Cystinuria with hyperuricemia and methioninuria: Biochemical study of a case

An otherwise typical cystinuric subject manifested several seemingly innocuous additional biochemical abnormalities: hyperuricemia, methioninuria and several serum amino acids in abnormal amounts. In contrast to findings reported in classic cystinuria, urinary cystine was decreased by homocysteine loading and temporarily decreased, followed by only a small increase after methionine loading. The response to taurine loading was atypical. Pyridoxine hydrochloride administration tended to correct some of the serum amino acid aberrations. Radiomethionine and radiotaurine administration revealed no absolute defect in the pathway between methionine and the metabolites of taurine. The response to penicillamine treatment was like that of the usual cystinuric patient. During methionine loading, urinary methionine was decreased, despite elevated serum levels, indicating that the methioninuria is not the result of a tubular defect.