Hepatitis-associated (Australia) antigen and Down's syndrome.

Hepatitis-Associated (Australia) Antigen (HAA) was detected in 13 (5.8%) of 223 patients with Down's syndrome and in 14 (3.7%) of 378 patients with other forms of mental retardation. The frequency of HAA was 2.4 per cent in 127 noninstitutionalized patients with Down's syndrome, and 10.4 per cent in 96 institutionalized patients. The frequency of HAA with Down's syndrome was lower on the average in Japan than in the United States or Germany. HAA was detected in one (1.3%) of 78 mothers of infants with Down's syndrome. Our study suggests that maternal exposure to HAA, as reflected by the presence of either HAA or anti-HAA, was not associated with the subsequent birth of an infant with Down's syndrome.