The Different Types of Down Syndrome
Genetic DiseasesDown Syndrome

Types of Down Syndrome

Types of Down Syndrome
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Updated on February 2, 2026
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Down syndrome affects 1 in every 640 babies born in the United States each year.

 Although nearly all children born with Down syndrome share some common challenges and characteristics, the wide-ranging condition has several types that can present in different ways.

What Is Down Syndrome?

Down syndrome is a genetic condition in which someone is born with an extra full or partial copy of the 21st chromosome, says Mary Pipan, MD, a behavioral pediatrician and the director of the Trisomy 21 Program at Children’s Hospital of Philadelphia. The extra genetic material is present from conception, so you are either born with Down syndrome or you are not.

Every chromosome carries dozens, hundreds, or even thousands of specific genes. The 21st chromosome has hundreds of genes, and at least two of them — and potentially more — contribute to Down syndrome. These genes are located in the so-called Down syndrome critical region, a chromosome 21 segment that may contain genes responsible for many features of Down syndrome, including distinct facial features.

Because every cell in the body typically has the extra 21st chromosome, people with Down syndrome may have physical and intellectual impairments and medical conditions that affect every part of the body, Dr. Pipan says.

3 Types of Down Syndrome

There are multiple types of Down syndrome. Doctors may test for them during pregnancy by screening blood, using an ultrasound, and examining cells or DNA of the fetus or placenta. If a baby shows physical signs of Down syndrome after birth, doctors may perform additional tests.

The type of Down syndrome depends on how chromosome 21 is present in a person’s cells.

Trisomy 21 Down Syndrome

Trisomy 21 Down syndrome occurs when one of the parents’ pairs of chromosome 21 fails to separate, known as nondisjunction.

 This leaves the embryo with three copies of chromosome 21 instead of two, and it is replicated in every cell. The most common form of Down syndrome, this type accounts for 95 percent of all cases.

Translocation Down Syndrome

This occurs when the extra full or partial chromosome 21 attaches to one of the other 23 chromosomes. It accounts for about 3 percent of Down syndrome cases.

Unlike other types of Down syndrome, translocation Down syndrome can be inherited. A parent could have a balanced translocation, meaning genetic material from chromosome 21 resides on another chromosome but is not considered extra, and the parent may not show symptoms. During reproduction, however, the translocation can become unbalanced — leading to the extra chromosome 21 or genetic material that causes Down syndrome.

As a potential parent, you can undergo genetic testing to determine if you have chromosome translocation. This condition puts a pregnancy at a 30 percent risk of miscarriage, and your doctor may recommend testing if you are attempting a pregnancy after a miscarriage.

Talk to your healthcare team about options for testing and pregnancy, which may include in vitro fertilization.

Mosaic Down Syndrome

Also called mosaicism, this occurs when some but not all cells contain an extra copy of chromosome 21. This is the rarest type of Down syndrome, accounting for 2 percent of cases.

People with mosaic Down syndrome may see milder neurological and intellectual impairments than those with other types of Down syndrome. They also have less of a risk of developing Alzheimer’s disease, which is otherwise common among people with Down syndrome after age 40.

Understanding the Range of Down Syndrome Characteristics

Every person with Down syndrome is unique, and that extends to how their form of the condition is expressed, says H. Craig Heller, PhD, a professor of biology and the director of the Center for Down Syndrome Research at Stanford University in Palo Alto, California.

While many people with Down syndrome will have similar physical, medical, and intellectual traits, these characteristics often differ in severity, Dr. Heller says.

Physical Characteristics

A flattened face — especially across the nose — and upward-slanted, almond-shaped eyes are two common physical traits associated with Down syndrome.

“Facial-cranial features, for example, are nearly always present [in people with Down syndrome],” Heller says.

Other common physical characteristics include following:

  • Short neck
  • Small hands and feet
  • Small stature
  • Rounded and small ears
  • Lack of muscle tone
  • Loose joints
  • Large tongue

  • Single crease in the palm

Potential Health Challenges

Some people with Down syndrome do not experience any medical-related effects from their condition. Others, Heller says, may experience problems that include the following:

  • Hearing loss
  • Poor eyesight and eye diseases
  • Digestive issues
  • Low bone density
  • Obstructive sleep apnea
  • Heart issues, including heart defects at birth
  • Obesity and weight management concerns

  • Dementia and Alzheimer’s disease later in life

Intellectual and Developmental Differences

Although everyone is different, children with Down syndrome may have cognitive developmental challenges. They may have problems learning new things, making decisions, and focusing.

“There can be effects on learning and memory, and specifically the ability to form long-term memories,” Heller says.

They may start walking, talking, and sitting at a later age than children without Down syndrome, and therapy can lead to improvements.

Other common traits may be positive.

“Children with Down syndrome are generally really social and outgoing, for example,” Pipan says. “Every individual with Down syndrome has their own strengths and weaknesses. Given the right support, they can accomplish a lot.”

The Takeaway

  • There are three types of Down syndrome, a genetic condition that occurs when someone is born with an extra full or partial copy of the 21st chromosome.
  • In trisomy 21 Down syndrome, the most common type of the condition, a person has three copies of chromosome 21 instead of two.
  • Translocation Down syndrome, which occurs when all or part of chromosome 21 attaches to another chromosome, can be inherited, in addition to being the result of a random chromosomal change at conception.
  • Mosaic Down syndrome is the rarest form of the condition, and it may have less pronounced symptoms than other types.
  • Although people with Down syndrome may share similar physical traits, health challenges, and intellectual issues, no two people with the condition experience it the same way.

Resources We Trust

Additional reporting by Tony Stasiek.

EDITORIAL SOURCES
Everyday Health follows strict sourcing guidelines to ensure the accuracy of its content, outlined in our editorial policy. We use only trustworthy sources, including peer-reviewed studies, board-certified medical experts, patients with lived experience, and information from top institutions.
Resources
  1. Living With Down Syndrome. Centers for Disease Control and Prevention. November 22, 2024.
  2. Down Syndrome. Eunice Kennedy Shriver National Institute of Child Health and Human Development.
  3. Chapman LR et al. Gene Expression Studies in Down Syndrome: What Do They Tell Us About Disease Phenotypes. International Journal of Molecular Sciences. March 4, 2024.
  4. Down Syndrome Tests. MedlinePlus. January 20, 2026.
  5. What Causes Down Syndrome? Eunice Kennedy Shriver National Institute of Child Health and Human Development. January 8, 2026.
  6. Down Syndrome. Mayo Clinic. November 12, 2024.
  7. About Down Syndrome. National Down Syndrome Society.
  8. Al-Hafez L et al. Can Genetic Testing Explain the Cause of Recurrent Miscarriages? UT Southwestern Medical Center. February 19, 2025.
  9. Xicota L et al. The Effects of Mosaicism on Biological and Clinical Markers of Alzheimer's Disease in Adults With Down Syndrome. eBioMedicine. December 2024.
  10. Macroglossia. Cleveland Clinic. March 17, 2022.
  11. Single Palmar Crease. MedlinePlus. April 5, 2025.
  12. Ptomey LT et al. Weight Management Recommendations for Youth With Down Syndrome: Expert Recommendations. Frontiers in Pediatrics. February 3, 2023.
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Nan Du

Nan Du, MD, MPH

Medical Reviewer

Nan Du, MD, MPH, is an instructor at Harvard Medical School and an attending physician at Boston Children’s Hospital. She received her Doctor of Medicine in 2016 from the Warren Alpert School of Medicine at Brown University and completed her pediatric residency at Yale–New Haven Hospital in 2019.

She also has a master’s in public health on clinical effectiveness, with a focus on environmental toxin exposures, health services research, and large databases. She completed her pediatric gastroenterology fellowship at Boston Children’s Hospital.

Currently, she works as a clinician scientist at Boston Children’s Hospital researching celiac disease and early infant nutrition.

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