Two siblings of hyperphenylalaninemia: suggestion to a genetic variant of phenylketonuria.

A sibling case of hyperphenylalaninemia without phenylpyruvic aciduria was described. An oral loading of phenylalanine revealed a delay of clearance of serum phenylalanine, a slight elevation of serum tyrosine, and an increased urinary excretion of phenylpyTuvic acid and o-hydroxyphenylacetic acid. Phenylalanine hydroxylase in the liver was found to be of about one-tenth the normal activity. These findings suggest that hyperphenlyalaninemia may be a genetic variant of phenylketonuria.