Rare hereditary COL4A3/COL4A4 variants may be mistaken for familial focal segmental glomerulosclerosis

Abstract

Focal segmental glomerulosclerosis (FSGS) is a histological lesion with many causes, including inherited genetic defects, with significant proteinuria being the predominant clinical finding at presentation. Mutations in COL4A3 and COL4A4 are known to cause Alport syndrome (AS), thin basement membrane nephropathy, and to result in pathognomonic glomerular basement membrane (GBM) findings. Secondary FSGS is known to develop in classic AS at later stages of the disease. Here, we present seven families with rare or novel variants in COL4A3 or COL4A4 (six with single and one with two heterozygous variants) from a cohort of 70 families with a diagnosis of hereditary FSGS. The predominant clinical finding at diagnosis was proteinuria associated with hematuria. In all seven families, there were individuals with nephrotic-range proteinuria with histologic features of FSGS by light microscopy. In one family, electron microscopy showed thin GBM, but four other families had variable findings inconsistent with classical Alport nephritis. There was no recurrence of disease after kidney transplantation. Families with COL4A3 and COL4A4 variants that segregated with disease represent 10% of our cohort. Thus, COL4A3 and COL4A4 variants should be considered in the interpretation of next-generation sequencing data from such patients. Furthermore, this study illustrates the power of molecular genetic diagnostics in the clarification of renal phenotypes.

Figure 1. Family DUK6696 proband biopsy

(A) Masson's trichrome stain at 10X. There is segmental glomerular sclerosis in the hilar region with moderate interstitial fibrosis, clusters of foam cells in the interstitium, and tubular atrophy. (B) Periodic acid-Schiff stain of tissue from same individual.

Figure 2. COL4A3 variants in Family DUK6696

(A) Reference chromatogram in exon 7. (B) Reference chromatogram in exon 34. (C) Chromatogram of heterozygous E131fsX151 variant in father, exon 7. (D) Chromatogram of heterozygous Q936X variant in mother, exon 34. (E, E’, E’’) Chromatograms of the three affected siblings showing E131fsX151 and Q936X compound heterozygous variants in trans.

Figure 3. Family DUK6534 proband biopsy

A and B) The same glomerulus stained with periodic acid-Schiff (A) and hematoxylin and eosin (B) showing segmental sclerosis with hyalinosis (arrows) and adhesion to Bowman capsule. C and D) Electron microscopy from the same individual showing two different capillary loops. Both have localized effacement of podocyte foot processes. Area of basement membrane denudation with loss of podocyte cytoplasm (arrow). Glomerular basement membranes are slightly irregular but are of normal thickness with no lamination.

Figure 4. COL4A3 and COL4A4 variants relative locations

(A) Cartoon of the α3 collagen(IV) protein illustrating the locations of variants described in this study. (B) Cartoon of the α4 collagen(IV) protein illustrating the locations of variants described in this study. “7S” and “NC1” refer to the canonical cysteine-rich, 25-amino acid N-terminal domain and the C-terminal globular non-collagenous domains respectively which flank the central triple helical domain. Blue diamonds represent missense variants and red diamonds represent frame shift and nonsense variants.