Project outline:

Study of Learning Ability, Development and Genes

Background

Intellectual disability (ID) in childhood is common with a prevalence rate of around 2.6% (Emerson, 2003). Children with ID have substantially higher rates of persistent comorbid psychiatric disorders (ADHD, ASD, Conduct Disorders, Anxiety Disorders), around 4-7 times higher than the general population (e.g., Einfeld et al., 2006; Emerson, 2003; Emerson & Hatton, 2007; Emerson & Einfeld, 2010). The most strongly associated childhood diagnoses are ADHD (odds ratio=10 compared with non-ID controls) and autistic spectrum disorder (ASD; odds ratio=75; Emerson, 2003). Comorbid psychopathology in children with ID is important because it increases parent stress more than the severity of ID, raises the cost of care and has a long term impact on adult outcomes (Herring et al., 2006).

The majority of children with mild-moderate ID have no clearly identifiable cause for their ID (Einfeld et al., 2006). Although multiple common gene variants, comorbid neurological illness and psychosocial disadvantage contribute to the aetiology, there is growing evidence that the rate of subtle chromosomal anomalies (deletions and duplications), known as copy number variants (CNVs), is elevated in those with previously unexplained ID (Girirajan, et al., 2010; Ropers, 2008; Sagoo et al., 2009). As a result of this work, some UK clinical genetics services are offering array CGH diagnostic services and a recent consensus statement recommends using chromosomal microarrays in the first tier of investigating developmental delay (Miller et al., 2010).

In a recently completed study of ADHD (Williams et al., 2010) we found a significantly elevated rate of CNVs in those with ID + ADHD (36%) than amongst controls (7%) or those with ADHD alone (11%). This is actually a higher CNV rate than previously reported for idiopathic ID (around 10%-12% for significant CNVs) and leads us to postulate that in individuals with idiopathic ID, the presence of large, rare CNVs in ID is clinically important because it might increase the risk of comorbid neuropsychiatric disorder. We now propose to explicitly examine whether the presence of large, rare CNVs in children with idiopathic ID is associated with a broad range of psychopathology (not ADHD only).

Aims

* To investigate in children with mild/moderate Intellectual Disability (IQ test score less than 70) whether subtle chromosomal anomalies (CNVs) are associated with;

- The presence of psychopathlogy

- Higher levels of ADHD and autism scores

- Higher levels of aggression

- Lower levels of adaptive functioning

As such the primary outcome measures is the child's psychopathology and the main predictor is the presence of a Copy Number Variant (CNV).

Hypotheses

Children with Intellectual Disability and CNVs will have higher rates of psychopathology and lower levels of functioning

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