A 6-year-old girl has become increasingly lethargic over the past 2 weeks. On examination, she has puffiness around the eyes. Her temperature is 36.9degC, and her blood pressure is 100/60 mm Hg. Laboratory findings show serum creatinine, 0.7 mg/ dL; urea nitrogen, 12 mg/dL; and cholesterol, 217 mg/dL. Urinalysis shows pH, 6.5; specific gravity, 1.011; 4+ proteinuria; lipiduria; and no blood or glucose. The 24-hour urine protein level is 3.8 g. The child's condition improves after glucocorticoid therapy. Which of the following findings by electron microscopy is most likely to characterize this disease process?

A child with nephrotic syndrome and no other clinical findings is most likely to have minimal change disease, a name that reflects the paucity of pathologic findings. There is a fusion of podocyte foot processes, which can be seen only by electron microscopy. This fusion leads to selective proteinuria of low molecular weight proteins (albumin). Variability of basement membrane thickening may be seen in Alport syndrome. The mesangial matrix is expanded in some forms of glomerulonephritis (e.g., IgA nephropathy) and other diseases, such as diabetes mellitus, but not in minimal change disease. Reduplication of the glomerular basement membrane may be seen with membranoproliferative GN. Subepithelial electron-dense humps represent immune complexes and are seen in postinfectious GN.