Abstract
Cystinuria is a hereditary disorder due to a defect in the renal transport of dibasic amino acids consisting of cystine, lysine, arginine and ornithine. The disorder has been known to develop recurrent urolithiasis clinically. Recently the screening for aminoaciduria, however, revealed that most of the patients with cystinuria existed as “biochemical cystinuria” without manifestation of urinay calculi. Throughout our experience of screening for aminoaciduria, we had the impression that there might be a higher frequency of cystinuria among the mentally retarded children.
The present study was undertaken in order to elticidate this question. Cyanide-nitroprusside reaction was tested on the urine specimens from 4852 normal children and from 1325 mentally retarded children, in Osaka district. The specimens which gave a positive reaction was quantitatively analyzed for amino acids. Three cases of homozygotes (all four amino acids excreted in excess) and 12 heterozygotes (only lysine and cystine excreted in excess) were found in the mentally retarded group, whereas one case of homozygote and 9 cases of heterozygotes were found in the normal group. This indicates a significantly higher frequency of cystinuria in the mentally retarded children than in the normal children, not only in homozygotes but also in heterozygotes.
Oral loading test lysine (150 mg/kg) was performed in order to investigate intestinal absorption of lysine in these cases. It was found that the intestinal absorption rate in cystinuria with mental retardation was statistically lower than those who have normal mentality. Lysine is the only essential amino acid among four dibasic amino acids. The patient with cystinuria may be apt to fall in deficiency in lysine because of genetic handicap of its transport, particularly its poor absorption in the gut. A possibility was postulated that the deficiency in lysine during infancy may influence upon brain developement.
