Chromosomal abnormalities ascertained in the collaborative perinatal survey of 7- and 8-year-old children

The overall frequency of chromosome abnormalities (0.48%) was similar to that found in newborn infant studies (0.55%). Twenty-one chromosomally abnormal children were identified. The principal difference between the present study and newborn surveys was the lower frequency of autosomal trisomies. This was most likely due to a combination of death and lack of identification of such individuals. The absence of any XXX girls in the study may be due to the same factors. The frequency of XYY boys (0.14%) was identical to that observed in newborn surveys. Two of the three XYY children had severe behavioral problems prior to the cytogenetic studies, and one was already under psychiatric therapy before the age of 7. Knowledge of their keryotypes, therefore, could not in any way have influenced their development. It is of considerable interest that only one abnormality was definitely found as a result of the use of banding techniques that would likely not have been detected with conventional staining. Several others, such as three of the structural abnormalities of the X chromosome might easily have been interpreted as normal without banding. There are at least two explanations for the failure to detect any partial autosomal monosomies or trisomies, and both probably are at least partially correct. Since institutional children and children who died before the age of seven were not involved in the present study, it is likely that there were few or no children in the study population with small unbalanced rearrangements. In addition, with the greater experience now available, it is apparent that the type of G-banding employed in this study is probably not the best banding technique for the detection of such small abnormalities. Hence, small abnormalities could have been missed, particularly in poor cultures.