An abnormal Cgamma 4 gene among the negro population.

An analysis of the IgG4-CH3 antigenic determinants by means of specific antisera using a hemagglutination-inhibition procedure among different populations has been done. Thus 3.67% of sera from Negroids have been found completely deficient in normal IgG4 subclass. Sera without normal IgG4 contained the other IgG subclasses. Family studies shown the transmission of an abnormal Cgamma 4 gene. Hypothesis of gene deletion, point mutation or gene hybridization were postulated. This last hypothesis seems the most valuable.