Abstract
The child with sex chromosome variations is an ideal population for investigating the relationship between brain, behavior, and genetics. The child with XXY is the most common chromosomal disorder with an incidence of 1:600 births. Yet, this disorder rarely is entertained as a diagnostic possibility when speech or motor dysfunction is observed in young children. Until recently, ascertainment bias, small study samples, and methodological flaws have beset the few research studies on children with these disorders. In spite of these shortcomings, there is a characteristic neurodevelopmental profile that is evolving. There is an increased incidence of language-learning disabilities with dyslexia by school age. As infants and toddlers, these infants have neuromotor and speech dysfunction within the first year of life. This article postulates that the language and motor dysfunction is caused by infantile presentation of developmental dyspraxia rather than a neuromaturational lag. The motor planning deficits continue through adulthood. Although the deficits in the young children with XXY are milder in comparison to Fragile X, the effect on their lives and their families can be quite significant. The importance of early identification and intervention cannot be overstated since brain plasticity is tantamount in the first five years of life.