Permanent chemical phenylketonuria and a normal phenylalanine tolerance in two sisters with a normal mental development

A positive ferric chloride reaction was found at routine examination of the urine of a 14 year old mentally normal girl, admitted for complaints of headache and other meningitis-like symptoms. It turned out that she excreted permanently increased amounts of phenylpyruvic, phenyllactic and o-hydroxyphenylacetic acids, but phenylacetic acid (free plus conjugated) was normal. Fasting serum phenylalanine was not increased nor was urinary phenylalanine. On loading with L-phenylalanine (100 mg/kg) a normal serum phenylalanine response followed, but urinary phenylpyruvic, phenyllactic and o-hydroxyphenylacetic acids increased further. Phenylacetic acid responded too, but remained in the normal range. In addition to the above-mentioned abnormalities the urine contained a still unidentified abnormal acid, which also increased after loading with phenylalanine. Her 12 year old healthy sister showed the same chemical abnormality. Two older brothers and the parents had normal excretions. The enzyme defect has not been identified. As a possibility the defective decarboxylation of phenylpyruvic acid is proposed