If you are an individual with autism or a parent of a child on the spectrum, it's perfectly natural to wonder about the causes of this mysterious disorder. You may recognize symptoms of autism spectrum disorders (ASD) in other members of your family and question whether there may be a hereditary link. Over the years, many scientific studies have examined the question of whether and to what extent genetics play a role in autism.
Understanding Autism's Genetic Link
Since the 1970s, hundreds of studies have examined the potential genetic basis for autism. Early research was limited to twin studies, but when the human genome was mapped in the 1990s and early 2000s, research became more focused. Studies began to identify specific genes that were implicated in ASD.
Keep the following in mind as you read research studies about autism and genetics:
- According to the National Institute of Health, it's likely that autism is the result of a combination of multiple genetic mutations or a genetic mutation and one or more environmental factors.
- Researchers have identified hundreds of potential genetic differences in people with autism.
- Since only some of the genetic markers for autism are widely understood, there is no conclusive genetic test for the disorder.
- According to the National Institute of Mental Health, sporadic autism, defined as cases where there is no family history of autism, account for approximately 90 percent of autism cases.
- Identical twins, who share the same genetic material, are far more likely than fraternal twins or siblings to share an autism diagnosis as well.
Recent Research into the Genetic Causes of Autism
Several recent studies have worked to further the knowledge of the medical and scientific community about the origins of this disorder. Learning about recent research can help you make sense of this complicated topic.
Large Genetic Study Identifying Dozens of Genes for Autism
An exhaustive genetic study published in the journal Nature in 2010 examined blood samples from nearly 1,000 children who had been diagnosed with an ASD, as well as samples from those children's parents. As part of the testing, they compared those children's genes with one million different gene variants already mapped out in the human genome.
The study found that dozens of genetic mutations may be responsible for autism and that in almost six percent of cases, the child is the only one to carry those mutations. This indicates that in some cases, a mutation may have occurred in the egg or sperm cells prior to the child's conception. Because this study found so many different gene variants linked to autistic disorders, it may not present a clear path toward identifying the cause of autism. Researchers stress that even larger studies are necessary to determine trends.
Study Finding Genetic Link and Possible Explanation of Male/Female Disparity
One 2011 study in the journal Neuron examined nearly 1000 families in which one child was diagnosed with autism and found that several mutations may cause the disorder. In fact, many siblings who do not carry the diagnosis may have harmless but rare mutations that are associated with autism. These mutations, which involve missing or duplicated genetic information, are called "copy number variants" (CNV). They are very rare in the regular population but much more common in families with autism.
The researchers found that females were much more resistant to the effects of these mutations than male, which may be the reason autism is much more prevalent in boys.
Study of Almost 400 Twin Pairs Indicating Genetic and Environmental Link
A study by the University of California at San Francisco examined almost 400 pairs of twins in which at least one member had been diagnosed with autism. The results were published in the journal Archives of General Psychiatry in 2011.
Of the twin pairs studied, the results indicated that 31 percent of fraternal twins shared the ASD diagnosis, while identical twins had a 77 percent chance of both being diagnosed. This pointed to a genetic link, but scientists were most interested in what the fraternal twin results indicated. The study found that the chance of fraternal twins both developing autism was significantly higher than the chance of any sibling pair of different ages developing this disorder. They concluded that some environmental factor also played a role, probably during pregnancy or early infant development.
Genetically Engineered Mouse Study Indicating Brain and Behavior Differences
Another study published in the Proceedings of the National Academy of Sciences in 2011 studied genetically modified mice. These mice had chromosomal deletions similar to one genetic component of autism.
Researchers examined the behaviors and brains of mice with these chromosomal deletions and found that they were very similar to some of the traits of autism. For instance, the mice engaged in repetitive behaviors, were hyperactive, and had trouble sleeping. Physically, eight regions of the mice's brains were abnormal. The researchers caution that while this indicates some genetic role in autism, it does not encompass all genetic components or types of ASD.
2011 Sibling Study Pointing to Possible Genetic Link
A study published in Pediatrics in 2011 examined the prevalence of autism in siblings. The study involved almost 700 infants who were born to families in which one child had already been diagnosed with autism. The study found that the likelihood of a second sibling developing autism was about 19 percent.
The researchers are collecting genetic material from the study participants to determine how much of this link is related to genetic factors. They expect that if there is a genetic mutation in both the child with autism and the parent, the risk of autism in siblings would be much higher.
Study Involving Oxytocin Receptor Gene
A 2011 study in the Journal of Neurodevelopmental Disorders found that abnormalities in a gene responsible for receptors of the hormone oxytocin were more common in individuals diagnosed with autism. Oxytocin is associated with facilitating breastfeeding and increasing empathy and perspective-taking. It is also involved in social interactions and modulation of fear and anxiety.
This study included more than 2,300 individuals with ASD. Researchers found that oxytocin receptor genes were abnormal in many of these individuals and that this could indicate a predisposition toward autism.
Article Discussing Current Genetic Research into Autism
An article in the scientific journal Trends in Cognitive Sciences discussed a decade's worth of genetic studies in the area of autism. The article maintained that only 10 to 20 percent of ASD cases could be accounted for using the genes currently identified as related to autism.
The authors point out that these studies share a common theme: that genetic factors influence neurological pathways. This connection provides a tool for future researchers to determine what accounts for the similarities and differences in various autism spectrum disorders.
Study Examining Whether Parental Mental Health Concerns Are Related to Caregiving
Research has indicated that parents of children on the autism spectrum are more likely to suffer from a variety of mental health concerns. A 2011 study in the Journal of Developmental and Physical Disabilities examined whether these mental health issues, which can include anxiety, depression and obsessive-compulsive behaviors, are the result of caring for a child with autism or are a genetic factor that may predispose a family to autism.
The study, which included more than 700 parents, found that underlying genetic factors were more likely to be responsible for parents' mental health issues.
Implications for Families
For parents of children on the spectrum, understanding the genetic basis of autism can help assuage feelings of guilt. However, these findings can also cause friction within the family. If you're a parent of a child on the autism spectrum, keep the following tips in mind when considering the genetic basis for the disorder:
- Avoid pointing fingers within your family. While it may be tempting to point out autistic traits in other family members, it is unlikely to be productive.
- Don't be disappointed if genetic testing doesn't turn up any answers. Because of the high number of implicated genes, there are few genetic tests that can identify autism.
- It is important to remember that according to the National Institute of Health, autism is not caused by parenting style.
- Remember that regardless of the diagnosis or genetic implications, your child is still your child.
- When making decisions for your family, such as whether to have another child despite the potential increased risk of autism, always do your homework and openly communicate with one another.
No One Gene Is Responsible
Decades of research support the idea that autism is, at least in part, a genetic disorder. However, the vast number of genes involved and the multitude of environmental factors that may also play a role make it clear that there is no one gene responsible for the disorder. Researchers are studying the genetic aspects of ASD all the time, and each new study provides a few clues about how heredity influences autism.