Human Complement C4B Allotypes and Deficiencies in Selected Cases With Autoimmune Diseases.

Area of Science:

• Immunology
• Human Genetics
• Molecular Biology

Background:

• Human complement C4 (C4) is a highly diverse and heritable component of humoral immunity.
• C4 plays critical roles in immune defense and is implicated in autoimmune and inflammatory diseases.

Purpose of the Study:

• To investigate the genetic basis of C4 polymorphisms, including C4A and C4B deficiencies.
• To understand the impact of C4 diversity on autoimmune disease pathogenesis.

Main Methods:

• Analysis of C4A and C4B protein diversity and gene copy number variations (CNVs).
• Sequencing and characterization of C4 variants and mutants in healthy individuals and patients.
• Development of specific detection techniques for identified C4 variants.

Main Results:

• Identified C4B7 allotype linked to R729Q variation and C4B deficiency due to frameshift mutations.
• Discovered a recurrent haplotype with defective C4B genes and splice site mutations in a family with lupus-related mortality.
• Characterized a novel C4B W660x mutation in an East-Asian patient with anti-NMDA receptor encephalitis, recurrent in East-Asians but not SLE patients.
• Annotated C4 sequences, identifying variation clusters near functional sites.

Conclusions:

• C4 genetic diversity, including CNVs and specific mutations, significantly impacts C4 function and is associated with autoimmune diseases.
• Novel C4 variants and mutations have been identified and characterized, providing tools for diagnosis and understanding disease mechanisms.
• Further research into C4 polymorphisms can elucidate its role in immune response and disease susceptibility.