Genetics of cystinuria in an inbred population

After the identification of 2 cystinurics in a large eastern Virginia isolate a population study was undertaken to identify carriers of the gene and others who could be affected by it. Of 102 individuals 3 additional homozygous cystinurics and 27 possible carriers were found. The cystinuria gene shows a highly variable expression, although all those affected and carriers could be traced to 1 couple who married about 1890. These studies demonstrate that there is considerable variation in urinary concentrations of cystine even in an affected population. No form of therapy should be based on random or isolated samples.