Prognostic Value of glomerular collagen IV immunofluorescence studies in male patients with X-linked alport syndrome

Abstract

Background and objectives X-linked Alport syndrome (X-AS) is caused by mutations of the COL4A5 gene, which encodes for the collagen IV a5 chain (a5[COLIV]), resulting in structural and functional abnormalities of the glomerular basement membrane (GBM) and leading to CKD. The aim of the present study was to evaluate the prognostic value of residual collagen IV chain expression in the GBM of patients with X-AS. Design, setting, participants, & measurements The medical records of 22 patients with X-AS from 21 unrelated families collected between 1987 and 2009 were reviewed (median age at last follow-up, 19.9 years; range, 5.4-35.1 years); GBM expression of a1, a3, and a5(COLIV) chains was assessed by immunofluorescence microscopy. Results GBM distribution of the a5(COLIV) chain was diffuse in 1 and segmental or absent in 21 of the 22 patients; the expression of the a3(COLIV) chain was diffuse in 5 of 22 patients and segmental or absent in 17 of 22 patients. Patients with diffuse staining for the a3(COLIV) chain presented with proteinuria significantly later (median age, 16.9 versus 6.1 years; P=0.02) and reached an estimated GFR < 90 ml/min per 1.73 m2 at an older age (median age, 27.0 versus 14.9 years; P=0.01) compared with patients with segmental or absent staining. Two thirds of patients with abnormal a3(COLIV) expression by immunofluorescence studies had null or truncating COL4A5 mutations, as opposed to none of the 4 tested patients with diffuse a3(COLIV) chain glomerular distribution. © 2013 by the American Society of Nephrology.