CASE FILES: BIOCHEMISTRY
B IO C H E M IS T R Y PE A R L S
The porphyrias are a group of inherited disorders resulting from spe-
cific enzymatic defects of the heme biosynthetic pathway.
The major types of porphyria are each caused by mutations in one
of the genes required for heme production.
The first step in heme formation is the rate-limiting condensation reac-
tion between succinyl-CoA and glycine to form S-aminolevulinic
acid (ALA). This reaction is catalyzed by a mitochondrial matrix
enzyme, ALA synthase (ALAS).
Forms of porphyria include ALAS deficiency porphyria, acute inter-
mittent porphyria, congenital erythropoietic porphyria, erythro-
poietic protoporphyria, hepatoerythropoietic porphyria, hereditary
coproporphyria, porphyria cutanea tarda, and variegate porphyria.
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Sassa S. Modern diagnosis and management of the porphyrias. Br J Haematol