Characteristics of patients with coexisting DNAJB9-associated fibrillary glomerulonephritis and IgA nephropathy.

BACKGROUND

Coexistence of fibrillary glomerulonephritis (FGN) and immunoglobulin A (IgA) nephropathy (IgAN) in the same kidney biopsy (FGN-IgAN) is rare, and the clinicopathologic characteristics and outcome of this dual glomerulopathy are unknown.

METHODS

In this study, 20 patients with FGN-IgAN were studied and their characteristics were compared with 40 FGN and 40 IgAN control patients.

RESULTS

Concurrent IgAN was present in 1.8% of 847 consecutive FGN cases and was the second most common concurrent glomerulopathy after diabetic nephropathy. FGN-IgAN patients were overwhelmingly White (94%) and contrary to FGN patients were predominantly (60%) males. Compared with IgAN patients, FGN-IgAN patients were older, had higher proteinuria, a higher incidence of renal insufficiency, and a lower incidence of microhematuria and gross hematuria at diagnosis. Six (30%) patients had malignancy, autoimmune disease or hepatitis C infection, but none had a secondary cause of IgAN or clinical features of Henoch-Schonlein purpura. Histologically, all cases exhibited smudgy glomerular staining for immunoglobulin G and DnaJ homolog subfamily B member 9 (DNAJB9) with corresponding fibrillary deposits and granular mesangial staining for IgA with corresponding mesangial granular electron-dense deposits. On follow-up (median 27 months), 10 of 18 (56%) FGN-IgAN patients progressed to end-stage kidney disease (ESKD), including 5 who subsequently died. Serum creatinine at diagnosis was a poor predictor of renal survival. The proportion of patients reaching ESKD or died was higher in FGN-IgAN than in IgAN. The median Kaplan-Meier ESKD-free survival time was 44 months for FGN-IgAN, which was shorter than IgAN (unable to compute, P =0.013) and FGN (107 months, P = 0.048).

CONCLUSIONS

FGN-IgAN is very rare, with clinical presentation and demographics closer to FGN than IgAN. Prognosis is guarded with a median renal survival of 3.6 years. The diagnosis of this dual glomerulopathy requires careful evaluation of immunofluorescence findings, and electron microscopy or DNAJB9 immunohistochemistry.