The term thin glomerular basement membrane disease (TBMD) refers to a condition characterised by thinning of the GBM at electron microscopy examination and, clinically, by isolated
hematuria, frequently occurring in other family members, with no extra-renal manifestations. Progression towards
chronic renal failure (CRF), although rare, has been reported and blood pressure is high in 30-35% of cases during follow-up. TBMD is generally considered different from
Alport syndrome since immunohistological investigation does not show abnormalities of
type IV collagen alpha chains in the GBM, as frequently observed in Alport patients; moreover, in familial cases, the disease is transmitted as autosomal dominant trait, rarely observed in
Alport syndrome. Genetic studies suggest that TBMD is a heterogeneous disease, but some cases may be related to mutations of COL4A3/COL4A4 genes, thus belonging to the spectrum of
type IV collagen diseases. TBMD may arise with other glomerular diseases, most frequently
IgA nephropathy, and it remains to be established whether these cases are a casual occurrence or whether a thinner than normal GBM predisposes to
immune complex deposition.