Immunogenetics of complement in mixed cryoglobulinaemia.

Area of Science:

• Immunogenetics
• Complement System Biology
• Molecular Medicine

Background:

• Low complement component 4 (C4) levels are characteristic of mixed cryoglobulinaemia (MC).
• The C4 gene, located in the human MHC region, exhibits significant copy number variation (CNV).
• Previous studies suggest factors beyond C4 depletion may influence MC pathogenesis.

Purpose of the Study:

• To investigate the association between C4 gene copy number (GCN), specific C4 allotypes, and clinical manifestations in mixed cryoglobulinaemia (MC).
• To analyze C4 gene copy number (GCN), C4A and C4B isotypes, and the presence of hypofunctional C4A6 and C4A0 allotypes in MC patients.

Main Methods:

• Real-time PCR was used to evaluate C4 gene copy number (GCN).
• Primer extension assays screened for the C4A6 allotype and a 2-bp insertion mutation.
• Cluster analysis (K-means) correlated genetic findings with clinical disease signs.

Main Results:

• MC patients exhibited fewer C4A gene copies and a lower C4A GCN index compared to controls.
• A significant increase in the C4A6 variant (rs41315824) frequency was observed in cryoglobulinaemic patients.
• Patients with fewer C4 gene copies showed a higher prevalence of severe complications like glomerulonephritis and neuropathy.

Conclusions:

• Polymorphisms in the C4 gene are associated with the clinical presentation of mixed cryoglobulinaemia (MC).
• C4 gene copy number and specific allotypes may influence disease severity and organ involvement in MC.