Hepatitis associated antigen and the ABO locus in Down's syndrome.

The recent observation by Arndt-Hansen et al. (1974) of increased frequency of blood group A over group O in blood donors positive for the hepatitis associated antigen has been investigated in Down's syndrome, in order to establish if this could account for the increased frequency of the antigen in that syndrome. Seventy-one of 227 subjects with Down's syndrome (31.3%) were found to be positive for the antigen by haemagglutination, and comparison of these with the HAA-subjects failed to reveal any differences in the ABO blood groups.