49,XXXXY syndrome: A study of neurological function in this uncommon X and Y chromosomal disorder

49,XXXXY is a rare chromosomal variation characterized by deficits in motor, language, and cognitive domains. This study reports on the neurological function and dysmorphic features in the largest cohort to date. Seventy-two boys with 49,XXXXY were evaluated on a variety of domains including a neurological examination and neuromotor assessments including the Beery Buktenica Developmental Test of Visual-Motor Integration, Sixth Edition, the Bayley Scales of Infant and Toddler Development, Third Edition (BSID-III), and the Bruininks-Oseretsky Test of Motor Proficiency, Second Edition. Results supported previous literature by describing high occurrences of truncal and extremity hypotonia, which significantly impacts on motor milestones and ambulation in this population. The boys presented with dysmorphic features including epicanthal folds, frontal bossing, and synophrys. Visual perception skills were mildly impaired and cranial nerves were typically intact, however capabilities in motor coordination and fine motor precision were greatly delayed, supporting deficits in refined and controlled hand movements versus widespread visual deficits. Preschool boys treated with testosterone replacement had significantly increased scores when compared to the untreated group on the BSID-III Psychomotor Development Index, further supporting previous research indicating that testosterone replacement may have a positive impact on neurodevelopmental outcomes in males with additional X chromosomes. Boys with 49,XXXXY may benefit from hormonal treatment in conjunction with early intervention services to address their significant motor deficits.