Prominent glomerular basement membrane (GBM) reflecting a segmental and increase in thickness (subjective estimate) with no evidence of electron dense deposits by EM. Thickening is measured from endothelial to visceral epithelial plasma membrane and mainly attributable to an increase in thickness of the lamina densa, generally to an overall thickness more than 2 standard deviations greater than that of the normal mean GBM thickness for health age- and sex matched individuals. [from
HPO]