Low incidence of null alleles of the fourth component of complement (C4) in elderly people.

Allotype frequencies of three complement proteins (C2, factor B, and C4) encoded on the sixth chromosome were tested in 150 "young" (under 53 yrs) and 131 "old" (over 62 yrs) healthy Hungarian individuals. In women, we found significant differences in BF*F allotype frequencies between the two age groups. A marked decrease of null alleles for C4 was observed especially in men. In the "old" age group, the total frequency of the non-expressed, "null" (Q0) alleles of the C4 protein dropped to almost one third of the "young" ones. The decrease was even larger (a 5.5-fold decrease in the incidence) among men. The relative risk of those having C4B*Q0 allele not to survive a "critical age period" of 53-62 yrs for males and 58-62 yrs for females was calculated to be 12.4 and 2.85, respectively. Our data substantiate the view that the expected life time is genetically determined and it can be forecast partly by the analysis of the antigens encoded on the sixth chromosome.