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Years of research, more and more cases are diagnosed, and scientists still don’t know exactly what causes autism in children. However, they find more and more risk factors. It is good to know which ones.
Knowledge about the causes of autism is becoming more and more desirable and important for a growing number of families. The prevalence of this disorder increased by an estimated 2006% in 08-23, according to a report published last week by the Centers for Disease Control and Prevention in Atlanta.
In most cases, scientists can’t tell parents what caused their child’s autism, says Thomas Insel, director of the US National Institutes of Mental Health. Mostly the causes of autism – which is probably not a single condition but a group of diseases with related symptoms – remain a mystery.
Over the years, scientists had only a few proven facts about the disease: for example, it affects boys four times more often than girls, for example. Recently, however, researchers have confirmed a number of factors that increase the risk of autism, many of which are related to problems that arise very early in life – such as during pregnancy or childbirth, and even during the production of eggs and sperm, explains Craig Newschaffer, professor at Drexel University of Philadelphia.
To better understand the causes of autism, researchers from four prominent universities are tracking the health of 1200 mothers of autistic children in a project called EARLI, Early Autism Risk Longitudinal Investigation. Because researchers know these women are at high risk of having a second child with autism, they track their subsequent pregnancies very closely by analyzing blood, urine, hair and even collecting dust from their homes, says Newschaffer, one of the study’s co-authors. The researchers also asked pregnant women to write down any illnesses they contracted, as infections during pregnancy are also suspected of contributing to the development of autism.
Doctors can confidently reassure parents that one thing doesn’t cause autism – vaccines, says Paul Offit, head of the infectious disease department at Children’s Hospital in Philadelphia. Over 20 studies have found no link between autism and vaccines, given alone or in combination.
Scientists have tips on other risk factors:
Geny
About 15-20 percent. autistic children have a genetic mutation that contributes to the development of their disorder, says Insel. Certain genetically determined diseases, such as Fragile X Syndrome and Rett Syndrome, are well known to increase the risk of autism. But even if genes would make a major contribution to the development of this disorder, it is possible that most children have a unique mutation or set of mutations, says David Amaral, research director at the University of California, Davis.
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Family history
If parents have one child with autism, the risk of having another child with this disorder is close to 20%. – according to a groundbreaking study by scientists from the University of California at Davis. In the case of those who have two autistic children, the probability that the third will also be autistic is as much as 32 percent, comments the author of the study, Sally Ozonoff.
Environment pollution
One Californian study published last year found that babies whose mothers lived near the highway during pregnancy were more likely to be diagnosed as autistic.
Older parents
Both older fathers and older mothers have a higher risk of having children with autism, says Newschaffer. Research by scientists from Israel and the Harvard School of Public Health also suggests that fertility treatments, which are more commonly used in elderly patients, are associated with a higher risk of this disorder.
Prematurity and a small weight of the newborn
A study published in October 2011 in the journal Pediatrics found that 5 percent of children who weighed less than 2 kilograms after birth were diagnosed with autism before the age of 21.
Leki
Many studies show that the anticonvulsant drug valproic acid may increase the risk of autism in children who have been exposed to it before birth. Another study published last year found a higher risk of the disorder among children exposed in utero to anti-depression drugs. In contrast, prenatal vitamin use has been associated with a lower risk of autism.
You are pregnant in a short period of time
A 2011 study found that babies born less than a year after their older siblings were diagnosed with autism three times as often as babies born three years after their last pregnancy.
Text: Liz Szabo