Attention-Deficit/Hyperactivity Disorder (ADHD) is a neurodevelopmental disorder characterized by an ongoing pattern of inattention, hyperactivity, and impulsivity. These symptoms are pervasive, affecting multiple contexts of a person’s life, and are considered developmentally inappropriate for their age. The condition often begins in childhood and can continue into adulthood, causing difficulties in daily life, including school, work, and social relationships.
The Genetic Basis of ADHD
ADHD is highly heritable, with genetic factors playing a significant role in its development. Research, particularly twin and family studies, consistently indicates a strong genetic component, with heritability estimates often ranging from 70% to 80%.
The genetic basis of ADHD is complex, generally involving multiple genes rather than a single gene. This polygenic nature means that many gene variants, each with a small effect, accumulate to increase an individual’s likelihood of developing the disorder. While specific genes linked to dopamine regulation, such as DRD4 and DAT1, have been associated with ADHD, no single gene has been identified as its sole cause.
Inheritance From Mothers and Fathers
ADHD genes can be inherited from either parent. There is no scientific evidence suggesting ADHD is inherited more predominantly from one parent over the other. A parent’s ADHD diagnosis, whether from the mother or the father, is an equally strong predictor of ADHD in their children.
Contributions from both parents’ genetic makeup interact to influence a child’s risk. For instance, a child might inherit a combination of small-effect genes from both parents, even if neither parent individually has the full disorder. If one parent has ADHD, their child has an increased chance of developing the condition, with some studies suggesting this likelihood can be up to 56%. The risk further increases if both parents have ADHD, but this does not imply a bias toward either parental line.
Non-Genetic Influences on ADHD
While genetics are the primary risk factor, environmental and other non-genetic factors can also influence the development or expression of ADHD. These factors are not sole causes but can interact with an individual’s genetic predispositions. For example, prenatal exposures, such as maternal alcohol or nicotine use during pregnancy, have been linked to an increased risk of ADHD-like symptoms.
Other environmental influences include premature birth and low birth weight. Early childhood exposure to toxins like lead can also contribute to problems resembling ADHD. These environmental factors primarily exert their effects very early in life.
Assessing Family Risk
If a parent or close biological relative has ADHD, it increases the likelihood of a child developing the condition, though it is not a guarantee. The relative risk for first-degree relatives of someone with ADHD is estimated to be 5 to 10 times higher than in the general population. A family history of ADHD is considered a risk factor, not a definitive diagnostic tool.
Diagnosis of ADHD involves a comprehensive evaluation by healthcare professionals. This includes a detailed history of symptoms, their impact on daily functioning, and screening for other conditions that may mimic ADHD. There are no specific lab tests, such as blood tests or imaging, that can diagnose ADHD. Individuals concerned about ADHD symptoms in themselves or their children should consult with a healthcare provider for a thorough assessment and appropriate guidance.