Primary glomerular fibrosis: a new nephropathy caused by diffuse intra-glomerular increase in atypical type III collagen fibers.

A 38-year-old Japanese man suffering from nephrotic syndrome and slowly progressive impairment of renal function underwent renal biopsy. Light microscopy revealed diffuse lobular accentuation of glomerular tufts, occupied by homogeneous material which was eosinophilic, lightly stained with periodic acid silver methenamine and deeply with aniline blue. Further examinations using an electron microscope after treatment with phosphotungstic acid revealed that this material exhibited a diffuse increase in fibers having a periodicity of 65 +/- 4 nm (mean +/- SD) like type III collagen fibers and was reactive to the anti-type III collagen monoclonal antibody. In addition, the serum level of procollagen III peptides was markedly elevated to 221 ng/dl (normal range 2-13 ng/dl). However, the fibers were peculiarly curved and frayed as reported in the nail-patella syndrome, but were not observed in the lamina densa of the glomerular basement membrane (GBM) as seen in this syndrome. No family history or physical findings of bony and nail dystrophy, no laboratory data or pathological findings compatible with already described renal diseases including mesangiocapillary glomerulonephritis, light chain disease, immunotactoid nephropathy, amyloidosis, and non-amyloidotic fibrillary glomerulonephritis were observed. These data strongly suggest that the nephropathy is caused by a primary increase in atypical type III collagen fibers in glomeruli (primary glomerular fibrosis), which to our knowledge has not yet been described in the English literature.