A 4-year-old boy exhibits swelling of his eyes and ankles. What is the most likely associated finding in his disorder?

The presence of fusion of epithelial foot processes on electron microscopy is indicative of minimal change disease, which is a common cause of nephrotic syndrome in children, particularly in the 4- to 6-year-old age group. This condition is characterized by significant proteinuria, hypoalbuminemia, and generalized edema, which can manifest as swelling of the eyes and ankles, as seen in the provided scenario.

In minimal change disease, the hallmark finding on kidney biopsy is the effacement (or fusion) of podocyte foot processes, which disrupts the normal filtration barrier of the glomeruli, leading to increased protein leakage into the urine. Although biopsies may not always be performed in children due to the classic presentation, if they were, this finding would confirm the diagnosis.

Other options correspond to different conditions. For example, "apple green" birefringence with Congo red staining is associated with amyloidosis, while low complement levels and increased anti-streptolysin O titers are relevant in post-streptococcal glomerulonephritis. Presence of ANCA staining is involved in small-vessel vasculitis, which does not align with the symptoms exhibited by the child in this case. Thus, the fusion