Sherman et al. (1994) stated “… increasing maternal age is one of the most important factors in human reproductive failure, as well as being a leading contributor to mental retardation among live-borns.” Hassold et al. (1993) commented that “The association between increasing maternal age and trisomy is arguably the most important etiologic factor in human genetic disease. Nevertheless, we know almost nothing about its basis”; and likewise Wolstenholme and Angell (2000) observed “… there is still no consensus of opinion as to how aneuploidy arises in man, and there is a surprising lack of understanding of the basic mechanism(s) of the well-established links to maternal age.” Some suggested factors are outlined in Chapter 3 (p. 39).
The maternal age effect in DS—whatever it may be—has been considered to operate upon oögenesis, predisposing to nondisjunction of chromosome 21 predominantly at the first meiotic division.1
In more general terms, segregation of some other chromosomes is vulnerable to the maternal age effect; and, thus, “older women” who are pregnant run an increased risk for having a pregnancy with trisomies 13, 16, and 18, 47,XXX and 47,XXY, as well as trisomy 21. There is also a slight maternal age association with disorders due to uniparental disomy (Ginsburg et al., 2000), this point being discussed in more detail in Chapter 22. Advanced maternal age—or to use the preferable expression of Ginsburg et al. “mothers at advanced childbearing age”—is a common indication for prenatal diagnosis, although becoming less predominant due to the impact of maternal serum and ultrasound screening.
Chapter. 8932 words. Illustrated.
Subjects: Clinical Genetics
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