Analysis of multiple mutations in the hALG6 gene in a patient with congenital disorder of glycosylation Ic

Congenital disorder of glycosylation Ic is caused by mutations in the hALG6 gene that encodes an alpha-1,3 glucosyltransferase. This enzyme is require d for the addition of the first glucose residue to the lipid-linked oligosa ccharide precursor for N-linked glycosylation. Here we describe the biochem ical and molecular analysis of a patient with three mutations in the hALG6 gene The maternal allele has an intronic G --> A mutation resulting in skip ping of exon3 (IVS3 + 5G > A). This produces a nonfunctional enzyme as show n by its inability to restore normal glycosylation in a Saccharomyces cerev isiae strain lacking a functional ALG6. The paternal allele has two mutatio ns. One is a deletion of three bases (895-897delATA) leading to an in-frame deletion of isoleucine 299 (delI299) located in a transmembrane domain. Th e second mutation on the same allele 911T > C causes a F304S change. When e xpressed in the ALG6 deficient yeast strain, this allele restores glycosyla tion but the mRNA is unstable or inefficiently transcribed, contributing to the impaired glycosylation in the patient. (C) 2000 Academic Press.