LMX1B-Associated Nephropathy With Type III Collagen Deposition in the Glomerular and Tubular Basement Membranes

Abstract

Variants in the LMX1B gene cause nail-patella syndrome, a rare autosomal dominant disorder characterized by dysplasia of nails, patella and elbow abnormalities, iliac "horns," and glaucoma. We describe an adult man with nephrotic syndrome and no systemic manifestations of nail-patella syndrome at the time of his initial kidney biopsy. His kidney biopsy was initially interpreted as a form of segmental sclerosis with unusual fibrillar deposits. At the time of consideration for kidney transplantation, a family history was notable for end-stage renal disease in 3 generations. Subsequent reanalysis of the initial biopsy showed infiltration of the lamina densa by type III collagen fibrils, and molecular studies identified a pathogenic variant in one allele of LMX1B (a guanine to adenine substitution at nucleoide 737 of the coding sequence [c.737G>A], predicted to result in an arginine to glutamine substitution at amino acid 246 [p.Arg246Gln]). This variant has been described previously in multiple unrelated families who presented with autosomal dominant nephropathy without nail and patellar abnormalities.

Keywords: LMX1B; LMX1B-associated nephropathy; focal segmental glomerulosclerosis (FSGS); hereditary FSGS; kidney biopsy; nail-patella syndrome; nephrotic syndrome; next-generation sequencing; renal-limited; type III collagen.