COL4A2 and chronic kidney disease: (b) CFB and C1 S are members of the complement system that is activated in several glomerular immune-complex diseases, and in progressive tubulointerstitial fibrosis [26], a feature of several chronic renal diseases in our data.(c) COL4A2 is an isoform of collagen type IV whose mutations have been found to alter the glomerular basement membrane directly affecting glomerular filtration, and thereby renal function [27].