Is Autism Hereditary? Unpacking the Genetic Link

Autism spectrum disorder (ASD) is a neurodevelopmental condition characterized by social communication difficulties, sensory processing deficits, and repetitive behaviors or interests. While the exact causes of ASD remain a subject of ongoing research, it is widely recognized that both genetic and environmental factors play a role in its development. Answering the question “is autism hereditary?” has been a major focus of scientific inquiry due to the high estimates of heritability associated with the condition.

At the same time, researchers emphasize that autism is a complex disorder influenced by a constellation of genetic and non-genetic elements. This article delves into the current understanding of the genetic links to autism spectrum disorder, exploring the intricate interplay between genes, brain development, and environmental influences that contribute to its manifestation. Additionally, it examines the diagnostic processes, potential comorbidities, and management approaches related to this increasingly prevalent neurodevelopmental condition.

Understanding Autism Spectrum Disorder (ASD)

Autism spectrum disorder (ASD) is a neurological and developmental disorder that affects how people interact with others, communicate, learn, and behave. According to the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), people with ASD often have difficulty with communication and interaction with other people, restricted interests, and repetitive behaviors that affect their ability to function in school, work, and other areas of life.

Definition and Characteristics of ASD

Autism is known as a “spectrum” disorder because there is wide variation in the type and severity of symptoms people experience. People of all genders, races, ethnicities, and economic backgrounds can be diagnosed with ASD, and it can be a lifelong disorder, although treatments and services can improve symptoms and daily functioning.

Common characteristics of ASD include:

Social Communication/Interaction Behaviors

• Making little or inconsistent eye contact
• Appearing not to look at or listen to people who are talking
• Infrequently sharing interest, emotion, or enjoyment of objects or activities
• Not responding or being slow to respond to one’s name or verbal bids for attention
• Having difficulties with the back and forth of conversation
• Often talking at length about a favorite subject without noticing others’ lack of interest
• Displaying facial expressions, movements, and gestures that do not match what is being said
• Having an unusual tone of voice that may sound sing-song or flat and robot-like
• Having trouble understanding another person’s point of view or predicting their actions
• Difficulties adjusting behaviors to social situations
• Difficulties sharing in imaginative play or making friends

Restrictive/Repetitive Behaviors

• Repeating certain behaviors or having unusual behaviors, such as repeating words or phrases (echolalia)
• Having a lasting intense interest in specific topics, such as numbers, details, or facts
• Showing overly focused interests, such as with moving objects or parts of objects
• Becoming upset by slight changes in routine and having difficulty with transitions
• Being more or less sensitive than others to sensory input, such as light, sound, clothing, or temperature

People with ASD may also experience sleep problems, irritability, and sensory processing issues.

Prevalence and Demographics

According to the CDC’s Autism and Developmental Disabilities Monitoring (ADDM) Network, an average of 1 in every 36 (2.8%) 8-year-old children in the U.S. were estimated to have ASD in 2020. ASD is 3.8 times more prevalent among boys (4.3%) than girls (1.1%). The prevalence rates vary across racial and ethnic groups, with autism being lower among white children (2.4%) compared to Black (2.9%), Hispanic (3.2%), and Asian or Pacific Islander (3.3%) children. These changes reflect an improvement in outreach, screening, and de-stigmatization of autism diagnosis among minority communities.

Core Symptoms and Associated Features

The two core symptoms of ASD are challenges with social communication and interaction skills, and restricted and repetitive behaviors.

Social communication and interaction challenges may include difficulties with starting and taking turns in conversations, sharing interests or emotions, understanding others’ thoughts or feelings, making eye contact, understanding body language and facial expressions, regulating tone of voice, expressing feelings, seeking emotional comfort, making friends, understanding boundaries and personal space, and feeling overwhelmed in social situations.

Restricted and repetitive behaviors may involve repetitive movements, play or speech patterns (stimming, lining up toys, echolalia), insistence on sameness and need for routine, intense and highly focused interests, and under- or over-sensitivity to sensory stimulation.

Other associated features of ASD may include using alternative forms of communication, difficulty with executive functioning, trouble with fine motor skills and coordination, needing help with daily living skills, and difficulty regulating and communicating emotions, which may sometimes result in harmful or self-injurious behaviors, sensory overload, meltdowns, or shutdowns.

Is Autism Hereditary? Genetic Factors in ASD

The recurrence risk of autism spectrum disorder (ASD) in siblings of affected children is 2% to 8%, and it rises to 12% to 20% if one considers siblings showing impairment in one or two of the three domains affected in autism, respectively. Moreover, several twin studies have suggested that this familial aggregation is best explained by shared genes rather than shared environment. Interestingly, the variation of autistic traits in the general population has also been shown to be highly heritable, with a similar level of genetic influence as autism itself, although the results are heterogeneous (heritability 40% to 80%).

Heritability and inheritance patterns

The hereditary nature of ASD is now a clear scientific fact, but there is still some uncertainty regarding its extent. A meta-analysis in 2016 reviewed 6413 sets of monozygotic and dizygotic twins with at least one child diagnosed with ASD. Their results suggest an estimated heritability of 0.64–0.91, which has since been confirmed by others, suggesting a currently accepted heritability rate for ASD of 0.7–0.8. This implies the presence of a similar degree of genetic component as, for example, that of body height or attention deficit hyperactivity disorder (ADHD), which is otherwise comorbid with autism.

Studies on siblings of people with ASD show a strong genetic link. Male siblings are 3 times more likely to be autistic than females, and younger siblings are 8-17 times more likely to be autistic than those in the general population. Even second-degree relatives have a higher chance.The only consensus regarding the mode of inheritance of autism is that it is not Mendelian, at least in a vast majority of cases. Several studies were initially in favor of a polygenic model. Therefore, the initial strategy to unravel genetic factors increasing autism risk was to build large cohorts for linkage and association studies. Given the lack of replication of the results, consortia gathering several cohorts were created to increase the power of the studies, but without clear results.

Identified genetic variations and syndromes

ASD is associated with hundreds of genetic diseases and conditions, most of which are extremely rare. Approximately 45% of people with autism are intellectually disabled (ID), 50% live with ADHD, and 30% have epilepsy. While ADHD has a very significant genetic component, the same is still only plausible for ID and some types of epilepsy.

The prevalence of ASD is much higher (up to more than 60 times) than the population average for certain genetic syndromes with at least 0.01% frequency, as summarized in Table 2.

[Table showing prevalence of ASD in genetic syndromes]

It is striking that the prevalence of ASD is much higher than the population average for the listed syndromes. In addition, there are several other very rare genetic disorders associated with autism (Angelman, Joubert, Smith–Lemli–Opitz, and Timothy syndromes, etc.), the prevalence of which is extremely low. To date, approximately 20–35% of individuals diagnosed with ASD have some genetic abnormalities, which present a very diverse phenotypic picture, further complicating the possibility of establishing uniform clinical and diagnostic categories.

The DNA sequence changes underlying ASD can be very diverse, ranging from single nucleotide changes to the appearance of entire extra chromosomes, from rare mutations to very common polymorphisms, and from de novo variants to hereditary ones. The picture is further complicated by the blurred boundaries and a lot of overlap between the categories, as well as the interpretational differences of modifications affecting the genome.

According to two studies, the prevalence of de novo chromosomal rearrangements is higher in subjects from simplex families (one affected individual) compared with subjects from multiplex families, which is consistent with the high rate of notable de novo mutations identified in probands from simplex families. This is also consistent with the results of studies which have shown that familial aggregation of subclinical autistic traits may occur only in multiplex families, suggesting differential mechanisms of genetic transmission of autism in the population.

Role of genetics in ASD development

Many of the genes associated with ASD are involved in the development of the brain. The proteins produced from these genes affect multiple aspects of brain development, including production, growth, and organization of nerve cells (neurons). Some affect the number of neurons that are produced, while others are involved in the development or function of the connections between neurons (synapses) where cell-to-cell communication takes place, or of the cell projections (dendrites) that carry signals received at the synapses to the neuron. Many other genes associated with ASD affect development by controlling (regulating) the activity of other genes or proteins.

The cause of ASD is unknown, but genes and brain development are likely involved. People with ASD may have more neurons than usual in certain areas of the brain. These abnormalities are thought to underlie social, communication, and cognitive challenges.

First, specific genetic syndromes like Rett syndrome or Fragile-X syndrome, or cytogenetic abnormalities, the most common being the 15q11-q13 duplication of the maternal allele, associated with ASD affect synaptic plasticity. Moreover, the first mutations identified in idiopathic autism involve synaptic genes like NLGN3 and NLGN4X, or SHANK3. Results were enriched by the development of whole-genome screening methodologies which have shown that genetic structural variation contributes significantly to autism. The detection of copy number variations (CNVs), with constantly increasing resolution, consistently confirmed the importance of the synaptic function in autism. Several subsequent studies showed CNVs in the NLGN-NRXN-SHANK pathway, and other synaptic genes such as SynGAP and DLGAP2 (Table I).

It is now clear that there is a huge genetic heterogeneity in ASD, involving both locus heterogeneity and allelic heterogeneity. The exome sequencing studies suggest that the recent results predicting up to 234 loci contributing to ASD risk are probably even an underestimation. Some important web resources cataloguing genetic contributors in ASD include the SFARI Gene database, the AutDB database (http://www.mindspec.org/autdb.html), and the Autism Chromosome Rearrangement Database (http://projects.tcag.ca/autism/).

Synapse-related risk genes include those encoding cell-adhesion proteins such as neuroligins, neurexins, and cadherins; synaptic vesicle cycling proteins synapsin-1 (SYN1) and synapsin-2 (SYN2); ion transport proteins such as sodium voltage-gated channel alpha subunit 2 (SCN2A), calcium voltage-gated channel subunit alpha1 E (CACNA1E), calcium voltage-gated channel auxiliary subunit beta 2 (CACNB2), potassium voltage-gated channel subfamily Q members 3 and 5 (KCNQ3 and KCNQ5), potassium voltage-gated channel subfamily D member 2 (KCND2), glutamate receptor signaling protein SH3 and multiple ankyrin repeat domains 3 (SHANK3), synaptic Ras GTPase activating protein 1 (SYNGAP1), and gamma-aminobutyric acid type A receptor gamma3 subunit (GABRG3).

Additional susceptibility loci impact transcription of other proteins through various mechanisms. For example, multiple studies have found an increased de novo mutation load in regulatory elements of ASD risk genes in patients (Turner et al., 2016, 2017; Short et al., 2018). The broad class of susceptibility genes that impacts transcription and chromatin-remodeling pathways includes MeCP2, UBE3A, chromodomain helicase DNA binding protein 8 (CHD8), activity dependent neuroprotector homeobox (ADNP), pogo transposable element derived with ZNF domain (POGZ), fragile X mental retardation protein (FMRP), and RNA binding forkhead box (RBFOX) genes.

Copy number variations (CNVs) are submicroscopic structural variants in chromosomes that include duplications, deletions, translocations, and inversions, sometimes stretching several kilobases (Marshall et al., 2008). CNVs can either be inherited or arise de novo (Thapar and Cooper, 2013). Many genes may be affected by these changes, but not all are necessarily drivers of disease. Studies have found a higher load of rare, genic CNVs in autistic individuals, implicating these variants in ASD pathology (Sebat et al., 2007; Pinto et al., 2010; Pizzo et al., 2019).

Genes with epigenetic-modulating functions are highly involved in ASD susceptibility. A recent review of 215 candidate genes estimated that 19.5% are epigenetic regulators, suggesting the potential for diverse disease phenotypes from few pathogenic variants (Duffney et al., 2018).

Behavioral and Psychiatric Comorbidities

Individuals with autism spectrum disorder (ASD) often meet criteria for at least one additional psychiatric disorder (Rosen, Mazefsky, Vasa, & Lerner, 2018). Common co-occurring psychiatric disorders in individuals with ASD include anxiety disorders, mood disorders, attention deficit hyperactivity disorder (ADHD), obsessive-compulsive disorder (OCD), and oppositional defiant disorder (ODD; Buck et al., 2014; Di Martino et al., 2017; Joshi et al., 2010; Leyfer et al., 2006; Simonoff et al., 2008).

Common co-occurring conditions (e.g., ADHD, anxiety, depression)

Previously reported prevalence rates indicate that between 70% to 95% of children and adolescents with ASD have at least one co-occurring psychiatric disorder (Gjevik, Eldevik, Fjaeran-Granum, & Sponheim, 2011; Joshi et al., 2010; Leyfer et al., 2006; Simonoff et al., 2008), 41% to 60% of children and adolescents with ASD have two or more co-occurring disorders, and as many as 24% of children and adolescents with ASD have three or more co-occurring disorders (Di Martino et al., 2017; Simonoff et al., 2008). Similarly, between 73%-81% of adults with ASD meet criteria for at least one current co-occurring psychiatric disorder (Buck et al., 2014; Hofvander et al., 2009; Joshi et al., 2013; Vohra, Madhavan, & Sambamoorthi, 2016).

Other common comorbid conditions in ASD include anxiety disorders, obsessive-compulsive disorders, attention deficit hyperactivity disorders, and mood disorders. Recognizing these medical conditions is important because many of them could stimulate or exacerbate the abnormal behavior that occurs in children with autism.

Challenges in diagnosis and management

These high rates of co-occurring psychiatric disorders have significant clinical implications for individuals with ASD. The presence of one or more concurrent disorders can mask the expression of ASD symptoms and delay the diagnosis of ASD until later in childhood or early adolescence (Mazefsky et al., 2012), and the treatment of co-occurring disorders often requires additional psychosocial and pharmacological treatments (de Bruin, Ferdinand, Meester, de Nijs, & Verheij, 2007; Joshi et al., 2010; Leyfer et al., 2006).

Due to symptom overlap, diagnostic overshadowing, and ambiguous symptom presentation in ASD, the assessment of co-occurring conditions in ASD is complex and challenging. Likewise, individual difference factors, such as age, intellectual functioning, and gender, may influence the presentation of co-occurring symptoms.

Impact on individual functioning and quality of life

Co-occurring psychiatric disorders may exacerbate ASD symptoms (de Bruin et al., 2007; Leyfer et al., 2006), interfere with optimal outcomes for ASD treatments (Joshi et al., 2010; McDougle, Stigler, & Posey, 2003), and predict worse long-term outcomes in individuals with ASD (Kamio, Inada, & Koyama, 2013; Kraper, Kenworthy, Popal, Martin, & Wallace, 2017).

Results demonstrated that certain emotional and behavioral symptoms are differentially associated with domains of health-related quality of life (HRQoL). This indicates that comorbid emotional and behavioral problems should be considered when measuring HRQoL in children with ASD, and treating comorbid emotional/behavioral problems could improve HRQoL and functioning in certain domains for this population.

Nonetheless, this investigation highlighted the additional burden of comorbid emotional and behavioral symptoms and the negative associations between certain emotional/behavioral problems and domains of functioning. Results suggest that decreasing social withdrawal may improve social functioning and quality of life in youth with ASD.

Diagnostic Evaluation and Genetic Testing

Importance of early diagnosis

An ASD diagnosis relies on the  parents’ reports and observations. Early screening is recommended at 9, 18, and 24/30 months. Early intervention is crucial, ideally around preschool age (2-3 years old).

Diagnostic criteria and assessment tools

The American Psychiatric Association’s Diagnostic and Statistical Manual, Fifth Edition (DSM-5) provides standardized criteria to help diagnose ASD. There are many tools to assess ASD in young children, but no single tool should be used as the basis for diagnosis. Diagnostic tools usually rely on two main sources of information—parents’ or caregivers’ descriptions of their child’s development and a professional’s observation of the child’s behavior.

Some commonly used screening tools include:

1. The Modified Checklist for Autism in Toddlers, Revised with Follow-Up (M-CHAT-R/F), a 20-item questionnaire for parents or caregivers to assess children aged 16 to 30 months.
2. The Ages and Stages Questionnaire (ASQ), a general developmental screening tool.
3. The Screening Tool for Autism in Toddlers (STAT), specifically designed for community service providers to assess young children.
4. The Social Communication Questionnaire (SCQ), a 40-item questionnaire for caregivers to screen for ASD in children between four and 40 years old.
5. The Parents’ Evaluation of Developmental Status (PEDS), a parent interview to assess a child’s overall development.

Some diagnostic tools used include the Autism Diagnosis Interview-Revised (ADI-R), the Childhood Autism Rating Scale (CARS), the Gilliam Autism Rating Scale, Second Edition (GARS-2), and the Autism Diagnostic Observation Schedule-Generic (ADOS-G), a formal assessment that follows a semi-structured and standardized approach to evaluate social interaction, communication skills, play, and creativity using materials for individuals suspected of having ASD.

Genetic testing methods (e.g., chromosomal microarray, whole-exome sequencing)

Genetic counseling can provide information to families of children with ASD about the etiology, identify underlying medical risks, and determine recurrence risks for family members. The American College of Medical Genetics and Genomics Practice Guidelines and the American Academy of Pediatrics (AAP) Guidelines suggest that every person with ASD should be offered a genetic evaluation.

The American College of Medical Genetics recently recommended chromosomal microarray as the first line evaluation for children with ASD, followed by karyotype or fragile X testing as second line. Exome sequencing, which looks at the DNA that codes for genes, can potentially find the cause of autism about 10% to 30% of the time, with a greater chance for genetic findings for people who have intellectual disability. The AAP also recommends specific genetic testing for Fragile X syndrome, which cannot be picked up by microarray or exome sequencing.

Genetic testing is rapidly evolving, and new information is constantly emerging, so it is important to stay in touch with genetic testing providers. Prospective studies are necessary to examine the phenotypes related to genetic differences, relative genetic yield, and cost-effectiveness of etiological evaluation.

Treatment and Management Approaches

Behavioral and educational interventions

Currently, there are no medications that can cure autism spectrum disorder (ASD) or alleviate all of its symptoms. However, various behavioral and educational interventions have been developed to address the specific needs and challenges faced by individuals with ASD. These interventions aim to improve social interaction, communication skills, and reduce problematic behaviors.

Applied Behavior Analysis (ABA) is recognized as the most extensively utilized and proven effective method for addressing the behavioral and educational needs of individuals with ASD. Federal, state, and national organizations in the US and UK consistently recommend ABA-based interventions as the first choice of assessment and treatment guidelines for ASD.

1. Early Intensive Behavioral Intervention (EIBI): EIBI is an ABA-based intervention designed to teach specific skills in language, cognitive function, self-help, social interaction, and motor skills using discrete trial training (DTT). It is provided by a team of professional therapists and implemented face-to-face with the child in a structured environment for several hours per day over a few years, with active parental participation required. Several review studies have reported significant improvements in IQ, adaptive behaviors, receptive and expressive language, daily communication, social interaction, and self-help skills in children receiving EIBI compared to treatment-as-usual groups.
2. Naturalistic Developmental Behavioral Intervention (NDBI): NDBI combines behavioral principles with a developmental approach that emphasizes social ability and learning in natural contexts. The Early Start Denver Model (ESDM) is a prominent example of NDBI that has been extensively investigated and found to improve social communication, language, and adaptive behaviors in young children with ASD.
3. Social Skills Training (SST): SST is a widely researched intervention aimed at improving social skills, a core symptom of ASD. It is typically delivered face-to-face by experts or teachers, and specific social skills such as greetings, initiating and responding to conversations, giving compliments, sharing, and matching facial expressions are taught through repetitive practice.
4. Augmentative and Alternative Communication (AAC): AAC is often used to enhance communication skills in individuals with ASD by teaching the use of alternative communication methods, such as visual cues, sign language, and communication aids. The Picture Exchange Communication System (PECS) is the most widely used AAC intervention, which teaches individuals to use pictures to communicate their needs.
5. Interventions for Comorbid Conditions: Individuals with ASD often experience comorbid conditions such as sleep problems, eating disorders, and toileting issues. Behavioral interventions based on ABA principles have been found effective in addressing these challenges. For example, techniques like contingent reinforcement, non-removal of the spoon, shaping, graduated guidance, scheduled toileting, and stimulus control have been used successfully in toilet training programs for individuals with ASD.
6. Cognitive Behavioral Therapy (CBT): As individuals with ASD grow into adolescence and adulthood, they may experience emotional difficulties such as depression, anxiety, and anger. Recent studies have shown that CBT, an evidence-based treatment for these conditions, can be successfully applied to adolescents and adults with ASD.
7. Parent-Mediated Interventions (PMI): PMI involves training parents to implement various intervention techniques directly with their children. These interventions have been frequently used for comprehensive early intervention and intervention of challenging behaviors, and they offer advantages such as high accessibility to treatment and high generalizability, as treatment is provided by parents in diverse real-life settings. Examples include the Parent-Implemented Early Start Denver Model (P-ESDM) and PMI for challenging behaviors like aggression and self-injurious behaviors.

Pharmacological treatments and considerations

While behavioral and educational interventions are the primary approaches for managing ASD, pharmacological treatments may be considered to address specific symptoms or comorbid conditions.

1. FDA-Approved Medications: The U.S. Food and Drug Administration (FDA) has approved the use of two antipsychotic medications, risperidone and aripiprazole, for treating irritability associated with ASD in children within certain age ranges. These medications are not specific for ASD but target associated symptoms such as aggression or irritability.
2. Off-Label Medications: Other medications, such as methylphenidate for attention-deficit/hyperactivity disorder (ADHD) symptoms, selective serotonin reuptake inhibitors (SSRIs) for obsessive-compulsive behaviors, and oxytocin nasal spray for improving social impairments, are sometimes used off-label to manage specific symptoms in individuals with ASD, although their effectiveness and safety in this population require further investigation.
3. Considerations for Medication Use: All medications carry risks, some of them serious, and families should work closely with healthcare providers to ensure safe use. Medications are typically prescribed on a trial basis to assess their effectiveness and potential side effects, and dosages or combinations may need to be adjusted to find the most effective treatment plan. Close monitoring and collaboration between families, caregivers, and healthcare providers are essential to ensure the medication plan is safe and beneficial.

Role of genetics in personalized medicine

As our understanding of the genetic factors contributing to ASD continues to evolve, there is potential for personalized medicine approaches tailored to an individual’s specific genetic profile.

1. Targeting Genetic Variations: Researchers have identified hundreds of ASD risk genes, and more are expected to be found through ongoing whole-genome sequencing and larger sample size studies. While each monogenic form of ASD is rare, different genes have been shown to converge on affecting a smaller number of common pathways, suggesting that particular biological pathways could be treatment targets rather than individual gene products.
2. Potential for Personalized Treatments: By examining genetic variations, researchers may be able to consider targeting common nutraceutical treatments on a personalized basis. For example, a large national survey found that families rated nutraceuticals, including folate and cobalamin, as having greater benefits than psychiatric and seizure medications for individuals with ASD.
3. Challenges and Future Directions: Despite the promising potential of personalized medicine approaches, there are challenges to overcome. Even monogenic or syndromic forms of ASD involve considerable heterogeneous symptom expression, and factors influencing shared versus distinct developmental outcomes need further investigation. Additionally, well-powered clinical trials targeting specific genetic variations have produced disappointing results so far, highlighting the need for continued research and refinement of personalized treatment strategies.

While the current management of ASD relies heavily on behavioral and educational interventions, ongoing research into the genetic underpinnings of the disorder holds promise for the development of more targeted and personalized pharmacological treatments in the future.

Conclusion

The complex interplay between genetics and environmental factors contributes to the development of autism spectrum disorder (ASD). While the extent of its hereditary nature is still being explored, the substantial influence of genetic variations is undeniable. ASD is associated with a diverse array of genetic abnormalities, many of which impact brain development and synaptic function. As our understanding of the underlying genetic mechanisms deepens, it paves the way for personalized medicine approaches and targeted treatments.

Despite the promising potential of genetics in advancing ASD management, behavioral and educational interventions remain the cornerstone of treatment. Applied Behavior Analysis (ABA), early intensive interventions, and social skills training have demonstrated significant improvements in various domains. Pharmacological treatments, while not curative, may address specific symptoms or comorbidities when used judiciously under close medical supervision. As research continues to unravel the complex genetic landscape of ASD, the future holds promise for more tailored and effective interventions.

Is autism hereditary? – FAQs

1. What is the extent of genetic influence on autism?
Autism is observed in about 2% of children, predominantly affecting males with a male-to-female ratio of 4:1. The heritability of autism spectrum disorders (ASD) is estimated to be between 70 and 90%. The origins of ASD involve a complex combination of genetic inheritance and environmental factors, with over 800 genes and numerous genetic syndromes linked to the condition, all potentially moderated by epigenetic factors.

2. From which parent is the autism gene most likely inherited?
While the specific origins of autism are not fully understood, genetics are known to be a significant factor. Historically, it was believed that autism was primarily passed down through mothers, due to its lower prevalence in females. However, current research indicates that the genes associated with autism are more commonly inherited from the father.

3. What is the primary cause of autism?
Genetic factors are the predominant cause of autism spectrum disorders (ASD), accounting for approximately 80-90% of the risk. Environmental influences make up the remaining 10-20% of the risk. The tendency of ASD to occur more frequently within certain families highlights the critical role of genetics.

4. Is the autism-related gene mutation dominant or recessive?
The gene mutations associated with autism are generally recessive. This means that the condition manifests only if an individual inherits the mutated gene from both parents, who may carry the mutation without showing any symptoms themselves. Additionally, many autism-related mutations are spontaneous or “de novo” mutations, which occur randomly and are not inherited from the parents.