Genetic Exploration of Familial/Syndromal Steroid Resistant Nephrotic Syndrome

SRNS is a highly genetically heterogeneous disorder. The genetic studies will focus on the monogenic forms of isolated or syndromal SRNS not linked to the already known loci, either autosomal recessive (to be studied in Paris and Ankara) or autosomal dominant (to be studied in Bergamo). The strategy will involve positional cloning including linkage analysis (and homozygosity mapping in consanguineous families) in the most informative families using Affymetrix mapping arrays, a search for additional families potentially linked to genetic intervals defined by the arrays, and sequence analysis of the most promising candidate genes in the potentially linked families. The candidate genes will be prioritized upon their potential up-regulation in the glomerulus as obtained by data mining and quantitative RT-PCR.

Once new genes have been identified, the characterization of the encoded proteins, if they are not known to be involved in podocyte or glomerulus physiology, will be undertaken using a combination of techniques available in the Paris and Bergamo laboratories, including the study of the subcellular localization of the proteins, their expression pattern in the developing and adult kidney, gene expression by in situ hybridization (especially if antibodies are not available), the identification of interacting proteins and functional testing of the implicated genes in the zebrafish (in collaboration with I.Drummond, Boston).

In addition, patients with sporadic forms of SRNS available from the registry cohort will be screened based on the phenotype of the familial cases with mutations, with the aim of identifying novel mutations and characterizing the whole range of phenotypes linked to mutations in these novel genes. These will supplement DNA biobanks already available in the different nephrogenetic laboratories, encompassing some 600 children with sporadic SRNS without NPHS1 or NPHS2 mutations.