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Cystinuria is an inherited disease characterized by the formation of cystine calculi in the kidneys, ureters, and bladder. Cystinuria is associated with mutation in the SLC3A1 and SLC7A9 genes. These defects prevent appropriate reabsorption of dibasic amino acids lysine, ornithine, and arginine. Cystinuria is classified as type I (silent heterozygotes) and non-type I (heterozygotes with urinary hyperexcretion of cystine). In molecular term, cystinuria is classified as type A (mutations on SLC3A1 gene) and type B (mutations on SLC7A9 gene). This report describes 7 patients with early onset of cystine calculus formation. We are report a new mutation in SLC3A1 gene in exon 1. A novel nucleotide substitution c.-29AG was found in exon 1 of the SLC3A1 gene, which had not been reported elsewhere previously.

Cystinuria, one of the first inborn errors of metabolism, is characterized by hyperexcretion of cystine, arginine, lysine, and ornithine into urine. Cystinuria is genetically classified into types A and B. Mutations in the SLC3A1 gene lead to type A, and type B is caused by mutations in the SLC7A9 gene. We described a 19-year-old woman that had early onset of cystine calculus formation at the age of 3 years. After DNA extraction and polymerase chain reaction, direct sequencing was performed. By these methods, a novel nucleotide substitution c.177GA in exon 3 of the SLC7A9 gene was found, which had not been reported elsewhere previously. This nucleotide substitution occurs in the extracellular domain of the SLC7A9 gene. In addition, a previously described intron variant c.1136+2/3delT (intron 6 of SLC3A1) in homozygosity status was detected in the patient. To our knowledge, this is the first report of novel nucleotide substitution c.177GA in exon 3 of the SLC7A9 gene.