Functional consequences of naturally occurring mutations in human uroporphyrinogen decarboxylase

Functional consequences of 12 mutations-10 missense, 1 splicing defect, and 1 frameshift mutation-were characterized in the uroporphyrinogen decarboxy lase (URO-D) gene found in Utah pedigrees with familial porphyria cutanea t arda (F-PCT). All but one mutation altered a restriction site in the URO-D gene, permitting identification of affected relatives using a combination o f polymerase chain reaction and restriction enzyme digestion. In a bacteria l expression system, 3 of the missense mutants were found in inclusion bodi es, but 7 were expressed as soluble proteins. Enzymatic activity of soluble , recombinant mutant URO-D genes ranged from 29% to 94% of normal. URO-D mR NA levels in Epstein-Barr-virus transformed cells derived from patients wer e normal (with the exception of the frameshift mutation) even though protei n levels were lower than normal, suggesting that missense mutations general ly cause unstable URO-Ds in vivo. The crystal structures of 3 mutant URO-Ds were solved, and the structural consequences of the mutations were defined . All missense mutations reported here and by others were mapped to the cry stal structure of URO-D, and structural effects were predicted. These studi es define structural and functional consequences of URO-D mutations occurri ng in patients with F-PCT. (Blood. 2001;98-3179-3185) (C) 2001 by The Ameri can Society of Hematology.