General Cognitive Abilities and Psychosocial Development in Children and Adolescents Having a Co-Twin with Down Syndrome.

Objective To examine the general cognitive and psychosocial development in children and adolescents having a co-twin with Down syndrome. Study design A case control study with an individually matched control group was conducted. Participants included families with twins discordant for Down syndrome as well as with typically developing twins. The group of unaffected co-twins aged four to 16 years was compared with a control group of typically developing twins in terms of general cognitive abilities, behavioral problems and prosocial behavior. The age and sex and the s composition of the twins were individually matched. The Sijnders-Oomen non-verbal intelligence test (SON-R) was applied to assess children’s IQ, and parents completed the Strength and Difficulties Questionnaire (SDQ). Results The unaffected co-twins did not differ from typically developing twins with respect to their IQ. Concerning the psychosocial development, significantly heightened values in unaffected co-twins twins were only obtained for the conduct problems scale (p=.01, r=.45), neither for the total difficulties score nor for the other behavioral problem scales significant differences were found. Conclusions The general cognitive development of the unaffected co-twin of children with Down syndrome is not affected by the presence of their Down syndrome twin. Unaffected co-twins showed increased conduct problems, which is most pronounced in the younger children..