Down's syndrome

Down's syndrome, formerly called mongolism, chromosomal aberration resulting in mental retardation and physical abnormalities. In about 95% of cases of Down's syndrome, there is an extra chromosome 21, making 3 in all, hence its technical name trisomy 21. The overall incidence is about 1 in every 700 live births, but there is a marked variability depending on maternal age: In the early childbearing years, the incidence is about 1 in every 2,000 live births; for mothers over age 50, it rises to about 1 in every 45 live births. The cause of this genetic disorder is unknown. Infants tend to be placid, rarely cry, and have flabby muscles. Physical and mental development are both retarded and the mean IQ is about 50. Down's syndrome children have smaller than average heads and moon-shaped faces. Their eyes are slanted, usually with epicanthal folds above the eyelids. The bridges of their noses are flattened, and their mouths are often held open because of their large, protruding, furrowed tongues. Their hands are short and broad, with a single crease across the palm, and short fingers. Their feet have wide gaps between the first and second toes, and there is a furrow on each sole. The life expectancy of these children is decreased by heart disease and by susceptibility to acute leukemia. Most of those without a major defect survive to adulthood, but the aging process seems accelerated, with death occurring in their 40s and 50s.