Persistent Mild Hyperphenylalaninemia in the Untreated State

Abstract

There is substantial evidence that phenylketonuria causes mental subnormality unless specific dietary treatment is begun early in infancy, but much less is known about other forms of hyperphenylalaninemia. We followed nine infants with persistent mild hyperphenylalaninemia from the neonatal period into early childhood. In addition we discovered three siblings and one mother with persistent mild hyperphenylalaninemia as a result of routine study of families in which an affected neonate was found. All 13 subjects remained on a normal diet. The blood phenylalanine concentrations of all infants were no higher than 12 mg per 100 ml (normal less than 2 mg per 100 ml), and these concentrations later remained below 8 mg per 100 ml. The IQ's of the biochemically affected subjects were normal and comparable to those of the unaffected siblings. School grades of the affected children attending school were "good." Dietary therapy appears not to be needed for persistent mild hyperphenylalaninemia.