[Use of modified Ayling's method for detection of homozygotes and heterozygotes for phenylketonuria gene].

Activity of phenylalanine hydroxylase from human leukocytes was shown to depend on concentration of phenylalanine and pteridine cofactor; optimal concentrations of the substances were estimated. Using this optimized procedure activity of phenylalanine hydroxylase was studied in leukocytes of homo- and heterozygotes by the phenylketonuria gene as well as in the cells of donors. The mean values of the enzymatic activity were distinctly different in the groups of homo-, heterozygote-bearing patients and in healthy persons, although a slight overlapping of the patterns was observed between the groups. Presence of "atypical" forms of phenylketonuria appears to be responsible for this overlapping. The modified procedure for estimation of phenylalanine hydroxylase activity in leukocytes might be used for differential diagnostics of phenylketonuria.