Genetic variations of the SLC7A9 gene: allele distribution of 13 polymorphic sites in German cystinuria patients and controls.

Cystinuria is a hereditary disorder of cystine and dibasic amino acid transport across the luminal membrane of renal tubules and intestine, resulting in recurrent nephrolithiasis. While mutations in the SLC3A1 gene cause type I cystinuria, patients with non-type I cystinuria carry mutations in the SLC7A9 gene. Both gene products form the renal amino acid transporter rBAT/b0,+AT affected in cystinuria. In the present study a total of 59 patients with different ethnic background were screened for sequence variations in SLC7A9, out of these 32 were of German origin. For determination of allele frequencies of detected polymorphisms, 58 healthy German controls were investigated. Molecular-genetic analysis was performed using single-strand conformation polymorphism analysis, restriction assays and sequencing. Allele frequencies were analyzed statistically for the detected polymorphisms. In addition to the 6 already known variants we identified 7 new polymorphisms. Statistical analyses showed a significantly different distribution of alleles between German patients and German controls in case of the polymorphisms c. 147C>T (exon 2), c.386C>T (exon 3), IVS3+22T>G, c.584C>T (exon 4), c.610T>C (exon 4), c.692C>T (exon 5), c.852C>A (exon 6) and c.872C>T (exon 6). In summary, our results show that cystinuria is a complex disease which is not only caused by mutations in SLC7A9 and SLC3A1, but also influenced by other modifying factors such as variants in SLC7A9.