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Understanding the Basics: Fast Facts About Down Syndrome

Understanding the Basics: Fast Facts About Down Syndrome

If you’ve newly met someone with Down syndrome—whether he or she is an immediate or distant family member, a friend or part of a friend’s family, a co-worker, a neighbor, or someone else—you may realize you don’t know much about the condition. So, here are some introductory facts about Down syndrome to help you better understand it.

Basic Facts About Down Syndrome

  • Down syndrome is named after British physician John Langdon Down, who first described this condition in 1866.
  • French physician Jérôme Lejeune discovered the chromosomal cause of this intellectual and developmental disability (IDD) in 1959.
  • While the vast majority of people are born with 46 chromosomes in each cell (half of them from the mother and half from the father), those with Down syndrome have an extra copy of chromosome 21 in each cell. This causes the condition, but we still don’t understand why it happens.
  • Chromosomes are bundles of genes that determine how a baby grows, develops, and functions in the womb and after birth.
  • About 6,000 babies are born with Down syndrome annually in the US. In other words, about 1 in 700 people have it. It’s the most common chromosomal condition.
  • There are three different types of Down syndrome. Trisomy 21, in which a person has an extra copy of chromosome 21 in every cell, accounts for about 95% of cases. People with translocation Down syndrome, which accounts for 3 to 4% of cases, have two copies of chromosome 21 in each cell, plus a full or partial extra chromosome 21 attached to a different chromosome. And the least common form is mosaic Down syndrome, in which a person has two copies of chromosome 21 in some cells and three copies in others.
  • This IDD occurs in people of all races, ethnicities, and economic levels.
  • Some physical features are quite common in individuals with Down syndrome. These include a face that’s flatter than typical; reduced height and muscle tone; a short neck; small hands, feet, and ears; small pinky fingers that sometimes curve toward the thumbs; a single line across the palms; a protruding tongue; slanted, almond-shaped eyes; and white spots on the irises.
  • While learning disabilities, speech and language delays, and other intellectual symptoms are common, their severity varies widely among individuals with Down syndrome. Most have mild to moderate intellectual impairment, and some children fare well in mainstream classrooms (and others do best in special education classes).
  • People with Down syndrome have their own personalities, talents, strengths, likes and dislikes, and other unique characteristics just as people without it do.
  • There’s no cure for Down syndrome. It’s a lifelong condition, but individuals with this IDD can lead happy, productive, fulfilling lives. They need varying levels of support, depending on the severity and types of symptoms they have.
  • Life expectancy for people with Down syndrome has been on the rise. While it previously had a relatively high mortality rate within the first year of life, and the average life expectancy was only 25 in 1983, today people with this condition can expect to live to at least 60 years old.

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