Effects of amino acid loads on a health infant with the biochemical features of Hartnup disease.

Hartnup disease (Baron, Dent, Harris, Hart, and Jepson, 1956) is an inborn abnormality of renal and intestinal transport involving the 'neutral' amino acids (the monoamino monocarboxylic amino acids, but excluding glycine, proline, hydroxyproline, and methionine). Mental and physical retardation, intermittent pellagra-like rash, and cerebellar ataxia are associated with this biochemical abnormality (Efron, 1965; Jepson, 1966). This paper describes investigations on an infant with the biochemical, though not, to date (age 16 months), the clinical features of Hartnup disease. The patient was discovered during a routine screening test for phenylketonuria when he gave a 'positive' Phenistix. Previous amino acid loading studies on patients with Hartnup disease (for example, Milne, Crawford, Girao, and Loughridge, 1960) have concentrated almost exclusively on the malabsorption and metabolism of tryptophan and the associated indoluria. We report the effects of lysine, histidine, and tyrosine loads on our patient compared with those on three control subjects. These three amino acids were chosen for detailed investigation because their urinary excretions were increased in our patient, and because the metabolic products derived from the action of intestinal bacteria would differ from those of tissue metabolism (compare Milne, Asatoor, Edwards, and Loughridge, 1961; Milne, 1964). The absorption of phenylalanine, and the influence of nicotinic acid supplements on amino acid absorption (de Laey, Hooft, Timmermans, and Snoeck, 1964), were also examined.