We present a case of
nephrotic syndrome caused by
semaphorin 3B-associated
membranous nephropathy. The patient was an 8-month-old male infant who presented with severe
proteinuria and
hypertension. He was treated with
prednisolone (PSL) for
nephrotic syndrome; however, remission was not achieved within 4 weeks. He was diagnosed with
steroid-resistant nephrotic syndrome and underwent kidney biopsy. Pathological examination revealed
membranous nephropathy with
IgG deposits on both the glomerular basement membrane (GBM) and the tubular basement membrane (TBM). He was treated with
cyclosporine (CsA) in addition to PSL and achieved complete remission. However, frequent relapses occurred after the discontinuation or tapering of
immunosuppressants. Two years
after treatment initiation, a second biopsy was performed and showed worsening of the disease, which required treatment with several
immunosuppressants to achieve complete remission. After that, we performed additional immunostaining for
semaphorin 3B, which confirmed the diagnosis of
semaphorin 3B-associated
membranous nephropathy. Although extremely rare in infantile cases,
semaphorin 3B-associated
membranous nephropathy should be considered in the differential diagnosis, as strong treatment with
immunosuppressants might be needed. In addition,
mycophenolate mofetil showed an effective clinical response in this case, indicating that it can be considered for future treatment strategies.