Article 1 Cornelia de Lange syndrome 1 De Lange Syndrome Down Syndrome 1 Down syndrome 1 Gestures 1 Humans 1 Intellectual Disability 1 Speech 1 adaptive behavior 1 adolescent 1 adult 1 clinical article 1 communication 1 communication disorder 1 controlled study 1 de Lange syndrome 1 developmental stage 1 female 1 genetics 1 gesture 1 groups by age 1 human 1 intellectual impairment 1 language ability 1 male 1 outcome assessment 1 patient participation 1 peer group 1 social engagement 1