http://bmj.com/cgi/content/full/324/7332/296/a
BMJ 2002;324:296 ( 2 February )
Letters
Any changes in prevalence of autism must be determined
Because
of the current concern over the rising incidence of autism the BMJ owes
its readers better information than a letter based on comments by a
focus group of interested parties.1 Would
the journal have published a letter from a focus group of parents
who believed that MMR vaccine (measles, mumps, and rubella vaccine)
had caused their child's autism? I doubt it.
Rigorous methods are especially important because of a controversial current
hypothesis.2
Fombonne has argued that despite reported increases in the
prevalence of autism in many countries, the true incidence has
remained constant. The impression of an increase, he argues, arises
only because of increased rates of detection.
There is no hard evidence to support this hypothesis. The only studies that
have explored the question have failed to find a "hidden
horde" of autistic children. Burd et al conducted a prevalence
study of autism in North Dakota.3 They
found a prevalence of 3.26 per 10 000 among a cohort of
children born between 1967 and 1983. A 12 year follow
up survey of the same cohort showed that the original prevalence
study had found 98% of the autistic children in the area; only one
child had been overlooked.4
Nylander and Gillberg screened adult psychiatric outpatients for evidence of
undiagnosed autistic spectrum disorders.5 This
population had not been screened for autism previously. The authors
hypothesised that they would find high rates of undiagnosed autism.
The screening procedure located 19 adults with autistic spectrum
disorders who had not received a prior diagnosis. However, the
prevalence in this group was only 2.7 per 10 000, a finding that
provides little support for a hidden horde hypothesis. The authors
note this point reluctantly, claiming that the observed prevalences
"should be regarded as an absolute minimum."
Many scientists and health professionals are uncomfortable about the data
regarding recent increases in rates of autism. A few have developed
extravagant theories as an expression of their discomfort.
Nevertheless, the simplest interpretation of the record supports the
conclusion that the incidence of autism has increased.
To avoid the consequences of complacency 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.
I am surprised that the BMJ would dignify such efforts. Good
science demands that we face the real data, no matter how
inconvenient the implications may be.
Mark F Blaxill
22 Fayerweather Street, Cambridge, MA 02138, USA Blaxill.Mark@BCG.com
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1. |
Heussler H, Polnay L, Marder E, Standen P, Chin Lyn U,
Butler N. Prevalence of autism in early 1970s may have been underestimated. BMJ
2001; 323: 633 |
|
2. |
Fombonne E. Is there an epidemic of autism? Pediatrics
2001; 107: 411-412 |
|
3. |
Burd L, Fisher W, Kerbeshian J. A prevalence study of
pervasive developmental disorders in North Dakota. J Am Acad Child Adolesc
Psychiatry 1987; 26: 70-73 |
|
4. |
Burd L, Kerbeshian J, Klug MG, McCulloch K. A prevalence
methodology for mental illness and developmental disorders in rural and frontier
settings. Int J Circumpolar Health 2000; 59: 74-86 |
|
5. |
Nylander L, Gillberg C. Screening for autism spectrum
disorders in adult psychiatric out-patients: a preliminary report. Acta
Psychiatr Scand 2001; 103: 428-434 |
|
Related letters in BMJ:
Prevalence of autism in early 1970s may have been
underestimated
Helen Heussler, Leon Polnay,
Elizabeth Marder, Penny Standen, Chin Lyn U, and Neville Butler
BMJ 2001 323: 633. [Letter]
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