The genetic structure of reciprocal social behavior: Support for a population based approach to genetic studies of autism

Use of continuous measures of autistic traits may greatly enhance the statistical power of genetic linkage studies of autism. In this study we examined the genetic structure of reciprocal social behavior (RSB) - a core component of the autistic phenotype - in an epidemiological sample of twin boys. Methods: One parent of 232 pairs of 7-15 year old male twins completed the Social Reciprocity Scale (SRS) and the Child Behavior Checklist (CBCL) on their children. The data were subjected to structural equation modeling using the statistical software, MX. Results: Using MX, the best fitting model for RSB was one which incorporated additive genetic influences (0.76, 90%C.I.:0.72-0.80) and unique environmental influences (0.24, 90%C.L: 0.19-0.29). There was no evidence for common environment, rater contrast, rater bias, or age effects. In bivariate analyses, estimates for overlap of genetic influences were as follows: 0.44 for RSB and externalizing behavior (EXT); 0.34 for RSB and internalizing behavior (INT); 0.5 for INT and EXT. Conclusion: Genetic influences on RSB in the general population are substantially independent of those for general psychopathology, and are similar in magnitude to what have been described for autism itself. This study supports the feasibility of a population-based approach to genetic studies of autism.