review
Modern diagnosis and management of the porphyrias
Shigeru Sassa
Laboratory of Biochemical Hematology, The Rockefeller University, New York, USA
Summary
Recent advances in the molecular understanding of the
porphyrias now offer specific diagnosis and precise definition
of the types of genetic mutations involved in the disease.
Molecular diagnostic testing is powerful and very useful in
kindred evaluation and genetic counselling when a diseaseresponsible mutation has been identified in the family. It is
also the only way to properly screen asymptomatic gene
carriers, facilitating correct treatment and appropriate genetic
counselling of family members at risk. However, it should be
noted that DNA-based testing is for the diagnosis of the gene
carrier status, but not for the diagnosis of clinical syndrome
or severity of the disease, e.g. an acute attack. For the
diagnosis of clinically expressed porphyrias, a logical stepwise
approach including the analysis of porphyrins and their
precursors should not be underestimated, as it is still very
useful, and is often the best from the cost-effective point of
view.
Keywords: porphyria, porphyrin, haem, d-aminolaevulinate
synthase, molecular diagnosis.
The porphyrias are uncommon, complex, and fascinating
metabolic conditions, caused by deficiencies in the activities
of the enzymes of the haem biosynthetic pathway. While
most of them are inherited, some may also occur as acquired
diseases. In addition, not all gene carriers of inherited
porphyrias develop clinical disease and there is a significant
interplay between the primary gene defect and the secondary
acquired or environmental factors. The enzyme deficiencies
can be either partial or nearly complete depending on the
types of genetic mutations. Depending on deficient enzymatic
steps, various porphyrins and their precursors are accumulated in tissues and are excreted in urine and/or stool.
Porphyrias can be classified either as (i) erythropoietic
porphyria, (ii) acute hepatic porphyria, or (iii) chronic hepatic
porphyria. Both erythropoietic porphyria and chronic hepatic
porphyria accompany cutaneous photosensitivity, but they
Correspondence: Prof. S. Sassa, MD, PhD, Laboratory of Biochemical
Hematology, The Rockefeller University, New York, NY 10021, USA.
E-mail: [email protected] and [email protected]
are not associated with neurological symptoms. In contrast,
acute hepatic porphyrias are characterised by neurological
symptoms. Some of them may have additional photosensitivity (Fig 1).
The haem biosynthetic pathway
The enzymatic steps and intermediates in the haem biosynthetic pathway are illustrated in Fig 2. In eukaryote cells, the
first enzymatic step and the last three steps occur in
mitochondria; the other four steps take place in the cytosol.
The two major cell types that are active in haem synthesis are
hepatocytes and bone marrow erythroblasts, and inherited
enzymatic defects in the porphyrias are chiefly manifested in
these cells.
The first intermediate of the haem biosynthetic pathway is
d-aminolaevulinic acid (ALA), a 5-carbon aminoketone, which
is formed in mitochondria by the condensation of glycine and
succinyl CoA by d-aminolaevulinate synthase (ALAS). Two
molecules of ALA are then condensed in the cytosol to form a
monopyrrole, porphobilinogen (PBG), by ALA dehydratase
(ALAD). Four molecules of PBG are combined by PBG
deaminase (PBGD), to form the first cyclic tetrapyrrole,
uroporphyrinogen I, which is then converted to uroporphyrinogen III by uroporphyrinogen synthase (UROS). Uroporphyrinogen III is decarboxylated by uroporphyrinogen
decarboxylase (UROD) to form coproporphyrinogen III.
Coproporphyrinogen III enters into the mitochondria, where
it is oxidatively decarboxylated by coproporphyrinogen oxidase (CPO) to form protoporphyrinogen IX. Protoporphyrinogen IX is then oxidised to protoporphyrin IX by
protoporphyrinogen oxidase (PPO). Finally, ferrous iron is
inserted into protoporphyrin IX by ferrochelatase to form
haem. Protoporphyrin IX is the immediate precursor of the
various haems and also of the chlorophylls. Information on
enzyme proteins, and genes for haem pathway enzymes is
summarised in Table I.
There is significant tissue-specific regulation for enzymes
in the haem biosynthetic pathway (Sassa, 2006a,b). For
example, there are two separate genes for ALAS, i.e. the
housekeeping and the erythroid-specific ALAS genes, which
are termed ALAS1 (or ALAS-N) and ALAS2 (or ALAS-E)
respectively. In addition, there are the housekeeping and the
erythroid-specific mRNAs for ALAD, the gene for PBGD
ª 2006 The Author
Journal Compilation ª 2006 Blackwell Publishing Ltd, British Journal of Haematology, 135, 281–292 doi:10.1111/j.1365-2141.2006.06289.x
Review
Symptoms
Products
Enzyme
Disease
ALAS2
XLSA
Erythroid
Microcytic anaemia
Sideroblasts
ALAD
ADP
Hepatic
Neurovisceral
Urinary ALA
HMBS
AIP
Hepatic
Neurovisceral
Urinary ALA, PBG
UROS
CEP
Photosensitivity
Haemolytic anaemia
Urinary & RBC
U’ gen I, C ’gen I
Photosensitivity
7-C porphyrin; faecal
isocoproporphyrin
Type
Glycine + Suc.CoA
δ-Aminolaevulinic acid
Porphobilinogen
Hydroxymethylbilane
(Nonenzymatic)
U’gen I
(UROS)
U’gen III
PCT
UROD
C’gen I
Erythropoietic
HEP
Hepatic/
Erythropoietic
C’gen III
CPOX
HCP
Hepatic
Haemolytic anaemia
Neurovisceral &
Photosensitivity
P’gen IX
PPOX
VP
FECH
EPP
Hepatic
Neurovisceral
Photosensitivity
Urinary ALA, PBG,
coproporphyrin
Urinary ALA, PBG;
faecal protoporphyrin
Proto IX
Fe2+
Erythropoietic
Photosensitivity
RBC protoporphyrin
faecal protoporphyrin
Haem
Fig 1. Classification of porphyrias Enzymatic defects, associated diseases, major symptoms and principal accumulation products are shown. ALAS2
defect is responsible for X-linked sideroblastic anaemia (XLSA) but is not associated with any porphyria, since the enzymatic defect blocks production
of ALA, the obligatory precursor for porphyrin formation. ALA dehydratase porphyria (ADP) and acute intermittent porphyria (AIP) are accompanied by acute hepatic porphyria but not by photocutaneous porphyria, because their enzymatic defects do not result in an increase in porphyrin
synthesis. Enzymatic defects beyond uroporphyrinogen synthase (UROS) are all associated with photocutaneous porphyrias, because they produce
excessive amounts of various porphyrins. Hereditary coproporphyria (HCP) and variegate porphyria (VP) are additionally associated with acute
hepatic porphyria. Suc.CoA, succinyl coenzyme A; P’gen, rotoporphyrinogen; Proto, protoporphyrin; U’gen, uroporphyrinogen; C’gen, coproporphyrinogen;. Adapted from Sassa S & Shibahara S. Disorders of Heme Production and Catabolism. In Handin RI, Lux SE, and Stossel TP, eds,
Blood: Principles and Practice of Hematology, 2nd ed, Philadelphia, Lippincott Williams & Wilkins, 2003, with permission).
(HMBS), and UROS, and the housekeeping and the
erythroid-specific enzymes for ALAS as well as for PBGD
(Table I). Haem-mediated regulation of ALAS is also tissuespecific; namely, ALAS1 expression in the liver is
repressed by haem, while ALAS2 in the erythroid bone
marrow is not.
General considerations
Pathogenesis
• All of the haem pathway intermediates are potentially toxic.
Their overproduction causes the characteristic neurovisceral
and/or photosensitizing symptoms.
• Porphyrins produce free radicals when exposed to ultraviolet light ( 400 nm). As a result, skin damage ensues in
the light-exposed areas, resulting in cutaneous porphyrias.
• In contrast to porphyrins, their precursors, e.g. ALA and
PBG, are associated with neurological symptoms of acute
hepatic porphyrias.
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• Porphyrins and their precursors are excreted in urine or
stool depending on their solubility. The water solubility of
porphyrins is directly attributable to the number of
carboxyl groups in each molecule (Falk, 1964). Accordingly, the water-soluble uroporphyrin is excreted into
urine, while the water-insoluble protoporphyrin is
excreted into bile and stool. Coproporphyrin is excreted
into both urine and stool because of its intermediate
solubility. Porphyrin precursors are essentially all excreted
into urine.
• During an acute attack, ALAS1, the hepatic isoform of the
first enzyme in the haem biosynthetic pathway is induced.
ALAS1 formation in normal hepatocytes is repressed by
feedback inhibition by the final product, haem. Metabolic
inhibition along the pathway in the liver leads to reduced
production of haem, resulting in derepression of ALAS1.
This leads to increased production of haem precursors in an
effort to overcome the metabolic block, and contributes to
the accumulation of intermediates prior to the deficient
ª 2006 The Author
Journal Compilation ª 2006 Blackwell Publishing Ltd, British Journal of Haematology, 135, 281–292
Review
Fig 2. Haem biosynthetic pathway Enzymes and intermediates of the haem biosynthetic pathway are shown. Step : ALAS. Step : ALAD. Step :
PBGD. Step : UROS. Step : UROD. Step : CPO. Step : PPO. Step : Ferrochelatase. The carbon atom that is derived from the a carbon of
glycine is shown as a bold red dot. The structure that is denoted by the brackets after step is the presumed intermediate whose pyrrole ring D
becomes rearranged to yield uroporphyrinogen III. At step , 1 mole of oxygen is consumed per 1 mole of water produced. CoA, coenzyme A.
(Adapted from Clinical Hematology, Philadelphia, Mosby Elsevier. Sassa S. Porphyrias. In Young NS, Gerson SL, and High KA, eds, Copyright 2006,
with permission from Elsevier).
enzymatic step. This abnormality continues until sufficient
haem synthesis is restored.
• There is significant interaction between the primary gene
defect in the haem biosynthetic pathway and environmental
factors for ALAS1 induction. Namely, patients with acute
hepatic porphyrias may not become symptomatic unless
these subjects are exposed to certain drugs, liver damage,
hormonal changes during the menstrual cycle, stress, or
starvation, which result in the induction of ALAS1.
Diagnosis
• Demonstration of porphyrin precursors, such as ALA and/or
PBG, is essential for the diagnosis of acute hepatic porphyrias.
• Porphyrin analysis is necessary for the diagnosis of
porphyrias with cutaneous photosensitivity.
• The logical stepwise approach is most useful when there are
clinical symptoms of the porphyrias (Sassa, 2004).
• Molecular diagnostic testing is powerful and very useful in
kindred evaluation and genetic counselling when a diseaseresponsible mutation has been identified in the family. It is
also the only proper way to screen asymptomatic gene
carriers.
Treatment
• Recognition and avoidance of precipitating events is the
first key part of treatment.
• Acute attacks of hepatic porphyrias should be treated
similarly by (i) avoiding the precipitating factors; (ii) providing sufficient amounts of calories as carbohydrates (glucose infusion); and (iii) intravenous infusion of haematin.
ª 2006 The Author
Journal Compilation ª 2006 Blackwell Publishing Ltd, British Journal of Haematology, 135, 281–292
283
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Table I. Enzymes and genes for haem biosynthesis.
Genome
Enzyme
d-Aminolaevulinate synthase:
Housekeeping
Erythroid-specific
d-Aminolaevulinate dehydratase:
Housekeeping
Erythroid-specific
Porphobilinogen deaminase:
Housekeeping
Erythroid-specific
Uroporphyrinogen Ill synthase:
Housekeeping
Erythroid-specific
Uroporphyrinogen decarboxylase
Coproporphyrinogen oxidase
Protoporphyrinogen oxidase
Ferrochelatase
Size (kb)
Gene symbol
Chromosomal location
cDNA (bp)
Protein (aa)
ALAS1
ALAS2
ALAD
3p21.1
Xp11.21
9q34
2199
1937
640
587
17
22
1149
1154
330
330
15Æ9
1086
1035
361
344
1296
1216
1104
1062
1431
1269
265
265
367
354
477
423
HMBS
UROS
UROD
CPOX
PPOX
FECH
11q23.3
11
10q25.2–q26.3
34
1p34
3q12
1q23
18q21.3
3
14
5Æ5
45
Organization*
11 exons
11 exons
13 exons
Exons 1A + 2-12
Exon 1B + 2-12
15 exons
Exons 1 + 3-15
Exons 2-15
10 exons
Exon 1 + 2B-10
Exon 2A + 2B-10
10 exons
7 exons
13 exons
11 exons
*Number of exons and those encoding housekeeping and erythroid-specific forms.
• Haemolytic anaemia in erythropoietic porphyrias may be
treated by blood transfusion.
• Cutaneous photosensitivity of erythropoietic protoporphyria may be treated by oral b-carotene, while that of
porphyria cutanea tarda (PCT) by phlebotomy, or oral
chloroquine.
Erythropoietic porphyrias
The characteristic features of each porphyric disorder are
described below. Porphyrins in red cells can cause photosensitive cell lysis, resulting in haemolytic anaemia. The two
homozygous erythropoietic porphyrias, congenital erythropoietic porphyria (CEP) and hepatoerythropoietic porphyria
(HEP), are associated with haemolytic anaemia of varying
degrees. In contrast, erythropoietic protoporphyria (EPP), a
heterozygous disease, rarely has accompanying haemolytic
anaemia. The effect of life-long anaemia in CEP or HEP may
lead to compensatory expansion of erythroid marrow, which
may result in pathological fractures, vertebral compression or
collapse, and shortness of stature. The haemolysis is also
associated with varying degrees of splenomegaly and the
production of pigment-laden gallstones.
Congenital erythropoietic porphyria
Congenital erythropoietic porphyria is an erythropoietic
porphyria inherited in an autosomal recessive fashion. It is
one of the most severely affected photosensitive disorders. The
primary abnormality is an almost complete absence of UROS
activity, previously termed uroporphyrinogen III cosynthase,
which results in massive accumulation and excretion of
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uroporphyrin I and coproporphyrin I. This is the only
porphyria that produces type I isomers in excess.
Uroporphyrinogen synthase catalyses the cyclization of the
linear tetrapyrrole, hydroxymethylbilane, to yield a tetrapyrrole, uroporphyrinogen III, the physiological isomer, which
ultimately leads to the formation of haem. This step involves
inversion of the pyrrole D ring of hydroxymethylbilane and
cyclization to uroporphyrinogen III (Fig 2) (Battersby et al,
1980). In the absence of UROS, as in CEP, hydroxymethylbilane is converted non-enzymatically to the non-physiological
porphyrin isomer, uroporphyrin I. Uroporphyrinogen I is then
enzymatically converted to coproporphyrinogen I via the
activity of UROD, but it cannot be metabolized further.
Mild to severe haemolysis in CEP is characterised by
anisocytosis, poikilocytosis, polychromasia, basophilic stippling, reticulocytosis, increased nucleated red cells, absence of
haptoglobin, increased unconjugated bilirubin, increased
faecal urobilinogen and increased plasma iron turnover.
Secondary splenomegaly may contribute to the anaemia, and
may also result in leucopenia and thrombocytopenia.
Anaemia can be so severe that some patients are transfusion-dependent. Splenectomy may reduce the need for
transfusions, although signs of ineffective erythropoiesis and
gallstones may continue.
Severe cutaneous photosensitivity usually begins in early
infancy and is manifested by increased friability and blistering
of the epidermis on the hands and face and other sun-exposed
areas. Pink or red-brown staining of nappies due to markedly
increased urinary porphyrins may be the first clue to the
disease. Bullae and vesicles contain serous fluid and are prone
to rupture and infection. The skin may be thickened, with
areas of hypo- and hyperpigmentation. Hypertrichosis of the
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face and extremities is often prominent. Sunlight, other
sources of ultraviolet light, and minor skin trauma increase
the severity of the cutaneous manifestations. Recurrent vesicles
and secondary infection can lead to cutaneous scarring and
deformities, as well as loss of finger nails and digits and severe
damage to the eyelids, nose and ears. Corneal scarring can lead
to blindness. Porphyrins deposited in the teeth produce a
reddish brown colour in natural light, termed erythrodontia.
Erythrodontia shows intense red fluorescence of porphyrins on
exposure to long wavelength ultraviolet light.
A variety of mutations that cause CEP have been identified
in the UROS gene, including missense and nonsense mutations, large and small deletions and insertions, splicing defects
and intronic branch point mutations (Fontanellas et al, 1996;
Desnick et al, 1998). UROS knockout in mice is embryonic
lethal, while some UROS mutants knocked into these animals
not only support the survival of the animals, but also develop
cutaneous photosensitivity similar to those observed in CEP
(Bishop et al, 2006). These findings suggest that this animal
model is useful for the study of the effects of UROS
mutations.
Urinary porphyrin excretion is markedly increased (up to
50–100 mg/d, normal range: <0Æ2 mg, or 0Æ3 lmol/d), and
consists mostly of uroporphyrin, hepta-carboxyl porphyrin,
and coproporphyrin, with lesser increases in hexa- and pentacarboxyl porphyrins (Fritsch et al, 1997). Urinary ALA and
PBG excretion are not increased. Faecal porphyrins are
markedly increased due to increased coproporphyrin I.
Circulating erythrocytes contain large amounts of uroporphyrin I and lesser, but still excessive, amounts of coproporphyrin
I. Red cell protoporphyrin may also be increased, which
reflects increased erythropoiesis. HEP is clinically very similar
to CEP but can be distinguished by the predominance of
protoporphyrin in red cells and isocoproporphyrin in stool.
There are three main components in the treatment of CEP,
(i) protection from sunlight and UV exposure; (ii) meticulous
skin care; and (iii) red cell transfusions and other haematological supportive care. Other therapeutic interventions
include, (i) treatment with hydroxyurea to reduce bone
marrow porphyrin synthesis (Guarini et al, 1994); (ii) splenectomy to reduce transfusion requirements in patients with
hypersplenism (Piomelli et al, 1986); and (iii) oral charcoal
treatment to facilitate faecal excretion of porphyrins (Tishler &
Winston, 1990). Allogeneic bone marrow transplantation has
also proved curative for patients with CEP (Kauffman et al,
1991; Thomas et al, 1996; Zix-Kieffer et al, 1996; Tezcan et al,
1998). Successful marrow transplantation results in marked
reduction of the photosensitivity and porphyrin levels.
Erythropoietic protoporphyria
Erythropoietic protoporphyria is characterised by a partial
deficiency of ferrochelatase activity. Cutaneous photosensitivity characteristically begins in childhood, but there is no
neurological involvement. This is probably the third most
common porphyria after acute intermittent porphyria (AIP)
and PCT, and the most common erythropoietic porphyria.
Molecular analysis of ferrochelatase mutations has revealed
missense mutations, splicing abnormalities, intragenic deletions, and possible nonsense mutations associated with functional deficiency of ferrochelatase (Ostasiewicz et al, 1995;
Todd, 1998). Among them, exon skipping was the most
predominant. It has been reported that (i) a C fi T transition
at position $-$23 in intron 1 (NT) reduces ferrochelatase
activity; but (ii) the NT allele alone is not sufficient to bring
about EPP, even in its homozygous state; and (iii) both a
mutant allele (M) and the Nr allele in trans are necessary for
the clinical expression of EPP (Gouya et al, 1999). Thus,
ferrochelatase activity in patients can be defined as M-M, or
M-NT, silent gene carriers as M-NC, and normal controls as
NC-NC, NC-NT, or NT-NT (increasingly reduced ferrochelatase
activity). This model accounts for the fact (i) why normal
controls have a wide range of ferrochelatase activity; (ii) why
silent gene carriers have higher ferrochelatase activity than
patients; and (iii) why patients with EPP have less than 50% of
ferrochelatase activity. This model explains the majority of EPP
cases, the rest being true autosomal recessive disease.
Cutaneous photosensitivity begins in childhood, affects sunexposed areas, such as face and dorsum of hands, and is
generally worse in spring and summer. Common symptoms
include itching, painful erythema and swelling, which can
develop within minutes of sun exposure (Poh-Fitzpatrick,
1984). Diffuse oedema of the skin in sun-exposed areas may
resemble angioneurotic oedema. On occasion, burning and
itching can occur without obvious skin damage. Petechiae and
purpuric lesions may occur. Skin lichenification, leathery
pseudovesicles and nail changes can be pronounced.
Bone marrow reticulocytes are the primary source of the
excess protoporphyrin that accumulates in tissues and is
excreted in faeces in EPP. Bone marrow fluorescence is almost
entirely in reticulocytes rather than nucleated erythroid cells.
Protoporphyrin is markedly increased in erythrocytes and
plasma, and excreted in stool. Unlike other porphyrias, there is
no increase in porphyrin excretion in urine. In contrast to iron
deficiency anaemia and lead poisoning, in which increased
erythrocyte protoporphyrin is chelated with zinc, erythrocytic
porphyrin in EPP is exclusively free protoporphyrin (Lamola
et al, 1975). There is no increase in plasma porphyrin
concentrations in the two former conditions (Poh-Fitzpatrick
& Lamola, 1976).
Oral administration of b-carotene is useful for treating EPP
(Mathews-Roth et al, 1977). b-Carotene doses of 120–180 mg
daily in adults are usually required to maintain serum carotene
levels in the recommended range of 11Æ16–14Æ88 lmol/l, but
doses up to 300 mg daily may sometimes be needed. Suntanning, resulting from better tolerance of sunlight, may lead to
further protection. Cholestyramine and other porphyrin
absorbents, such as activated charcoal, may be helpful. Other
therapeutic options include red blood cell transfusions,
exchange transfusion and intravenous haematin to suppress
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erythroid and hepatic protoporphyrin production, as well as
liver transplantation. While liver transplantation can be
temporary beneficial, the new liver is susceptible to protoporphyrin-induced damage.
Acute hepatic porphyrias
The most common neurovisceral complaints in acute hepatic
porphyrias are abdominal pain (occurring in 85–95% cases),
vomiting (43–88%), constipation (48–84%), muscle weakness
(42–60%), mental symptoms (40–58%), limb, head, neck,
chest pain (50–52%), hypertension (36–54%), tachycardia
(28–80%), convulsion (10–20%), sensory loss (9–38%), fever
(9–37%), respiratory paralysis (5–12%) and diarrhoea (5–
12%) (Waldenstrom, 1957; Goldberg, 1959; Stein & Tschudy,
1970). While the exact mechanism underlying these complaints is not yet well understood, various hypotheses have
been put forward. For example, (i) excess amounts of PBG or
ALA may cause neurotoxicity (Meyer et al, 1998); (ii)
increased ALA concentrations in the brain may inhibit
gamma-aminobutyric acid release (Mueller & Snyder, 1977;
Brennan & Cantrill, 1979); (iii) haem deficiency may result in
degenerative changes in the central nervous system (Whetsell
et al, 1984); (iv) decreased haem synthesis in the liver results in
decreased activity of hepatic tryptophan pyrrolase (TP), a
haem-dependent enzyme, possibly resulting in increased levels
of brain tryptophan and increased turnover of 5-hydroxytryptamine, a neurotransmitter (Litman & Correia, 1985); (v) as all
of the porphyrias that are associated with neurovisceral
complaints show increased urinary excretion of ALA (ADP),
or of ALA and PBG [AIP, hereditary coproporphyria (HCP)
and variegate porphyria (VP)], and ALA increases lipid
peroxidation, ALA-mediated lipid peroxidation may underscore the acute crisis of porphyria (Bechara, 1996); and (vi) TP
deficiency results in decreased plasma melatonin levels (Puy
et al, 1996), which may result in the loss of protection against
ALA-mediated lipid peroxidation.
ALA dehydratase porphyria (ADP)
ALA dehydratase porphyria (ADP) is the rarest form of the
inherited porphyrias. Only six cases have been reported that
were molecularly confirmed to be due to ALAD mutations:
three German males (Ishida et al, 1992; Doss et al, 2004), one
Swedish baby boy (Thunell et al, 1987; Plewinska et al, 1991),
one elderly Belgian man (Hassoun et al, 1989; Akagi et al,
2000), and an American male (Akagi et al, 2006). It is an
autosomal recessive disorder resulting from a homozygous
deficiency of ALAD in five reported patients, while it was due
to a clonal expansion of a mutant ALAD allele in a late-onset
disease in the Belgian patient. While clinical ADP is rare, the
frequency of genetic carriers for ALAD deficiency, i.e. heterozygotes, in the normal population is as high as 2%, according
to a study performed in Sweden (Thunell et al, 1987).
Although subjects heterozygous for ALAD deficiency are
286
asymptomatic, they may be at a higher risk than normal
individuals for developing ADP when exposed to environmental chemicals or conditions that further influence deficient
ALAD activity (Akagi et al, 2000).
In addition to the inherited enzymatic deficiency, ALAD
activity can be inhibited by a number of substances including
divalent heavy metal ions. By virtue of its zinc displacing
activity from the enzyme, lead potently inhibits ALAD activity
(Granick et al, 1978). Over 99% of lead in blood is found in
erythrocytes, of which over 80% is bound to ALAD (Bergdahl
et al, 1997), and patients with lead poisoning are associated
with marked inhibition of ALAD activity in red cells. They also
develop neurological symptoms, some of which resemble those
seen in ADP. The most potent inhibitor of ALAD is
succinylacetone (Sassa & Kappas, 1983), a structural analogue
of ALA, which is found in the urine and blood of patients with
hereditary tyrosinemia type 1 (Lindblad et al, 1977). As a
result, approximately 40% of children with hereditary tyrosinaemia develop the signs and symptoms of ADP, suggesting
that succinylacetone results in the significant inhibition of
haem synthesis in the liver.
The ADP is characterised by the markedly increased
production of ALA, such that ALA production is 10–20 times
that of PBG. AIP, on the other hand, is characterised by
increased production of both ALA and PBG, often to a
comparable extent. The fact that AIP and ADP are clinically
indistinguishable suggests that ALA or its metabolites, rather
than PBG, may be the neurotoxic agent. This is further
supported by the finding, that patients with hereditary
tyrosinaemia frequently develop ADP along with its neurological abnormalities, most likely via the marked inhibition of
ALAD by succinylacetone.
Treatment of ADP, as with other acute hepatic porphyrias, is
two-fold: (i) acute attacks are treated by withdrawal of the
offending agent (if any), infusion of glucose, and, if the patient
is still symptomatic, intravenous infusion of haem preparations or administration of inhibitors of haem oxygenase, (ii)
future attacks are prevented by avoiding agents known to
stimulate ALAS activity and by avoiding those agents known to
inhibit ALAD activity.
Acute intermittent porphyria
Acute intermittent porphyria is due to inherited (autosomal
dominant) mutations of the PBGD gene (HMBS) leading to
deficient activity of the enzyme. This is the most important
acute hepatic porphyria, both in its incidence and clinical
severity. The enzyme activity is 50% of normal in those who
inherit the genetic trait. There is no difference in erythrocyte
PBGD activity between patients and latent gene carriers. The
prevalence of AIP in the United States is thought to be 5–10
per 100 000. It is more common in northern European
countries, such as Sweden (60–100 per 100 000), Britain and
Ireland. More than 200 mutations of the PBGD gene have been
described to date in AIP.
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Journal Compilation ª 2006 Blackwell Publishing Ltd, British Journal of Haematology, 135, 281–292
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Acute intermittent porphyria is more common in women
than in men, and very rare in children. Symptoms may appear
at or any time after puberty. The major clinical manifestations
of AIP, including abdominal pain and other neurovisceral and
circulatory disturbances, are due to effects on the nervous
system. Neurological and visceral symptoms are almost always
intermittent and usually occur in acute attacks that develop
over a few hours or days. The disease can be disabling but is
only occasionally fatal. Abdominal pain has been reported in
85–95% of cases, followed by tachycardia (80%). Abdominal
pain is usually severe, steady and poorly localised, but may be
cramping. A variety of mental symptoms, pain in limbs, head,
neck, or chest, muscle weakness and sensory loss can occur.
Weakness most commonly begins in the proximal muscles and
more often in the arms than in the legs.
The course of the neurological manifestations is highly
variable. Sudden death may occur, presumably due to cardiac
arrhythmia. Acute attacks of porphyria may resolve quite
rapidly. The disease may be complicated by electrolyte
abnormalities. Hyponatraemia is common during acute
attacks, and may help to suggest the diagnosis. This is
sometimes due to the syndrome of inappropriate antidiuretic
hormone secretion. The urine is often dark red in colour, due
to the presence of porphobilin, the oxidised product of PBG.
Mice with PBGD deficiency induced by gene targeting
display some of the symptoms observed in patients with AIP,
such as impaired motor function, ataxia, increased levels of
ALA in plasma and brain, and decreased haem saturation of
liver tryptophan pyrrolase (Lindberg et al, 1996). This model
should be useful to further define the mechanisms of
neurological damage in acute porphyrias.
Precipitating factors. An inherited deficiency of PBGD is not in
itself sufficient to cause clinical expression of AIP, as the great
majority ( 90%) of individuals who inherit a deficiency of
PBGD never develop porphyric symptoms. There is
considerable evidence that endocrine factors and steroid
hormones play an important role in precipitating the acute
attack of AIP (Sassa, 1996). Thus, acute hepatic porphyrias are
rarely seen before puberty, but are quite common at puberty or
after, and particularly often in the premenstrual phase in
women.
Drugs. Drugs are among the most important factors that
precipitate acute attacks of acute porphyria, with barbiturates
and sulphonamide antibiotics being most common (Anderson
et al, 2001). A significant number of commonly used drugs are
widely agreed to be either safe or unsafe for use in patients with
AIP. Many of these can be found on a dedicated web site
(http://www.porphyria-europe.org). However, knowledge
about the safety of many drugs and other over-the-counter
preparations in acute porphyrias is yet incomplete. Most drugs
that exacerbate AIP have the capacity to induce ALAS activity
in the liver. As mentioned above, this process is closely
associated with the induction of cytochrome P450 enzymes, a
process that increases the demand for hepatic haem synthesis.
Nutritional factors. Reduced energy intake, usually instituted in an effort to lose weight, commonly contributes to
attacks of AIP. Thus, even brief periods of starvation during
weight reduction, postoperative periods, or intercurrent illness
should be avoided. Starvation induces haem oxygenase-1 (HO1) activity, which can lead to depletion of regulatory hepatic
haem pools and contribute to ALAS induction. Transcription
of ALAS1 can also be upregulated by the peroxisome
proliferators-activated receptor c-coactivator 1a (PGC-1a).
Under conditions of low glucose, PGC-1a production increases, leading to increased levels of ALAS1, creating conditions
for attacks of acute porphyrias (Handschin et al, 2005).
Glucose and other forms of carbohydrate are effective in
treating acute attacks of porphyria.
Smoking. Chemicals in tobacco smoke, such as polycyclic
aromatic hydrocarbons, are known inducers of hepatic cytochrome P450 enzymes and haem synthesis. An association
between cigarette smoking and repeated attacks of porphyria
was found in a survey of 144 patients with AIP in Britain (Lip
et al, 1991). As a result, smoking cessation may have particular
health benefits in patients with acute porphyrias.
Infections, surgery and stress. Attacks of porphyria may
develop during intercurrent infections and other illnesses, after
major surgery, and psychological stress. Most of these conditions are known to increase hepatic HO-1 activity (Rodgers &
Stevenson, 1990).
All individuals with AIP, whether active or latent, have a
50 % deficiency of PBGD activity in the liver. Urinary ALA
and PBG are always markedly increased in symptomatic
patients with AIP (Aarsand et al, 2006) and even in some
asymptomatic individuals with the inherited enzyme deficiency
(Floderus et al, 2006). PBG in urine is oxidised to porphobilin
upon standing, which gives a dark-brown colour to urine, and
often referred to as ‘port-wine reddish urine’. Urinary ALA
and PBG levels may decrease to normal if the disease becomes
inactive for a prolonged period. Urinary porphyrins are also
markedly increased. Circulating concentrations of ALA and
PBG in plasma (or serum) are substantially increased (Floderus et al, 2006).
Diagnosis can be established by the demonstration of
reduced PBGD activity in erythrocytes (about 50% of normal)
in type I and type III AIP patients. Type II AIP patients show
normal PBGD activity in erythrocytes, but have reduced PBGD
activity in non-erythroid cells, such as fibroblasts or lymphocytes (Sassa, 1996). Patients with the clinically expressed disease
excrete increased amounts of ALA and PBG in the urine, and
often even during clinical remission. During an acute attack of
AIP, there are further massive increases in excretion of these
precursors (ALA 25–100 mg/d; PBG 50–200 mg/d). Some
latent gene carriers who are characterised by reduced PBGD
activity similar to patients also show increased ALA and PBG
excretion. The Watson–Schwartz test has been widely used as a
screening test for urinary PBG (Watson & Schwartz, 1941). It is
useful for evaluating the efficacy of treatment on acute crisis.
While the test may occasionally be associated with false-positive
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findings, it is quick and quite sufficient for the rapid diagnosis
of an acute attack of AIP. The column method of Mauzerall and
Granick is quantitative and more specific, and can determine
the amounts of both ALA and PBG (Anderson et al, 2001). For
this reason, the column method of Mauzerall and Granick is
now more widely used than the Watson–Schwartz test to avoid
possible biological false-positive findings. All participating
laboratories in the UK External Quality Assurance now use
the column method, instead of the Watson–Schwartz test.
Elevated levels of urinary ALA may additionally be seen in ADP,
HCP and VP, while elevated levels of both ALA and PBG may
be seen in HCP and VP.
Detection of PBGD mutations in AIP provides 95%
sensitivity and around 100% specificity (Kauppinen, 2004),
and has quickly been incorporated into good clinical practice.
It can definitively confirm or exclude the diagnosis of AIP.
While it is powerful and specific, and is very useful in pedigree
screening and in genetic counselling, its application at the
population level is not recommended, unless the frequency of
gene carriers is locally very high (Kauppinen, 2004). DNA
testing of AIP also determines the gene carrier status, rather
than the severity of the disease. The same consideration applies
to the diagnosis of most other acute hepatic porphyrias.
The treatment of acute attack is essentially the same for AIP,
ADP, HCP and VP. Intravenous administration of carbohydrate (as dextrose) should be given to provide a minimum of
300 g of carbohydrate per day. Glucose and insulin together
might also be more effective than glucose alone, as insulin
blunts the PGC-1a effect (Handschin et al, 2005). Intravenous
haematin administration is the treatment of choice, which
curtails urinary excretion of ALA and PBG, acute attacks, and
perhaps the severity of neuropathy. Reconstitution of haematin for intravenous infusion should be made according to the
protocol described recently (Anderson et al, 2006). Normosang
[Orphan Europe (UK) Ltd, Henley-on-Thames, UK], is a
stable haematin solution complexed with arginine (Mustajoki
et al, 1989). It is known to cause lesser vascular complications,
such as phlebitis than the conventional haematin solution.
Liver transplantation was attempted in a 19-year-old woman
with severe AIP. It successfully reduced urinary porphyrin
precursor excretion to normal, and improved her quality of life
(Soonawalla et al, 2004). Thus liver transplantation might be
considered for selected patients with the severest forms of AIP,
though it has not been successful in ADP. Nasal or subcutaneous administration of long-acting agonist of luteinizing
hormone-releasing hormone inhibits ovulation and greatly
reduces the incidence of perimenstrual attacks of AIP in such
women (Anderson et al, 1990a). Pain, which is invariably
present and severe, can be treated with frequent regular doses
of narcotic analgesics.
Hereditary coproporphyria
Hereditary coproporphyria is an autosomal dominant hepatic
porphyria due to a deficiency of coproporphyrinogen oxidase
288
(CPO) activity. HCP is markedly less frequent than AIP and
VP. HCP has identical clinical symptoms as AIP, except for its
cutaneous photosensitivity, which is entirely absent in AIP.
It is generally thought that HCP may be a milder disease
than AIP (Brodie et al, 1977), but there have also been a few
fatalities from respiratory paralysis in HCP. Molecular
analysis of several families with HCP, including the homozygous dominant form and the harderoporphyria variant, has
revealed a variety of mutations in the CPO gene (Martasek,
1998). In a series of 53 cases of HCP in Germany, the
incidence of symptoms was 89%, 33%, 28%, 25% and 14 %,
for abdominal pain, neurological, psychiatric, cardiovascular
and skin symptoms respectively (Kuhnel et al, 2000). The
disease is latent before puberty, and symptoms are more
common in adult women than men. This porphyria is
exacerbated by many of the same factors that precipitate
attacks in AIP, including barbiturates and other drugs, and
endogenous or exogenous steroid hormones. Symptoms can
occur in association with the menstrual cycle. The risk of
hepatocellular carcinoma may be increased in this porphyria,
as in AIP and VP. A few homozygous HCP cases, with
cutaneous lesions beginning in early childhood, have also
been reported.
The most prominent biochemical feature of HCP is a
marked increase in urinary and faecal coproporphyrin,
predominantly isomer type III, typically 10–200 times compared with controls (Martasek, 1998). Urinary ALA, PBG and
uroporphyrin are also increased during acute attacks. In
harderoporphyria, a variant form of HCP, faecal excretion of
harderoporphyrin (tricarboxylate porphyrin) and coproporphyrin is increased. Treatment of acute attacks of HCP is
identical to the treatment of AIP. The identification and
avoidance of precipitating factors is also essential for HCP.
Variegate porphyria
Variegate porphyria is an autosomal dominant acute hepatic
porphyria, due to a deficiency of PPO activity, the penultimate
enzyme in the haem biosynthetic pathway. The disease is
termed variegate because it can present itself either with
neurological manifestations, cutaneous photosensitivity, or
both.
In most countries this porphyria is less commonly recognised than AIP. However, VP is quite common in South Africa,
where it was first reported in 1945. The high prevalence among
South African whites (approximately 3 of 1000) is due to
genetic drift or the ‘founder effect’, and most VP cases in South
Africa can be traced to a man or his wife who emigrated from
Holland and were married in 1688 (Dean, 1982). As many as
20 000 South Africans may carry this gene, which is now found
to be R59W mutation of the PPO gene (Meissner et al, 1996).
The acute attack is identical to that seen in AIP, and may
include abdominal pain, tachycardia, vomiting, constipation,
hypertension, neuropathy, back pain, confusion, bulbar paralysis, psychiatric symptoms, fever, urinary frequency and
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dysuria. Hyponatraemia with evidence of sodium depletion or
inappropriate antidiuretic hormone secretion can occur during
acute attacks. Attacks of VP are generally milder than in AIP,
and recurrent attacks are less common. Cutaneous photosensitivity is more common than in HCP. Skin manifestations
generally occur, and are usually of longer duration. They are
very similar to those seen in PCT and HCP, and include
increased fragility, vesicles, bullae, erosions, milia, hyperpigmentation and hypertrichosis of sun-exposed areas. Photosensitivity may be less commonly associated with VP in northern
countries, where sunlight is less intense (Kirsch et al, 1998).
Faecal protoporphyrin and coproporphyrin and urinary
coproporphyrin are markedly increased when VP is clinically
active. Urinary ALA, PBG and uroporphyrin are also increased
during acute attacks but may be normal or only slightly
increased during remission. Plasma porphyrin is commonly
increased in VP, and its analysis is more sensitive than that of
faecal porphyrins (Hift et al, 2004). Increased plasma porphyrin in VP is readily detected as a fluorescence emission
maximum at 626–628 nm. This is a specific finding in VP
(Enriquez et al, 1993), as fluorescence emission peaks in EPP
and PCT are found at 636 nm and 618–622 nm respectively
(Enriquez et al, 1993). Biliary porphyrins are also increased.
The risk of gallstones may be increased in VP, which consist
mainly of protoporphyrin. The X porphyrin fraction (etheracetic acid-insoluble porphyrins extractable from faeces by
urea-Triton) is increased in VP. Rare homozygous VP patients
have markedly increased erythrocyte Zn-protoporphyrin
(Whatley et al, 1999).
Chronic hepatic porphyria
Patients with chronic hepatic porphyria, such as PCT, are
associated with significant chronic cutaneous photosensitivity,
but they do not accompany neurological symptoms. Petechiae
and purpuric lesions may occur. Skin lichenification, leathery
pseudovesicles and nail changes can be pronounced. Chronic
blistering lesions may develop; the fluid-filled vesicles rupture
easily and the denuded areas become crusted and heal slowly;
secondary infection is common. Previous areas of blisters may
appear atrophic, or brownish. Facial hypertrichosis, scarring
and hyperpigmentation may result.
Porphyria cutanea tarda
Porphyria cutanea tarda is due to a profound deficiency of
uroporphyrinogen decarboxylase (UROD) activity in liver.
The disease has been classified into three subtypes. Type I
PCT has decreased hepatic UROD activity, but normal
erythrocyte UROD activity, and is found in sporadic fashion
without family history. Type II PCT has decreased UROD
activity both in red cells and in liver, and occurs in multiples
in a family. Type III PCT is similar to type II with respect
to familial occurrence, but erythrocyte UROD activity is
normal.
A variety of mutations of UROD have been identified in
PCT (McManus et al, 1996; Mendez et al, 1998; Christiansen
et al, 2000). All but two were each found in only one family.
UROD mutations have also been found in HEP, the homozygous form of UROD deficiency, but they were mostly unique
and usually not found in PCT (Meguro et al, 1994).
Chronic blistering lesions develop on sun-exposed areas of
skin. These are more common in the summer than winter. The
fluid-filled vesicles rupture easily and the denuded areas
become crusted and heal slowly. Previous areas of blisters may
appear atrophic, or brownish. Facial hypertrichosis and
hyperpigmentation are also common. All types of PCT
respond readily to repeated phlebotomy (Ippen, 1977). PCT
can also be treated with of chloroquine or hydroxychloroquine
(administered in very low dosage regimen). This is the
preferred therapy at some centres, especially for patients
without marked iron overload (Valls et al, 1994).
Porphyrins accumulate in large amounts in liver, and are
increased in plasma. Uroporphyrin and heptacarboxylporphyrin are predominantly increased in urine.
Multiple factors can contribute to inactivation or inhibition
of hepatic UROD in this disease, probably by an irondependent oxidative mechanism, including alcohol (Grossman
et al, 1979), hepatitis C infection (Fargion et al, 1992),
oestrogen (Grossman et al, 1979), human immunodeficiency
virus (HIV) (Egger et al, 2002), and factors that increase
hepatic iron content, such as mutations of the HFE gene (HFE)
associated with haemochromatosis (Roberts et al, 1997a,b).
Liver biopsy frequently shows haemosiderosis, and serum iron
and ferritin concentrations are increased. Patients often
develop cirrhosis, and may occasionally develop hepatoma
(Kordac, 1972).
HFE mutation is found in PCT more commonly than in
control populations, indicating that a tendency to iron
overload can predispose to PCT (Bonkovsky et al, 1998).
There is no increase in ALA or PBG in this disorder. Faecal
isocoproporphyrin is the biochemical stigmata of the UROD
deficiency, and its detection establishes the diagnosis of PCT
(or HEP) (Elder, 1998). Namely, isocoproporphyrin III is
formed from dehydroisocoproporphyrinogen III that is
normally a minor product but can accumulate from pentacarboxylate porphyrinogen III if UROD activity is reduced
(Elder & Chapman, 1970).
The identification and avoidance of precipitating factors is
the first line of treatment, particularly for patients with type I
PCT. Abstinence from alcohol should be recommended in all
types of PCT. Phlebotomy is usually effective in reducing
urinary porphyrin concentration, serum ferritin concentration,
serum transferrin saturation, and in induction of clinical
remission (Ippen, 1977). Phlebotomy should be undertaken
weekly or biweekly until serum transferrin saturation and
serum ferritin levels are normalised. It usually requires blood
withdrawal ranging from 2Æ5 l to 7 l. Serum transferrin
saturation and ferritin levels are correlated with urinary
porphyrin excretion, and the clinical syndrome, and should
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be used to assess the exhaustion of hepatic iron stores during
phlebotomy treatment, as well as to detect an early replenishment after remission (Rocchi et al, 1985). If phlebotomy is
ineffective, or contraindicated because of the presence of other
diseases, such as anaemia, low-dose chloroquine therapy may
be considered (Valls et al, 1994). Chloroquine is thought to
chelate porphyrins to facilitate their water-solubility, thus to
enhance their excretion into urine. Treatment of PCT associated with end-stage renal disease can be difficult, because
phlebotomy is contraindicated and chloroquine is not effective, presumably because kidney failure precludes excretion of
excess porphyrins mobilized from liver. Recombinant erythropoietin administration is now the treatment of choice for these
patients, as it can correct anaemia, mobilize iron and support
phlebotomy in this condition (Anderson et al, 1990b; Yaqoob
et al, 1992; Peces et al, 1994).
Hepatoerythropoietic porphyria
Hepatoerythropoietic porphyria is a rare form of porphyria,
which is due to a homozygous or compound heterozygous
deficiency of UROD. Only some 20 cases of HEP were reported
(Meguro et al, 1994). HEP resembles CEP clinically and
usually presents in infancy or childhood with red urine,
blistering skin lesions, hypertrichosis and scarring. Sclerodermoid skin changes may be prominent. Erythrocyte porphyrins
are increased, but they are predominantly type III isomers.
Some patients may be associated with haemolytic anaemia and
splenomegaly.
The biochemical findings in HEP, however, resemble those
that are observed in PCT, and include predominant accumulation and excretion of uroporphyrin, heptacarboxylate
porphyrin and isocoproporphyrins. Erythrocyte Zn-protoporphyrin concentration is increased in HEP. Treatment of
HEP is identical to that for CEP. Unlike PCT, phlebotomy is
not effective in this disease.
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