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LETTERS: Helen Heussler, Leon Polnay, Elizabeth Marder, Penny Standen, Chin Lyn U, and Neville Butler Prevalence of autism in early 1970s may have been underestimated BMJ 2001; 323: 633 [Full text]

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focus groups are now considered science?

Mark F Blaxill   (16 September 2001)

Prevalence of autism in the past may have been underestimated

William Whitehouse   (29 September 2001)

focus groups are now considered science? 16 September 2001
Mark F Blaxill Boston MA Send response to journal: Re: focus groups are now considered science?	The only thing more perplexing than the contents of this letter was that the BMJ chose to print it. In an environment of real and genuine concern over the rising incidence of autism, you owe your readers better information than anecdotal musings from a group of interested parties. Would you have printed a letter from a "focus group" of parents who believed MMR caused their child's autism? There is no substantive difference between these two forms of "research." This potential abuse of such methods would normally not be of great concern, but is critically important today because of a controversial and unsupported current hypothesis(1). Fombonne and others have argued that despite an apparent recent increases in the rate of autism prevalence in many countries, the actual incidence of this devastating disorder has remained constant. The impression of an increase, this hypothesis goes, has been created only because of greater rates of detection in recent years. There is therefore, proponents of this theory argue, no reason to be concerned over possible environmental causes of autism that would necessarily underlie an abrupt increase in incidence rates. Despite the prominence of its proponents, there is no hard evidence to support this hypothesis. In fact, the only studies of any depth that have explored the question have overwhelmingly failed to find the hypothesized "hidden horde" of autistic children from the 1970s, or for that matter, from any other period. Burd et al (2) conducted a prevalence study of autism in North Dakota. They found a low prevalence rate of 3.26 per 10,000 among a cohort of children born between 1967 and 1983. A twelve year follow up survey of the same cohort (3) showed that the original prevalence study had found 98% of the autistic children in the study area. One child with autism had been missed. In a similar study (4), Nylander and Gillberg screened adult psychiatric outpatients for evidence of undiagnosed autistic spectrum disorders. Unlike the North Dakota studies, this population had never gone through an earlier screening for autism (which presumably would have encouraged proper rates of initial diagnosis). The authors, based on the disease model advanced in (1) hypothesized that they would find high rates of undiagnosed adults with autism. The screening procedure did in fact unearth 19 autistic spectrum adults who had not received a prior diagnosis. However, the prevalence rate for this group was only 2.7 per 10,000, a finding that provides little support for the hidden horde hypothesis. The authors note this point reluctantly, claiming that the observed prevalence rates "should be regarded as an absolute minimum." They provide no guidance, though, for further research and offer no other candidate populations in which to search for the disabled victims of what has been widely considered a life- long disorder. For some reason, many scientists and health professionals find the data regarding sharp increases in autism rates to be an uncomfortable finding. A few have developed extravagant and unsupported theories as an expression of their discomfort. These theories deserve sharp critical examination because the simple interpretation of the existing data supports the conclusion that autism has increased quite strongly. Indeed, in light of the consequences of complacency, it would seem the burden of proof should lie with those who seek to dismiss decades of epidemiological research as flawed. Yet we are now offered "focus groups" as a new research tool. In the business world, we call this technique "mother-in-law" research, so I must confess surprise that the BMJ would dignify such efforts. Good science demands that we face the real data, no matter how inconvenient the implications may be. Sincerely, Mark F. Blaxill Cambridge MA References 1. Pediatrics 2001 Feb;107(2):411-2. Is there an epidemic of autism? Fombonne E. 2. J Am Acad Child Adolesc Psychiatry 1987 Sep;26(5):700-3. A prevalence study of pervasive developmental disorders in North Dakota. Burd L, Fisher W, Kerbeshian J. 3. Int J Circumpolar Health 2000 Jan;59(1):74-86. A prevalence methodology for mental illness and developmental disorders in rural and frontier settings. Burd L, Kerbeshian J, Klug MG, McCulloch K. 4. Acta Psychiatr Scand 2001 Jun;103(6):428-34. Screening for autism spectrum disorders in adult psychiatric out-patients: a preliminary report. Nylander L, Gillberg C.
Prevalence of autism in the past may have been underestimated 29 September 2001
William Whitehouse, Senior Lecturer in Paediatric Neurology University of Nottingham Send response to journal: Re: Prevalence of autism in the past may have been underestimated	Autistic Spectrum Disorders (ASDs) cover a range of disorders characterized by impairments in social interactions, pattern of communication and restricted, repetitive behaviours. We have previously demonstrated a 4-fold rise in the incidence of diagnosed ASDs in pre- school children from 1991&1992 to 1995&1996 in the West Midlands(1). Heussler et al(2)have reported reviewed data from the 1970s suggesting that by contempory standards the prevelance of ASDs in the 1970s was probably as high as it now appears. We undertook a time trend analysis of the West Midlands data set to see if the observed increase in incidence was compatible with a new biological aetiology or with improved diagnosis of essentially the same condition. Clinical data on the 148 children ascertained in the original study (1) was collected from the medical notes in a systematic way using a proforma. Complete data was available for analysis on 134. Data in the following domains were recorded: family history of ASD, developmental, neurological, other medical and psychiatric disorder; obstetric and past medical history; personal history of epilepsy and other neurological and medical disorder, learning difficulties and other developmental problems; abnormalities on physical examination including visual and hearing deficits. Linear by linear association tests were used to test for time- trends in the data. There were no significant trends found between any of the characteristics examined. To conclude there was no evidence for a change in the prevalence of associated clinical features in children with ASD over time. We failed to find an indication that the apparent rise in incidence was due to the emergence of a single new cause of autism. This result is consistent, however, with improved identification and diagnosis of ASDs in the population over time. William Whitehouse, Senior Lecturer in Paediatric Neurology, University of Nottingham Mark Abbas, Medical Student, University of Birmingham Judy Powell, Lecturer in Public Health & Epidemiology, University of Birmingham 1. Powell et al. Changes in the incidence of childhood autism and other autistic spectrum disorders in preschool children from two areas of the West Midlands, UK. Developmental Medicine & Child Neurology 2000:42:624-628. 2. Heussler et al. Prevalence of autism in early 1970s may have been underestimated. British Medical Journal 2001:323:633.