Autism and Down Syndrome

ASD 101: A Crash Course

Signs and Symptoms Vary

Although we are documenting some similarities in the way DS-ASD presents, autism is what is considered a spectrum disorder. This means that every child with DS-ASD will be different in one way or another. Some will have speech, some will not. Some will rely heavily on routine and order, and others will be relatively easy-going. Combined with the wide range of abilities seen in Down syndrome alone, DS-ASD can feel mystifying. It is easier if you have an understanding of ASD disorders separate from those of Down syndrome.

Autism, autistic-like condition, autistic spectrum disorder (ASD), and pervasive developmental disorder (PDD) are terms that mean the same thing, more or less. They all refer to a neurobehavioral syndrome diagnosed by the appearance of specific symptoms and developmental delays early in life. These symptoms result from an underlying disorder of the brain, which may have multiple causes, including Down syndrome. At this time, there is some disagreement in the medical community regarding the specific evaluations necessary to identify the syndrome or the degree to which certain "core features" must be present to establish the diagnosis of ASD in a child with Down syndrome. Unfortunately, the lack of specific diagnostic tests creates considerable confusion for professionals, parents, and others who are trying to understand the child and develop an optimal medical-care plan and an effective educational program.

There is general agreement that:

-- Autism is a spectrum disorder: it may be mild or severe.
-- Many of the symptoms overlap with other conditions, such as obsessive-compulsive disorder (OCD) or attention deficit hyperactivity disorder (ADHD).
-- ASD is a developmental diagnosis. Expression of the syndrome varies with a child's age and developmental level.
-- Autism can co-exist with conditions such as mental retardation, seizure disorder, or Down syndrome.
-- Autism is a life-long condition.

The most commonly described areas of concern for children with ASD include:

-- Communication (using and understanding spoken words or signs)
-- Social skills (relating to people and social circumstances)
-- Repetitive body movements or behavior patterns

Of course, there is inconsistency in these areas in all children, especially during early childhood. Children who have ASD may or may not exhibit all of these characteristics at any one time; nor will they consistently demonstrate their abilities in similar circumstances. Some of the variable characteristics of ASD we have commonly observed in children with DS-ASD include:

-- Unusual response to sensations (especially sounds, lights, touch, or pain)
-- Food refusal (preferred textures or tastes)
-- Unusual play with toys and other objects
-- Difficulty with changes in routine or familiar surroundings
-- Little or no meaningful communication
-- Disruptive behaviors (aggression, throwing tantrums, or extreme non-compliance)
-- Hyperactivity, short attention, and impulsivity
-- Self-injurious behavior (skin picking, head hitting or banging, eye-poking, or biting)
-- Sleep disturbances
-- History of developmental regression (especially language and social skills)

Sometimes these characteristics are seen in other childhood disorders, such as attention deficit hyperactivity disorder or obsessive-compulsive disorder.

Sometimes ASD is overlooked or considered inappropriate for a child with Down syndrome due to cognitive impairment. For instance, if a child has a high degree of hyperactivity and impulsivity, only the diagnosis of ADHD may be considered. Children with many repetitive behaviors may only be regarded as having stereotypy movement disorder (SMD), which is common in individuals with severe cognitive impairments.

Most parents agree that severe behavior problems are usually not easily fixed. Finding solutions for behavioral concerns is one reason families seek help from physicians and behavior specialists. Compared with other groups of children who have cognitive impairment, those with Down syndrome, as a group, are less likely to have behavioral or psychiatric disorders. When they do, it is sometimes referred to as having a "dual diagnosis." It is important for professionals to consider the possibility of a dual diagnosis (Down syndrome with a psychiatric condition such as ASD or OCD) because:

-- It may be responsive to medication or behavioral treatment.
-- A formal diagnosis may entitle the child to more specialized and effective educational and intervention services.

If you think your child may have ASD disorder, share this before or during your evaluation. Don't wait to see what might happen.


Estimating the prevalence or occurrence of ASD disorder among children and adults with Down syndrome is difficult. This is partly due to disagreement about diagnostic criteria and incomplete documentation of cases over the years. Currently, estimates vary between 1 and 10 percent. I believe that 5 to 7 percent is a more accurate estimate. This is substantially higher than we see in the general population (0.04 percent) and less than other groups of children with mental retardation (20 percent). Apparently, the occurrence of trisomy 21 lowers the threshold for the emergence of ASD in some children. This may be due to other genetic or other biological influences on brain development.

A review of the literature on this subject since 1979 reveals 36 reports of DS-ASD (24 children and 12 adults). Of the 31 cases that include gender, an astonishing 28 individuals were males. The male-to-female ratio is much higher than the ratio seen for autism in the general population. Additionally, in reports that include cognitive level, most children tested were in the severe range of cognitive impairment.

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