Detection of homozygotes and heterozygotes with methylenetetrahydrofolate reductase deficiency.

Specific enzyme assay is required for the diagnosis of homocystinuria due to methylenetetrahydrofolate reductase deficiency. A rapid and accurate method has been developed using "pure" peripheral lymphocyte preparations. Triplicate determinations showed highly reproducible results. With the use of the mean of triplicate determinations in the presence of flavinadenine dinucleotide, there was complete segregation among the homozygotes, heterozygotes, and normal subjects. This method provides a rapid diagnosis in affected subjects and a simple means for the determination of heterozygotes for genetic counseling.