How is acute porphyria inherited?

Each type of acute porphyria is the end result of an alteration in a hereditary particle of DNA known as a gene. This alteration is inherited so that each person with porphyria will often have a number of relatives who will also have inherited the altered gene. A different gene is altered in each type of acute porphyria. This means that when two or more people are affected in the same family they will have the same disease. A person newly diagnosed with porphyria will often have a number of relatives, both close and distant, who will also have inherited the altered gene responsible for the type of acute porphyria in their family. Many of these relatives may not know that they have inherited an acute porphyria gene and that they are therefore at risk of developing an acute attack and in variegate porphyria and hereditary coproporphyria, skin disease.

 

The gene alteration responsible for each type of acute porphyria is passed down through families in what is called an autosomal dominant pattern. Genes, which contain the blueprint for all the components required by the body, usually occur in pairs. Sometimes a small error can occur in the copying of one of these genes resulting in a permanent gene alteration which is called a mutation. When a mutation in only one of the pair of genes causes a disease, as is the case in the acute porphyrias, it is called an autosomal dominant mutation. This altered gene (mutation) may then be inherited from parent to child and the risk of an affected person passing this gene onto any of his or her offspring is one chance in two. This risk is the same even if the affected person has never had any symptoms of porphyria. Thus the disease often appears to have skipped a generation.