Introduction
Attention Deficit Hyperactivity Disorder (ADHD) is a condition typically diagnosed in childhood, characterised by three persistent core features: inattention, impulsive behaviour, and excessive or misdirected physical activity. These traits appear in all children from time to time, including those with Down syndrome — however, they may occur more frequently in children with Down syndrome than in their typically developing peers.
Prevalence of ADHD in Children with Down Syndrome
The precise prevalence of ADHD among children with Down syndrome is not yet definitively established, but ADHD-like symptoms are generally more common in younger children with Down syndrome than in the broader childhood population.
It is important to note that when complex symptoms such as stereotyped behaviours (repetitive actions) and anxiety co-occur with ADHD-like symptoms, this may point to an additional diagnosis such as autism spectrum disorder, bipolar disorder, or obsessive-compulsive disorder.
Uncomplicated ADHD is more common in younger children with Down syndrome. However, many school-aged children with this diagnosis also present with other behavioural conditions, including oppositional defiant disorder, conduct disorder, or features consistent with obsessive-compulsive disorder.
Medical Conditions That May Mimic ADHD
Hearing and Vision Issues
For a child to pay attention in the classroom, they must be able to hear and see adequately. Hearing and vision problems are common in children with Down syndrome. Ear infections are particularly frequent and, even when treated, can cause hearing loss for several weeks. Structural abnormalities of the middle ear may also result in mild to moderate lifelong hearing loss. Regarding vision, short-sightedness, long-sightedness, cataracts, and amblyopia (lazy eye) are all common in this population.
Monitoring Recommendations
- Auditory Brainstem Response (ABR) or Otoacoustic Emission (OAE) testing should be performed early in life — by three months of age at the latest — to establish a baseline.
- Hearing assessments should be conducted annually until age three, then every two years thereafter.
- Children with abnormal hearing results should be referred to an ENT specialist to address treatable causes of hearing loss.
- An ophthalmological assessment should be performed within the first year of life, with annual follow-up thereafter.
Gastrointestinal Issues
Individuals with Down syndrome are at increased risk of coeliac disease, an intolerance to gluten found in wheat and certain other grains. Symptoms can be subtle, manifesting as mild effects on energy levels and behaviour rather than overt digestive complaints. Severe constipation is also common and may lead to abdominal pain, loss of appetite, and disturbed sleep.
Current guidelines recommend coeliac disease screening between the ages of two and three years, including IgA anti-endomysial antibodies alongside total IgA levels. Bowel health should be reviewed at every clinical visit.
Thyroid Issues
Approximately 30% of individuals with Down syndrome will develop a thyroid condition at some point in their lives. Most will experience hypothyroidism (underactive thyroid), which can cause fatigue and lethargy; a smaller number will develop Graves' disease (overactive thyroid), which may present with irritability and restlessness. Both conditions can closely resemble inattention and behavioural difficulties.
Given the high prevalence of thyroid disease in this population, healthcare guidelines for Down syndrome recommend annual thyroid hormone blood tests.
Sleep Disorders
Sleep disorders are extremely common in individuals with Down syndrome, arising from various causes that share a common outcome: disrupted, non-restorative sleep. Unlike tired adults, tired children often present as hyperactive, irritable, and difficult to settle. Sleep deprivation consistently impairs concentration and the ability to acquire new information across all age groups.
Obstructive sleep apnoea — characterised by repeated brief pauses in breathing during sleep — is particularly prevalent. The airways of individuals with Down syndrome tend to be narrow and soft, making them susceptible to partial or complete obstruction during sleep due to enlarged tonsils or adenoids, or collapse of the airway walls on exhalation. Some affected individuals may wake hundreds of times per night to resume breathing.
Symptoms associated with obstructive sleep apnoea include: snoring, frequent movement during sleep, excessive daytime sleepiness, mouth breathing, and unusual sleep positions such as sleeping sitting upright or leaning forward.
Children suspected of having a sleep disorder should be referred to an accredited sleep centre for a comprehensive sleep study.
Communication Difficulties That May Resemble ADHD
Individuals with Down syndrome often face significant barriers to effective communication. Their receptive language skills (understanding what is said) typically far exceed their expressive language skills (ability to speak and articulate). Parents frequently describe this disparity, saying: "He knows what he wants to tell us, but he can't put the words together into sentences — or we simply can't understand him." This makes classroom participation considerably more challenging, and a child may express the resulting frustration through disruptive behaviour or apparent inattentiveness.
Educational Difficulties That May Resemble ADHD
Children with Down syndrome exhibit a wide range of learning styles, and the educational team may need to explore several approaches before identifying the most effective one. If content is delivered in a way that does not match the child's learning style — for example, relying on verbal instructions for a child who needs visual cues and hands-on stimuli — the child may present with apparent boredom, agitation, and hyperactivity.
The difficulty level of the material itself can also be a contributing factor. Concepts that are too advanced may cause the child to "switch off" and appear inattentive — a response that is equally common in children who are understimulated by content that is too simple for them.
Emotional Difficulties That May Resemble ADHD
Due to the communication challenges described above, individuals with Down syndrome may find it difficult to articulate verbally when they are feeling sad or angry. Significant life changes — such as bereavement or separation — can lead to a marked deterioration in behaviour at school or in the workplace.
Next Steps
If a parent has concerns about their child's attention span, impulsive behaviour, excessive restlessness, or misdirected physical activity, a comprehensive evaluation by a paediatrician and a child psychiatrist is essential. All masquerading conditions should be thoroughly ruled out before a diagnosis of ADHD is reached and treatment commenced.
Source: Information in this section has been reproduced under an exclusive agreement with the National Down Syndrome Society (NDSS). Available at: www.ndss.org