Familial Kidney Disease Phenocopying Hypertensive Nephropathy

Familial kidney disease is common in Cyprus and previous studies have found that the majority of families have mutations in Alport syndrome genes COL4A3/4/5. We have collected data from over 50 Turkish Cypriot families in whom kidney disease appears to follow an autosomal dominant pattern, and looked for pathological variants in these genes.

Probands from 55 families underwent massive parallel DNA sequencing using a glomerular gene panel for familial hematuria, and whole-exome sequencing (WES) was also performed in 22 of them. Clinical records were reviewed.

Likely pathogenic variants were identified in 7 of the 55 families (COL4A3 [3], COL4A4 [2], and COL4A5 [2]), leaving 48 unsolved families. Among the latter a common missense variant of uncertain significance (COL4A4:p.G545A), was present in 5 families (9.1%). In contrast to families with a pathogenic variant in COL4A3/4 and a clear glomerular phenotype the 5 families (54 patients with clinical and genetic data), manifested near dominant susceptibility with incomplete penetrance, presenting with hypertension, variable and intermittent microscopic hematuria, and minimal proteinuria, <1 g/day until the estimated glomerular filtration rate (eGFR) fell below 30 mL/min, after which it increased in some individuals. Of those over age 50, 20% had reached end-stage by median age of 66 (48-80) years.

We describe a kidney disease with mild hypertension that is more characteristic of a tubulointerstitial disease and phenocopies hypertensive nephropathy. While the variant COL4A4:p.G545A is not responsible for a Mendelian CKD phenotype, it appears to increases the susceptibility, acting as a hypomorphic variant contributing to Alport spectrum nephropathy. Early detection and treatment with ACE inhibitors should prolong kidney survival to an age where hemodialysis is avoided.