Down syndrome, temporal variation and fallout radiation revisited: statistical evidence

To revisit a study on the prevalence of Down Syndrome (DS) in the Fylde of Lancashire and ionizing radiation, using new birth data that allow better control for maternal age. Associations between ionizing radiation and DS prevalence have been controversial. Some studies link temporal variation in prevalence to ionizing radiation; others do not. Cases were ascertained in a prospective survey of major congenital malformations among residents in the Fylde of Lancashire between 1957 and 1991. New data on the birth maternal age distribution in the Fylde were obtained from the Office for National Statistics for most of the study period. Temporal clusters in prevalence rates were again detected using the Poisson log linear models used to measure the association between prevalence and ionizing radiation from atomic fallout. Significant effects of fallout radiation were found when maternal age was both controlled and not controlled for. Two DS prevalence peaks occurred during the study period. The first started in June 1958 and lasted for five months. The second lasted longer, starting in October 1962 and ending in August 1964. Although these peaks corresponded to peaks in fallout radiation dosage, they were not significant.