Lost in the hoopla over the Wakefield hearing in the UK and the "Vaccine trials" in the US are the increases in reported cases of autism in various parts of the world. The US reports have increased to 1 in 150 and the UK reports, by no less an authority than Simon Baron-Cohen himself, a 1 in 100 incidence of autism. Obviously some of those numbers are attributable to the changes in the DSM and in better awareness, diagnosis and reporting. But while everyone is aware of those factors no serious study or report actually attributes the entire increases in the incidence in autism to these factors alone, Baron-Cohen's opinion, and that of Neurodiversity bloggers notwithstanding.
The graph from the California Department of Developmental Services shows that reported incidence of autism increased by five times in the ten year period from 94 to 04. Undoubtedly the DSM change would be a substantial factor in that startling increase along with better awareness, diagnosis and reporting. But do environmental factors contribute to the increasing incidence of autism and if so to what extent? This is a serious question which is not answered by self assured opinions from Baron-Cohen. The medical tribunal will soon report its verdict on Mr. Wakefield and the US "Vaccine Court" may offer some insight on vaccines and thimerosal but as to environmental factors generally the jury may well be out for some time to come.
Harold wrote:
ReplyDelete“Obviously some of those numbers are attributable to the changes in the DSM and in better awareness, diagnosis and reporting. But while everyone is aware of those factors no serious study or report actually attributes the entire increases in the incidence in autism to these factors alone, Baron-Cohen's opinion, and that of Neurodiversity bloggers notwithstanding.”
Actually, you couldn’t be more wrong. Epidemiologists uniformly agree that changes in the DSM, better awareness, diagnosis and reporting (and diagnostic substitution) are the factors influencing increased prevalence of autism. Neurodiversity bloggers are merely reporitng that consensus. See quotes from a variety epi papers and investigators below.
“Prevalence findings from special education data do not support the claim of an autism epidemic because the administrative prevalence figures for most states are well below epidemiological estimates. The growing administrative prevalence of autism from 1994 to 2003 was associated with corresponding declines in the usage of other diagnostic categories.” Pediatrics. 2006 Apr;117(4):1028-37
“The prevalence of pervasive developmental disorder in Montreal was high, increasing in recent birth cohorts as found in most countries. Factors accounting for the increase include a broadening of diagnostic concepts and criteria, increased awareness and, therefore, better identification of children with pervasive developmental disorders in communities and epidemiologic surveys, and improved access to services. The findings ruled out an association between pervasive developmental disorder and either high levels of ethylmercury exposure comparable with those experienced in the United States in the 1990s or 1- or 2-dose measles-mumps-rubella vaccinations.” Pediatrics. 2006 Jul;118(1):e139-50
“We found that the estimated prevalences of the PDDs studied were probably underestimated. Furthermore, the increasing prevalence and incidence rates during the 1990s may well be explained by changes in the registration procedures and more awareness of the disorders, although a true increase in the incidence cannot be ruled out.”
Psychol Med. 2004 Oct;34(7):1339-46
“Better ascertainment of diagnosis is likely to have contributed to the observed temporal increase in rates of diagnosis of PDD, but we cannot exclude a real increase.”
BMC Med. 2004 Nov 9;2:39
“Changes in diagnostic criteria have expanded the concept of autism to a spectrum of disorders. Heightened public awareness of autism also has had an effect, due in large part to efforts of parent and advocacy groups, availability of more medical and educational resources, increased media coverage of affected children and families, and more training and information for physicians, psychologists, and other service providers. JAMA. 2003;289:49-55