An additional blood volume will be sampled in patients and controls during a scheduled biological check-up for the initial disease and viral genome of EBV, CMV, HHV6, HHV7 as well as adenovirus will be searched for using PCR reaction in total blood DNA extract. The frequency of a latent hybridization of virus genome within human genome will be compared between patients with steroid sensitive nephrotic syndrome and controls matched for age and sex. Secondary studies will include a comparison of steroid dependency in nephrotic patients according to the occurence of a latent viral hybridization, the epidemiology of idiopathic nephrotic syndrome in the Parisian area and a pharmacogenetic analysis of steroid sensitivity and dependency. If necessary, the chromosomal localization of viral hybridization will be studied with fluorescence in situ hybridization using specific probes.