Congenital nephrotic syndrome of the Finnish type is a serious renal disease belonging to the Finnish disease heritage. It appears as substantial proteinuria, hypoproteinemia and edema in a newborn. Kidney transplantation is the only effective treatment. The cause of the disease is a mutation in the gene encoding the nephrin protein. Nephrin is produced by the epithelial cell (podocyte) of the glomerulus. It is expressed in the slit membrane connecting the pedicles of the podocyte. This finding has revolutionized the concept of glomerular filtration and set off active research on the pathogenetic mechanisms of proteinuria.