The early childhood development of 17 boys with sex chromosome anomalies: a prospective study.

Seventeen boys with sex chromosome anomalies were identified at birth and followed up developmentally for two to five years. The 17 included 12 boys with 47,XXY, four with 47,XYY, and one with 46,XY/XXY mosaicism. None had major disabilities in physical, intellectual, or emotional growth. Some of the boys with 47,XXY were characterized as tall, inactive, poorly organized in motor functions, placid, and delayed in language; two of the four with 47,XYY were impulsive at 1 year of age. These deviations from normal were relatively mild; the boys were not found to be at high risk for grossly abnormal development in the early years.