Intellectual Disability and coexisting Autism and ADHD in Down syndrome - a population-based study

Abstract: The thesis investigated associated neurodevelopmental/neuropsychiatric aspects in a population-based cohort of 60 children and adolescents (5–17 years) with Down syndrome (DS).Forty-one subjects were comprehensively assessed by a clinical research team; 17 (41%) and 14 (34%) met DSM criteria for autism spectrum disorder (ASD) and attention-deficit/hyperactivity disorder (ADHD), respectively.Forty-nine subjects had a formal cognitive test and 11 had clinical assessments due to profound intellectual disability (ID). Mild ID (IQ 50–70) was found in 9% of the teenagers (13–18 years) and in 35% of the younger (5–12 years) children. Corresponding figures for severe ID (IQ <50) were 91% and 65%, respectively. The ID was more severe in individuals with coexisting ASD.Levels and profiles of autistic symptoms, according to ADOS Module-1, were analysed. Children with DS and ASD, with different levels of ID, had significantly more symptoms within all autism domains, than those with DS only – a difference which remained when subgroups with severe ID were compared. A considerable proportion of subjects with DS had ASD in addition to ID, but there was a group with DS and severe ID without ASD. The autism profiles of children with DS and ASD were similar to those of children with idiopathic autism. The commonly used investigation tools used to diagnose ASD in the study, seemed to be appropriate in this patient group.An intervention programme, including education for parents and school staff, adapted to the specific needs of schoolchildren with DS and ASD was performed and evaluated. Although the studied group comprised older children and adolescents, most of whom with severe or profound ID, they could achieve goals and skills previously not managed. In addition, the parents’ views on the intervention were encouraging.In conclusion, there is a need of awareness of the increased prevalence of ASD and ADHD in children with DS. We suggest that screening for ASD and ADHD should be implemented for children with DS at the age of 3–5 years and at early school years, respectively. We also suggest that children with DS should be re-evaluated regarding level of ID before entering secondary school.