Two new theories of autism: hyper-systemising and assortative mating
- Correspondence to:
Prof. S Baron-Cohen
Autism Research Centre, Department of Psychiatry, University of Cambridge, Douglas House, 18b Trumpington Road, Cambridge CB2 2AH, UK; sb205{at}cam.ac.uk
Commentary on the papers by Williams et al (see page 8) and Harrison et al (see page 16)
The autistic spectrum comprises four subgroups: Asperger’s syndrome (AS),1,2 and high, medium, and low functioning autism.3 They all share the phenotype of social difficulties and obsessional interests.4 In AS, the individual has normal or above average IQ and no language delay. In the three autism subgroups there is invariably some degree of language delay, and the level of functioning is indexed by overall IQ.* These four subgroups are known as autism spectrum conditions (ASC).
Williams and colleagues5 searched electronic databases and bibliographies to carry out a meta-analysis of 42 studies of prevalence of autism spectrum conditions (ASC). From this, their most generous estimate was 20 per 10 000, or 0.2%. Harrison and colleagues6 used the “capture–recapture” technique in Lothian, Scotland, and their prevalence estimate was 44.2 per 10 000, or 0.44%. This corresponds to 1 child in 225. These estimates are clearly much higher than was the case in the past, where prevalence was traditionally estimated to be 4 in 10 000.
BEYOND COUNTING AND PREVALENCE ESTIMATES
Now we know that ASC are common. How should we understand their causes? Harrison and colleagues6 find that the 13–15 year old age group who would have received their MMR during the data collection phase were actually less numerous than the 4–10 year old age group, suggesting this high rate cannot be due to the MMR vaccine (since both age groups were exposed to the MMR). Instead they argue that these data suggest better recognition, better recording of cases, and growth of services.
In terms of causes, the consensus is that ASC have a genetic aetiology,7 which leads to altered brain development,8,9,10,11 affecting social and communication …
