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Why do kids in Montreal and environs have so many more learning disabilities compared to the regions? I’m going to guess that the country kids go outside more.
Brad, Alison Cummins, Kate, and 2 others are discussing. Toggle Comments
I’ll venture a guess – I grew up in the country and we used to just call kids like that “slow”. There were no resources around to identify them as specifically helpable so unless they were really seriously developmentally challenged they just went through the same school everyone else did, but with worse grades and less attention paid to them unless they were discipline cases. Kind of how like in the old days people died of “consumption” a lot.
I could easily see that. It’s very similar to the “spike” in Autism diagnoses, as well as for NHL concussions.
But is the lack of medical resources in rural areas really that stark?
TED (trouble envahissant du développement) is french for PDD (Pervasive Developmental Disorder).
It includes autism and Asperger syndrome, also PDD NOS (not otherwise specified).
Much of the increase over time in autism diagnoses is diagnostic substitution. Kids used to be diagnosed as “retarded,” whereas now they are diagnosed as “autistic.” Unless you look at the entire basket of developmental problems in children and look at whether altogether the basket is bigger at different times or places, identifying a change in one element of the basket doesn’t tell you much. If “autism” is going up and “retardation” is going down, then it’s probably just a question of labels. If “autism” is going up and “retardation” is constant, then it could be a real increase in autism or it could be more active screening for the marginal (could just about pass as NT/neurotypical) kids so they can get a diagnosis. See this nice article: http://photoninthedarkness.com/?p=158
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“Consumption” was tuberculosis of the lungs. They died of it a lot because they didn’t have antibiotics. Now that we’re running out of antibiotics we can expect to start dying of it a lot again.
Depends on how rural, but compared to the big city with its multitude of specailist hospitals, yes. Even general diagnosis is only useful if treatment is available.
Alison makes a great point about diagnostic substitution; in some cases there also may be cultural issues at play and also basic issues such as access to doctors who can make a diagnosis. There’s also the possibility of environmental contaminants playing a role: exposure to lead, mercury, PCBs, PBDEs, phthalates, and organophosphate pesticides has been associated with a variety of neurological disorders, including ASDs (autism spectrum disorders). One study in California found an association between exposure to pollutants from automobile traffic and ASDs. All of these pollutants are likely more prevalent in urban environments than in rural areas.
I love Ian’s point that diagnosis is only as useful as the available treatment options. That makes a huge difference in diagnostic bias. For instance, interventions specific for autistic children are funded by the educational system in California, which means that the bias will be to find autism in marginal cases (might be something else which doesn’t have funded interventions, which isn’t helpful to anyone).
I’m less enthusiastic about Brad’s concern about environmental conaminants. Lead and mercury have not been associated with ASDs. People who insist that their autistic children are actually suffering from heavy metal poisoning subject their poor children to dangerous and painful chelation “treatments” with industrial solvents that do nothing for autism but sometimes kill the children. Autism has its origins in early fetal development — apparently the first eight weeks — so any posited environmental cause has to be mediated by the pregnant mother. Exposing a child to pollutants after it is born cannot cause autism.
Exposure of the mother to organophosphate pesticides has been associated with autism, but those are definitely more common in agricultural communities than in urban areas.
My preferred explanation would be the fashionable Vitamin D. People born (not conceived) in cities are at higher risk for schizophrenia, so it would be parsimonious to think that maybe people conceived (not born) in cities might be at higher risk for autism. Sadly, there is little evidence to support this hypothesis.
Actually there are a number of published studies showing associations between mercury exposure and ASDs, although there are also studies showing no connection so it’s not clear. The only thing that does seem clear is that concerns about thimerosal in vaccines is not connected to autism. But there are at least three studies showing higher mercury levels in blood, baby teeth, and urine of children with ASDs (presumably passed on from the mother), whereas a more recent study found no difference. A study in Texas also found an association between proximity to sources of mercury (power plants and industrial sources) and prevalence of ASDs.
All that said, current research suggests there is no single risk factor yet identified that can cause ASDs and it’s likely to be the result of a combination of genetic and environmental risk factors, parental age, etc.
Whoops, I wasn’t clear on thimerosal above — what I meant to write was the “concerns about thimerosal in vaccines” are unfounded, as there is no demonstrated connection to autism.”
I have a feeling that growing numbers of things like ADD and autism are part of a picture where we cannot stop and focus any more, we’re constantly scanning for new things in our environment – oh, I’m up for it, doing this blog, constant torrent of new data always coming in. No pauses, jump edits. The excitement of a hockey game is not enough – any pause is instantly filled with loud music and commercials.
I think it’s going to turn out that this gets transmitted to kids in the womb, chemically. I’m not a medical or scientific person so I can’t begin to frame a biochemical theory. No, I’m not thrilled with the idea that pregnant women should go live for nine months in a meditative retreat, but it might be a place to start.
There’s no reason to suspect mercury other than the crank fixation on thimerosal. Nothing we know about mercury suggests that it would cause autism, and globally the totality of evidence does not support a link. There are many more than five studies on autism and mercury.
Since autism rates seem to be constant over time, we should probably be looking at causes that are constant over time. When people of all ages are screened for autism using the same criteria, the rate is on the order of 1% for everyone from two years old to 88 years old. Children born today do not appear to be at significantly higher risk from children born in 1924.
So it’s solid that autism numbers are not up, it’s just diagnosis that’s up?
Data from the National Health Interview Survey in the US show an increase in the prevalence of ASDs in the US population (ages 5-17) from 0.1% in 1997 to 1.0% in 2010. I think if you look at these references you’ll find that the increasing prevalence cannot in fact be fully explained by changes in diagnostic criteria, age at diagnosis, inclusion of milder cases etc.
Centers for Disease Control and Prevention. 2009. Prevalence of autism spectrum disorders — autism and developmental disabilities monitoring network, United States, 2006. Morbidity and Mortality Weekly Report 58 (SS 10):1-20.
Hertz-Picciotto, I., and L. Delwiche. 2009. The rise in autism and the role of age at diagnosis. Epidemiology 20 (1):84-90.
King, M., and P. Bearman. 2009. Diagnostic change and the increased prevalence of autism. International Journal of Epidemiology 38 (5):1224-1234.
King, M.D., C. Fountain, D. Dakhlallah, and P.S. Bearman. 2009. Estimated autism risk and older reproductive age. American Journal of Public Health 99 (9):1673-1679.
Liu, K.Y., M. King, and P.S. Bearman. 2010. Social influence and the autism epidemic. American Journal of Sociology 115 (5):1387-434.
Shelton, J.F., D.J. Tancredi, and I. Hertz-Picciotto. 2010. Independent and dependent contributions of advanced maternal and paternal ages to autism risk. Autism Research 3 (1):30-9.
No, not solid. But neither is it solid that they *are* up. So looking for the cause of the rise in autism is premature until we know that there is a rise.
From the director of NIMH, Thomas Insel:
“This takes us back to the central question: has the number of children with ASD increased or not? Total population epidemiological studies suggest much or all of the increase is due to better and wider detection. Studies of administrative and services data suggest that better detection cannot fully explain the profound and continuing increase. Are we seeing more affected or more detected? The question is vitally important, but there is not one, simple answer just as autism is not a single, simple disorder.”
“However, regardless of cause, we now know that autism is very common. It therefore deserves a proper level of attention and resources, both for research and services for those on the spectrum.”
It’s completely fair to look for the causes of autism[s], but focussing on changes in the last thirty years is not warranted by what we know right now.
“I think if you look at these references you’ll find that the increasing prevalence cannot in fact be fully explained by changes in diagnostic criteria, age at diagnosis, inclusion of milder cases etc.”
Brad, you know I can’t look at these references without going to a medical library. (No, it’s not sufficient to read an abstract which is all we can access for free online.
And even if I did go to a medical library, not being an autism epidemiology researcher or anything similar, I simply don’t have the depth and breadth of familiarity with the whole of the literature to place your six papers in context.
Do you have links to credible discussions of the papers?
Alison: here’s a link to the source I got these from (which in the interest of disclosure is a report I am working on, although not as an author): http://www.epa.gov/ace/ace3draft/draft_pdfs/ACE3NeurodevelopmentalDisordersReviewPackage3-02-11.pdf. This chapter (still in draft) covers a number of neurodevelopmental disorders that may have environmental causes; ASDs are included here in one section although it’s certainly true that the environmental connection is the most tenuous compared with the other disorders discussed in that section. This report has gone through extensive peer and public review and should be published later this year.
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