By now most people interested in autism have read the CDC report, or at least read the news, regarding the new estimated prevalence rates of autism in the United States. Today I finally was able to read the full original report and have some brief general thoughts.

The report is based on the findings by the CDC Autism and Developmental Disabilities Monitoring Network. This network consists of a series of sites across the united states that calculate the rates of autism diagnoses for specific communities. The network first provided autism estimates based on data obtained in 2000 and then 2002. Last week’s report is based on data obtained in 2006. I have previously reviewed how the CDC prevalence rates for autism are obtained, so I will focus this post on highlighting some across state variability and differences between the 2002 and 2006 results. Read More

Diagnostic Substitution is one of the factors that have been proposed as a cause, or at least a contributing source, of the dramatic increases in autism observed during the last 10-15 years. The basic idea behind diagnostic substitution is that children that today receive a diagnosis of Autism, would have received a different diagnosis 20 years ago. Thus, the theory would suggest that there has not been an actual increase in the number of children affected, but instead simply a shift in the way conditions are classified.

Evidence for and against diagnostic substitution continue to accumulate. For example, last year I commented on a study showing that some adults that were diagnosed with pragmatic language impairment during their childhood actually meet diagnostic criteria for autism. But in an upcoming issue of the Journal of Autism and Developmental Disabilities, researchers from the California Department of Public Health report the findings of an examination in diagnostic coding practices in California during the past 20 years. Read More

A review of: M. D. Kogan, B. B. Strickland, S. J. Blumberg, G. K. Singh, J. M. Perrin, P. C. van Dyck (2008). A National Profile of the Health Care Experiences and Family Impact of Autism Spectrum Disorder Among Children in the United States, 2005-2006 PEDIATRICS, 122 (6) DOI: 10.1542/peds.2008-1057
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A summary of: Michael Waldman, PhD; Sean Nicholson, PhD; Nodir Adilov, PhD; John Williams, MD, MBA (2008). Autism Prevalence and Precipitation Rates in California, Oregon, and Washington Counties Arch Pediatr Adolesc Med, 162 (11), 1026-1034

The authors briefly reviewed epidemiological data suggesting that the highest autism rates in the USA are found on Northern and Western States, while the lowest autism rates are found in the deep south (e.g., Alabama). They concluded from these findings that an environmental trigger in these Northern and Western States (such as bad weather) may be a risk factor for the development of autism. To test this hypothesis, the authors examined precipitation rates in various counties within California, Oregon, and Washington and compared these rates to the prevalence of autism in said counties. The authors found that high rate of annual precipitation was associated with high rates of autism cases, even after controlling for variables such as county level income, population size, or access to specialized services. The authors argue that this association may be to a number of factors including 1) higher rates of television viewing in very young children (although no evidence was presented suggesting that young children in rainy counties watch more television than young children in less rainy counties), 2) vitamin D deficiencies due to less sun exposure (although no evidence was presenting suggesting that vitamin D is associated with autism, or that the rates of autism are higher in polar regions given the reduced sun exposure during winter months), 3) environmental triggers associated with playing indoors instead of outdoors, and 4) possible harmful chemicals transported by the rain.

Given the preliminary/speculative nature of this study, the manuscript was accompanied by a letter from Dr. Noel Weiss from the Department of Epidemiology of the University of Washington that, while arguing that these results may not advance our understanding of the causes of autism, lauds the editorial decision to accept this article for publication. Below I provide some excerpts of Dr. Waiss’ arguments:

First, Dr. Waiss provides a sensible interpretation of the findings:

…there are other possible explanations for the association with precipitation that they have observed. First, the criteria used to diagnose autism, and the completeness with which such diagnoses are identified by state agencies and regional centers, likely vary to a considerable extent across counties. Possibly, the degree of completeness of reporting itself is associated with levels of precipitation. In Oregon and Washington, for example, could it be that state agencies in the western, rainy, relatively urbanized counties have enumerated a greater proportion of children with autism than their counterparts in the eastern, arid, relatively more rural counties?

However, in response to concerns regarding the potential misinterpretation and misuse of the findings by the public, Dr. Waiss states that:

The primary audience for the article of Waldman et al is not the practicing pediatrician, and certainly, it is not a member of the public at large. These individuals cannot take away any practical message from it. Rather, the primary target is an investigator interested in the causes of autism, someone who might be able to test one or more of the etiologic hypotheses that derive from the research of Waldman et al.

I do not agree with Dr. Waiss on this last point. It is no longer the case that most scientific research is read mostly by relevant scientists. The audience of scientific peer reviewed articles has expanded dramatically, mostly due to the internet and the new level of activism and involvement with research by relevant communities (e.g., autism ).

Finally, in regards to the findings, the study does not in any way show or suggest that rain causes autism. It only states that there is an association between rainy counties and autism rates. This may be due to a large number of factors, most of which (e.g., differences in how diagnostic data is collected between counties) have nothing to do with rain.

A review of: Mouridsen, S.E., Bronnum-Hansen, H., Rich, B., Isager, T. (2008). Mortality and causes of death in autism spectrum disorders: An update. Autism, 12(4), 403-414. DOI: 10.1177/1362361308091653

The issue of life expectancy and mortality rates in people with autism is a largely understudied and seldom discussed topic. Studies of mortality in people with chronic psychiatric disorders usually show higher mortality rates at all ages than what is expected in the general population. Mortality rates refer to the number of death expected up to a specific age for specific cohorts. For example, what is the expected number of death within a cohort born in year 1973 by the time they are 30?

Only a couple of studies of mortality rates in people with autism have been conducted, one in California and one Denmark. Both studies showed that the mortality rate in people with austim was more than twice as that for the general population. The present study by the Danish team intended to expand on their original findings by examining the mortality rate and causes of death among a cohort of adults with ASDs who are now in their 40s. The sample included 341 adults with various diagnoses including autism (N=118), atypical autism (N=89), childhood disintegrative disorder (N=13), and asperger’s (N=121).

The mean age for the patients was 43.4 with a range of 26 to 60. A total of 26 patients have died by 2006 (7.6%). The expected number of deaths in the general population for a similar cohort was 13.5 (3.8%). Therefore, the mortality rate in the cohort of adults with ASDs was nearly twice of what is expected in the general population. However, this effect was significantly more pronounced among women. The mortality rate for woman with ASD was 4 times higher than what is expected in the general population. Surprisingly, these effects were not moderated (reduced) by IQ, which often reflects functional capacity. That is, within the group with ASDs, the mortality rates was the same for adults regardless of their IQ. The cause of death most commonly reported among the cohort with ASDs was epilepsy.