Polypoid change of the glomerular basement membrane.

A peculiar and previously undescribed alteration in the glomerular basement membrane, which we designate as polypoid change, was found in a 4-year-old child with mongolism (trisomy 21). Light and electron microscopical studies were performed. Although the pathogenesis and significance of this lesion remain uncertain, we have compared the lesion with known processes that affect the glomerular basement membrane.