New Phase Autism:
When autism was first described in the 1940s by Kanner and Asperger it was a rare condition. But now autism spectrum disorders (ASDs) appear to be reaching epidemic proportions. This argues against the possibility that genes alone might explain the rise – a change in the distribution of genes in the population requires dozens of generations, with strong selective pressures. There have certainly been many suggestions that the prevalence of ASD has steadily risen over the intervening years, with increasing skepticism that ASDs are primarily genetic disorders. But, unfortunately, the evidence has been patchy and there are many variables which cloud the issue. This chapter critically evaluates the evidence for a rise in autism.
Over the 1950s to 1970s there were no systematic surveys of the prevalence of ASD, and in the absence of a firm baseline it has been difficult to assess the possibility of a rise. Moreover, there has been a change in diagnostic criteria with successive updates of both US and international criteria, the most recent being DSM-IV1 and ICD-102 as discussed in Chapter 2. Is it possible that changes in diagnostic criteria might explain some of the rise?
The ICD-10 forerunner, ICD-9, covered the period 1979 up to and through 1992. While the diagnostic categories are not identical to ICD-10, autism disorders were clearly delimited – with specific recognition of speech delay, social interaction impairment, eye-gaze avoidance, and resistance to change.
DSM-III was established in 1980, and followed by a revised edition (DSM-III-R, 1987), to be replaced by DSM-IV in 1994. Though there have been