Autism is known to be familial and a recent study has shown that the genetic basis for autism is due to common genetic variation and not a rare gene. The study used epidemiological data from Sweden and a new method to analyze heritability due to a rare gene versus common genetic variation.
The study was carried out by researchers at various universities and Drs. Kathryn Roeder and Joseph D. Buxbaum were the lead scientists. These researchers were part of the Population-Based Autism Genetics and Environment Study Consortium. The study was reported in the journal Nature Genetics.
The study showed that most of the heritability was due to common genetic variation. This means that, in most cases, there is not one main gene that one inherits that lays the basis for autism. There is not one place in the genome to pinpoint the spot where a certain variation causes autism in a number of individuals. This common genetic variation can also be found in people who do not have autism as well.
The study also showed that rare de novo mutations can, however, contribute to individual liability, which means that a rare genetic mutation can be the basis for autism in some individuals. These rare gene mutations, however, are the explanations for some individuals but could not be used in any type of genetic screening test for the population.
A way to look at the results from the study is certain families may have many of the common genetic variants for autism, and therefore there is a higher prevalence of autism in the family, but it is only a certain combination of these genetic variants that must come together to cause autism. Another way it could work is the family may have many of the common genetic variants but it would take an additional rare mutation to occur to create the tipping point to autism.
Research studies that aim to determine the genetic basis for major diseases, such as autism, schizophrenia, diabetes and cancers, need to carry out projects that involve thousands of subjects. The reason for this is statistically analyses work best with large numbers. One of the key factors in this research study on autism is the Population-Based Autism Genetics and Environment Study Consortium, which was made possible by Sweden’s universal health registry, involved a large number of subjects. About 3,000 people with autism were included in this study and each was matched with a control subject. In addition, the scientists in this study were able to compare their results with a family study being carried out in the Swedish population that included data from twins and cousins. They also had information on the age of the father at birth and the psychiatric history of the parents of the subjects with autism. This amount and type of information is unprecedented in genetic studies.
The next step in this research will be to look further at the deletions and duplications in the genetic material that was found to be associated with autism. Also, spontaneous mutations will be considered in future research. Even though the rare spontaneous mutations were shown to account for a small amount of the risk for autism, these glitches were still seen to be important and may be key in understanding the underlying genetic basis for autism. Autism being shown to be related to common genetic variation will help to steer research on autism in the right direction.
By Margaret Lutze