According to a new study published in the February issue of Paediatrics, children born within one year of an older sibling may be three times more likely to be diagnosed with autism.
The study examined the effect of interpregnancy interval (IPI) - the duration between pregnancies and found it to be a potential risk factor for autism. Earlier studies have blamed environmental triggers of autism such as vaccines as opposed to maternal physiological triggers such as the womb environment. This study speculates that the maternal depletion of key nutrients such as folate due to close pregnancies could be a reason for the risk and that it may be possible to prevent autism with nutritional supplements. The study comes only a week after researchers found a 1998 study that linked vaccines to autism to be fraud and retracted it.
According to the CDC one in 110 children in the U.S. has an autism spectrum disorder (ASD). ASD is a group of developmental disorders that can range from mild to severe and that often affect social interaction and communication skills. The latest study suggests that the proportion of births occurring within two years of an earlier birth increased from 11% to 18% between 1995 and 2002.
For the study the team looked at 660,000 second-born children born in California from 1992 to 2002. Those children who were conceived within one year of an older sibling were more than three times as likely to be diagnosed with autism when compared to peers who were conceived more than three years after the birth of an older sibling. Children conceived 12 to 23 months after an older sibling were nearly two times more likely to be diagnosed with autism; children conceived two years to 35 months following an older sibling were one and a quarter times more likely to be diagnosed with autism. The researchers were confident of these results after taking into account other factors that may be related to closely timed pregnancies, such as maternal age and maternal education.
Study author Peter Bearman of the Jonathan Cole Professor of the Social Sciences at Columbia University in New York City said, “The robustness of the findings was really shocking.” He added, “It could be a biological factor, such as maternal depletion of nutrients like folate, or another process that hasn’t been described or discovered yet… If the mechanism is depletion of nutrients like folate, then women can make sure to take supplements of it, and if it is something else, it also may be readily modifiable.” He explained that the rates may be high because parents are more aware of the normal developmental processes. “Parents who have had closely spaced children are more aware of developmental dynamics and more likely to seek help if the child is not developing on the right trajectory,” he said. On this study he said, “Watch the science…. This is the first study, but there is a lot more work to be done.”
Andy Shih, vice president of scientific affairs at Autism Speaks however feels that even though this study is “significant and intriguing,” “It is not a simple picture…There has been a lot of attention on environmental postnatal factors of autism, but this study suggests that when you have children too closely together, you may not be providing an optimal womb environment.” As a note to women he added, “If you are worried or concerned, work with your obstetrician/gynecologist on your childbirth and reproductive strategy… As time progresses, we’ll soon know if this is something to think about in regard to family planning.”
Dan Khoury, chief of the section of developmental and behavioural paediatrics at Nationwide Children’s Hospital in Columbus, Ohio warned people to keep the results in perspective for example that the absolute risk of autism - 1%, is still on the low side. He said, “Closely spaced pregnancies increase the risk of autism, and that is really all we can say now…Pregnancy is very taxing on the mother and depletes a variety of nutritional stores, including iron and folate, so one theory is some deficiency of nutritional stores is at play, and if, in fact, that is what is causing this increased risk, we think we may be able to treat it through supplementation.” Fred R. Volkmar, a Irving B. Harris Professor and director at the Child Study Center at Yale University in New Haven added, “This is preliminary, and nobody else has seen this yet… We don’t know if it is true, or if it is true, why would it be true.”
Deletion of long non-coding RNA linked to rare neurodevelopmental disorder