Down syndrome: increased frequency of maternal meiosis I nondisjunction during the transitional stages of the ovulatory seasons.

In a month-of-birth study of Down syndrome (DS) individuals, we found--in agreement with a previous collaborative European study (Jongbloet et al. 1982)--a distribution of maternal meiosis I (Mat MI)-DS births, both graphically and statistically differing from that of both total births (P less than 0.05) and from that of the three other (Mat MII + Pat MI + Pat MII)-DS subcategories (P less than 0.001). In four subgroups, namely the DS individuals born in the years 1960-1979 and 1980-1983 and those from mothers less than or equal to 30 years, and greater than or equal to 31 years, analogous results were found. In addition, the Mat MI-DS individuals were shown to have been conceived more frequently during the "strong" change rate periods. i.e. the transitional stages of ovulatory breakthrough and breakdown, and less during the "weak" change rate periods, i.e. the periods of a rather stable ovulatory rate (P less than 0.05). The same results were found in two subgroups of individuals born 1960-1970 (P less than 0.055) and from mothers greater than or equal to 31 years (P less than 0.02). This interdependence estimated by linear regression in the total group (rs = 0.503; P less than 0.055) and in the subgroup greater than or equal to 31 years (rs = 0.556; P less than 0.05), supports the hypothesis that Mat MI nondisjunctions occur more frequently during the transitional stages of the ovulatory seasons, i.e. they are caused by seasonal pre-ovulatory overripeness ovopathy (SPOO).