Heterozygous carriers of classical phenylketonuria in a sample of the Turkish population: detection by a spectrofluorimetric method.

Blood obtained by finger prick from 209 presumed normal homozygotes and 42 heterozygotes for classical PKU was analyzed for plasma phenylalanine (Phe) and tyrosine (Tyr) by a fluorimetric method. Subjects were tested near midday and 3 hours after a protein-rich breakfast. The plot of Phe/Tyr (micromolar ratio) against Phe2/Tyr, permitted the detection of 11 heterozygotes among 209 controls. The accuracy of this method was checked by computation of a stepwise multivariate discriminant analysis, using Phe and Tyr (mumol/L), Phe/Tyr micromolar ratio and Phe2/Tyr as variables. Ten of the 11 subjects were recovered with a percentage of correct classification of over 90%, while one case had a percentage of 89.45%. The PKU gene frequency was found to be 1/19. This emphasizes the importance of a screening programme for PKU gene carrier status in Turkey.