Is collapsing C1q nephropathy another MYH9-associated kidney disease? A case report

Abstract

C1q nephropathy is a rare kidney disease that can present with nephrotic syndrome and typically has the histologic phenotype of either minimal change disease or focal segmental glomerulosclerosis (FSGS). Disagreement exists about whether it is a distinct immune complex-mediated glomerulopathy or it resides in the spectrum of FSGS-minimal change disease. Two African American patients with C1q nephropathy histologically presenting as the collapsing variant of FSGS (collapsing C1q nephropathy) and rapid loss of kidney function were genotyped for polymorphisms in the non-muscle myosin heavy chain 9 gene (MYH9). Both cases were homozygous for the MYH9 E1 risk haplotype, the variant strongly associated with idiopathic FSGS, collapsing FSGS in human immunodeficiency virus-associated nephropathy, and focal global glomerulosclerosis (historically attributed to hypertensive nephrosclerosis). Collapsing C1q nephropathy with rapid progression to end-stage renal disease appears to reside in the MYH9-associated disease spectrum.

Figure 1

Kidney biopsy findings for case 2. A. Photomicrograph of biopsy demonstrating the pattern of focal segmental glomerulosclerosis, collapsing variant. Note that collapsed lobules retain their individuality and are associated with hypertrophied/hyperplastic podocytes with intracytoplasmic vacuoles (arrow) some of which contain protein reabsortion droplets. (PAS stain. Original magnification 400X). B. Electron micrograph of biopsy. Note the prominent mesangial immune complex-type electron-dense deposits (arrow). (Uranyl acetate– Lead citrate. Original magnification 3300X).