The Genetics of Asperger's Syndrome: Is Asperger's Hereditary?
written by: Keren Perles
• edited by: Paul Arnold
• updated: 10/13/2010
Is Asperger's hereditary? The answer isn't as clear cut as you might think. Although Asperger's almost certainly has some genetic component, there are other factors that affect whether a person develops Asperger's syndrome.
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Is Asperger's Hereditary?
After looking around at families that have a child with Asperger's syndrome in them, you may ask the obvious question: "Is Asperger's hereditary?" After all, there are many families in which, after finding out that a child has Asperger's, the parents suddenly realize that they or several of their siblings or close relatives share some autistic traits that are common to those with Asperger's.
But is Asperger's hereditary? The answer is...sort of. Scientists have not yet identified a specific gene mutation that causes Asperger's, but there is some proof that the disorder has a genetic basis. Asperger's syndrome tends to run in families, and studies have shown that Asperger's may have an even stronger genetic link than other forms of autism. It is possible that there is a combination of alleles that determine whether a person develops Asperger's syndrome, as well as how strongly the syndrome affects them.
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One of the main ways in which researchers determine the heritability of a disorder is by conducting twin studies, in which they compare the existence of the disorder in identical and fraternal twins. Many studies in the 1990s and early 2000s showed that a higher percentage of monozygotic (identical) twins shared characteristics of Asperger's than dizygotic (fraternal) twins.
Critics of these studies claimed that they were too limited in scope because of the small number of twins that were included. In 2006, however, a twin study published in the Journal of the American Academy of Child and Adolescent Psychiatry examined 3400 pairs of twins and found that autistic traits had a very high likelihood of being hereditary. Like the previous (smaller) studies, the percentage of identical twins who shared AS characteristics also exceeded the percentage of fraternal twins who shared them. Interestingly, it has been hypothesized that the process of creating monozygotic twins itself may be a risk factor for autistic characteristics, which would skew the results of these studies considerably.
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Although studies about the genetics of autism abound, it is more difficult to find studies about the genetics of Asperger's syndrome. In 2005, a report looked at the family background of 58 people with Asperger's syndrome. Of these subjects, five percent of them had first-degree relatives who had Asperger's syndrome, and high percentages of them had family members who had previously been diagnosed with schizophrenia (19%) and depression (60%).
A different type of study actually examined the genes of people with Asperger's. In the first study of this kind, scientists at the University of Cambridge studied 68 genes in people who had Asperger's. These genes were linked to either the growth of neural cells, social behavior, or hormones that released sex steroid. The study found 27 of these genes to be linked to Asperger's syndrome, and researchers will be studying them further. This study was published in the journal "Autism Research" in 2009.
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Other Possible Causes of Asperger's Disorder
Of course, genetics is not the only aspect that is hypothesized to affect whether a person is diagnosed with Asperger's syndrome. Exposure to teratogens (chemicals that cause birth defects) during early pregnancy may also have an effect on whether a person develops Asperger's syndrome. Environmental causes after birth may also contribute to the development of Asperger's. Some suggested environmental causes include certain vaccines, heavy metals, infectious diseases, and childhood stress.
It is important to realize that the "Refrigerator Mother Myth," which maintained that poor parenting skills and cold, unemotional mothering caused Asperger's syndrome, has been long proven false. Many parents of children who have Asperger's are in fact extremely caring, although they may be carrying a tendency towards Asperger's in their own genes.