Twin Study Shows High Heritability of Autism

There have been several studies done in an effort to figure out whether or not there is a genetic link to autism. One that was published in March of 2015 involved twins. The results of the study found that genes may be more responsible for autism than previously thought.

The study was titled “Heritability of Autism Spectrum Disorder in a UK Population-Based Twin Sample”. It was published in JAMA Psychiatry on March 4, 2015. The objective of the study was “to establish the relative contributions of genetic and environmental factors in liability to autism spectrum disorder (ASD) and a broader autism phenotype in a large population-based twin sample and to ascertain the genetic/environment relationship between dimensional trait measures and categorical diagnostic constructs of ASD.”

All of the twins in the study were born in England and Wales between the years 1994 and 1996. There were a total of 6,000 twin pairs involved in the study. Some of the twins were identical twins and some were fraternal twins.

Identical twins share the exact same DNA. Fraternal twins share some DNA, but not more than siblings who are not twins would share. Identical twins are always the same gender. Fraternal twins can be the same gender. Or, the twins could be of opposite genders.

In-home evaluations were done on the twins. This included diagnostic interviews and play-based assessments. A total of 6,423 pairs of twins had the Childhood Autism Spectrum Test (CAST) done when they were around 7 years and 9 months old. 359 pairs of twins and the Development and Well-being Assessment (DAWBA) done when they were 10 years and 3 months old. 203 pairs of twins had the Autism Diagnostic Observation Schedule (ADOS) done when they were 13 years and 2 months old. There were other tests done as well.

The results of the study showed that autism is rooted in genetics 74% to 98% of the time. A total of 181 kids in the study ended up receiving an official autism diagnosis. The researchers found that if one twin had autism the risk that the other twin would also be on the autism spectrum was “significantly higher” in identical twins as compared to fraternal twins.

The National Institute of Neurological Disorders and Stroke (NIH) defines autism spectrum disorder as “a range of complex neurodevelopment disorders, characterized by social impairments, communication difficulties, and restricted, repetitive, and stereotyped patterns of behavior.” They also note that experts estimate that 1 out of 88 children who are 8 years old will have an ASD, and that males are four times more likely to have an ASD than females are.

Image by Becky Wetherington on Flickr.

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