The Dual Diagnosis of Down Syndrome and Autism

Until recently, it was believed that autism was rare in individuals with Down Syndrome. However, how common is autism in children with Down Syndrome? A review of the literature reveals that reported prevalence rates vary widely, ranging from 4% to 41%. This variation is largely due to differences in the methodologies used to identify autism. Most, if not all, tools employed in these studies are not specifically validated for individuals with Down Syndrome. Some studies rely on screening tools, while others use diagnostic assessments. Fortunately, a meta-analysis from 2015 (Richards, Jones, Groves, Moss & Oliver) examined the frequency of autism across various genetic conditions. It found a prevalence of 16% for autism in individuals with Down Syndrome, significantly higher than the 1.7% found in the general population.

Are There Any Risk Factors for Autism in Children with Down Syndrome?

Several studies have observed that the majority of patients with a dual diagnosis of Down Syndrome and autism are male. There is also evidence suggesting that certain medical conditions may increase the risk of autism in children with Down Syndrome. One such condition is infantile spasms, which has been statistically linked to a higher risk of autism. Additionally, lower IQ appears to be associated with an increased likelihood of autism.

Does Family History Play a Role?

Some studies have found that autism in children with Down Syndrome may be linked to family history, particularly if there are family members with autism, autistic traits, language difficulties, or developmental disorders.

How Do Children with Down Syndrome and Autism Present?

Parents often report concerns when their child is around three to three-and-a-half years old. Unfortunately, the time to diagnosis can be quite lengthy, with many families waiting until their child is four-and-a-half years old. This delay is unacceptably long.

Some of the common signs noticed by parents include:

• Repetitive behaviours such as hand-flapping, stimming, or head-banging.
• Perseverative behaviours, such as staring at ceiling fans or playing with the same toy repeatedly.
• Abnormal play, like lining up toys or sorting them rather than engaging in more typical play. Children may focus on a specific part of a toy, such as licking the eyes or nose of a doll, rather than playing with the whole object.

Children with a dual diagnosis may exhibit these behaviours more frequently and are often harder to redirect. They also display impaired social skills. Although children with Down Syndrome are generally known for their strong social skills, children with both Down Syndrome and autism may still greet others with a smile but struggle to maintain social interaction. They often show less imitation, less back-and-forth communication, and reduced shared attention.

Communication Difficulties

Parents frequently report communication impairments in children with a dual diagnosis. While speech delays are common in children with Down Syndrome, these impairments are more pronounced in children who also have autism. Studies show that verbal children with a dual diagnosis acquire language about six months later than those with Down Syndrome alone and have both expressive and receptive difficulties. Dysarthria and dyspraxia also contribute to their inability to express themselves well. Many children exhibit echolalia, repeating words without using them spontaneously.

Sensory Issues and Other Concerns

Many families report sensory sensitivities, such as a preference for low-sensory environments, refusal to participate in touch-related activities, and difficulties with loud noises, darkness, crowds, and being touched. Feeding issues and tantrums that are hard to explain or soothe are also common. Poor eye contact is often noted, although some children may make eye contact that is not sustained.

Parents also report delayed achievement of developmental milestones, which further distinguishes these children from others with Down Syndrome. There are often additional mood and behavioural issues, including tantrums, hyperactivity, self-injury, and anxiety. Children with Down Syndrome and autism show higher rates of ADHD and anxiety compared to children with only Down Syndrome. Additionally, around a third of children with a dual diagnosis may experience regression, often occurring later than in children with idiopathic autism.

Evaluation

There is no definitive protocol for evaluating children with both Down Syndrome and autism. Basic steps include ensuring the child can hear and see properly, checking thyroid function in accordance with guidelines, and ruling out any co-occurring medical conditions. Various assessment tools have been used, although many are not specifically validated for this population.

• M-CHAT: This is a freely available screening tool that has been found to be up to 80% sensitive in children with Down Syndrome aged 60 months or younger (verbal) or 72 months or younger (non-verbal), though it is not highly specific.
• Social Communication Questionnaire (SCQ): This is a 40-item parent screening tool that is useful for children with a chronological age of over four years and a developmental age of at least two years.
• Aberrant Behaviour Checklist (ABC): This tool has been validated for use in children with Down Syndrome and includes multiple scales and subscales. It is particularly useful based on data from Dr Capone’s group at Johns Hopkins.

Interventions

There is limited evidence on which interventions are most effective for children with a dual diagnosis of Down Syndrome and autism. However, parental reports suggest that addressing communication deficits, rigidity, social impairments, and mood and behaviour issues is essential. Setting long-term goals is critical, as these can help guide short-term objectives and therapy planning.

Parents have found Applied Behavioural Analysis (ABA) to be particularly helpful. ABA treatment goals are tailored to the age and ability level of the child and can address various skill areas such as communication, social skills, self-care (e.g., showering, toileting), play and leisure, motor skills, and academic learning. Schools and parental support are also valuable interventions.

Supporting communication is a key priority, as it has a significant impact on reducing behavioural difficulties. This can involve unaided systems, such as sign language, or aided systems, which can be basic (e.g., pointing to letters, words, or pictures) or high-tech (e.g., computer systems that allow children to touch pictures or letters that then “speak” for them).