Protein-bound plasma homocyst(e)ine and identification of heterozygotes for cystathionine-synthase deficiency.

We measured protein-bound plasma homocyst(e)ine in 15 normal adult subjects and nine heterozygotes for homocystinuria due to cystathionine beta-synthase deficiency. The mean (+/- SD) concentrations obtained in the two groups of subjects were 4.35 +/- 1.50 and 9.16 +/- 3.40 mumoll-1, respectively. The mean values were significantly different, although the levels of three heterozygotes overlapped those of the control range. This method allows preliminary screening of the heterozygotes for homocystinuria and can be carried out by laboratories that have only facilities for amino acid analysis.