Porphyrias are caused by mutations in genes that encode enzymes in heme synthesis. In normal physiology, heme synthesis begins in the mitochondrion, proceeds into the cytoplasm, and finishes back in the mitochondrion. Heme is produced in all cells, but 80% of all heme is produced in erythropoietic cells in bone marrow and 15% in parenchymal cells in the liver, where turnover of hemoproteins is high. In<unk> , over 100 mutations have been identified on the long arm of chromosome 11 at the HMBS gene, which codes for the cytoplasmic enzyme porphobilinogen deaminase. This deficiency prevents heme synthesis, which can not be completed and the metabolite porphobilinogen accumulates in the cytoplasm.<unk>  is an autosomal dominant porphyria resulting in about 50% normal activity of the affected enzyme. The penetrance of<unk>  is incomplete with only 10% of gene carriers experiencing<unk>  attacks suggesting role for other modifying genes or environment. The exact mechanism of<unk>  attacks is not clear. The most favored hypothesis is that porpholobilinogen buildup causes a toxic effects on neurons. The autonomic and peripheral nervous system are more vulnerable than the central nervous system because they are not protected by the blood-brain barrier. This explains findings such as abdominal pain and tachycardia. Some individuals may be more likely to develop paresis based on increased susceptibility of neurons to toxins.
Acute intermittent porphyria
Hepatic porphyria
Variegate porphyria
Erythropoietic porphyria
Hepatoerythropoietic porphyria
Woodhouse–Sakati syndrome
Diarrhetic shellfish poisoning
Porphyria