Background Although there is good evidence that autism is a multifactorial disorder, an adequate understanding of the genetic and non-genetic causes has yet to be achieved.
Methods Empirical research findings and conceptual reviews are reviewed with respect to evidence on possible causal influences.
Results Much the strongest evidence concerns the importance of susceptibility genes, but such genes have yet to be identified. Specific somatic conditions (such as tuberous sclerosis and the fragile X anomaly) account for a small proportion of cases. Over recent decades there has been a major rise in the rate of diagnosed autism. The main explanation for this rise is to be found in better ascertainment and a broadening of the diagnostic concept. Nevertheless, some degree of true rise cannot be firmly excluded. However, the epidemiological evidence on the main hypothesized environmental explanation, namely the measles-mumps-rubella vaccine, is consistently negative.
Conclusion Progress on the elucidation of the causes of autism will be crucially dependent on the combination of epidemiology with more basic science laboratory studies.