Decreased thickness of the glomerular basement membrane (GBM), measured from endothelial to visceral epithelial plasma membrane and mainly attributable to a decrease in thickness of the lamina densa, generally to an overall thickness more than 2 standard deviations less than that of the normal mean GBM thickness for health age- and sex matched individuals. May be focal or diffuse, although the term thin GBMs generally implies thinning of over 50% of GBMs. [from
HPO]