Clarifying autism: two types of core behaviors vary independently

More guidance in understanding autism. Core traits, like social impairment and obsesssions, don't necessarily go together.

The genetic relationship between individual differences in social and nonsocial behaviours characteristic of autism.

Dev Sci. 2005 Sep;8(5):444-58. Related Articles, Links
Ronald A, Happe F, Plomin R.
Social Genetic and Developmental Psychiatry (SGDP) Centre, Institute of Psychiatry, King's College London, UK. a.ronald@iop.kcl.ac.uk

Two types of behaviours shown in children - those reflecting social impairment and nonsocial obsessive repetitive behaviours - are central to defining and diagnosing autism spectrum disorders (ASDs). Parent and teacher data on social and nonsocial behaviours were obtained from a community sample of >3000 7-year-old twin pairs. Social and nonsocial behaviours were only modestly correlated, and it was found that some individuals had extreme scores on either social or nonsocial scales but not both. Genetic model-fitting showed that social and nonsocial behaviours are both highly heritable, but their genetic overlap is modest, with most of the genetic influence being specific to either social or nonsocial behaviours. Considering these behaviours separately might help clarify gene-brain-behaviour pathways in future research.

The impliction is these are different genetic syndromes, and clinical autism occurs when an unlucky child gets stuck with either an extreme form of one of them or parts of both. It also relates autism more closely to OCD.