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Research into autism causes continues

Gardener H. Pediatrics. 2011;doi:10.1542/peds.2010-1036.

A cascade of events during labor and delivery may contribute to an increased risk for autism later in life, but data are still needed, according to an analysis published online this week.

Hannah Gardener, ScD, and colleagues from the University of Miami published data from a meta-analysis of 40 studies published before April 2007. The researchers noted several circumstances that may have been linked to subsequent autism development, notably oxygen deprivation, anemia and growth retardation. Other events included low birth weight, maternal hemorrhage, congenital malformations, multiple births, abnormal birth positions, low Apgar scores and others.

The researchers said factors that were not “associated with autism risk included anesthesia, assisted vaginal delivery, post-term birth, high birth weight, and head circumference.”

“There is insufficient evidence to implicate any one perinatal or neonatal factor in autism etiology, although there is some evidence to suggest that exposure to a broad class of conditions reflecting general compromises to perinatal and neonatal health may increase the risk,” the researchers wrote, adding that their research “underscores the need for large, prospective, population-based studies with the goal of elucidating the early-life modifiable risk factors.”

Disclosure: The researchers reported no relevant financial disclosures.

In the August issue of Pediatrics, an extremely well-presented article on perinatal and neonatal risks for autism was published. This comprehensive meta-analysis included 40 publications through March 2007 that were viewed as eligible for inclusion. In addition to the risk factors known to have an increased risks associated with autism, the analysis identified those circumstances where data and methodology were insufficient to place them in the high-risk group.

The risk factors identified with at least a 1.5 RR of developing autism were: Prolonged labor, cord complications, birth injury, maternal hemorrhage, born 4 weeks or more preterm, birth weight less than 2,000 g (even greater if birth weight was less than 1,500 g), and congenital malformations.

In our collective efforts to get to the bottom of this striking increase in the rate of autism nationwide, we are all not surprised about the large number of factors that are implicated by this meta-analysis and the lack of single causality of this trend in autism. The unifying factor of fetal hypoxia is also quite apparent, as all of these factors have this condition as an often common outcome to variable degrees. Unfortunately, the overall prevalence of these factors has not significantly worsened during these past 30 years, and in many instances has actually improved ( more in certain locales and settings than others). Thus, though plausible as contributing factors to this increasing prevalence of autism, most would continue to conclude that we have not found the single, or even multiple, magic bullet that would explain the growing presence of autism. This very well-done study adds fuel to the arguments that decreasing prematurity and all of its complications and focusing on minimizing perinatal risk factors is laudable and important. However, solving these alone will not provide us with the true cause of autism, nor will it allow the greater pediatric community to craft a targeted intervention. It would reflect our gains in the approach to sudden infant death syndrome (SIDS) and decreasing its incidence. Changing sleep position and enhancing sleep safety has apparently decreased the incidence of SIDS substantially, but it has not permitted us to say that the problem has been totally eliminated.

Clearly, there is much more work to do to better understand the complete risk factor bundle that contributes to autism, but by eliminating the most significant of our perinatal and neonatal risk factors, we can perhaps slow the rise of new cases. Time will tell.

Steven P. Shelov, MD, MS
Infectious Diseases in Children Editorial Board member

Disclosure: Dr. Shelov reported no relevant financial disclosures.

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