**1. Introduction**

The major reason why there are so many controversial issues in autism is because it is such a heterogeneous condition. There are no sub-types of autism at this time, despite almost fifty years of searching for them. This quest continues but there is doubt whether it will succeed. There are no diagnostic biomarkers in autism or indeed, in psychiatry as a whole. This in a way, is what distinguishes psychiatric diagnoses from medical diagnoses like diabetes. Of course, there are many conditions associated with autism like tuberous sclerosis, but that is quite a different matter to having a biomarker specifically for autism. There is also a great deal of heterogeneity in relation to aetiological factors. There are a large amount of genes involved of small effect, associated with autism and the number is continually increasing, but there is no specific pattern of genetic findings for autism and unlikely to be again because of heterogeneity. We need new research paradigms for research in psychiatry. The medical model will not suffice.
