A CASE OF HYPERLYSINEMIA: BIOCHEMICAL AND CLINICAL OBSERVATIONS

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Abstract
Clinical and biochemical observations on a mentally retarded 4-year-old boy who has a lysinuria and hyperlysinemia are presented and discussed. He differed clinically from the three patients described previously in that he did not have marked muscle weakness. His endogenous renal clearance of lysine while fasting was twice the upper limit of normal for children, and after fasting his plasma lysine level had decreased to within the normal range. After a test dose of lysine (150 mg/kg orally) his plasma lysine level was increased from 2.43 to 15.2 mg/100 ml after 2½ hours, and after 7 hours it was still 7 mg/100 ml. No evidence for the degradation of a significant amount of lysine by any new pathway could be obtained. Homoarginine was identified in his urine and detected in his blood; homocitrulline was measured in his urine. α-Aminoadipic acid could not be detected in his urine. Nα and N\g=elunate\-Acetyllysines were identified in his urine at approximately three times the concentration as in the urine of a normal child of the same age; neither of these derivatives had been identified previously as components of human urine. The possibility is suggested that in this patient the lysine abnormality may be coincidental with and not a causative factor for his mental retardation.

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