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Neurodevelopmental disorders are conditions that affect the development of the brain and nervous system, leading to challenges in learning, behavior, or cognitive function. Examples include autism spectrum disorder, intellectual disability, ADHD, and others. A question many parents ask is: what causes neurodevelopmental disorders? The truth is that these disorders often arise from a combination of factors. Broadly, causes can be grouped into genetic influences, environmental exposures, and other risk factors. Understanding these can help families make informed decisions, especially with tools like whole genome preimplantation genetic testing in the family-planning stage.

Genetic Causes of Neurodevelopmental Disorders

Genetics plays a significant role in many neurodevelopmental disorders. Research shows that a substantial portion of cases can be traced to genetic factors – for example, Orchid’s guide on intellectual disability notes that over 30% of such cases are linked to a specific genetic cause. These genetic causes range from chromosomal differences (such as an extra or missing chromosome, as seen in Down syndrome) to single-gene mutations (for instance, mutations causing Fragile X syndrome or Rett syndrome). Some mutations are inherited from parents, while others occur de novo (spontaneously) in the embryo with no family history. Even when no single genetic glitch is to blame, multiple genes can subtly contribute to a child’s neurodevelopmental risk. In fact, many conditions like autism are polygenic, meaning they result from the combined effect of many genes. (For example, scientists have identified dozens of genes where rare changes can lead to autism.) Overall, genetics establishes the baseline risk – explaining why neurodevelopmental disorders often run in families or appear more frequently with certain inherited syndromes.

Environmental Factors and Exposures

Genetics alone doesn’t paint the full picture. Environmental factors before and around birth can significantly impact brain development and contribute to neurodevelopmental disorders. Some key environmental influences include:

• Prenatal infections: If a mother contracts certain infections during pregnancy (such as rubella or cytomegalovirus), the developing baby’s brain may be affected, increasing the risk of developmental disorders.
• Exposure to harmful substances: Alcohol use during pregnancy is a well-known cause of neurodevelopmental problems (as seen in fetal alcohol spectrum disorders). Other toxins, like high levels of lead or mercury, and certain medications (for example, the anti-seizure drug valproate), have been linked to developmental delays and autism risk.
• Birth complications: Problems during delivery or the neonatal period can play a role. Extreme prematurity, very low birth weight, or periods of oxygen deprivation at birth can lead to lasting neurological and developmental challenges (such as cerebral palsy or cognitive impairments).

These environmental factors can disrupt crucial phases of brain development. Unlike genetic causes that are written in the DNA, many environmental risks can be reduced with good prenatal care – for instance, vaccinations to prevent infections, avoiding alcohol and smoking during pregnancy, and managing maternal health conditions.

Other Risk Factors and Multifactorial Causes

In most cases, neurodevelopmental disorders have multifactorial causes – meaning they arise from a mix of genetic predispositions and environmental influences. Often, no single cause can be pinpointed. Instead, multiple small risk factors add up. For example, advanced parental age is associated with higher risk: older fathers have a greater chance of new gene mutations in their sperm, and older mothers face higher odds of chromosomal abnormalities in pregnancy. Family history also matters; having one child with a neurodevelopmental disorder (like autism) slightly increases the risk for siblings, reflecting shared genetics and environment. As Orchid’s guide on autism spectrum disorder explains, only about 20–30% of autism cases can be tied to a specific genetic variant, while the rest result from a complex interplay of genes and environment. This interplay might involve a child inheriting certain susceptibility genes that only lead to a disorder if combined with particular environmental triggers or stressors. Because of this complexity, many neurodevelopmental conditions are still not fully understood – researchers continue to study how various factors converge to alter early brain development.