Parental age and unbalanced Robertsonian translocations associated with Down syndrome and Patau syndrome: comparison with maternal and paternal age effects for 47, + 21 and 47, + 13

Data are analysed on livebirths with trisomic syndromes associated with unbalanced Robertsonian translocations born from 1968 to 1981 and reported to the New York State Chromosome Registry. The maternal ages of reported cases were compared with those of the livebirths in the general population who were born in the same year. The number of translocations studied, the mean case-control differences in years in maternal age (and the standard errors of the mean) were respectively, as follows: D/21 mutants, n= 36. – 0·1 (±0·9); G/21 mutants, n= 46, + 1·5 (±0·8); D/13 mutants, n= 16, + 0·6 (± 1·5); D/21 inherited, n= 12, – 1·0 (± 1·4); G/21 inherited, n= 3, – 0·3 (± 4·4); and D/13 inherited, n= 6, + 2·1 (± 2·4). There was little change in any category if the few cases diagnosed prenatally were included. Only the value for the G/21 mutants is significantly different from zero at the 0·05 level. (The results on G/21 mutants in maternal age are consistent with an earlier Japanese report of an increase of about 2 years over the control values.) The distribution of maternal ages suggests that G/21 mutants may be produced both by maternal age-independent, and maternal age-dependent components. The data on D/21 mutants, however, do not indicate the negative association with maternal age reported in Japan. Differences between this study and the Japanese study in analyses of controls may explain this slight variation. But in any event both studies reveal no evidence for an increase in maternal age for unbalanced D/21 mutant or D/21 inherited translocations associated with Down syndrome. This is evidence against the hypothesis that relaxed selection during gestation, after recognition of pregnancy, accounts for the maternal age effects of 47, + 21. In comparison with the results on Robertsonian translocations, the case-control differences in maternal age in years (and the standard errors of the mean) for 47. + 21 for 2148 livebirths was + 4·6 (± 0·2), and for 2354 cases including those diagnosed prenatally was + 5·3 (± 0·2). The most likely value for an estimated total of 2292 cases of 47, + 21 livebirths that would have been reported in the absence of prenatal diagnosis was + 5·1 (± 0·2). For 47, + 13, for 98 livebirths the mean case-control difference in maternal age in years was + 1·5 (± 0·7) and for 116 cases including those diagnosed prenatally was + 3·2 (± 0·7). The most likely value for an estimated 108 cases of 47, + 13 in the absence of prenatal diagnosis was + 1·7 (± 0·6). The data on 47, + 13 livebirths confirm suggestive trends from earlier studies at prenatal diagnosis that the maternal age association of this trisomy is weaker than for 47, + 21 or 47, + 18. With regard to paternal age effects, there was no evidence for case-control differences in paternal age (after controlling on maternal age as well as year of birth) for any category of defect analysed.