Familial C4B deficiency and immune complex glomerulonephritis
1Department of Nephrology, Hospital Fernando Fonseca, Lisbon, Portugal. ksoto.nefro@gmail.com
Clinical Immunology (Orlando, Fla.)
|June 29, 2010
Summary
Complete C4B deficiency was identified in a patient with Membranoproliferative Glomerulonephritis (MPGN) type III, challenging known complement roles. This highlights the importance of genetic and functional complement testing in glomerulopathy patients.
Area of Science:
- Immunology
- Genetics
- Nephrology
Background:
- Complement C4B deficiency is rare and its association with glomerulonephritis is not fully understood.
- Membranoproliferative Glomerulonephritis (MPGN) type III involves immune deposits in the kidneys.
- The classical complement pathway plays a role in immune response and tissue homeostasis.
Observation:
- A young female patient presented with Membranoproliferative Glomerulonephritis type III, exhibiting significant C4 and IgG deposits in renal biopsies.
- Genetic analysis revealed homozygous C4B deficiency due to a homozygous monomodular RCCX genotype with single long C4A genes.
- Low C4 levels were observed in other family members, some with heterozygous C4B deficiency, but without renal disease or infections.
Findings:
- The patient's homozygous C4B deficiency was directly linked to her MPGN type III diagnosis.
- HLA typing showed specific homozygous alleles (A*02, Cw*06, B*50, DRB1*08, DQB1*03) in the patient.
- The study identified a complete C4B deficiency in the patient and heterozygous deficiency in relatives, challenging established roles of C4A and C4B.
Implications:
- These findings necessitate a re-evaluation of the pathophysiological roles of C4A and C4B in immune-mediated diseases.
- Functional assays, C4 allotyping, and genotyping are crucial for diagnosing and understanding glomerulopathies associated with low complement levels.
- This case underscores the importance of comprehensive genetic and functional complement analysis in patients with unexplained glomerulonephritis and immune deposits.
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