Autism Spectrum Disorder - Causes

Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder with complex and multifaceted causes. The scientific community generally believes that the development of this condition results from interactions among genetic, environmental, and biological factors. Recent studies indicate that genetic factors play a central role in the pathogenesis of autism, but environmental exposures, prenatal health, and certain acquired factors may also increase risk.

The pathophysiological mechanisms of ASD involve abnormalities in brain neural development, including the formation of neural connections, dysregulation of neurotransmitters, and structural abnormalities in specific brain regions. How these biological changes interact with genetic and environmental factors remains an ongoing area of scientific exploration. Researchers are gradually piecing together this complex puzzle using genomics, epidemiology, and clinical observations.

Genetic and Family Factors

Genetic abnormalities are among the most significant risk factors for ASD. Studies show that if there is a family member with autism, the likelihood of siblings being affected is 10 to 30 times higher than in the general population. This genetic predisposition is primarily associated with gene mutations, chromosomal abnormalities, and polygenic interactions.

Approximately 20% of autism cases are directly related to specific gene mutations, such as defects in SHANK3, NLGN3, NRXN1, which affect neuronal communication. Additionally, chromosomal deletions or duplications (such as abnormalities in regions 15q11.2 or 22q11.2) are also linked to increased autism risk. These genetic variations may lead to abnormal cortical development, impacting social behavior and cognitive patterns.

• Single-gene mutations: Mutations in genes like FOXP1 and CHD8 can affect neuronal generation during critical periods of brain development.
• Complex genetic interactions: Small variations across multiple genes may accumulate to reach a pathogenic threshold, accounting for about 40-60% of cases.
• Family history influence: In monozygotic twins, if one twin is affected, the other has up to an 80% chance of developing autism, far higher than the 10-20% in dizygotic twins.

Environmental Factors

Environmental exposures and maternal health during pregnancy are considered key factors that may trigger autism in genetically susceptible individuals. Maternal contact with harmful substances, infections, or nutritional deficiencies during pregnancy can interfere with fetal brain development. The mechanisms of gene-environment interactions are not yet fully understood, but several key factors have been identified:

Maternal infections during pregnancy are among the most concerning environmental risks. Infection with influenza, rubella, or autoimmune diseases during the first three months of pregnancy may increase the risk of autism in the fetus. Inflammatory responses caused by viruses or bacteria can disrupt neuronal differentiation during critical periods of brain development.

Exposure to environmental toxins such as air pollution, heavy metals (like lead and mercury), or pesticides has also been associated with increased autism risk.

• Air pollution: Long-term exposure of pregnant women to PM2.5 or traffic pollutants may lead to abnormal fetal brain development. Studies show that children of mothers living in highly polluted areas have a 1.5-fold increased risk.
• Medication use: Use of antiepileptic drugs (such as valproate) or antidepressants (like SSRIs) during pregnancy may interfere with fetal brain chemical signaling systems.
• Nutritional deficiencies: Insufficient folate intake is linked to increased autism risk, as folate is involved in DNA synthesis and methylation processes critical for fetal neural development.

Lifestyle and Behavioral Factors

Parents' lifestyle and behavioral patterns may indirectly influence the risk of autism in offspring. Factors such as parental age, prenatal health habits, and socioeconomic status are included in research analyses. These factors can affect the fetal environment or exacerbate genetic predispositions.

Men over 40 years old have a 2.5 times higher risk of having a child with autism compared to fathers under 30. Older sperm may accumulate more DNA damage, and the rate of chromosomal abnormalities in older eggs also increases. Maternal exposure to tobacco, alcohol, or poor diet during pregnancy can lead to placental dysfunction, affecting oxygen and nutrient supply to the fetus’s brain.

• Maternal smoking during pregnancy: Nicotine constricts placental blood vessels, reducing oxygen supply necessary for brain development. Studies show that children of mothers who smoke have a 30-50% increased risk.
• Parental obesity: Pre-pregnancy or pregnancy BMI over the threshold is associated with increased autism risk, possibly related to chronic inflammation and metabolic disturbances affecting developmental signaling pathways.
• Stress and psychological state: Long-term exposure to high-stress environments during pregnancy elevates cortisol levels, which may interfere with the development of the amygdala and prefrontal cortex in the fetal brain.

Other Risk Factors

Besides major genetic and environmental factors, other biological and medical conditions are also associated with autism risk. Premature birth, low birth weight, multiple pregnancies, and certain pregnancy complications can disrupt critical periods of brain development.

Babies born more than 15 days preterm have a 2-3 times higher risk of autism compared to full-term infants. Preterm infants often have incomplete white matter development, which can impair neural signal transmission. Infants with birth weight below 2500 grams show a higher proportion of cortical structural abnormalities, related to impaired neuroglial development.

Incidence rates are also higher in twins or triplets by 20-30%, possibly due to intrauterine nutritional competition, placental insufficiency, or uneven oxygen and nutrient distribution. Additionally, pregnancy complications such as hypertension and eclampsia can affect placental vascular development, indirectly impacting brain development.

• Delivery complications: Difficult labor leading to hypoxia, amniotic fluid embolism, or fetal distress can cause neuronal damage.
• Immune system abnormalities: Maternal autoimmune diseases (such as Hashimoto’s thyroiditis) may lead to antibodies crossing the placenta and attacking fetal neural tissue.
• Environmental toxins: Exposure to phthalates (like DEHP) or pesticides (such as organophosphates) during pregnancy may interfere with fetal hormonal regulation systems.

The etiology of ASD is the result of multifactorial interactions, with genetic predisposition forming the basis, and environmental stimuli potentially triggering latent risks. The gene-environment interaction hypothesis suggests that individuals with certain genetic susceptibilities may exhibit accelerated neurodevelopmental abnormalities when exposed to specific environmental stimuli. Studies indicate that approximately 30-40% of the risk can be attributed to genetic factors, with the remainder related to environmental and acquired factors. This complexity necessitates a comprehensive approach to prevention and diagnosis, integrating genetic counseling, preconception health management, and environmental protection measures.

 

Frequently Asked Questions

What are the key signs for early detection of autism spectrum disorder?

Research indicates that the critical period for detecting ASD is between 18 months and 3 years of age. Parents should observe whether their child exhibits behaviors that are markedly different from peers, such as low interest in eye contact, delayed speech development, repetitive movements, or extreme sensitivity to environmental changes. Early medical evaluation is recommended if abnormalities are noticed.

What is the long-term impact of family support on children with autism spectrum disorder?

Family support is vital for the development of children with autism. Establishing stable routines, providing structured communication training, and encouraging positive reinforcement behaviors can significantly improve social skills and quality of life. Parents should learn special education techniques and utilize resources from government or non-profit organizations to support their child's growth over the long term.

What special educational arrangements are needed for students with autism spectrum disorder in school?

Schools should develop an Individualized Education Program (IEP) tailored to each student's needs, including visual aids, dedicated learning spaces with reduced stimuli, and trained teachers to assist with social skills training. Small class sizes and personalized tutoring can effectively enhance learning efficiency and peer interaction.

What are common misconceptions about autism spectrum disorder in society?

Common misconceptions include beliefs that individuals with autism lack empathy or have intellectual disabilities. In reality, these views are not universally applicable. Some individuals may excel in specific areas, and their social difficulties often stem from neurodevelopmental differences rather than emotional or intellectual deficits. Public education is essential to improve understanding.

How can technology assist in improving communication abilities in individuals with autism spectrum disorder?

Assistive communication technologies, such as speech output programs on tablets, can help non-verbal individuals effectively express their needs. Virtual reality (VR) is also used to simulate social scenarios, helping patients practice conversations and interpret body language. These technological tools should be used under the guidance of professionals to achieve optimal results.