Saturday, May 19, 2012

Trisomy 21 - Down Syndrome

When I started this series on the various trisomy genetic disorders, I knew this day would come. How does one even attempt to summarize Down Syndrome in a short blog post? I'll start with the disclaimer that none of my primers are intended to be all-inclusive. They're just a starting point to begin to familiarize the public at large with conditions that sometimes are quite rare and unknown. Down Syndrome doesn't really fit the unknown category, but it may fit the misunderstood category. People may think they know what Down Syndrome is, but have some serious misconceptions mixed in with their facts. My hope is this primer will make you want to learn more. Down Syndrome doesn't really fit the rare category either. Trisomy 21 is the most common single cause of birth defects, and occurs in approximately 5 of every 10,000 births. The condition is named for John Langdon Down, who described the condition in 1866. Dr. Jerome Lejeune linked Down Syndrome with an extra copy of Chromosome 21 in 1959.

Like all trisomy disorders, Down Syndrome occurs when there are three copies of one chromosome (Chromosome 21 in this case) or part of a chromosome. You can look at my general post on Trisomy to learn how this happens. It is an entirely random genetic mutation that cannot be prevented. Genetic counseling is advisable for people who have a family history of Down Syndrome, women above the age of 35, or parents who already have a child with Down Syndrome. Trisomy 21 can be diagnosed prenatally. Screening tests may indicate a higher risk for Down Syndrome and more conclusive diagnostic tests such as amniocentesis can confirm the diagnosis. These tests may carry risks of their own which should be considered carefully.

Each individual with Down Syndrome will be affected differently, but there are several common characteristics, including:
  • decreased muscle tone
  • single crease in palm of the hand
  • cognitive delays
  • impulsive behavior
  • short attention span
  • heart defects - atrial septal defect or ventricular septal defect
  • eye problems - cataracts, corrective lenses
  • gastrointestinal blockage - esophageal or duodenal atresia
  • hearing problems
  • narrow airway - sleep apnea
With improved medical treatment options, the average lifespan for individuals with Down Syndrome is nearly the same as normative peers. With early intervention and supportive family, individuals with Down Syndrome can graduate from high school, attend college, and maintain productive careers. Finally, I think I've shared this before, but I want to emphasize that each individual has something to contribute to society, and we have more in common than we may think. Please watch this short video by a young man with Down Syndrome and his parents. It is well worth your time.

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