Co-occurring motor, language and functional impairments in children evaluated for autism spectrum disorder

Autism spectrum disorder (ASD), a common neurodevelopmental disorder (NDD), is characterised by the presence of core symptoms sufficiently severe to cause functional impairment but otherwise highly heterogenous. The core social deficiency is now considered a continuous trait with no natural cut-off between ASD and subthreshold autistic symptoms. Although they do not meet the diagnostic criteria for ASD, such traits are found to overlap with diagnosed ASD genetically and to present with the same comorbidities and functional impairments, including an increased risk for motor and language difficulties. Developing a better understanding of how co-occurring motor and language deficits may interact with core ASD symptoms to impact overall functioning is important for adapting diagnostic and clinical services accordingly. The variable and often early presentations of these symptoms also represent potential markers of subgroups within the autism spectrum. The overall aim of this thesis was to study co-occurring motor and language impairments and their potential relationship with symptom severity and functional impairment in children with a broad range of autistic symptoms through a dimensional approach, that is, distinguishing the children as diagnosed with ASD or diagnosed with subthreshold autistic symptoms (non-ASD). Participants were recruited from an ongoing large multisite study on NDDs in Norway (BUPgen), in which children were eligible to participate if a suspicion of ASD led to their being evaluated for ASD by public specialist health services. While the first and second studies presented in this thesis (Papers I and II) were based on clinical data from the main study (N = 490 and N = 177, respectively; 4–18 years), the third study (Paper III) was based on an in-depth evaluation of motor, language and overall functioning collected from a local subsample (N = 20; 6–18 years). The categorical approach (ASD/non-ASD) used in recruitment and group comparisons was supplemented by a dimensional approach in assessments and analyses whereby ASD symptomatology, core developmental skills and functional impairment were examined as continuous traits within the whole group of children with autistic symptoms, regardless of diagnostic category. Results for both groups were compared to norms for typically developing Norwegian children. The first study involved an investigation of early motor skills (age of onset of independent walking [AOW]), as well as the relationship between AOW and severity of autistic symptoms with different measures (Autism Diagnostic Interview-Revised [ADI-R], Social Communication Questionnaire [SCQ] and Social Responsiveness Scale [SRS]). Potential sex differences were also investigated. While the AOW was found to be more delayed in children diagnosed with ASD compared to children with subthreshold symptoms, significant delays were found in both groups compared to population norms. Moreover, AOW was associated with the severity of core ASD symptoms (ADI-R, SCQ), even after adjustment for cognitive abilities. The second study investigated the extent of and relationship between early language delay (non-attainment of phrase speech at two years of age), current language deficits (the Children’s Communication Checklist Second Edition [CCC-2]) and social impairment (SRS). While early language delays were more common among males and associated with structural language deficits, pragmatic language and social skills did not differ significantly between children with and without language delay. Structural language deficits were common and strongly associated with reduced pragmatic competence regardless of diagnostic group (ASD/non-ASD), while pragmatic impairments were most profound in children with ASD. The aim of the third study was to provide a more detailed skill profile of school-aged children evaluated for ASD and to explore the co-occurrence and potential impact of motor and language impairments on overall functioning. Therefore, a standard clinical evaluation was extended with measures on current motor (Developmental Coordination Disorder Questionnaire 2007 [DCDQ’07], Movement Assessment Battery for Children – 2 [MABC- 2]), language (CCC-2) and social skills (SRS), as well as overall functional impairment (Developmental Disability-Children’s Global Assessment Scale [DD-CGAS]). We found that most children had motor and/or structural language deficits in addition to their social impairments. Furthermore, better motor performance was associated with better structural language and social skills. Functional impairment was associated with core ASD symptoms. In addition, limited participation in physical education and out-of-school activities was common. Taken together, these results suggest that motor and language deficits are common and under-recognised. They often present early and should be anticipated and assessed when evaluating children for suspected ASD. These deficits may need specific interventions that complement those targeting social skill deficits and other ASD core symptoms