What are the laboratory findings in cystinuria?
The key laboratory finding is a large amount of cystine in the urine. There are also increased urinary levels of 3 other amino acids with a similar structure — lysine, arginine, and ornithine. The membrane transport for cystine is unique to cystine but serves to transport all 4 so-called dibasic amino acids — lysine, arginine, orthnithine and, of course, cystine. This excess of amino acids in the urine constitutes aminoaciduria. Some persons (heterozygotes) carrying just one gene for cystinuria have aminoaciduria, although milder. There are actually 3 types of cystinuria. Carriers of 2 of these types of cystinuria (types II and III) show abnormal amounts of cystine in their urine. How is cystinuria inherited? The genetics of cystinuria are complicated. There are, as mentioned, 3 types of cystinuria. They are termed cystinuria type I (abbreviated CSNU1), cystinuria type II (CSNU3), and cystinuria type III (CSNU3). Each type of cystinuria can be inherited as an autosomal recessive trai