Table 3.

Classification of the Hereditary Porphyrias

Type of PorphyriaGene(s)MOIFindings
Neurovisceral 1Photocutaneous
Hepatic ADP ALAD AR+0
AIP HMBS AD+0
HCP CPOX AD++
PCT type II 2 UROD AD0+
HEP 3AR0+
VP PPOX AD++
Erythropoietic CEP 4 UROS AR0+
GATA1 XL
EPP FECH AR0+ 5
XLP ALAS2 XL0+ 5

0 = no symptoms; + = mild to severe symptoms; AD = autosomal dominant; ADP = ALA dehydratase-deficiency porphyria; AIP = acute intermittent porphyria; AR = autosomal recessive; CEP = congenital erythropoietic porphyria; EPP = erythropoietic protoporphyria; HCP = hereditary coproporphyria; HEP = hepatoerythropoietic porphyria; MOI = mode of inheritance; PCT = porphyria cutanea tarda; VP = variegate porphyria; XL = X-linked; XLP = X-linked protoporphyria

1.

Porphyrias with neurovisceral manifestations have been considered "acute" because symptoms usually occur acutely as discrete, severe episodes; however, some affected individuals develop chronic manifestations.

2.

PCT is primarily an acquired, iron-related disorder with multiple susceptibility factors. Approximately 20% of individuals with PCT have a heterozygous pathogenic variant in UROD, the gene encoding uroporphyrinogen decarboxylase, which is referred to as PCT type II (familial). In PCT type I (sporadic, ~80% of individuals with PCT) UROD is normal. Type III (rare) is also familial due to inherited factors other than UROD variants. Types I-III are clinically indistinguishable and respond to the same treatments.

3.

HEP is the homozygous form of PCT type II (familial).

4.

CEP is most commonly associated with biallelic UROS pathogenic variants and inherited in an autosomal recessive manner; on rare occasion, CEP is caused by mutation of GATA1 and inherited in an X-linked manner.

5.

Photocutaneous manifestations of EPP and XLP are acute and non-blistering, in contrast to the chronic blistering in the other cutaneous porphyrias (including VP).

From: Variegate Porphyria

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