SLC7A9 and cystinuria: Cystinuria caused by SLC3A1 mutations is usually an autosomal recessive disease and SLC3A1 heterozygotes have no apparent phenotype, but cystinuria caused by SLC7A9 mutations is usually autosome dominant inheritance with 86% of SLC7A9 heterozygotes having abnormal urinary dibasic amino acid levels and some of them will develop into Cystine stones [28].