Selective vitamin B12 malabsorption with proteinuria (Imerslund-Najman-Gräsbeck-syndrome): ultrastructural examinations on renal glomeruli.

Renal biopsy material obtained from a 6 year old girl suffering from an Imerslund-Najman-Gräsbeck-syndrome was examined by light- and electron-microscopy. Clinically the patient presented the characteristic intrinsic factor independent vitamin B12 malabsorption with severe megaloblastic anemia and a benign nephropathy with non-selective proteinuria. Electron microscopic examination of the prenal glomeruli showed no obvious alterations of the Electron microscopic examination of the renal glomeruli showed no obvious alterations of the capillary basement membranes but revealed a considerable diffuse dilatation of the rough endoplasmic reticulum in the podocytes with accumulation of a finely fibrillar material within the widened cisternae. This finding is interpreted as an indication that the synthesis and/or secretory activities of the podocytes, as far as the basement membrane is concerned, and thus the basement membranes themselves, may be altered with the consequence of an increased permeability of the filtration barrier. Because proteinurie contrary to anemia did not respond to parenteral vitamin B12 therapy and therefore is obviously not vitamin B12 dependent, it is assumed that both vitamin B12 malabsorption and glomerulopathy in this hereditary disease are established by a pleiotropic gene or two closely associated genes.