Genomic and functional investigations of mutations of the SLC3A1 gene in cystinuria

Background: Cystinuria is the second most frequent autosomal recessively inherited disorder in Europe, and it is based on a disturbance of the transepithelial transport of cystine and amino acids in the proximal renal tubule as well as in the intestinum. From the point of view of the urologist, patients suffering from cystine stones represent an important population because they develop a great number of recurrences which necessitate frequent stone removal.

Methods/results: Advances in the field of molecular genetics have rendered it possible to correlate genotype and phenotype of these patients. In the candidate gene, the SLC3A1 gene, 25 mutations in patients suffering from cystinuria have been described so far. Investigations in our patients (n = 15) as well as results obtained by other study groups have revealed an average detection rate of approximately 50%. The low rate as well as in-depth physiological analyses of the individual mutations indicate that the SLC3A1 is a subunit of a heteromeric complex. This supposition is supported by the structure of the transporter as well as by biochemical analyses of the urine of cystinuric patients and their relatives. Investigations on other genomic segments and candidate genes localized there are being performed. However, it has already appeared that cystinuria is not based on alterations of one single gene, but that a variety of factors combine in the development of this disease.

Conclusions: To be able to offer a molecular genetic diagnosis for patients suffering from cystinuria, the search for mutations of the SLC3A1 gene is being expanded and a screening for other candidate genes set up which are designed to early recognize the risk factors of cystinuria as well as to be able to initiate early therapy.