Successfully treated C3 glomerulopathy in which protein and genetic analyses were useful for diagnosis.

C3 glomerulopathy is a rare disease that results in nephritis due to complement dysregulation and is characterized by C3 deposition in the glomerulus. Dysregulation of the alternative pathway underlies the pathogenesis, but activation of the terminal pathway is also common. The disease is often caused by acquired rather than genetic factors, i.e., autoantibodies against C3 or C5 converting enzyme (convertase) and other complement-related proteins. We report a case of C3 glomerulopathy diagnosed by renal biopsy that responded well to corticosteroids and went into complete remission within two months. Analysis of complements and complement-related proteins revealed a low level of C3 and a high level of soluble terminal pathway protein complex (sC5b-9). Under genetic analysis about complement-related genes, no pathogenic variant was observed. Based on these findings, we diagnosed this patient with C3 glomerulopathy with autoantibodies. Corticosteroids had a marked effect, which also supports this speculation. Analyses of complements and complement-related proteins, and genetic variants may be useful in understanding the pathogenesis of C3 glomerulopathy and in selecting treatment options.

A case diagnosed with IgA nephropathy during a complete remission of minimal change nephrotic syndrome treated with rituximab.

We herein report a case of IgA nephropathy in a 20-year-old male who maintained a complete remission of minimal change nephrotic syndrome (MCNS) through the administration of rituximab (RTX). He was diagnosed with nephrotic syndrome at 4 years of age. After he relapsed frequently, he was diagnosed with MCNS at 8 years of age based on the findings of a kidney biopsy. At 13 years of age, RTX therapy was initiated to maintain a complete remission after steroid treatment. MCNS recurred twice, including the time in which the interval between the RTX administrations was long. Whenever he relapsed, remission induction was achieved using steroids, and remission maintenance was achieved using RTX. Five months after the 7th RTX administration, the serum IgA level started to increase. After the 9th RTX administration, he demonstrated microhematuria despite the urinary protein level indicating complete remission. At the 10th administration, the urinary protein and the red-blood cell casts were also observed. A renal biopsy was performed 84 months after the initial administration of RTX, and the patient was diagnosed with complications of IgA nephropathy. RTX is not considered to be a useful treatment for IgA nephropathy. The reasons for this are due to the fact that IgA1 does not decrease even following the administration of RTX, because B cells residing in the mucosa may not be deleted by RTX, and IgA production may also continue due to the presence of CD20- long-lived plasma cells. Even when administering RTX, if there are findings of glomerulonephritis on urine testing, the possibility of IgA nephropathy must be considered.