Autism is coming to be conceptualised as a dimensional disorder, located at the extreme of the distribution of traits found in the general population (Constantino and Todd, 2004). This raises two questions of theoretical and clinical significance:

1. At what point do autistic traits become functionally impairing in the general population of children?

2. Do risk factors for autistic social communication could operate right across the range of impairment, and not just on those at the extreme of the distribution?

We examined these questions using data from ALSPAC (Skuse, Mandy, Steer et al., 2009), looking at the associations between a parent-report measure of social communication impairment (the Social Communication Disorders Checklist (SCDC); Skuse, Mandy & Scourfield, 2005) and independent measures of intelligence and teacher-reported functional impairment (Strengths and Difficulties Questionnaire (SDQ); Goodman et al., 2003). Two notable, novel findings emerged from this study (Constantino, 2009).

Firstly we demonstrated that in middle childhood even mild, sub-clinical social communication impairments are associated with social, emotional and behavioural impairments at school. This was true across the range of social communication impairment, with no step-function or obvious threshold above which social communication traits became clinically significant. This has implications for teachers and clinicians when seeking to support children without an autism spectrum disorder (ASD), but who nevertheless have elevated levels of autistic traits.

Secondly we described a SCI by gender by verbal IQ (VIQ) interaction. VIQ was protective against social communication impairment for females across the full range of abilities but not for males. Above average VIQ did not offer extra protection for males, and there was some suggestion that high VIQ may even operate as a risk factor for social communication impairment in males. This striking and original finding has the potential to elucidate the development of Asperger's syndrome, which is associated with high VIQ and a large male to female ratio (9:1).

We propose to use further data from ALSPAC to replicate and elucidate these findings. Specificly we aim to investigate the following:

Continuities and changes in the associations between SCI and functional impairment.

We aim to replicate our analyses of SCDC and SDQ data from middle childhood, using data collected when participants were c.11 years old. This will enable us to take a longitudinal, developmental perspective, examining continuities and changes in the way in which SCI serves as a risk factor for maladaption in childhood. Such research will in turn offer insights for clinicians and teachers seeking to better understand and treat behavioural, social and emotional maladaption in middle and later childhood.

Gender, IQ and autistic traits

We aim to further investigate the finding that VIQ is protective against social communication impairment across the range of abilities for females but not males. Firstly this will involve testing the replicability of this gender by VIQ interaction using a measure of social communication impairment taken in later childhood. Secondly we aim to use WISC-III subtest data to investigate which specific components of VIQ are driving the not-linear trend we observed. This will offer insight into the neurocognitive mechanisms involved in the development of high-functioning ASD and Asperger's syndrome in males. Thirdly we aim to test whether a distinct sub-group exists on the autistic spectrum comprising males who have both high VIQ and high social communication impairments. This will involve consideration of whether this group is stable over time, and whether they have a distinct pattern of cognitive, social and emotional strengths and vulnerabilities compared to other groups in the sample (high VIQ, high SCI females; high VIQ, low SCI males; low VIQ, high SCI males). We propose to include measures of neurodevelopment (attention, face and voice emotion recognition) relevant to the clinical syndrome of autism.

Our proposed investigation will be useful to clinicians diagnosing high-functioning ASDs, and will potentially help to reduce heterogeneity in studies aiming to identify the aetiology of ASDs.

REFERENCES

Constantino JN. How Continua Converge in Nature: Cognition, Competence and Autistic Syndromes.J Am Acad Child Adolesc Psychioatry. 2009;48: 97-8.

Constantino JN, Todd RD. Autistic traits in the general population: a twin study. Arch Gen Psychiatry. 2003;60:524-530.

Goodman R, Ford T, Simmons H, Gatward R, Meltzer H. Using the Strengths and Difficulties Questionnaire (SDQ) to screen for child psychiatric disorders in a community sample. Int Rev Psychiatry. 2003;15:166-172.

Skuse DH, Mandy WPL, Scourfield J. Measuring autistic traits: heritability, reliability and validity of the Social and Communication Disorders Checklist. Br J Psychiatry. 2005;187:568Y572.

Skuse DH, Mandy WPL, Steer CD et al. Social Communication Competence and Functional Adaption in a General Population of Children: Preliminary Evidence for Sex-by-Verbal IQ Differential Risk. 2009;48: 128-37.