Authors:

Ring, H., Woodbury-Smith, M., WATSON, P., Wheelwright, S. & Baron-Cohen, S.

Reference:

Year of publication:

2008

CBU number:

6752

Abstract:

Introduction: Autism Spectrum Disorders are characterized by a high degree of clinical heterogeneity, but the extent to which this variation represents a severity gradient versus discrete phenotypes is unclear. The description of discrete endophenotypes, should they exist, is important for genetic linkage and association studies, and may help explain the limited replicability across molecular genetic studies of the ASDs. Method: Responses to the Autism Spectrum Quotient (AQ) for 388 adults with a higher functioning autism spectrum disorder, diagnosed according to the DSM-IV, were analyzed using complete linkage hierarchical cluster analysis. Replicability of the solution identified was established by randomly dividing the study group into two, and conducting two independent analyses separately on both samples. Results: For both analyses, all cluster models were consistent with a continuous severity gradient. Using a three-cluster solution, clusters reflecting 'mild', 'moderate' and 'severe' symptom states were produced, with a gradient across the five domains of the AQ. For a four cluster solution an additional 'imagination preserved' group was demonstrated. Conclusion: This study provides further evidence for a continuous severity gradient in those with an autistic spectrum disorder at the higher-IQ end of the spectrum, but also indicates that subgroups weighted towards particular symptom profiles may exist. Possible explanations for this and the implications for genetic studies are discussed.

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