Restricted genetic defects underlie human complement C6 deficiency

Area of Science:

• Immunology
• Genetics
• Molecular Biology

Background:

• Complement C6 homozygous deficiency (C6D) is infrequently observed in Caucasian populations.
• C6D exhibits a higher prevalence among African-Americans, suggesting specific genetic underpinnings.
• The clinical manifestations of C6D can include Neisseria meningitidis infections and autoimmune conditions.

Purpose of the Study:

• To investigate the molecular basis of C6D in individuals of African descent living in France.
• To identify specific genetic mutations within the C6 gene responsible for C6D.
• To correlate genetic findings with clinical presentations in affected individuals.

Main Methods:

• Genomic DNA analysis of seven unrelated black individuals with C6D.
• Direct polymerase chain reaction (PCR) amplification of exons 6, 7, and 12 of the C6 gene.
• Nucleotide sequencing of amplified DNA fragments to identify mutations.

Main Results:

• Three patients were found to have a homozygous single-base deletion (1936delG) in exon 12.
• Four patients presented compound heterozygous deletions, involving exon 7 (1195delC) or exon 6 (878delA) in conjunction with the exon 12 deletion (1936delG).
• All patients exhibited undetectable levels of antigenic C6.

Conclusions:

• The study confirms a restricted pattern of genetic defects associated with homozygous C6 deficiency in individuals of African descent.
• Specific mutations in exons 6, 7, and 12 of the C6 gene are identified as the cause of C6D in this population.
• These findings contribute to understanding the genetic epidemiology of complement deficiencies.