Down Syndrome

What is Down syndrome?

Down syndrome is a condition in which babies are born with extra genetic material from chromosome 21. The extra chromosome is associated with other conditions such as varying degrees of developmental delay and intellectual disability, characteristic facial features, and increased risk of certain health conditions. The degree of these conditions varies greatly from child to child.

Down syndrome is the most common genetic birth defect, affecting approximately 1 in every 691 babies. The condition, itself, does not have a cure. But, treatment is available for many of the symptoms and conditions that can accompany the diagnosis.

Life expectancy for people with Down syndrome is about 55-60 years, though average life span has increased greatly over the past 50 years and is still rising with some individuals with Down syndrome living into their eighties.

What are the 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 percent of people with the condition. 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 to 4 percent 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 percent 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.

What medical conditions are associated with Down syndrome?

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:

  • congenital heart defects, which occur in almost half of children born with Down syndrome
  • 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, 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, often well-managed with medication
  • ear infections and hearing impairment
  • visual or hearing impairment
  • 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

How we care for Down syndrome

At The Boston Children’s Hospital Down Syndrome Program we offer multidisciplinary clinical evaluations for people with Down syndrome from birth until the age of 22 years. Our program is within the Boston Children’s Hospital Developmental Medicine Center. With each appointment, we are also able to make referrals and connections with any of our other specialty clinics at Boston Children’s Hospital. We strive to provide resources, advocacy, and supports to all families, depending on their individual needs.