title: Characterization of two missense variants in the hydroxymethylbilane synthase gene in the Israeli population, which differ in their associations with acute intermittent porphyria.
abstract: Acute intermittent porphyria (AIP) is an autosomal dominant disorder of heme biosynthesis caused by molecular defects in the hydroxymethylbilane synthase (HMBS) gene. In this study, we report two novel missense sequence variations in the HMBS gene, T59I (C176T) and V215M (G643A), in two patients with clinical symptoms compatible with acute attacks of porphyria. However, only the patient who carried V215M presented with full AIP-affirming biochemical evidence. Both variant proteins were expressed in a prokaryotic system and characterized in vitro. Recombinant T59I and V215M had residual activity of 80.6% and 19.4%, respectively, of that of the wild type enzyme. Moreover, changes in K(m), V(max) and thermostability observed in the recombinant V215M suggest a causal relationship between V215M and AIP. The association between the T59I substitution and AIP is less obvious. Based on our investigation, substitution T59I is more likely to be a mutation with a weak effect than a rare form of polymorphism. This study demonstrates that in vitro characterization of missense variations in the HMBS gene can provide valuable information for the interpretation of clinical, biochemical and genetic data, for establishing a diagnosis of AIP. It also highlights the fact that there are still many aspects to be investigated concerning AIP and corroborates the need to report new data that can help to clarify the genotype-phenotype relationship.
authors.affiliation: Zentrallabor, Stadtspital Triemli, Zürich, Switzerland.
authors.forename: Xiaoye
authors.initials: X
authors.lastname: Schneider-Yin
authors.forename: Dana
authors.initials: D
authors.lastname: Ulbrichova
authors.forename: Rivka
authors.initials: R
authors.lastname: Mamet
authors.forename: Pavel
authors.initials: P
authors.lastname: Martasek
authors.forename: Christopher C
authors.initials: CC
authors.lastname: Marohnic
authors.forename: Avner
authors.initials: A
authors.lastname: Goren
authors.forename: Elisabeth I
authors.initials: EI
authors.lastname: Minder
authors.forename: Nili
authors.initials: N
authors.lastname: Schoenfeld
mesh_terms: D000293:Adolescent; D000328:Adult; D016022:Case-Control Studies; D004252:DNA Mutational Analysis; D004795:Enzyme Stability / Q000235:genetics; D005190:Family; D005260:Female; D008040:Genetic Linkage; D006801:Humans; D011163:Hydroxymethylbilane Synthase / Q000235:genetics* / Q000378:metabolism; D007557:Israel; D020125:Mutation, Missense; D017118:Porphyria, Acute Intermittent / Q000235:genetics*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D011994:Recombinant Proteins; D011163:Hydroxymethylbilane Synthase