COL4A3 and Nephropathy: Interestingly, among the patients with nephropathy of unknown origin, a genetic defect was found in 17.1% of them, with a broad range of mutations, encompassing defects of collagen (either COL4A3, COL4A4, COL4A5), UMOD-associated tubulointerstitial disease, mutations in PKD1, and other less frequent defects.