A reanalysis of the New York State prenatal diagnosis data on Down's syndrome and paternal age effects.

This paper reanalyzes the data from the Hook and Cross (1982) paper in this journal concerning the association between Down's syndrome and paternal age. The New York State (NYS) data are compared with a large European collaborative study by Ferguson-Smith and Yates (1984). The maternal-age-dependent risks in the NYS data were found to be significantly higher than in the European data. When the NYS data was divided into three groups by means of the paternal age, a marked two-peaked distribution was found. The maternal-age-dependent risk was high when the fathers were up to 33 years old, low when the fathers' ages were 34-39 years and high again when the fathers were at least 40 years old. The differences were significant. The results speak in favour of the existence of temporal, geographic, or environmental variations in the risk for de novo trisomy 21, as well as of a paternal age effect. The existence of a "paternal age effect" in at least some populations is confirmed. If the results of this paper are confirmed in other investigations, it will be necessary to revise present genetic counselling rules towards far more individually specified considerations.