Journal Article

Functional Modeling of Vitamin Responsiveness in Yeast: A Common Pyridoxine-Responsive Cystathionine β-Synthase Mutation in Homocystinuria

Cecilia E. Kim, Paula M. Gallagher, Anne B. Guttormsen, Helga Refsum, Per M. Ueland, Leiv Ose, Ivar Følling, Alexander S. Whitehead, Michael Y. Tsai and Warren D. Kruger

in Human Molecular Genetics

Volume 6, issue 13, pages 2213-2221
Published in print December 1997 | ISSN: 0964-6906
Published online December 1997 | e-ISSN: 1460-2083 | DOI: http://dx.doi.org/10.1093/hmg/6.13.2213
Functional Modeling of Vitamin Responsiveness in Yeast: A Common Pyridoxine-Responsive Cystathionine β-Synthase Mutation in Homocystinuria

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Cystathionine β-synthase (CBS) deficiency is an autosomal recessive disorder which results in extremely elevated levels of total plasma homocysteine (tHcy) and high risk of thromboembolic events. About half of all patients diagnosed with CBS deficiency respond to pyridoxine treatment with a significant lowering of tHcy levels. We examined 12 CBS-deficient patients from 10 Norwegian families for mutations in the CBS gene and identified mutations in 18 of the 20 CBS alleles. Five of the seven patients classified as pyridoxine-responsive contain the newly identified point mutation, G797A (R266K). This point mutation is tightly linked with a previously identified ‘benign’ 68 bp duplication of the intron 7-exon 8 boundary within the CBS gene. We tested the effect of all of the mutations identified on human CBS function utilizing a yeast system. Five of the six mutations had a distinguishable phenotype in yeast, indicating that they were in fact pathogenic. Interestingly, the G797A allele had no phenotype when the yeast were grown in high concentrations of pyridoxine, but a severe phenotype when grown in low concentrations, thus mirroring the behavior in humans. These studies show that the G797A mutation is an important cause of pyridoxine-responsive CBS deficiency and demonstrate the utility of yeast functional assays in the analysis of human mutations.

Journal Article.  4704 words.  Illustrated.

Subjects: Genetics and Genomics

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