Basement membrane nephropathy: a new classification for Alport's syndrome and asymptomatic hematuria based on ultrastructural findings.

Renal biopsy specimens from 19 patients with asymptomatic hematuria, normal glomeruli on light microscopic examination, and negative immunofluorescence were studied to characterize the ultrastructural changes of the glomerular basement membrane. Three groups of patients were identified. Four patients (group 1) had type I basement membrane nephropathy, characterized by marked thickening and lamellation of the basement membrane in a pattern resembling that of Alport's syndrome. Seven patients (group 2) had type II basement membrane nephropathy, which was characterized by extensive attenuation of the basement membrane with only occasional small areas of lamellation or fragmentation. Eight patients (group 3) had moderate variability in basement membrane thickness with no other structural alterations. The authors propose that this pathologic classification be used in patients with asymptomatic hematuria as a basis for long-term clinical investigations, in hopes of distinguishing the natural history of each group.