Ultrastructural changes in the glomerular basement membrane of patients with Laurence-Moon-Biedl-Bardet syndrome.

Renal disease, although not a cardinal feature of the Laurence-Moon-Biedl-Bardet syndrome (LMBBS), occurs in more than 70% of patients and is an important cause of morbidity and mortality. Renal ultrastructural changes have not been well delineated. We have studied glomeruli from three patients with LMBBS and have found similar ultrastructural changes in glomerular basement membrane (GBM). Two patients had decreased renal function, hypertension, and markedly abnormal intravenous urograms with reduced concentration of dye and abnormal pelvicalyceal systems; one patient had normal renal function and minimal distortion of the pelvicalyceal system of one kidney. Ligh microscopy revealed varying degrees of increase in mesangial cellularity and matrix. These changes involved almost all glomeruli and were segmental. The abnormalities ranged from mild mesangial cell proliferation to complete sclerosis of the glomerular tuft. Ultrastructural study revealed marked alterations of the glomerular basement membrane: effacement of the trilaminar architecture, segmental and irregular thickening alternating with thinning and rarefaction, accumulation of granular and fibrillary material within the inner third of the GBM. These ultrastructural changes may be the earliest and primary glomerular abnormality seen in LMBBS because they were seen in a patient who had minimal changes on light microscopy.