Environment as important as genes in autism, study finds

LONDON Sat May 3, 2014 4:41pm EDT

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LONDON (Reuters) - Environmental factors are more important than previously thought in leading to autism, as big a factor as genes, according to the largest analysis to date to look at how the brain disorder runs in families.

Sven Sandin, who worked on the study at King's College London and Sweden's Karolinska institute, said it was prompted "by a very basic question which parents often ask: 'If I have a child with autism, what is the risk my next child will too?'"

The findings, published in the Journal of the American Medical Association (JAMA), suggest heritability is only half the story, with the other 50 percent explained by environmental factors such as birth complications, socio-economic status, or parental health and lifestyle.

The study also found that children with a brother or sister with autism are 10 times more likely to develop the condition, three times if they have a half-brother or sister with autism, and twice as likely if they have a cousin with autism.

"At an individual level, the risk of autism increases according to how close you are genetically to other relatives with autism," said Sandin. "We can now provide accurate information about autism risk which can comfort and guide parents and clinicians in their decisions."

People with autism have varying levels of impairment across three common areas: social interaction and understanding, repetitive behavior and interests, and language and communication.

The exact causes of the neurodevelopmental disorder are unknown, but evidence has shown it is likely to include a range of genetic and environmental risk factors.

As many as one in 50 school-age children in the United States are diagnosed with autism, although some of these will be milder cases that have been diagnosed partly because of better recognition of autism symptoms by carers and doctors. In Europe, experts say the rate is around one in 100 children.

For this latest study, researchers used Swedish national health registers and analyzed anonymous data from all 2 million children born in Sweden in between 1982 and 2006, 14,516 of whom had a diagnosis of autism.

The researchers analyzed pairs of family members, identical and non-identical twins, siblings, maternal and paternal half-siblings and cousins.

The study involved two separate measures of autism risk – heritability, which is the proportion of risk in the population that can be attributed to genetic factors, and relative recurrent risk which measures individual risk for people who have a relative with autism. 

Most previous studies have suggested heritability of autism may be as high as 80 to 90 percent. But this new study, the largest and most comprehensive to date, found genetics factors only explained around half of the cause of the disorder.

"Heritability is a population measure, so whilst it does not tell us much about risk at an individual level, it does tell us where to look for causes," said Avi Reichenberg, of the Mount Sinai Seaver Center for Autism Research, who worked on the study while he was at King's College London.

He said he was surprised by the results, as he did not expect the importance of environmental factors to be so strong.

"Recent research efforts have tended to focus on genes, but it's now clear that we need much more research to focus on identifying what these environmental factors are," he added.

(Editing by David Gregorio)

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Comments (5)
bepatienz wrote:
This article poses a false dichotomy between “heritable” genes and genetic changes that are present in the embryo but are note present in either parent: “de novo” mutations.

The risk of ASD clearly increases with what the authors would consider to be “environmental” factors–that is, alterations in DNA sequence or DNA methylation that are not present in either parent. These sorts of prenatal changes–which, BTW, occur months or years before the administration of the vaccines that naive people have long blamed for ASD–are not a dog whistle for those who believe that vaccines cause ASD; in fact, they implicate prenatal factors that predate such vaccinations.

May 03, 2014 11:01pm EDT  --  Report as abuse
MAthari wrote:
Genetics can, at most account for 1% of the variation in brain disorders and genetically based disorders are generally organic or diffuse and accompany physical disorder. GWAS has failed to locate any magical single or combination of genes that would indicate a genetic proximate cause.

Heritable is a misnomer. It only means similarity. If both you and your parent grew up in an old house with conditions conducive to lead poisoning, the similarity between your deficits and your parent’s deficits would be considered heritable but in reality would be environmental. If you grew up next to a super fund site, a refinery, a garbage burning facility, on and on; and you parent was exposed to similar toxins, it shows up as heritable.

We need better exclusionary criteria before we go calling heritable what its not.

May 04, 2014 10:44am EDT  --  Report as abuse
rethinkautism wrote:
Isn’t time we give some serious consideration to one of the most common environmental exposures to both pregnant women and children? We now have two large population studies that show an association between the prenatal use of ACETAMINOPHEN(paracetamol or Tylenol)and adverse neurodevelopment.

The first study by Brandlistuen et al 2013 found that 3 year old children exposed to long term acetaminophen use during pregnancy had substantially adverse developmental outcomes including a 70% increased risk of behavioral and motor problems, as well as, double the risk of communication problems. The second study by Liew et al. 2014 found that prenatal exposure to acetaminophen increased the risk of ADHD, behavioral problems and hyperkinetic disorders in 7 year olds.

Acetaminophen exposure can potentially account for the 4-5 times higher prevalence among males. Males are differentially exposed and differentially susceptible to acetaminophen toxicity. The WHO and AAP recommend 5-7 doses of acetaminophen with the circumcision procedure. The acetaminophen sales timeline corresponds with the autism prevalence time line and there is substantial biologic plausibility.

May 05, 2014 3:35pm EDT  --  Report as abuse
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