Some epidemiological characteristics of Down's syndrome in Hungary.

Down's syndrome seems to be an adequate indicator condition of germinal numerical chromosome mutation. The true birth prevalence of Down's syndrome was 1.2 +/- 0.1 per 1000 total births in Hungary 1973-1982. The rate of undernotification and misdiagnosis was 25% and 5%, resp. A significant deviation was detected in the occurrence of Down's syndrome in twenty territorial-administrative units of Hungary due to the different ascertainment. The maximum figures may represent the true birth prevalence. No significant monthly variation, i.e., seasonality was found in the birth of Down's syndrome. A Surveillance of Down's syndrome was established in 1980 based on the Hungarian Congenital Malformation Registry.