X-Linked Protoporphyria

**Semantic type:** Disease or Syndrome

**Definition:** An X-linked dominant porphyria caused by gain of function mutations in the ALAS2 gene, encoding 5'-aminolevulinate synthase 2 (5-aminolevulinate synthase, erythroid-specific, mitochondrial), which lead to overproduction of protoporphyrin and its accumulation in the blood, liver, and skin. Excess protoporphyrin in the blood may lead to iron deficient anemia, while accumulation in the liver may contribute to the formation of gallstones and subsequent obstruction of the bile ducts. Exposure to sunlight activates protoporphyrin in the skin, leading to severe pain, burning, and itching.

**Synonyms:** - XLDPP - XLP