Down Syndrome vs Autism – Symptoms, Causes, Differences

Down syndrome (DS) is a condition in which a child is born with an extra copy of the 21st chromosome.

Children who have this syndrome tend to have certain features and characteristics (like – a short neck and a flat face), plus, they have some degree of intellectual disability. In the present day, the average lifespan of an individual with DS is about 60 years.

An estimated 10 percent of children with DS have other conditions, like attention deficit hyperactivity disorder (ADHD) or autism spectrum disorder (ASD).

In the US, this syndrome occurs in 1 out of every 800 infants with more than 6,000 children born with DS every year. All individuals with DS develop Alzheimer’s disease, the most common form of dementia. The first symptoms might first appear when they are in their mid to late 40s or early 50s.


Though not all people with DS have the same physical characteristics, some of the more common include:

  • flattened face;
  • short height;
  • small head;
  • poor muscle tone;
  • short neck;
  • excessive flexibility;
  • protruding tongue;
  • relatively short fingers and small feet;
  • upward slanting eyelids;
  • tiny white spots on the colored part of the eye;
  • unusually shaped ears;
  • shorthands with a single crease in the palm.

Additionally, individuals with DS may have slow motor development and delayed language development.


In most patients, it occurs when there is an extra copy of chromosome 21. This form of DS is called trisomy 21. The extra chromosome causes serious problems with the way the brain and body develop.

There is one leading risk factor for DS – maternal age. For instance:

  • a 25-year-old woman has a 1 in 1,200 chance of having a baby with DS;
  • a 35-year-old woman has a 1 in 350 chance;
  • a 40-year-old woman has a 1 in 100 chance;
  • a 49-year-old woman has 1 in 10 chance.

It can be identified after birth by direct observation and genetic testing or during pregnancy by prenatal screening followed by diagnostic testing.

There are 3 different types of DS:

  1. The most common type of DS is trisomy 21, which accounts for about 95 percent of all cases.
  2. Translocation – it accounts for approximately 3-4 percent of patients with DS. Translocation happens when an extra part or a whole extra chromosome 21 is present, however, rather than being a separate chromosome 21, it is attached to a different chromosome.
  3. Mosaicism – it accounts for less than 1 percent of individuals with DS. It is diagnosed when there is a mixture of 2 types of cells, some containing 47 and some containing 46 chromosomes. The cells with 47 chromosomes contain an additional chromosome 21.


There is currently no cure for DS, but the treatment focuses on helping the child to develop as well as possible, offering emotional support for the child and parents, and watching for early signs of health problems.


Autism spectrum disorder (ASD) is a complex neurobehavioral condition that covers a large spectrum of skills, symptoms, and levels of impairment. It has more than doubled since 2001, and in the present day, it affects 1 in 189 girls and 1 in 42 boys.


Each child with ASD is likely to have a unique level of severity and pattern of behavior — from low functioning to high functioning.

A child who shows common signs and symptoms of this disorder:

  • has trouble expressing emotions and needs;
  • has trouble relating to others;
  • is sensitive to taste, smell, or sound;
  • avoids eye contact;
  • needs routines;
  • prefers to be alone;
  • doesn’t get signals from the tone of voice, body language, and expressions;
  • repeats phrases, words, or actions;
  • dislikes being embraced.


While researchers are still investigating the cause of ASD, it is likely that it has numerous causes involving both our environment and our genes, or a combination of the two. Causes may include:


Mothers who have viral or bacterial infections during pregnancy are more likely to give birth to babies who later develop ASD.


Obese mothers have increased chances to give birth to babies who later develop this disorder.

Medical Conditions

ASD tends to occur more than expected among people who have certain medical conditions, like – tuberous sclerosis (the growth of numerous noncancerous tumors in numerous parts of the body), fragile X syndrome (a genetic condition that causes intellectual disability), phenylketonuria (inherited condition which increases the levels of phenylalanine in the blood), and congenital rubella syndrome.


According to research, children with ASD have up to 10 times more aluminum in their brains than what is considered normal in adults. Hence, it is thought that aluminum in vaccines may cause ASD.

Other factors include:

  • air pollution;
  • gestational diabetes (occurs during pregnancy, especially around the 24th week);
  • maternal prenatal medication use;
  • the use of certain antidepressants during pregnancy;
  • high maternal age at the time of birth of the child;
  • emotional trauma in the mother’s life before she even became pregnant;
  • a folate (a vitamin part of the B-complex vitamins) deficiency in the mother at the time of conception.


There is no cure for ASD. Nevertheless, an early diagnosis and targeted intervention can help in reducing the impact of a child’s ASD on his or her functioning considerably.

Note – many parents of children with ASD report that behavior improves notably when their children eat a diet free of protein casein (dairy products) and gluten.

Down Syndrome vs Autism – Differences

DS is a genetic disorder with physical features and can’t be prevented. On the other hand, ASD has multiple causes with specific behaviors and can be prevented (at least partially). Both are not curable.

Images credit – Shutterstock

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2 thoughts on “Down Syndrome vs Autism – Symptoms, Causes, Differences”

    • This depends on many factors, but many children show symptoms of autism by 12 to 18 months of age or earlier.


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