The authors investigated the age of the parents and grandmothers of 262 children with simple trisomy 21. In cases in which the mother was under 30, the mean grandmaternal age was higher than that of the controls. This might mean that some of these cases, being the children of old mothers, began their lives as trisomic zygotes. The authors assume that not only maternal but also paternal mosaicism might be significant. They evaluate their results in light of genetic counseling and in consideration of practical conclusions that can be used in prenatal genetic diagnosis.
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