ABSTRACT
Abnormalities of chromosome number occur in about one of every 200 newborns. Approximately half of these cases involve sex chromosome abnormalities (SCA). Prospective studies of SCA newborns identified in screening programs have provided the opportunity to observe the developmental course of the conditions. Two physiological processes have been implicated as potential mediators between the direct effects of SCA and observed behavioral changes. First, numerous investigators have hypothesized that SCA may alter normal patterns of brain growth. A second hypothetical causal mechanism that might explain some of the alterations in behavior and cognitive development takes into account modified endocrine functions that occur in some of the SCA karyotypes. Fifty-three percent of all nonmosaic SCA subjects, a much larger proportion, received a diagnosis of psychosocial impairment. Most investigative efforts have focused on the occurrence of abnormal development in SCA children. However, the recognition and study of successful adaptation in SCA individuals is of equal importance.
