Homozygous or hemizygous mutations in glomerular filtration barrier genes, such as the COL4A3/4/5 genes, result in Alport syndrome (AS) [3,4,5], while homozygous mutations in the NPHS1 and NPHS2 genes result in congenital nephrotic syndrome [6,7]. The gene discussed is COL4A3; the disease is Alport syndrome.