RECENT DATA ON CYSTINURIA

Cystinuria is characterized by defective reabsorption of four dibasic aminoacids, cystine, arginine, ornithine, and lysine by the proximal r enal tubules and enterocytes. It contributes about 1-2 % of renal lith iases overall and 6-8 % of renal lithiases in pediatric patients. Thre e types of cystinuria are classically differentiated, based on urinary excretion of the four amino-acids in heterozygotes and on their intes tinal absorption in homozygotes. The rBAT gene on chromosome 2 has bee n shown to be responsible for the transport of dibasic and neutral ami no-acids. Positive linkage has also been demonstrated between cystinur ia and three markers on the short arm of chromosome 2. Mutations of th e rBAT gene have been demonstrated only in Type I cystinuria, indicati ng that cystinuria is genetically heterogeneous. A study of seven fami lies is reported. Two families had two affected siblings each. All 14 parents were heterozygous for the disease. The cystinuria was I/I in f our families, I/II in one family, and III/III in two families. Four di fferent mutations were found. All occurred in patients with type I dis ease. To date, there is no evidence that the severity of cystinuria is correlated with the type of mutation.