Integration of Genetic Testing and Pathology for the Diagnosis of Adults with FSGS.

Abstract

FSGS and nephrotic syndrome studies have shown that single gene causes are more likely to be found in pediatric cases than adults. Consequently, many studies have examined limited gene panels in largely pediatric cohorts. Whole-exome sequencing was performed in adults with FSGS diagnosed between 1976 and 2017 in the Toronto GN Registry. An expanded panel of 109 genes linked to FSGS, glomerular basement membrane abnormalities, as well as causes of pediatric ESKD including congenital abnormalities of the kidney and urinary tract (CAKUT) and nephronophthisis, were examined. The cohort was composed of 193 individuals from 179 families. Nearly half (49%) developed ESKD at a mean age of 47±17 years. The genetic diagnostic rate was 11%. Of definitely pathogenic variants, 55% were in COL4A (A3/A4/A5), 40% were in podocyte genes, and 5% were in CAKUT genes. Many, but not all individuals with COL4A definitely pathogenic variants had some evidence of glomerular basement membrane abnormalities. The estimated mean survival/age of kidney failure for individuals with COL4A definitely pathogenic variants was 58 years (95% confidence interval, 49 to 69), far later than what has been reported in the literature. Likely pathogenic variants were identified in an additional 9% of the cohort, with most in COL4A. Correlation with glomerular basement membrane morphology suggested a causal role for at least some of these likely pathogenic variants. Even with an expanded gene panel, we find that COL4A disorders are the leading monogenic cause in adults diagnosed with FSGS. This article contains a podcast at https://www.asn-online.org/media/podcast/CJASN/2019_01_15_CJASNPodcast_19_02_.mp3.