There is increasing recognition of the importance of genetic factors in the development of focal segmental glomerulosclerosis and related proteinuric disorders. Recently, four genes have been identified which, when defective, cause focal segmental glomerulosclerosis or nephrosis. All of these genes appear to be important in the maintenance of glomerular podocyte function. However, not all cases of familial nephrosis or proteinuria are explained by defects in these genes.