Down syndrome and Autism Spectrum Disorder: similarities and differences in symptomatology

Very often, in children with Down syndrome, the symptoms of autism can be confused with possible manifestations of the syndrome itself

Autism Spectrum Disorder is a disorder of neurodevelopment, i.e. the maturation of the nervous system

Alterations in the maturation of the nervous system affect the biochemical and physiological processes underlying its functioning and lead to abnormalities in the development of social, communication and behavioural skills.

Autism Spectrum Disorder affects approximately 1% of the population and is characterised by the presence of two main symptoms:

  • Persistent deficits in communication and social interaction;
  • Restricted and repetitive behaviours, interests and activities.

It manifests itself from the early years of life with a frequency 4-5 times higher in males than in females.

The use of the term ‘spectrum’ reflects very well the wide variety of symptoms, which can range from extreme severity to markedly milder deficits.

It is estimated that between 6% and 19% of individuals with Down syndrome also have an Autistic Spectrum Disorder.

Today, there is ample evidence that the onset of Autism Spectrum Disorder can be attributed neither to educational errors nor to family conflicts.

Currently, it is believed that Autism Spectrum Disorder is caused by one or more genetic factors interacting with environmental factors.

Genetic studies conducted on families have shown that first-degree relatives of people with autism are between 20% and 80% more likely to develop the disease than people who have no affected relatives.

Studies conducted on twins show that 60% of monozygotic twins (who therefore have the same genetic heritage) share a diagnosis of autism.

In short: there is no doubt that autism has an important genetic basis.

As far as the environmental component is concerned, several studies have shown that a high percentage of children with autism suffered complications before birth, during childbirth and in the neonatal period.

Other environmental risk factors are the age of the parents at conception, in particular a high age of the father and mother or conversely a very young age of the mother, and extremely premature birth (before 26 weeks).

Assumptions about vaccinations as a cause of autism are devoid of any scientific basis.

The symptoms of Autism Spectrum Disorder are grouped into two broad categories: socio-communicative deficits and behavioural alterations

The first category includes:

  • Deficiencies in social-emotional reciprocity (e.g., abnormal social approaches, reduced sharing of interests);
  • Deficits in non-verbal communicative behaviours used for social interaction (e.g., abnormal eye contact, deficits in the use and understanding of gestures);
  • Deficits in the development, understanding and management of social relationships. Often these children may have a reduced need for physical contact, few friendships, little sharing with other people.

The second category includes certain behavioural alterations, such as:

  • Stereotyped gestures (rocking, clapping, head banging);
  • Ritualised behaviour and adherence to routines that lack flexibility;
  • Problematic behaviour such as self-harm and aggression.

Autism is often associated with intellectual disability (or mental retardation) and many individuals exhibit unusual behavioural responses to sense stimuli (sensory cues).

Some children seem indifferent to pain or high temperatures, others are extremely sensitive, to the point of not tolerating a caress or contact with clothes.

Other children have finer hearing (so they are much more bothered by noises, they struggle for example with many people, they are frightened by the sound of a hoover). They often smell or touch objects to get information about their surroundings.

The diagnosis of Autism Spectrum Disorder is based on the joint work of a team of experienced professionals (doctors and psychologists), who make use of clinical observation and information on the child’s developmental history using tests for cognitive and behavioural assessment.

Other investigations, such as laboratory or instrumental tests, may be necessary to identify possible biological causes.

Very often, in children with Down syndrome, a second diagnosis (of Autism Spectrum Disorder) may be postponed or missed, as the symptoms of Autism Spectrum Disorder may be confused with those of the syndrome itself.


Precisely for this reason, a specialist visit is advisable if the child with Down Syndrome manifests the following behaviour:

  • Has a reduced sharing of interests, emotions or feelings;
  • Is unable to initiate or respond to social interactions;
  • Has impaired verbal and non-verbal skills;
  • Has difficulty sharing play or making friends;
  • Has no interest in peers;
  • Seems happiest playing alone;
  • Insists on uniformity and routine;
  • Has very limited and repetitive interests;
  • Shows hyper- or hyporeactivity in response to sensory stimuli or shows no real fear of danger.

The objectives of the treatment of Autism Spectrum Disorder in children are geared towards improving social-communication skills and reducing problematic behaviour.

It is therefore necessary for both the child and the family to be supported by a multi-specialist and professional team consisting of doctors, psychologists and speech therapists for specific behavioural treatment.

The involvement of the family is crucial.

To date, no drug therapy can cure Autism Spectrum Disorder, but some drugs may be useful in treating certain associated symptoms such as self-injury, aggression, stereotyped movements and hyperactivity.

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