What Is Down Syndrome?

People with Down syndrome have 47 chromosomes instead of the usual 46. The most common form, in which faulty cell division causes a baby to receive three chromosomes instead of two on the 21st chromosome pair, is known as Trisomy 21. But all forms of Down syndrome involve having all or part of an extra 21st chromosome in some or all of a person's cells. Down syndrome occurs in about one in 733 births.

· Forty percent of children with Down syndrome have congenital heart defects. They also have a higher incidence of respiratory, vision and hearing problems and are at increased risk of Alzheimer's disease, childhood leukemia and thyroid conditions.

· The life expectancy of people with Down syndrome has increased from 25 years in 1983 to 55 years, thanks largely to medical and technological advances, particularly in the ability to repair congenital heart defects.

· All people with Down syndrome have intellectual disabilities and developmental delays, but the range of disability can vary from mild to severe.

· The number of births of Down syndrome children has declined by 8 percent since 1989, and the number is expected to decline further after a recommendation last year by the American College of Obstetricians and Gynecologists that all mothers undergo screening for Down syndrome.

· The incidence of birth of children with Down syndrome increases with a mother's age. But because of the higher fertility rate of younger women and previous guidelines that younger women did not need screening, 88 percent of children born with Down syndrome are born to women under 35.

· Eighty percent of pregnant women who receive a definitive prenatal diagnosis of Down syndrome choose to terminate their pregnancies.

SOURCE: National Down Syndrome Society; National Association for Down Syndrome; Dr. Brian Skotko, co-author "Common Threads: Celebrating Life With Down Syndrome" and pediatrician at Children's Hospital of Boston.