ABSTRACT
DEFINITIONS AND CLINICAL FEATURES Down syndrome is the condition of duplication of the 21st chromosome or a translocation at this site and is also referred to as trisomy 21. The incidence of this condition is 1/700 live births making it the most
common birth condition in the United States. In fact, some studies show that an increasing prevalence may be occurring in this country, especially in women over the age of 35.
