Down Syndrome Symptoms & Causes

At Boston Children’s Hospital, we understand that if your child has been diagnosed with Down syndrome, you may have a lot of questions and concerns about your child’s health and future. Every individual has unique strengths, talents, and skills.  People with Down syndrome attend school, recreational activities, and work within their communities.  People with Down syndrome can contribute to their family, friends, and society in many wonderful ways.  Remember, it is difficult for any parent to predict what their child’s unique capabilities will be.  We will help you to discover and nourish your child’s gifts, and to help you enable your child to reach their greatest potential.

What Causes Down syndrome?

Down syndrome is a common genetic syndrome caused by having all or part of an extra chromosome 21.  The most common type of Down syndrome is also known as “Trisomy 21” due to the fact that there are three copies of this chromosome instead of the usual two.

  • Normally, the mother's egg and the father's sperm each start out with 23 chromosomes. When the egg and sperm meet at conception, a child inherits 23 chromosomes from each parent, ending up with 23 pairs of chromosomes, and a total of 46 chromosomes.
  • In Down syndrome, a change occurs during cellular division such that the egg or sperm has two copies of chromosome #21 and a total of 24 chromosomes. This is called “nondisjunction.”  Researchers are still unsure of what causes the cells to divide in this manner.
  • If this egg or sperm is fertilized, the baby ends up with three copies of the #21 chromosome or"Trisomy 21":. This extra genetic material causes the variety of health and developmental issues in Down syndrome.

What are the different types (genetic causes) of Down syndrome?

There are three different types of Down syndrome:

  • Trisomy 21 is the most common cause of Down syndrome, and accounts for 95% of people with Down syndrome.  Trisomy 21 occurs when a child is born with a full three copies of the 21st chromosome, rather than the usual two, and therefore has 47 chromosomes instead of 46 chromosomes.
  • Translocation Down syndrome accounts for 3-4% of people with Down syndrome. Translocation refers to material from chromosome 21 being attached (or translocated) on to another chromosome (for example, a piece of chromosome 21 may be attached to chromosome 14).  In most cases, the translocation is “de novo” occurring in the formation of the egg or sperm and affects only the fetus. Sometimes, a parent can carry a “balanced translocation” in which there is a rearrangement but no loss or addition of chromosomal material. This does not affect the parent but leads to a higher chance that a future pregnancy will carry the translocation.  However, if a rearranged chromosome is passed on, there can be an “unbalanced” translocation in the fetus resulting Down syndrome.  The clinical features of people with Translocation Down syndrome are indistinguishable from those with Trisomy 21.
  • Mosaic Down syndrome (mosaisicim) accounts for less than 1% of people with Down syndrome. Children born with Mosaic Down syndrome have some cells with three copies of chromosome 21 and some cells that have the usual pair. Clinically, babies born with Mosaic Down syndrome can have the same features and health problems seen in babies born with Trisomy 21 or Translocation Down syndrome. However, the presence of cells with the normal number of chromosomes may result in fewer characteristics of Down syndrome in some people.

Are there any medical conditions associated with Down syndrome I should be concerned about?

  • children with Down syndrome typically have intellectual disability, hypotonia (low muscle tone) and characteristic facial features, such as upward slanted eyes and a flattened nasal bridge.  Some medical conditions are more common in individuals with Down syndrome, therefore special tests and extra medical care are needed.
  • children with Down syndrome have an increased risk for certain medical conditions.  Health care guidelines exist to help clinicians screen and manage these conditions.  Some of these conditions include:
  • oongenital heart defects, which occur in almost half of children born with Down syndrome. Some children require surgery to correct their heart.
  • pulmonary hypertension, a condition that affects arteries in the heart and lungs, and which often resolves in the newborn period.
  • gastrointestinal malformations such as Hirschsprung’s disease and Duodenal Atresia. These are usually treated, often with surgery, in the newborn period.
  • seizures, especially a type called “infantile spasms” in babies or other types of seizures in older children.  These are often well-managed with medication.
  • ear infections and hearing impairment. Some children may require ear tubes.
  • visual or hearing impairment.  Some children may use glasses.
  • atlantoaxial instability (cervical spine vertebrae may be more flexible causing a small but increased risk for spinal cord injury or compression).
  • obesity/Overweight
  • childhood leukemia
  • thyroid conditions, such as hypothyroidism
  • colds and respiratory infections, like bronchitis, and pneumonia
  • sleep dysfunction and obstructive sleep apnea

Signs and symptoms of Down Syndrome 

Down syndrome can affect a child physically, cognitively, and behaviorally. Remember that every child with the condition is unique and may possess these characteristics to different degrees or not at all.


A child with Down syndrome will have some, but perhaps not all, of the following features:

  • eyes that slant upward, from inner corner to outer corner
  • small ears that may fold over slightly at the top
  • a smaller than average mouth, and larger appearing tongue
  • a smaller than average nose, with a flattened nasal bridge
  • short, stocky arms and legs. Some children also have a wide space between the big toe and second toe.
  • some babies with Down syndrome have short necks and small hands with short fingers
  • one single crease that goes straight across the palm, and a second crease that curves down by the thumb, rather than having three creases in the palm of the hand
  • shorter than average height
  • low muscle tone (hypotonia) throughout the body and increased looseness or flexibility in the joints

Developmental, Cognitive, and Behavioral Symptoms

  • Most children with Down syndrome have delays in meeting developmental milestones.  They typically learn to walk and talk at later times than children without Down syndrome. 
  • Children with Down syndrome often have mild to moderate cognitive impairment and intellectual disability
  • Children with Down syndrome often have specific patterns of cognitive and behavioral features including:
    • Strengths in in social engagement and social behavior, visual learning, and word reading. 
    • Challenges with attention span, verbal memory, and expressive communication.
  • Tailored and specialized educational programs and support enable children with Down syndrome to learn and grow at their own pace.
  • Behavioral problems such as stubborrness, impulsivity, and temper tantrums may be more common in children with Down syndrome
  • A child may use “self talk” (talking out loud to himself) as a way of understanding and processing information

Frequently Asked Questions (FAQ) about Down Syndrome

Q: What is Down syndrome?

A: Down syndrome is a common genetic syndrome caused by having all or part of an extra chromosome 21.  The most common type of Down syndrome is also known as “Trisomy 21” due to the fact that there are three copies of this chromosome instead of the usual two.

Q: What causes Down syndrome?

A: Down syndrome is caused by the presence of extra chromosomal material. This happens during the time of conception.  Instead of having the usual number of 46 chroosomes, a baby with Down syndrome typically inherits an extra copy of chromosome 21, and is born with 47 chromosomes.  The extra genetic material results in physical and developmental changes.

Q: What are my chances of having a child with Down syndrome?

A: The chances of having a baby with Down syndrome increases with the mother’s age. Even though age alone can’t predict the number of pregnancies that will result in Down syndrome, this is the general guideline:

  • 1 in 1,000 for mothers under age 30
  • 1 in 400 for mothers older than 35
  • 1 in 60 for mothers older than 42

Prenatal testing for the condition is available to any expectant parent who desires that information.

Q: Do symptoms become progressively worse?

A: Down syndrome is not a progressive condition.  Therefore, symptoms do not get progressively worse over time. However, some of the complications associated with Down syndrome can occur at different stages in a child’s life. While some symptoms are present when a child is born, others can emerge during childhood, adulthood, or in elderly patients.

Because different symptoms can emerge at different stages, it’s important to see a Down syndrome specialist who can determine what’s typical and what’s not typical for people with Down syndrome.

Q: Can my child with Down syndrome have children?

A: Although there have been rare exceptions, men with Down syndrome are not expected to be able to father a child. Women with Down syndrome may have decreased fertility. In any pregnancy, a mother with Down syndrome has about a 50 percent chance of conceiving a child with Down syndrome if the father does not have Down syndrome, though many pregnancies result in miscarriage.

Q: Does Down syndrome limit what my child can do?

A: Although your child may learn skills at a slower pace than children without Down syndrome, a child with Down syndrome should still be able to do most things that any young child can do, such as walking, talking, dressing and being toilet trained. Encouragement and support are the best tools to use to help your child reach developmental milestones.  Early developmental therapies, such as Early Intervention, can help babies and toddlers with Down syndrome develop skills.

Q: Can my child go to school, despite having Down syndrome?

A: Yes. There are special programs beginning in the preschool years to help children with Down syndrome develop skills as fully as possible. Many children with Down syndrome can, to some extent, be integrated in the regular classroom. With Early Intervention and special education, the outlook for children with Down syndrome is far brighter than it once was.  More and more people with Down syndrome attend college and work in their communities after graduating from high school.

Q; How serious is the cognitive and intellectual disability that accompanies Down syndrome?

A: The degree of cognitive and intellectual disability that accompanies Down syndrome varies widely, ranging from mild to moderate to severe. However, most cognitive and intellectual disability falls within the mild to moderate range.  Not all areas of cognition are affected equally. Each person has unique strengths and weaknesses.

Q. What does “mild to moderate intellectual disability” mean?

A. Children with mild intellectual disability are usually able to do everyday things like read, hold a job, and take public transportation independently. Children with moderate intellectual disability probably need more support.

Q: What is the long-term outlook for my child?

A: The average life span for people with Down syndrome has increased dramatically since the early 1900s and many people with the condition achieve independence, hold jobs, and move into assisted living arrangements. Although there may be some challenges, with the right treatment and care, your child will have every opportunity to live a happy and fulfilling life.

Issues relating to school and education are usually a top concern for children with Down syndrome.  Therefore, it is important to , seek out educational assistance programs as early as possible.  Early Intervention and Special education services are provided through each community to children with disabilities.  Our team can help you to navigate different options available to you.  There are many different types of therapy and educational strategies that can help support learning, development, and behavior. Visit the Treatment tab to learn more about the various therapy options.

Questions to Ask Your Doctor

You will probably have a lot of questions on your mind before meeting with your child’s doctor. At the appointment, it can be easy to be overwhelmed with information and forget the questions you wanted to ask.

A lot of parents find it helpful to write down questions before the visit. That way, when you talk to your child’s clinician, you can be sure that all your concerns and questions are addressed.  Your clinicians are also open to learning from families.  You may want to share information that you have learned at conferences, and from your reading and experience.

Some questions you might ask include:

  • What kinds of treatment will my child need?
  • What social and behavioral problems should I expect?
  • How can I help my child focus on his strengths?
  • How should I talk to my child or my child’s siblings about this condition?
  • Do I need to restrict my child’s physical activity?
  • Do I need to make changes to my child’s home and school routines?
  • What kind of follow up care will my child need?