What Causes Autism? Take Your Pick.

What causes autism?  The list continues to grow.  Even if all the science is perfectly good, it would be understandable if concerned laypeople just threw up their hands in frustration.

In BMJ [formerly British Medical Journal], Dheeraj Rai and colleagues finger antidepressants:

In utero exposure to both SSRIs and non-selective monoamine reuptake inhibitors (tricyclic antidepressants) was associated with an increased risk of autism spectrum disorders, particularly without intellectual disability. Whether this association is causal or reflects the risk of autism with severe depression during pregnancy requires further research. However, assuming causality, antidepressant use during pregnancy is unlikely to have contributed significantly towards the dramatic increase in observed prevalence of autism spectrum disorders as it explained less than 1% of cases.

The Daily Beast mentions ultrasound:

Manuel Casanova, a neurologist who holds an endowed chair at the University of Louisville in Kentucky, is one medical doctor who is listening. Casanova contends that Rakic’s mice research helps confirm a disturbing hypothesis that he and his colleagues have been testing for the last three years: that ultrasound exposure is the main environmental factor contributing to the exponential rise in autism. 

The Wall Street Journal cites studies on insecticides and air pollution:

Researchers at an international conference on autism on Friday presented three new studies lending strength to the notion that environmental influences before birth may play a role in the risk for the condition.

In one study, pregnant women who were exposed to certain levels of air pollution were at increased risk of having a child with autism. Another presentation suggested that iron supplements before and early in pregnancy may lower the risk, and a third suggested some association between use of various household insecticides and a higher risk of autism.

A release from the University of Manchester discusses research into birth weight:

The biggest study of fetal growth and autism ever has reported that babies whose growth is at either extreme in the womb, either very small or very large, are at greater risk of developing autism.

It is the first time that a clear link has been made between babies who grow to above average size at birth and risk of Autism Spectrum Disorder and follows from a study of more than 40,000 child health records in Sweden.
...

To view the paper, published in The American Journal of Psychiatry, click here. To view the editorial article in the Journal about the research, please click here.

Causation: Take Your Pick

One reason why there is so much debate and confusion about autism is that research on causation seems to point in multiple directions. In the past week alone, news accounts have mentioned findings on air pollution, brain overgrowth, antidepressants, and low birth weight.

From The Wall Street Journal:

"The evidence is growing that air pollution can affect the brain," says medical epidemiologist Heather Volk at USC's Keck School of Medicine. "We may be starting to realize the effects are broader than we realized."

Reviewing birth records, Dr. Volk and her colleagues calculated that children born to mothers living within 1,000 feet of a major road or freeway in Los Angeles, San Francisco or Sacramento were twice as likely to have autism, independent of gender, ethnicity and education level, as well as maternal age, exposure to tobacco smoke or other factors. The findings were published this year in the journal Environmental Health Perspectives.

"Based on our data, it looks like air pollution might be a risk factor for autism," Dr. Volk says. Still, there are so many possible genetic and environmental influences that "it is too soon for alarm," she says.

From AFP:

A post-mortem analysis of half a dozen autistic boys showed that their brains were heavier and contained many more neurons than counterparts without the disorder, US researchers said Tuesday.

The study, while small, suggests that brain overgrowth may be occurring in the womb, according to the findings published in the November 9 issue of the Journal of the American Medical Association.

From Cox Newspapers:

As scientists strive to find what's behind a spike in autism, especially in boys, a new study has raised the possibility that antidepressants taken by their mothers may be a culprit, a finding that has set off concern for women and their doctors.

Rodents exposed to the antidepressant Celexa displayed autismlike changes in their brain structure and their pups' behavior, especially the males, according to the study, published last month in Proceedings of the National Academies of Sciences.

Celexa is a commonly prescribed antidepressant in a class that includes Lexapro, Zoloft and Prozac.

Another study, published in July in Archives of General Psychiatry, found that autistic children were twice as likely as other children to have been exposed to antidepressants before birth. First-trimester exposure created nearly four times the risk.

From The Washington Post:

THE QUESTION Might the tiniest of newborns face a bigger chance of developing autism?

THIS STUDY involved 623 children who were born in the mid-1980s weighing 4.4 pounds or less. Their health was assessed periodically, including screening for autism spectrum disorders at age 16 and evaluations to confirm the diagnosis, using standardized measures, at age 21. Overall, 5 percent of the youths had autism spectrum disorder diagnoses, a rate described as five times that found in the general U.S. population. The lower the birth weight, the higher the likelihood of an autism diagnosis, with a 10.6 percent prevalence among those who weighed 3.3 pounds at birth and a 3.7 percent prevalence at 4.4 pounds.

Low Birth Weight and Autism

MedPage Today reports:

Children weighing less than 2,000 g (4.4 pounds) at birth may be more prone to autism spectrum disorders, a population-based study suggested.

The estimated prevalence of autism spectrum disorders reached 5% in a regional low birth weight cohort, Jennifer A. Pinto-Martin, PhD, MPH, of the University of Pennsylvania in Philadelphia, and colleagues found.

That screen-detected prevalence was five times higher than expected from the general population, the group noted in the November issue of Pediatrics

The CDC reported a 0.9% prevalence among 8-year-olds across the United States in 2006.

"This prospective study, using rigorous diagnostic procedures, confirms that the rate of autism spectrum disorders is elevated among low birth weight/preterm survivors," the researchers wrote in the paper.

That low birth weight and prematurity put children at risk of cognitive and motor disability has been well established, but their link with autism spectrum disorders was largely through retrospective studies and those that screened without diagnostic confirmation, the group noted.

Amanda Gardner writes at USA Today:

Although researchers have yet to confirm a cause-and-effect relationship between low birth weight and autism, the new findings may help explain the recent increase in the ASD rate in the U.S., Pinto-Martin says.

"The number of children with a diagnosis of autism is on the rise and [we] haven't been able to explain why," she says. "It's partly a function of awareness and better diagnosis, but we do a better job of keeping tiny babies alive and this may be one consequence of that." [emphasis added]