X-linked protoporphyria (XLP), a condition closely associated with the overproduction of protophyrin IX [PPIX], is associated with a variety of gain-of-function mutations, mainly deletions in exon 11, that result in increased δ-aminolevulinic acid synthase 2 (ALAS2), the enzyme responsible for the initial step in erythroid heme biosynthesis [8,9]. The gene discussed is ALAS2; the disease is X-linked lymphoproliferative disease.