromatosis gene (HFE) mutations p.C282Y and p.H63D, are increased

in patients with types 1 and 2 PCT (Chap. 414). Excess alcohol is a

long-recognized contributor, as is estrogen use in women. HIV is probably an independent but less common risk factor that, like hepatitis C,

does not cause PCT in isolation. Multiple susceptibility factors that

appear to act synergistically can be identified in individual patients.

PCT patients characteristically have chronic liver disease and sometimes cirrhosis and are at risk for hepatocellular carcinoma. Various

chemicals can also induce PCT; an epidemic of PCT occurred in eastern Turkey in the 1950s as a consequence of wheat contaminated with

the fungicide hexachlorobenzene. PCT also occurs after exposure to

other chemicals, including di- and trichlorophenols and 2,3,7,8-tetrachlorodibenzo-(p)-dioxin (TCDD, dioxin).

Diagnosis Porphyrins are increased in the liver, plasma, urine, and

stool. The urinary ALA level may be slightly increased, but the PBG

level is normal. Urinary porphyrins consist mostly of uroporphyrins

and heptacarboxylate porphyrin, with lesser amounts of coproporphyrin and hexa- and pentacarboxylate porphyrins. Plasma porphyrins are

also increased, and fluorometric scanning of diluted plasma at neutral

pH can rapidly distinguish VP and PCT (Table 416-3). Isocoproporphyrins, which are increased in feces and sometimes in plasma and

urine, are diagnostic for hepatic URO-decarboxylase deficiency.

Type 2 PCT and HEP can be distinguished from type 1 by finding

decreased URO-decarboxylase in erythrocytes. URO-decarboxylase

activity in liver, erythrocytes, and cultured skin fibroblasts in type 2

PCT is ~50% of normal in affected individuals and in asymptomatic

heterozygous family members. In HEP, the URO-decarboxylase activity

is markedly deficient, with typical levels of 3–10% of normal. Over 145

mutations have been identified in the UROD gene (Human Gene Mutation Database; www.hgmd.org). Of the mutations listed in the database,

~65% are missense or nonsense, and ~8% are splice-site mutations.

Many UROD mutations have been identified in only one or two families.

TREATMENT

Porphyria Cutanea Tarda

Alcohol, estrogens, iron supplements, and, if possible, any drugs

that may exacerbate the disease should be discontinued, but this

step does not always lead to improvement. A complete response

can almost always be achieved by the standard therapy, repeated

phlebotomy, to reduce hepatic iron. A unit (450 mL) of blood can

be removed every 1–2 weeks. The aim is to gradually reduce excess

hepatic iron until the serum ferritin level reaches the lower limits

of normal. Because iron overload is not marked in most cases,

remission may occur after only five or six phlebotomies; however,

PCT patients with hemochromatosis may require more treatments

to bring their iron levels down to the normal range. To document

improvement in PCT, it is most convenient to follow the total

plasma porphyrin concentration, which becomes normal sometime after the target ferritin level is reached. Hemoglobin levels or

hematocrits and serum ferritin should be followed closely to prevent development of iron deficiency and anemia. After remission,

continued phlebotomy may not be needed. Plasma porphyrin levels

are followed at 6- to 12-month intervals for early detection of recurrences, which are treated by additional phlebotomy.

An alternative when phlebotomy is contraindicated or poorly

tolerated is a low-dose regimen of chloroquine or hydroxychloroquine, both of which complex with the excess porphyrins and

promote their excretion. Small doses (e.g., 125 mg chloroquine

phosphate twice weekly) should be given, because standard doses

can induce transient, sometimes marked increases in photosensitivity and hepatocellular damage. Studies indicate that low-dose

hydroxychloroquine is as safe and effective as phlebotomy in PCT.

Hepatic imaging can diagnose or exclude complicating hepatocellular carcinoma. Treatment of PCT in patients with end-stage renal

disease is facilitated by administration of erythropoietin.

Because hepatitis C virus (HCV) is a common precipitating

factor causing PCT, the recent development of oral direct-acting

antivirals for HCV has proven effective as a first primary treatment

in HCV-infected PCT patients.

■ HEREDITARY COPROPORPHYRIA

HCP is an autosomal dominant hepatic porphyria that results from

the half-normal activity of COPRO-oxidase. The disease presents with

acute attacks, as in AIP. Cutaneous photosensitivity also may occur,

but much less commonly than in VP. HCP patients may have acute

attacks and cutaneous photosensitivity together or separately. HCP

is less common than AIP and VP. Homozygous dominant HCP and

harderoporphyria, a biochemically distinguishable variant of HCP,

present with clinical symptoms in children (see below).

Clinical Features HCP is influenced by the same factors that cause

attacks in AIP. The disease is latent before puberty, and symptoms, which

are virtually identical to those of AIP, are more common in women. HCP

is generally less severe than AIP. Blistering skin lesions are identical to

PCT and VP and begin in childhood in rare homozygous cases.

Diagnosis COPRO III is markedly increased in the urine and feces

in symptomatic patients and often persists, especially in feces, when

there are no symptoms. Urinary ALA and PBG levels are increased

(but less than in AIP) during acute attacks but may revert to normal

more quickly than in AIP when symptoms resolve. Plasma porphyrins

are usually normal or only slightly increased, but they may be higher

in cases with skin lesions. The diagnosis of HCP is readily confirmed

by increased fecal porphyrins consisting almost entirely of COPRO III,

which distinguishes it from other porphyrias.

Although the diagnosis can be confirmed by measuring COPROoxidase activity, the assays for this mitochondrial enzyme are not available and require cells other than erythrocytes. To date, >90 mutations

have been identified in the CPOX gene, ~70% of which are missense or

nonsense (Human Gene Mutation Database; www.hgmd.org). Detection of a CPOX mutation in a symptomatic individual permits the

identification of asymptomatic family members.

TREATMENT

Hereditary Coproporphyria

Neurologic symptoms are treated as in AIP (see above). Phlebotomy

and chloroquine are not effective for the cutaneous lesions.