How common is Down syndrome?
Down syndrome is the most common chromosomal condition occurring in the human population. It occurs once in approximately every 733 live births. Down syndrome does not discriminate, and affects people of all ages, races, and economic levels. There are more than 400,000 people in the United States today living with Down syndrome.
Down syndrome is one of the most common genetic birth defects, affecting about 1 in 800 babies (1). According to the National Down Syndrome Society, there are approximately 350,000 individuals with Down syndrome in the United States (2). What causes Down syndrome? Down syndrome is caused by extra genetic material from chromosome 21. Chromosomes are the structures in cells that contain the genes. Each person normally has 23 pairs of chromosomes, or 46 in all. An individual inherits one chromosome per pair from the mother’s egg and one from the father’s sperm. When an egg and sperm cell join together, they normally form a fertilized egg with 46 chromosomes. Sometimes something goes wrong before fertilization. A developing egg or sperm cell may divide incorrectly, sometimes resulting in an egg or sperm cell with an extra chromosome number 21. When this cell joins with a normal egg or sperm cell, the resulting embryo has 47 chromosomes instead of 46. Down syndrome also is called trisomy 21
Down syndrome is the most common single cause of human birth defects. About 1 out of every 660 babies is born with Down syndrome.[1] How is it diagnosed? Down syndrome can either be diagnosed in utero (via amniocentesis) or, most commonly, after birth. After birth, it can usually be diagnosed based on distinctive physical features: • small head (microcephaly) • flat face • upward slanted eyes • single deep crease across the palm of hand, and short fingers • wide space between the big toe and second toe • hypotonia (low muscle tone) • mouth tends to stay open with tongue sticking out The baby’s blood can be tested to confirm the Trisomy 21. Where do we get started as new or expectant parents of a baby with Down syndrome? A good starting place is downloading, printing, and reading the brochure A Promising Future Together: A guide for new and expectant parents from the National Down Syndrome Society. This brochure addresses many issues including health concerns, growth and development, ea
