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Down Syndrome (Trisomy 21)

Down syndrome is a condition in which a baby is born with an extra chromosome. Chromosomes are small “packages” of genes in the body. They determine how a baby’s body forms during pregnancy and how, as the baby grows in the womb and after birth, the baby’s body functions. Normally, a baby is born with 46 chromosomes. Babies born with Down syndrome have an extra copy of one of these chromosomes. This extra copy changes the body’s and brain’s normal development and causes developmental and physical problems for the baby.

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This effort is supported by funding from the U.S. Centers for Disease Control and Prevention Environmental Public Health Tracking Program, Cooperative Agreement Number 5U38EH000619-02. The contents of this Website are solely the responsibility of the authors and do not necessarily represent the official views of the Centers for Disease Control and Prevention.