Autism and Down syndrome are separate conditions, but it’s possible for a person to have both.

If you’re reading this, you might know someone with Down syndrome or someone who’s autistic. You may even know someone with a dual diagnosis of both.

Autism spectrum disorder (ASD) and Down syndrome (DS) are both complex and lifelong. Though they share some characteristics, they have more qualities that set them apart.

ASD and DS are not the same conditions, but they can occur together. About 20% of people with Down syndrome are also autistic.

There are some distinct and key differences between autism and Down syndrome.

Autism spectrum disorder

Autism is a neurodevelopmental difference that can affect a person’s abilities in language, social interaction, and behavior. People with ASD present with a broad range of traits and can seem completely different.

The Centers for Disease Control and Prevention (CDC) estimates that about 1 in 44 children are autistic.

Doctors identify autism by observing and assessing a child’s behavior and developmental history. It’s possible to spot ASD behaviors in someone as young as 2 years of age, but some autistic people aren’t identified until they’re older or even adult.

It’s usually impossible to tell that a person is autistic just by looking at them.

Down syndrome

Down syndrome is a chromosomal condition. It’s the most common genetic disorder in the United States, affecting about 1 in 700 babies born.

Medical testing called karyotyping can check for the chromosomal differences associated with DS.

It’s possible to diagnose DS before birth using prenatal karyotype testing. A doctor can also identify DS characteristics at birth during an exam and confirm with a blood test.

Multiple factors can contribute to the cause of autism, including:

  • genetics, both gene mutations and family history
  • environmental factors, such as pesticide exposure during pregnancy or birth trauma that restricted the supply of oxygen to the baby
  • biological factors, such as infection during pregnancy and inflammation

Meanwhile, Down syndrome is a chromosome disorder. It occurs more frequently in pregnancies with mothers age 35 or older.

There are three types of DS:

  • Trisomy 21. Every cell has a third copy of chromosome 21 (usually, each chromosome has only 2 copies).
  • Mosaic Down syndrome. Some cells have 3 copies of chromosome 21, and other cells have only 2 copies.
  • Translocation Down syndrome. This is when an extra piece or extra whole copy of chromosome 21 is attached to a different chromosome.

Autism and Down syndrome have some shared characteristics. In other ways, they’re quite different.

For example, many autistic people prefer to keep to themselves. They may appear withdrawn or indifferent. On the other hand, people with DS are often social and friendly.

Many autistic people don’t follow a usual pattern for learning language. Some never speak. Others learn to speak and then lose language development.

Meanwhile, the language development of people with DS is similar to that of typically developing children.

Other differences include:

AutismDown syndrome
Minimal or no use of gesturesUse of signs and symbolic gestures
May act as though other people are inanimate objectsTries to copy others
Parallel play (plays beside others)Joint attention (plays with others)

Autism exists on a broad spectrum and has various behavioral expressions. For example, some autistic people use gestures, have common language skills, and enjoy spending time with friends.

DS is also likely to cause individuals to learn and progress more slowly. ASD includes a wide range of intellectual abilities — from severe delays to gifted, or superior levels of intelligence.

Traits shared by both ASD and DS include:

  • preference for routine
  • less responsive to the sound of their name
  • expressive language differences
  • atypical eye contact
  • sensory differences
  • repetitive play
  • challenging behaviors
  • focused interests
  • anxiety
  • developmental differences
  • reduced reciprocal conversation

Autism doesn’t affect the way a person looks. However, DS causes recognizable physical changes, including:

  • upward slanted eyes
  • short neck with extra skin at the back
  • small head
  • small ears and mouth
  • white spots on the iris of each eye
  • reduced muscle tone
  • flat facial features
  • hands that are wide and short, with short fingers

Both ASD and DS usually occur with health issues. The degree to which they affect each person can vary.


  • seizures
  • gastrointestinal issues
  • sleep disorders
  • pain threshold differences
  • metabolic differences

Down syndrome:

  • congenital heart defects
  • cataracts and poor vision
  • hearing loss
  • hip issues
  • leukemia
  • obesity
  • hypothyroidism
  • constipation
  • sleep apnea
  • infection susceptibility
  • dementia
  • Alzheimer’s disease

The goal of autism treatment for children and adults is to support each individual to make daily life easier. For some autistic people, that might be speech therapy or social skills training. Others might benefit from academic support or physical therapy.

Sometimes, doctors prescribe medication to treat co-occurring conditions like attention deficit hyperactivity disorder (ADHD) or mood disorders.

Much like autism treatment, Down syndrome treatment is tailored to the needs of the individual. Many support services are similar to those provided for autism but with different objectives.

For example, a speech pathologist might help an autistic child assemble words into complete sentences. For a child with Down syndrome, the focus might be more about the clear pronunciation of those words.

In addition to the types of health and education professionals Down syndrome shares with autism, DS can also result in significant medical needs, such as surgery for heart defects and cancer treatment.

Many autistic people and people with Down syndrome lead full lives. Both diagnoses are common enough that there’s a wealth of knowledge and support available to individuals and families who need it.

The Autism Society is a place to start for information and education. The National Down Syndrome Society has useful resources and programs. The Disability Rights Education & Defense Fund can help with civil and human rights advocacy, as well as training and public policy.

Autism and Down syndrome can occur together, but because autism is diagnosed by observing behavioral differences, it may not be as noticeable in a young child with Down syndrome.

If your child with DS seems less social than others, a doctor can advise about the possibility of an ASD and DS dual diagnosis.