Title: Genetics - American Porphyria Foundation
Headings: Genetics
Genetics
Inheritance of the Porphyrias
Basic Genetics

Content: PCT is unique as it is the only porphyria where most patients do not have mutations in a gene, but instead have acquired, or sporadic, PCT. Type
Inheritance
Deficient Enzyme
Gene
ALA-Dehydratase Porphyria (ADP)
Autosomal recessive
ALA-Dehydratase
ALAD
Acute Intermittent Porphyria (AIP)
Autosomal dominant
Hydroxymethylbilane synthase (Porphobilinogen deaminase)
HMBS
Congenital Erythropoietic Porphyria (CEP)
Autosomal recessive
Uroporphyrinogen III synthase
UROS
Porphyria Cutanea Tarda (PCT), familial form
Autosomal dominant
Uroporphyrinogen decarboxylase
UROD
Hepatoerythropoietic Porphyria (HEP)
Autosomal recessive
Uroporphyrinogen decarboxylase
UROD
Hereditary Coproporphyria (HCP)
Autosomal dominant
Coproporphyrinogen oxidase
CPOX
Variegate Porphyria (VP)
Autosomal dominant
Protoporphyrinogen oxidase
PPOX
Erythropoietic Protoporphyria (EPP)
X-linked Protoporphyria (XLP)
Autosomal recessive
X-linked
Ferrochelatase
δ-Aminolevulinate synthase 2
FECH
ALAS2
The inherited porphyrias are either autosomal dominant (inherited from one parent), autosomal recessive (inherited from both parents), or X-linked (the gene is located on the X-chromosome). " Autosomal" genes always occur in pairs, with one coming from each parent. Individuals with an autosomal dominant form of porphyria have one mutated gene paired with a normal gene, and there is a 50% chance with each pregnancy that the mutated gene will be passed to a child. Dominant genetic disorders occur when only a single copy of an abnormal gene is necessary for the appearance of the disease. The abnormal gene can be inherited from either parent, or can be the result of a new mutation (gene change) in the affected individual. The risk of passing the abnormal gene from affected parent to offspring is 50% for each pregnancy regardless of the sex of the resulting child. Individuals with an autosomal recessive type of porphyria have mutations on both copies of a specific gene, one passed to them from each of their parents. Each of their children will inherit one mutated gene for that porphyria, and the child will be a “carrier” but will not have symptoms. In X-linked disorders, the gene is located on one of the sex chromosomes, called the X-chromosome.