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Trisomy 21
Monday, 21 July 2003
Thursday, 14 July 2005
Down Syndrome


Trisomy 21, which is also referred to as Down Syndrome (DS), is a genetic syndrome which affects approximately 1/700 live births, making it the most common chromosomal disorder. Down syndrome presents with classic facial features, distinctive physical characteristics and varying degrees of developmental delay and mental retardation.


As mentioned above, 1 out of every 700 infants is born with Down Syndrome. For unknown reasons, slightly more males than females are affected. Although children with DS are born to mothers of all ages, the risk of having a child with DS increases as women age. After the age of 40 years the chance for having a child with DS increases to 1/100.

Signs and Symptoms

The classic facial appearance and decreased muscle tone are often present at birth. Other characteristics and long-term effects may not be present until later in the child’s life or even adulthood. This is an extensive list of features of which children with Down Syndrome may only have a few:

  1. Facial features: A flat facial profile, a somewhat depressed nasal bridge and a small nose, upward slanting of the eyes, epicanthal folds (small skin folds on the inner corner of the eyes), small ears with down folding earlobes, enlarged and protruding tongue (which is caused by a small lower jaw), small round head, and a small neck with extra skin folds.
  2. Eyes and ears: Strabismus (crossed eyes), nystagmus (shaking of the eyes), refractive errors (need for glasses), and hearing loss. Later in life, cataracts or glaucoma may occur.
  3. Muscles and bones: Low muscle tone, increased joint flexibility, a palmar crease on the hands, short broad hands, a space between big and second toe, and short stature.
  4. Development: A wide range of developmental delay that may affect intelligence, motor development, language, and interpersonal skills.
  5. Heart: About ½ of children are born with heart problems, usually related to the structure of the heart (such as abnormal connections between the chambers of the heart, known as either ventricular or atrial septal defects).
  6. Gastrointestinal tract: Narrowing of the small intestine causing vomiting early on in life, an annular pancreas (the pancreas wraps around the intestinal tract) and difficulty absorbing nutrients from food.
  7. Endocrine/hormonal: Altered levels of thyroid hormones, either hypothyroidism (decreased thyroid activity) or hyperthyroidism (increased thyroid activity) and obesity.
  8. Malignancy: Increased susceptibility to developing leukemia.
  9. Infections: Increased susceptibility to acute and chronic infections such as ear infections.
  10. Behavior: May have behavioral concerns or attention problems. Adults are at-risk for developing Alzheimer’s disease.

Possible Causes

Down Syndrome occurs when there are three copies of the genetic information found on chromosome 21. Usually, two copies of each chromosome are found in a cell. DS most commonly occurs when a child has a complete extra copy of chromosome 21 and this extra chromosome is found in every cell. However, DS can also be caused by an extra copy of only a part of chromosome 21 and there are times when the extra genetic material is only present in some cells.


At times the diagnosis of Down Syndrome may be suspected prior to the infant being born, or the infant may be diagnosed after birth when some of the above features are noticed. During pregnancy the diagnosis may be made using: 1. Ultrasound: Increased folds in the neck region may be noticed. This may also be used to evaluate for other features of DS such as heart or intestinal defects. 2. Alpha-fetoprotein levels: This is often checked in women while they are pregnant and if abnormal, may warrant further evaluation for Down Syndrome. 3. Amniocentesis: In women who are at-risk for Down Syndrome (over 34 years old) or any other risk factors, amniocentesis is recommended and can provide cells from the baby to evaluate for Down Syndrome. A karyotype is a genetic test done to confirm a clinical diagnosis of Down Syndrome. This test allows the doctor to look at the chromosomes and see if there is extra chromosome 21 information present.


There is no cure for Down Syndrome, but the individual medical problems which the children may face can be addressed. Surgical procedures are available for repairing the heart, intestinal and other problems. Antibiotics are used to treat infections, such as ear infections, which may occur frequently in young children. It is also important to monitor for the development of leukemia, thyroid problems, obesity or behavioral concerns. Early intervention is key for providing the best outcome physically and developmentally. Physical therapy is advised to strengthen muscles and increase muscle tone. Enrollment in developmental centers beginning in infancy and special education programs during school years will help with developmental and learning delays.


The number of children with Down Syndrome who are living into adulthood has increased significantly over the past 20 years due to the improved treatment of medical problems, especially heart defects. With good medical care children with Down Syndrome often live happy and productive lives.

Connect with other parents

In the spirit of community and support, Madisons Foundation offers the unique service of connecting parents of children with rare diseases. If you would like to be connected to other parents of children with this disease, please fill out this brief form.


National Down Syndrome Society
Cmprehensive information source for Downs Syndrome including information on the newest research, resources, advocacy, news & events and community support.

DS Health Issues
A website with a wealth of information for parents including medical information, a featured Down Syndrome research article of the month, health guidelines, personal stories and links to other websites.

Down Syndrome
A great site with information about the syndrome as well as support groups available around the world.

National Down Syndrome Congress
A website that focuses on providing families with support and also addressing the need for public policy and community awareness.

Google Search for Trisomy 21

References and Sources

McCance K (2002). Pathophysiology: the biologic basis for disease in adults and children, 4th ed, Mosby, 126-7 Handbook of Pathophysiology, Springhouse Publishers, c.2001p.100-102 Marino, BS. USMLE: Blueprints in Pediatrics. c.1998, p.95-6 Roizen, NJ and Stark, AR. “Epidemiology; clinical features; and diagnosis of Down syndrome.” UpToDate. Online Accessed on June 6, 2005. Roizen, NJ and Stark, AR. “Management of Down syndrome.” UpToDate. Online Accessed on June 6, 2005.