C4B deficiency associated with membranoproliferative glomerulonephritis

Area of Science:

• Nephrology
• Immunology
• Genetics

Background:

• Systemic lupus erythematosus (SLE) can present with renal involvement, often indicated by urinary abnormalities like hematuria and proteinuria.
• Complement component deficiencies, particularly C4B deficiency, have been anecdotally linked to renal diseases, though the exact mechanisms are not fully elucidated.

Observation:

• A 10-year-old girl presented with persistent microscopic hematuria and proteinuria, initially suspected to be SLE due to renal biopsy findings.
• Despite the suspicion of SLE, the patient lacked typical autoantibodies and specific clinical symptoms.
• Throughout the observation period, the patient exhibited persistently low levels of the 4th component of complement (C4B).

Findings:

• Genetic and allotyping analyses confirmed a complete deficiency in C4B.
• Corticosteroid treatment led to a positive response in the patient's urinary abnormalities.
• The persistent low C4B levels and the resolution of urinary findings with treatment suggest a direct link between C4B deficiency and the observed nephropathy.

Implications:

• This case underscores the importance of considering complement deficiencies, specifically C4B deficiency, in the differential diagnosis of unexplained nephropathies, even in the absence of classic autoimmune markers.
• Further research into the role of C4B in renal health may reveal novel therapeutic targets for complement-mediated kidney diseases.
• Understanding the genetic basis of complement deficiencies can aid in predicting and managing associated renal pathologies.