Signs and Symptoms Vary

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 more easy-going. Combined with the wide range of abilities seen in Down syndrome alone, it can feel mystifying. It is easier if you have an understanding of autism spectrum disorders (ASD) separate from 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 trying to understand the child and develop an optimal medical care and 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 intellectual disability, 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 any of 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 across similar circumstances. Some of the variable characteristics of ASD 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 (esp. 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 to other groups of children with 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, and
• A formal diagnosis may entitle the child to more specialized and effective educational and intervention services.
   

Incidence

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%. This is substantially higher than is seen in the general population (.04%) and less than other groups of children with intellectual disability (20%). 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 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.

Generally, the cause of ASD is poorly understood, whether or not it is associated with Down syndrome. There are some medical conditions in which ASD is more common such as Fragile-X syndrome, other chromosome anomalies, seizure disorder, and prenatal or perinatal viral infections. Down syndrome should be included in this list of conditions. The impact of a pre-existing medical condition such as Down syndrome on the developing brain is probably a critical factor in the emergence of ASD disorder in a child.

Brain Development and ASD

The development of the brain and how it functions is different in some way in children with DS-ASD than their peers with Down syndrome. Characterizing and recording these differences in brain development through detailed evaluation of both groups of children will provide a better understanding of the situation and possible treatments for children with DS-ASD.

A detailed analysis of the brain performed at autopsy or with magnetic resonance imaging (MRI) in children with autism shows involvement of several different regions of the brain:
 

• The limbic system, which is important for regulating emotional response, mood and memory
• The temporal lobes, which are important for hearing and normal processing of sounds
• The cerebellum, which coordinates motor movements and some cognitive operations
• The corpus callosum, which connects the two hemispheres of the cortex together

The cerebellum and corpus callosum is different in appearance in these children compared to those with Down syndrome alone.

Brain Chemistry and ASD

The neurochemistry (chemistry of the brain) of autism is far from clear and very likely involves several different chemical systems of the brain. This information provides the basis for medication trials to impact the way the brain works in order to elicit a change in behavior.


An analysis of neurochemistry in children with ASD alone has consistently identified involvement of at least two systems.

• Dopamine: regulates movement, posture, attention, and reward behaviors; and
• Serotonin: regulates mood, aggression, sleep, and feeding behaviors.

Additionally, opiates, which regulate mood, reward, responses to stress, and perception of pain, may also be involved in some children.
 

Detailed studies of brain chemistry in children with DS-ASD have not yet been done. However, clinical experience in using medications that modulate dopamine, serotonin or both systems has been favorable in some children with DS-ASD.