Wednesday, August 1, 2018

Inheritance Patten in Porphyria

Some types of porphyria are inherited in an autosomal dominant pattern, which means one copy of the gene in each cell is mutated. This single mutation is sufficient to reduce the activity of an enzyme needed for heme production, which increases the risk of developing signs and symptoms of porphyria. Autosomal dominant porphyrias include acute intermittent porphyria, most cases of erythropoietic protoporphyria, hereditary coproporphyria, and variegate porphyria. Although the gene mutations associated with some cases of porphyria cutanea tarda also have an autosomal dominant inheritance pattern, most people with this form of porphyria do not have an inherited gene mutation.
Other porphyrias are inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. Most often, the parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but do not show signs and symptoms of the condition. Porphyrias with an autosomal recessive pattern of inheritance include ALAD deficiency porphyria, congenital erythropoietic porphyria, and some cases of erythropoietic protoporphyria.
When erythropoietic protoporphyria is caused by mutations in the ALAS2 gene, it has an X-linked dominant pattern of inheritance. The ALAS2 gene is located on the X chromosome, which is one of the two sex chromosomes. In females (who have two X chromosomes), a mutation in one of the two copies of the gene in each cell may be sufficient to cause the disorder. In males (who have only one X chromosome), a mutation in the only copy of the gene in each cell causes the disorder. Males may experience more severe symptoms of the disorder than females. A characteristic of X-linked inheritance is that fathers cannot pass X-linked traits to their sons.
Mutations in the UROD gene are related to both porphyria cutanea tarda and hepatoerythropoietic porphyria. Individuals who inherit one altered copy of the UROD gene are at increased risk for porphyria cutanea tarda. (Multiple genetic and nongenetic factors contribute to this condition.) People who inherit two altered copies of the UROD gene in each cell develop hepatoerythropoietic porphyria.

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