A yeast assay for functional detection of mutations in the human cystathionine beta-synthase gene.

Mutations in the human cystathionine beta-synthase (CBS) gene are known to cause homocystinuria and may also be a significant risk factor for premature atherosclerosis. We have previously shown that the human CBS protein can substitute for the endogenous yeast CBS protein in Saccharomyces cerevisiae. We now show that expression of three different CBS mutants known to be associated with reduced enzyme activity in humans fail to complement growth in the yeast assay. In addition, we have used the yeast CBS assay to identify eight mutant CBS alleles in cell lines from patients with CBS deficiency. These mutant alleles include two previously identified and five novel CBS mutations. Our results also demonstrate that the yeast CBS assay can detect a large percentage of individuals heterozygous for mutations in CBS. This system should be useful in determining the relationship between CBS mutations and human disease.