Chemical properties of glomerular basement membrane in congenital nephrotic syndrome.

Glomerular basement membranes have been isolated from kidneys of three children presenting with a congenital nephrotic syndrome. The histology of renal tissue was characterized by an increase of the mesangial area mainly due to matrix. Immunofluorescent studies showed no positive staining. After isolation, the glomerular basement membranes contained no more cellular contaminants than normal membranes. Isolated abnormal membranes exhibited, as normal preparations, less than 1% DNA, RNA, phospholipids or glycosaminoglycans. Since the protein content of both membrane preparations was comparable, significant contamination by non-proteic material did not seem likely. Although the amino acid and carbohydrate composition of both normal and abnormal membranes was very similar, the folowing statistically significant differences were observed: diseased membranes exhibited an increased number of hydroxylysine, 3- and 4-hydroxyproline residues, and an increased content of glucosyl-galactosyl-hydroxlysine units. The data suggest that, in the congenital nephrotic syndrome, the production of disaccharide-rich glomerular basement membrane subunits is enhanced, which could interfere with the packing of the peptide chains and therefore account for the altered permeability of the membrane observed in this disease.