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Egenis · Research

Developmental trajectories of sub-classifications of autism spectrum disorder

Ginny Russell

Start date



There is much literature arguing that early identification of ASD is crucial in order to treat and manage these disorders effectively. There is also much research geared towards early identification of children with ASD, especially regarding the development of screening tools to identify children at risk at younger ages. Intervention must be carried out early (before aged 3), it is often argued, in order to catch children at crucial neuroplastic developmental stages. On the other hand, there is a group of children who show impairment in key symptoms of autism, such as speech and language, at young ages, but catch up later. 40-60% of children with developmental delay in speech are in the normal range by the time they are 4. Therefore it is difficult to distinguish a two year old with language difficulties who is a ‘late developer’ from one who will go on to have lifelong impairment.

This project will analyse the effects of early or late diagnosis to ascertain whether improvements in behavioural profiles after identification are more dramatic in the early diagnosed group, as the pro-early diagnosis literature suggests it should be, whilst co-varying for other important factors such as IQ and sub classification.


Developmental trajectory of behaviour symptomatic of ASD will show more improvement for children diagnosed early than those diagnosed later.


Three recent comprehensive systematic reviews of interventions for Autism Spectrum Disorders published in 2011 in the journal Pediatrics found that the evidence base for efficacy of interventions for ASD was generally weak. One problem identified was that much research on ASD looks for improvement in outcomes for all children with any type of ASD. Within autism spectrum disorders presentation can be highly heterogeneous, ranging for example from a child of high intelligence but restricted focused interests and one-sided conversation to one with intellectual impairment, no speech, catatonia and repetitive motor movements. Despite this wide range in presentation, little has been established about for developmental trajectories particular children or sub-groups.

These systematic reviews called for a strong future focus on participant characteristics associated with greater or lesser gains as children receive help as they mature. This project will address this call by separating autistic children by their characteristics to assess differences in developmental trajectories between these sub-groups. As well as early or late-diagnosed children, within the ASD group, children are classified as either low-functioning or high-functioning, according to whether they have lower of higher IQ. There are also clear differences in symptom presentation which are laid out in the diagnostic criteria for the main sub-conditions within the autism spectrum; Asperger’s syndrome, classical autism (also known as childhood autism) and atypical autism. All these differences in trajectory between all these domains will be explored.


This study aims to plot the developmental trajectories of each sub-group for a range of behaviours including social behaviour, communication and externalising behaviours. Comparison groups will be defined by early/late diagnosis, sub-classification, and by high or low functioning (IQ). For data resolution to achieve this, a large longitudinal birth cohort with a population-sized sample will be employed; The Danish National Birth Cohort (which has a sample size of approximately 100,000). This cohort has linked records to the Danish National Psychiatric Register which details ASD diagnoses and sub classifications, and has repeatedly measured well-validated behavioural scales such as the Strengths and Difficulties Questionnaire (SDQ) which has been administered to the entire cohort at various ages. Differing developmental trajectories of various SDQ measures, will be examined whilst taking into account age of diagnosis.