All cells in your body contain genes, which are made up of DNA, the molecule that holds the instructions for how your body grows, works and looks. Genes are contained in tiny, spaghetti-like structures called chromosomes inside the cell’s nucleus. Typically, there are 46 chromosomes in each cell, 23 that are passed on from your mother and 23 from your father.
A baby born with Down syndrome has an extra copy of a specific chromosome: chromosome 21. This extra genetic material can impact how the brain and body mature and leads to varying degrees of intellectual and developmental disability.
The extra chromosome also puts the baby at increased risk for certain health conditions, including heart defects, hearing loss, vision problems, seizures, sleep disorders, infections and thyroid problems, typically hypothyroidism (underactive thyroid).
People with Down syndrome often have distinctive physical features. These include a flattened face with a flat nose, almond-shaped eyes that slant upward, tiny white spots on the iris (colored part of the eye), poor muscle tone or loose joints, small stature, short neck, small hands and feet, small ears, and a single line across the palms of the hands (called a palmar crease).
People with Down syndrome typically have some degree of developmental disability, but it’s generally mild to moderate. They may be slow to reach developmental milestones such as crawling, walking and talking. Mental and social delays may result in impulsive behavior, poor judgment, short attention spans and slow learning.
The syndrome is named for English physician John Langdon Down, who published an accurate description of a person with the ailment and originally classified it in the 1860s. In 1959, French physician Jérôme Lejeune identified Down syndrome as a chromosomal condition.
Each year, about 6,000 babies in the United States are born with the condition. That works out to about one in every 700 babies (less than 1 percent). More than 400,000 people are living with Down syndrome in the US today. It’s the most common chromosomal condition diagnosed in the country.
There are three types of Down syndrome:
• Trisomy 21 is the most common, affecting about 95 percent of people with Down syndrome. With trisomy 21, each cell in the body has an extra copy of chromosome 21.
• Translocation Down syndrome affects about 3 percent of people with the syndrome. In this case, an extra part or entire extra chromosome 21 is present, but it’s attached to — or “translocated” — to a different chromosome, often chromosome 14.
• Mosaic Down syndrome is rare, occurring in only about 1 percent of cases. “Mosaic” means “mixture” or “combination.” With mosaic Down syndrome, some of the body’s cells have three copies of chromosome 21 and others have the typical two copies.
Researchers believe that many factors contribute to the development of Down syndrome but don’t know exactly how it occurs. They do know that the risk of having a baby with Down syndrome increases with the age of the expectant mother – especially 35 or older. The risk is also higher if the mother previously had a baby with Down syndrome.
Health care providers typically offer testing for Down syndrome as part of routine prenatal care. There are two types of tests: screening and diagnostic. Screening tests, which include blood tests and ultrasound, can help determine a baby’s risk for Down syndrome.
If the screening tests show the baby is at high risk, the parent may decide to undergo diagnostic testing, which can confirm Down syndrome is present. Diagnostic tests involve taking a sample of the baby’s blood, amniotic fluid or tissue for testing. However, with diagnostic testing — which includes chorionic villus sampling (CVS), amniocentesis and percutaneous umbilical blood sampling (PUBS) — there is some risk of miscarriage, fetal injury and preterm labor.
The doctor can also diagnose Down syndrome after birth based on the physical signs of the ailment. The doctor will also take a blood sample and send it to a lab for a chromosomal analysis called a karyotype to confirm the diagnosis.
There is no treatment for Down syndrome. Experts recommend early intervention with specialized services to help the child maximize potential and have the best outcome. These services include an Individualized Education Program (IEP), which addresses the child’s special needs in school, and physical, occupational, speech and behavioral therapy.
Children with Down syndrome can learn and develop skills; they just reach goals at a different pace than typical kids. With ongoing therapy and support, most people with Down syndrome can attend school, work and become active members of their community.
Let’s celebrate them during this National Down Syndrome Awareness Month.