News & Views

Issue No. 11, 2008

Awareness about autism has risen over the past decade, but little is known about the dual diagnosis Down syndrome and autism. In this News and Views issue, we discuss this dual diagnosis.

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In the spotlight

Down Syndrome and Autism Spectrum Disorders—A Dual Diagnosis
By Sietske Heyn, Ph.D.

Not long ago, it was believed that Down syndrome could not co-occur with a psychiatric or behavioral disorder such as autism.  Parents were simply told that the behavior of their child was due to Down syndrome and no further assessment was made, even if the parents sensed that their child was somehow acting differently compared to other children with Down syndrome. 

Today, many people still don’t realize that a person with Down syndrome can have mental health concerns just like the rest of us.  This lack of awareness is surprising, if one considers that about 18-38% of children with Down syndrome have some form of mental health issue, ranging from attention deficit hyperactivity disorder to depression.  Fortunately, awareness and knowledge about the co-existence of Down syndrome and psychiatric and behavioral disorders is increasing.

The combination of Down syndrome and autism spectrum disorders (ASD) was considered rare until quite recently.  Now, several publications suggest that about 1 in 20 children with Down syndrome might have ASD—a 25 times higher chance than in the general population. A look at the scientific literature with keywords “Down syndrome” and “autism” reveals less than 300 publications, most of which compare and contrast Down syndrome and autism as separate disorders, not as a dual diagnosis.  However, while only about 20 publications actually talk about the co-existence of the two disorders, most of these studies were published within the last decade.  Clearly, research into this area is picking up.

As the name implies, ASD is not a single disorder, but a group of pervasive developmental disorders with a wide range of symptoms that can vary in severity.  Unlike Down syndrome, which can be confirmed by a genetic test, there is no diagnostic test to confirm ASD.  ASD is diagnosed by observation only, using certain defined criteria. 

A person with ASD usually shows impaired development and cannot function socially in a way that most people do.  For a person with ASD it is difficult to interact and communicate with others, and often his or her behavior is restricted, stereotyped and repetitive. People with ASD make poor or no eye contact, they are often disinterested in social interaction and can be anxious or withdrawn in everyday circumstances. They have poor use of spoken words or no speech at all, and may have difficulty understanding spoken words, signs and gestures.  They are often not capable of imaginative play and they often show persistent patterns or ritualistic behavior, or repetitive body movements, or both. In addition to these specific diagnostic features, people with ASD may also have phobias, sleeping and eating disturbances, temper tantrums, and (self-directed) aggression. There are many different types of ASD, including infantile autism (onset prior to age 3), pervasive developmental disorder, and late-onset autism (onset after 3 years).  In Down syndrome, late-onset autism is most common. 

Making a diagnosis of ASD is difficult under any circumstance, but in a person with Down syndrome it is even more challenging: “With mental impairment, it is difficult to separate autism and other related issues into neat compartments,” says Dr. Melanie Manning a geneticist at the Lucile Packard Children’s Hospital Down syndrome clinic at Stanford University.  It is not easy to differentiate between behavior that is due to Down syndrome and behavior that might be related to other factors. 

For example, one person with Down syndrome and undiagnosed, but suspected ASD, watches the same video of a friend’s wedding every single day and has done so for the past six years.  She also watches wheel of fortune every day and gets very upset if this routine is disrupted for any reason.  These are very repetitive behaviors, but by themselves, they don’t warrant a diagnosis of ASD or any other neurobehavioral disorder—a lot of people with Down syndrome love to watch the same show on TV or video over and over.

Asked whether she sees a lot of children with this dual diagnosis at her clinic, Dr. Manning answers “No.”  “We see a lot of children with language delays and problems with social interactions, but they usually don’t meet all criteria for ASD.”

On the other hand, Dr. George Capone, a clinician from Down syndrome clinic at the Kennedy Krieger Institute in Baltimore sees a lot of children with Down syndrome and ASD.  The clinic at the Kennedy Krieger Institute specializes in this dual diagnosis and there is a definite referral bias.  But even so, Dr. Capone points out that despite increased awareness among parents and clinicians, there is some reluctance to promote awareness of this dual diagnosis. “Often it is ignored or not discussed openly, sometimes for cultural reasons or because people are afraid of being stigmatized.”

In addition, there is an ongoing debate among clinicians as to whether it is useful to put another label on these children with Down syndrome.  If a child with Down syndrome has a profound learning disability and many other mental health issues, adding a specific diagnosis of ASD serves little purpose.  However, in other cases, a formal diagnosis could help explain why a specific child with Down syndrome acts differently from other children with Down syndrome.  “Sometimes people seek help because what is offered through Down syndrome support groups does not meet their child’s needs,” says Dr. Capone.  In this case, a thorough assessment and a formal diagnosis may help parents better understand what is going on with their child and may enable them to offer better support.  In some cases, a diagnosis could lead to partial treatment of certain behavior, which is beneficial to the child and the family.  For practical purposes, a formal diagnosis can help get school services and programs.

Are all children with Down syndrome at a higher risk for developing ASD?  According to Dr. Capone, there are several probable risk factors that may be seen prior to the recognition or onset of ASD.  Low IQ, repetitive or ritualistic movements, postures or utterances (stereotypy), lack of eye contact, inability to “process” spoken language, and infantile spasms (a form of epilepsy) are all potential risk factors.  In addition, ASD is more often observed in males. This is true for Down syndrome as well as ASD in general.

What is the future prognosis for these children?  Dr. Capone points out that there are three big factors to keep in mind.  First, what are the level of intellectual disability and the rate of progress.  Second, how well do these children communicate with speech, gestures, or picture exchange.  And third, are there behaviors that interfere with everyday activities.

Why is ASD more common in people with Down syndrome?  The answer to this question is unknown.  Down syndrome is a complex neurodevelopmental disorder that involves changes in the structure and function of cells in the brain that lead to difficulties with learning and memory.  Perhaps the alterations in the structure and function of brain cells are enough to predispose children with Down syndrome to ASD.  Or perhaps, as Dr. Capone puts it, “there may be neurobiological and medical factors that are unique in these kids with Down syndrome and ASD that are different from the rest of individuals with Down syndrome.”  More research is needed to answer this question.

Regardless of what we know today about the causes of this dual diagnosis, early detection is essential to help parents find the best support available to maximize the potential of their children.

Many thanks to Dr. George Capone, Dr. Melanie Manning, Dr. Manpreet Singh, and Dr. Heidi Feldmann for their valuable input.