Kidney pathological findings of MYH9-related disease: a cross-sectional nationwide survey in Japan.

Background: MYH9-related disease (MYH9-RD) is characterized by macrothrombocytopenia, hearing loss, and progressive kidney dysfunction. Due to thrombocytopenia, kidney biopsy is seldom performed, and pathological findings remain unclear. Although case reports have described focal segmental glomerulosclerosis (FSGS) and glomerular basement membrane (GBM) abnormalities like Alport syndrome, no cross-sectional studies of MYH9-RD have been performed. This study aimed to clarify kidney pathological findings through a nationwide survey.

Methods: We conducted a nationwide survey of MYH9-RD patients and collected tissues from kidney biopsies, along with immunofluorescence and electron microscopy images. Multiple pathologists examined all samples.

Results: Nine kidney biopsy samples were included. Mesangial matrix expansion was observed in all samples (100%), while FSGS was observed in two (22%). Segmental foot process effacement was observed in all samples (100%), with irregularly aggregated podocyte dense material in seven (78%). Immunofluorescence analysis revealed that three samples (33%) had immunoglobulin and/or complement deposition: the types of depositions varied among patients. Electron dense deposits (EDD) were found in five samples (56%). GBM abnormalities - thinning, irregular thickening, and splitting of the lamina densa - were observed in five samples (56%), but no basket-weave appearance was noted. Endothelial cell swelling was found in seven samples (78%).

Conclusions: Mesangial expansion and segmental foot process effacement were commonly observed in MYH9-RD patients. Additional findings included immunoglobulin and complement deposition with EDD, and GBM abnormalities. Although patients may have had relatively severe disease, which limits generalizability, these results provide valuable insights into the disease mechanisms and potential therapeutic targets of MYH9-RD.