Introduction
Children with both Down syndrome and autism spectrum disorder differ from other children in a variety of ways. Some are verbal, others are not. Some rely heavily on routine and structure, while others are more flexible. When this is considered alongside the wide range of abilities already associated with Down syndrome alone, understanding autism spectrum disorder as a separate condition becomes both clearer and more manageable.
Terminology and Definitions
Autism, autistic-like features, autism spectrum disorder (ASD), and pervasive developmental disorder (PDD) are terms that largely overlap in meaning. All refer to a neurobehavioural syndrome diagnosed on the basis of specific symptoms and developmental delays presenting in early childhood. These symptoms arise from an underlying brain disorder that may have several causes, including Down syndrome.
There is ongoing debate within the medical community regarding the diagnostic criteria required for ASD in a child with Down syndrome, and the degree to which specific "core features" must be present. The absence of definitive diagnostic tests gives rise to considerable confusion among clinicians, families, and others seeking to understand the child and develop optimal programmes.
Core Principles
- Autism is a spectrum disorder: it may be mild or severe.
- Many features overlap with OCD and ADHD.
- Diagnosis is developmentally linked — expression changes as the child matures.
- Autism can co-occur with intellectual disability, epilepsy, and Down syndrome.
- Autism is a lifelong condition.
Key Areas of Concern
- Communication: Use and comprehension of spoken language and gesture.
- Social skills: Interaction with others and adaptation to social situations.
- Repetitive behaviours: Body movements or patterns of behaviour characterised by repetition.
Variable Features of ASD in Down Syndrome
- Unusual responses to sensory stimuli (sounds, lights, touch, or pain).
- Food refusal (types, textures, or flavours).
- Atypical play patterns with toys and objects.
- Difficulty accepting changes to routine or familiar environments.
- Weak or absent communication.
- Disruptive behaviours (aggression, meltdowns, marked non-compliance).
- Hyperactivity, short attention span, and impulsivity.
- Self-injurious behaviour (skin picking, head banging, eye poking, biting).
- Sleep disturbances.
- A history of developmental regression, particularly in language and social skills.
Dual Diagnosis and Its Importance
ASD is sometimes overlooked in a child with Down syndrome on the grounds of cognitive impairment. It is, however, essential for clinicians to consider a dual diagnosis for two important reasons:
- The co-occurring condition may be responsive to pharmacological or behavioural treatment.
- A formal diagnosis may enable access to more specialised educational and intervention services.
Prevalence
Current estimates range between 1% and 10% — higher than the general population (0.04%) but lower than other intellectual disability groups (20%). A review of the literature since 1979 revealed that 28 of 31 documented cases were male — a markedly higher ratio than in the general autism population.
Brain Chemistry
At least two neurochemical systems play a role: dopamine (regulates movement, attention, reward) and serotonin (regulates mood, aggression, sleep, feeding). Clinical experience with medications modulating these systems has yielded positive outcomes in some individuals with DS-ASD.
Source: Reproduced under an exclusive agreement with the National Down Syndrome Society (NDSS) — www.ndss.org