Dense Deposit Disease with Elevated Serum C3 in a Child with Steroid-Resistant Nephrotic Syndrome: A Case Report

ABSTRACTBackground: Dense deposit disease (DDD) is a rare C3 glomerulopathy characterized by dysregulation of the alternative complement pathway, typically presenting with low serum C3 levels. We report an unusual case of biopsy-proven DDD with elevated serum C3 in a child presenting as steroid-resistant nephrotic syndrome (SRNS).Case Presentation: A 5-year-old male child, born of second-degree consanguineous marriage, presented with nephrotic syndrome at age 2 years. After 12 weeks of non-response to standard steroid therapy, renal biopsy confirmed DDD. Notably, serum C3 was elevated (191 mg/dL; reference: 80-150 mg/dL) with normal C4 (27.70 mg/dL). The patient showed partial response to continued steroids and was subsequently started on mycophenolate mofetil (MMF) 600 mg/m²/dose twice daily. At 15-month follow-up on MMF, the patient remains in clinical remission with intermittent low-grade proteinuria and no edema.Conclusions: This case highlights that DDD can present with elevated serum C3, challenging the conventional diagnostic paradigm. Clinicians should not exclude C3 glomerulopathy based solely on normal or elevated complement levels. Renal biopsy remains the gold standard for diagnosis. MMF may be an effective therapeutic option in pediatric DDD.