Autism spectrum disorder (ASD) is a complex neurodevelopmental condition characterized by diverse presentations in communication, social interaction, and patterns of behavior. Many individuals and families are curious about the role genetics plays in autism and whether genetic testing can provide answers.
Genetic Foundations of Autism
Autism has a significant genetic component, with research demonstrating that genetic factors contribute substantially to its development. Twin studies estimate heritability between 60% to 90%, indicating an individual’s genetic makeup plays a considerable role.
While influential, autism is not typically caused by a single gene. Instead, it involves a complex interplay of multiple genes, often hundreds, interacting with environmental factors. For many cases, the precise genetic cause remains unidentified. Genetic changes can be inherited from parents or occur spontaneously as new mutations in the individual.
Available Genetic Testing Approaches
When autism is suspected, several genetic tests investigate potential underlying factors. These tests examine an individual’s DNA to identify variations that might be associated with the condition. Each test targets different kinds of genetic changes, offering varying levels of detail.
Chromosomal Microarray (CMA) is a common genetic test recommended for individuals diagnosed with autism spectrum disorder, developmental delay, or intellectual disability. CMA scans the entire genome to detect large-scale genetic changes, specifically missing or extra DNA pieces known as copy number variants (CNVs). These deletions or duplications can impact brain development and have been linked to autism.
Whole Exome Sequencing (WES) provides a more detailed analysis by focusing on the exome, the protein-coding regions of genes. Although the exome represents only about 1% of the genome, it contains approximately 85% of known disease-related genetic variations. WES can identify smaller genetic changes, such as single nucleotide variants and small insertions or deletions, that might contribute to autism.
Targeted gene panels analyze a specific set of genes already known to be associated with autism or neurodevelopmental disorders. These panels can range from covering a few dozen to over a hundred genes. They offer a focused way to screen for known genetic links, often being less costly than more comprehensive sequencing methods.
What Genetic Tests Reveal and Do Not Reveal
Genetic tests can identify specific underlying genetic conditions or risk factors associated with autism. For instance, tests can detect syndromes like Fragile X syndrome or specific copy number variants (CNVs) with a known link to autism. Identifying such a genetic finding can provide an explanation in some cases, occurring in about 10% to 30% of individuals tested with WES, with a higher chance for those with intellectual disability.
No single genetic test can definitively diagnose autism. Autism is a clinical diagnosis based on behavioral assessments and developmental history, not solely on genetic markers. Even if a genetic variant associated with autism is identified, it doesn’t always mean it’s the sole cause, as genetics often interact with environmental factors.
A negative genetic test result does not rule out an autism diagnosis. Many autism cases lack an identifiable genetic cause through current testing, and the field is still evolving. Additionally, some genetic changes found may be classified as “variants of uncertain significance” (VUS), meaning their role in autism is not yet clear due to insufficient information. Such results require ongoing research.
Why Families Explore Genetic Testing
Families explore genetic testing for several reasons, despite its limitations in definitively diagnosing autism. One primary motivation is to identify an underlying genetic syndrome with other health implications beyond autism. This knowledge can lead to better medical management and proactive screening for conditions like epilepsy or certain cancers.
Understanding a genetic cause can also provide insights into the likelihood of autism recurring in future pregnancies. While the general recurrence risk for a subsequent child in families with one child with autism is around 10% without a known cause, identifying a specific genetic variant can significantly refine this estimate, potentially lowering it to 1% or increasing it to as high as 50% depending on the type of genetic change. For some families, a genetic finding offers explanation, reducing the “diagnostic odyssey” of seeking answers. It can also connect families to specific support groups or research opportunities.
Understanding Genetic Test Outcomes
Interpreting genetic test results for autism can be complex due to varied findings. Results typically fall into categories: positive (a known autism-associated variant), negative (no significant variants), or a variant of uncertain significance (VUS). A VUS indicates a genetic change whose impact and connection to autism are unclear.
Genetic counselors play a central role in guiding families through this process, both before and after testing. They help explain the types of tests available, their potential findings, and limitations, ensuring families make informed decisions. After testing, genetic counselors interpret the results, discuss their implications for the individual and family, and provide support. This expert guidance is crucial because results are one piece of information for autism understanding and management.