A major international study of 6454 families with autistic children shows that autism is not caused by mutations in a single gene but by several genetic mutations. Overall, the genetic variants that increase the likelihood of autism and schizophrenia significantly overlap those associated with educational attainment. Despite this fact, people with autisim often have great difficulty in completing higher education.
Many people have autistic traits, and some more than others. Similar to all spectrum disorders, autism varies from infantile autism to barely autistic. In between is a broad and varied spectrum of individual diagnoses such as Asperger syndrome. According to a major research study in Nature Genetics, the degree of autism results from the combined effect of many genes.
“The strong genetic component of the development of autism results from not one but many genes, and the degree of autism strongly depends on how many of these genes have mutations. Further, many of these genes that are associated with increased risk of autism also increase the risk of schizophrenia and also greatly overlap with the genes associated with educational attainment,” explains an author of the article, Jakob Grove, Associate Professor, Department of Biomedicine, Aarhus University and the Lundbeck Foundation Initiative for Integrative Psychiatric Research (iPSYCH).
Children differ from the adults
The study is based on substantial international data in which the parents and children from 6454 families with autistic children had their genetic profile mapped through exome sequencing, which maps the DNA sequences in all the body’s genes. This means that the study determined and compared about 30 million DNA base pairs for each child and parent.
Since the children and not the parents in the participating families were diagnosed with autism, the researchers could compare the gene variants in all their genes using a new method called polygenic transmission disequilibrium. This is based on the fact that each parent transmits one of their two copies of each gene to their children.
Children are therefore expected to become an average of their parents. However, when a child is taller than both parents, for example, one reason may be that they have more total gene variants for height than each parent has. By comparing the children and adults in the 6454 families in which children were diagnosed with autism and the parents were not, we could therefore measure the extent to which the children had received additional gene variants for autism than each of their parents had.
Ability to focus in depth
The research was carried out in connection with a major study supported by the Lundbeck Foundation that aims to map the genetic background for the autism spectrum. This provides a very clear picture of the link between seemingly unconnected diseases and characteristics. Although previous research had suggested a genetic link between autism, intelligence and education, this could theoretically have been attributed to other possible causes or artefacts (caused by the scientific procedures themselves).
“The novel aspect here is that people with autism – regardless of whether they are highly intelligent or not – generally inherit more gene variants that are associated with educational attainment than their healthy siblings and parents. This excludes the previously mentioned artefacts, and we can therefore almost certainly conclude that people with autism are more genetically predisposed to traits that are advantageous in carrying out and completing an educational programme.”
For example, this may include the ability to focus in depth which, for people with autism, is not usually determined by free will but rather that they are inherently fascinated by the details. Indeed, most people with autism do not complete higher education.
Not surprising after all
Unfortunately, another mental disorder may result from the autistic gene profile because many people with autism have many of the same gene variants that are associated with an increased risk of schizophrenia. Although the two disorders are very different, they also share general similarities. Schizophrenia is a mental disorder that alters thought processes and behaviour, creating difficulty in differentiating between reality and individual perception. Under stress, people with autism may have similar symptoms.
Both people with schizophrenia and people with autism tend to be socially inhibited and have difficulty communicating and making eye contact. Nevertheless, individuals with autism are able to proficiently benefit from several educational programmes such as mathematics and physics. This genetic link between these three states is thus perhaps not as surprising as it seems.
Although the research now demonstrates a genetic link between autism, educational attainment and schizophrenia, there is still a long way to go to understand the functions of the discovered genes and whether this knowledge can be translated into effective treatment for people with schizophrenia.
“Polygenic transmission disequilibrium confirms that common and rare variation act additively to create risk for autism spectrum disorders” has been published in Nature Genetics. In 2015, the Novo Nordisk Foundation awarded a grant to co-author Manuel Mattheisen for the project Gene Environment Interactions in Mental Illnesses – Integrating the G with the E.