[Predisposition of Down syndrome to chronic infection with the hepatitis B virus].

In order to know in Down's Syndrome (DS) the age of infection by hepatitis B virus (HBV), the incidence of evolution to a chronic carrier status and the optimal age for vaccination against this virus, a study of the prevalence of HBV-markers was carried out in 302 mentally retarded children: Group I, 51 pre-schoolchildren with DS (mean age 2.9 +/- 1.6 years); Group II, 72 schoolchildren with DS (mean age 13.8 +/- 3 years) and Group III, 179 schoolchildren with other types of mental retarded (OMR). Children from group II and III attended the same school as external day-pupils. Fifty eight percent of schoolchildren with SD presented at least one HBV-marker while this percentage was of 25% in schoolchildren with OMR (p > 0.05) or pre-schoolchildren with DS (p > 0.005); DS schoolchildren become also HBV chronic carrier with higher frequency than ORM schoolchildren (40 vs 17) (p > 0.05) and they maintained HBV replication in a higher proportion of cases (36 vs 4) (p > 0.05). In conclusion children with DS acquire easily HBV infection and this occurs when they attend the school independently that the school is a closed or an open institution. They also become more frequently HBV chronic carriers and they maintain HBV replication; so, they must be vaccinated before they begin to attend school and they must be treated with antiviral agents as soon as possible.