TRISOMY 21 - A congenital condition which is characterized by moderate to severe mental retardation, slanting eyes, a broad short skull, broad hands, and short fingers. Other congenital abnormalities include heart defects, esophageal atresia, and an increased incidence of acute lymphocytic leukemia. All of these findings are secondary to trisomy (an extra chromosome) of the 21st chromosome. Trisomy 21 can be detected in the first few months of pregnancy by amniocentesis. Risk factors include prior Down's child and mothers who become pregnant after age 40.