NPHS1 and focal segmental glomerulosclerosis: New studies of the molecular biology of the podocyte and identification of genes mutated in rare familial forms of FSGS and nephrotic syndrome, such as nephrin, WT-1, transient receptor potential cation channel-6 (TRPC-6), phospholipase C epsilon, α-actinin-4 and podocin, have given important new insights into mechanisms of progressive glomerulosclerosis.