Nephrin has been identified as a disease causing molecule responsible for congenital nephrotic syndrome of Finnish type, in which the proteinuria starts in utero or immediately after birth (ref. 1). It is an immunoglobulin-like transmembrane adhesion protein having eight Ig motifs. Nephrin forms a structural backbone of the slit diaphragm through a head-to-head, trans-homo-interaction at the N-terminal ectodomains.