Dr Chaplin notes that neither the possible causes nor the treatment of catatonia were discussed in our paper. As the Journal requires papers to be 3000-5000 words long, we decided to focus on the clinical picture of catatonia in autism and its prevalence. We have written and intend to publish a second paper dealing with causes and treatment and are grateful to Dr Chaplin for providing us with the opportunity to write a few more words on these subjects.

The individuals in the study had all been seen by one or more clinicians before the tertiary referral to Elliot House. During the course of the multiple assessments, possible underlying causes, including schizophrenia, depression, obsessive-compulsive disorder and identifiable brain pathology such as parkinsonism, would have been considered. These conditions, together with autistic spectrum disorders and catatonia, are defined and diagnosed only on history and clinical picture and there is overlap of clinical features among them all. In the individuals in our study, the developmental history and clinical picture, including the “bizarre/psychotic” behaviour in some people, fitted best with autistic spectrum disorders. We do not argue that psychiatric conditions, such as schizophrenia, cannot occur in association with autistic disorders. The point of our paper is that catatonia can occur as a complication of autistic spectrum disorders alone.

Twenty-one individuals in our study had received psychotropic medication for possible psychiatric conditions, and two people were treated with electroconvulsive therapy, all without useful effect on the catatonic features. The side-effects of neuroleptic medication were considered as possible causes of the catatonia. Of the 21 individuals who were medicated 10 were given drugs only after the onset of catatonia. The temporal relationships were difficult to establish for the other 11, but there was no clear evidence for cause and effect.

When considering aetiology, an important point is that many of the features described in discussions of catatonic phenomena are also characteristic of autistic disorders. This has interesting implications for the nature of autism and catatonia, and their relationship to each other and to other psychiatric conditions associated with impairments of motor function. This will be the subject of a separate paper.