-To establish a cystinuria data base (clinical data and DNA bank) from European populations.
-To describe the spectrum of mutations in the rBAT gene causing cystinuria type I.
-To study the structure-function relationship of the rBAT transporter.
-To search for the gene(s) responsible for cystinuria type II and III.
-To clarify the cystinuria phenotypes based on the clinical, biochemical and genetic studies.
-To identify the promoter region of the rBAT gene that directs the gene expression of rBAT to epithelial cells of the S3 segment of the nephron.
This is a multidisciplinary project, where 6 research groups, including clinicians, biochemists, an electrophysiologist and genetecits, to achieve a better understanding of the molecular basis of cystinuria, a common inherited aminoaciduria with a prevalence ranging between 1:7000 and 1:15.000. The disease is divided into three phenotypes.
The new advances in cystinuria research, at the molecular level, have been performed by our groups: i) description of mutations in the rBAT gene (named SLC3Al in GDB) causing cystinuria type I and ii) type II and type III cystinuria are not due to mutations in the rBAT gene. The precise objectives of this proposal are listed below:
1) Development of a cystinuria data base, already iniciated by the International Study of the Genetic Renal Diseases (ISGRD) and creation of the corresponding DNA data bank;
2) Characterization of new mutations in the rBAT gene;
3) To study the relationship between structure and function in rBAT transporter mutants;
4) Search for other genes responsible for cystinuria types II and III;
5) Identify, characterise, purify, and if possible to clone the putative light subunit of the rBAT protein;
6) To identify the promoter region of the rBAT gene that will allow in cell culture models as well as "in vivo" (transgenic mice) to direct the gene expression to the epithelial cells of the S3 segment in the nephron.
The cystinuria data bank will support a high enough number of cases to permit the study of the genotype-phenotype relationship, in addition this will provide a suitable amount of rare type II cystinuria families to perform exclusion map studies. To define the spectrum of rBAT mutations it will be necessary to fully characterise the promotor region of the rBAT gene. Clinical classification and linkage studies will determine which families are not linked to the rBAT gene and will generate enough informativity for use in exclusion map studies. This will identify the candidate chromosomal regions for the genes responsible for cystinuria types II and III map. The next step will be to clone these genes. At the protein level if we are able to clone the putative "light" subunit of the rBAT protein we will perform the bichemical and molecular genetics studies to demonstrate the function of rBAT plus the "light" subunit as an active tertiary exchanger for cystine and dibasic amino acids (bO,+-like system) as well as the responsability of the "light subunit" in cystinuria. Simultaneously we will define the relationship between structure and function of the rBAT transporter mutants, by expressing them either in oocytes or in mammalian cells, studying the transport activity, performing structural and cellular biology studies and by reconstituting the wild type and mutant rBAT transporters. Finally at the end of this work a phenotype-genotype correlation will be established.
Funding SchemeCSC - Cost-sharing contracts
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