Aberrant proteoglycan composition of the glomerular basement membrane in a patient with Denys-Drash syndrome

Background. To ascertain whether changes in proteoglycans are involved in the pathogenesis of the nephrotic syndrome in Denys-Drash syndrome (DDS), we analysed the glycosaminoglycan (GAG) content and composition of the glomerular basement membrane (GBM) in one child with this disorder and in children of comparable age who had died from unrelated disorders. Methods. The diagnosis of DDS was confirmed by the presence of a previously described mutation in the WT1 gene (a tumour suppressor gene). The GAG content and composition of the GEM and tubular basement membrane (TBM), both in the Denys-Drash patient as well as age-matched control infants, was analysed by biochemical studies and indirect immunofluorescence studies. Finally we investigated the urinary GAG excretion of the Drash patient. Results. The biochemical studies revealed that the total GAG content in the GEM as well as TBM was comparable in the Drash patient and the control group. However, the GAG composition of the GEM of the patient was clearly different, with relatively more chondroitin sulphate. The urinary GAG content (expressed as mg GAG/mmol creatinine) was elevated in the Denys-Drash patient due to an increased heparan sulphate (HS(GAG)) excretion. Indirect immunofluorescence (IF) studies for the core protein of human GEM heparan sulphate proteoglycan (HSPG) showed a similar linear staining of all renal basement membranes in the patient and the controls. A monoclonal antibody directed against the HS chain of HSPG (MoAb 403) displayed a strong GEM and a weak TBM staining of normal kidneys. Kidney tissue from the Drash patient displayed a reduced staining of the GEM with MoAb 403. IF studies for chondroitin sulphate proteoglycan (CSPG) showed increased staining of the mesangium and glomerular capillary loops in the Denys-Drash patient which is in agreement with the biochemical studies. No discernible differences in distribution or quality of staining with antibodies against collagen type IV and laminin were observed. Conclusions. These biochemical and immunohistochemical results indicate that in our patient the proteoglycan composition of the GEM is altered. This alteration may play a role in the pathogenesis of proteinuria in this syndrome.