Screening for PKU heterozygosity in bipolar affectively ill patients.

There were no significant differences noted between bipolar manic-depressive patients and normal controls for plasma phenylalanine or tyrosine following an L-phenylalanine loading test given to determine if some affective illness may be related to the heterozygous phenotypic expression of phenylketonuria (reduced liver phenylalanine hydroxylase). The test was able to distinguish known PKU heterozygotes from the other subjects. It is possible that other heterozygous states may be implicated in the development of some psychiatric disorders.