C2 deficiency in blood donors and lupus patients: prevalence, clinical characteristics and HLA-associations in the Brazilian population.

The objective of the present study was to investigate the prevalence, clinical characteristics, and HLA association of C2 deficiency in the Brazilian population. The frequency of C2 deficiency profile (C2Q degree profile) was 2.2% among 1503 blood donors and 6.6% among 166 patients with systemic lupus erythematosus (SLE). A higher incidence of clinical manifestations possibly related to immune complex disease was observed among blood donors with C2Q degree profile and their relatives with C2Q degree profile when compared to the normal C2 relatives. The comparison of clinical and laboratory features between SLE patients with C2Q degree profile and those with normal C2 revealed earlier disease onset, higher frequency of oral ulcerations and lower frequency of anti-native DNA antibodies in the first group. The HLA study conducted on 18 individuals with C2Q degree profile (11 blood donors and 7 SLE patients) confirmed the previously reported association with the antigens HLA-A25, B18 and DR2, supporting the concept that probably most C2 deficiency cases, throughout the world, are due to a single mutation in the C2 gene in linkage disequilibrium with the A25B18DR2 haplotype.