Understanding ADHD: The Most Common Neurodevelopmental Disorder

Attention Deficit Hyperactivity Disorder (ADHD) represents the most frequently diagnosed neurodevelopmental condition, affecting an estimated 5-10% of school-aged children worldwide and persisting in approximately 2-5% of adults. While exact figures vary according to methodology and locale, these estimates illustrate how ADHD can influence lives from childhood well into adulthood.

What Are Neurodevelopmental Disorders?

Neurodevelopmental disorders encompass a diverse group of conditions that affect early brain development, including ADHD, autism, and learning differences such as dyslexia. These conditions often become more apparent as children grow, since delays in expected skills – such as communication, social interaction or learning – tend to emerge when peers begin to hit those milestones. In ADHD, for instance, difficulties with concentration, impulse control or hyperactivity may not be obvious until a child faces increasing academic or social demands.

How ADHD Affects Everyday Life.

ADHD may manifest as challenges in completing tasks – be it because of distractions, organisational difficulties or a tendency to misplace belongings – and can also impact behaviour, leading to forgetfulness or restlessness. These characteristics can influence a person’s ability to learn, maintain friendships or succeed in day-to-day activities. In the absence of a diagnosis or appropriate support, such obstacles often remain unaddressed, increasing the risk of anxiety, depression or low self-esteem.

Diagnosing ADHD.

There is no single genetic marker or brain scan that definitively indicates ADHD. Instead, a formal diagnosis relies on whether an individual meets a set of criteria set out in recognised diagnostic guidelines, such as those published by the National Institute for Health and Care Excellence (NICE) or the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) in the US. In practice, healthcare professionals assess whether a child exhibits at least six of the core symptoms of inattention – or at least five for adults. Those diagnosed also need to exhibit six symptoms of hyperactivity-impulsivity (five for adults), persisting for a minimum of six months and evident across multiple settings, for example in home and school.

Typical inattention symptoms include:

- Difficulty sustaining concentration (for example, struggling to listen in class or overlooking details)

- Forgetting to complete or turn in tasks

- Becoming easily distracted by unrelated stimuli

Hyperactivity-impulsivity symptoms may involve:

- Frequent fidgeting or an inability to remain seated when expected

- Excessive talking or difficulty playing quietly

- Interrupting conversations or finding it hard to wait one’s turn

Some individuals display predominantly inattentive features (formerly termed ‘ADD’), whereas others show mainly hyperactive-impulsive traits. If both sets of symptoms are present, the diagnosis is ‘combined‐type’ ADHD.

Reliability of Diagnosis.

One challenge with the diagnostic criteria is that the listed symptoms are not unique to ADHD; for instance, difficulties concentrating can also arise from depression or anxiety. This is why clinicians emphasise that such symptoms must significantly interfere with day-to-day functioning – be it in school, work or social situations – rather than merely being occasional frustrations. The key question is whether these challenges are persistent enough to hinder educational or occupational progress. Moreover, ADHD traits can fluctuate over time. Some children may not meet full criteria until academic demands increase, while others who once fitted the diagnostic threshold may later find their symptoms diminish. In cases of ‘subthreshold ADHD’, where a person exhibits some but not all required symptoms, substantial difficulties can still occur. Such individuals often benefit from targeted support, even if they do not receive a formal ADHD label.

Gender Differences.

Boys are diagnosed with ADHD more frequently than girls, with a male-to-female ratio historically reported as high as 4:1 in childhood. Part of this discrepancy arises because the diagnostic criteria tend to capture hyperactive, easily noticeable behaviours, which are traits more common among boys. Girls, on the other hand, often present with inattentive symptoms, which are quieter and thus more likely to go unrecognised by parents, teachers or doctors. Consequently, girls and women may receive a diagnosis later in life, frequently when they develop coexisting issues such as anxiety or depression.

Genetics of ADHD.

Research indicates a strong hereditary component: heritability estimates range from 70 to 80 per cent, meaning that genetics account for the majority of individual differences in ADHD traits. First-degree relatives of someone with ADHD are at considerably higher risk than the general population. However, ADHD is not governed by a single ‘ADHD gene’. Instead, it is polygenic – thousands of common genetic variants each make very small contributions to overall risk. These variants, spread throughout the population, mean that ADHD traits exist on a continuum with no clear cut-off between those who do and do not meet diagnostic criteria.

Role of Environment.

Although genetic factors play a major role, environmental influences are also important. For example, being younger than classmates can lead to higher rates of referral for ADHD assessment, not because these children have different genetics, but because their behaviour stands out more in comparison to older peers. Likewise, a supportive family environment – where parents adapt their approaches to a child’s specific needs – can mitigate difficulties and sometimes delay a diagnosis. Conversely, if a parent has undiagnosed ADHD, recognising and responding to a child’s ADHD traits can be more challenging, potentially masking or intensifying the child’s symptoms.

Further Information and Support.

ADHD need not define a person’s potential. With accurate understanding and tailored strategies – such as behavioural interventions, adjustments in educational settings or, when appropriate, medication – many people with ADHD thrive in creative, fast-paced careers or roles that align with their strengths. The most important thing will be getting the advice and support necessary. Beyond Clinics is a private ADHD clinic in Greater Manchester. We offer expert ADHD assessment and treatment for children and adults navigating ADHD. Reach out to our specialist team and find out how we can help.