Down syndrome [John L. Down, English physician, 1828–1896] , a congenital condition characterized by varying degrees of cognitive impairment and multiple defects. It is the most common chromosomal abnormality of a generalized syndrome and is caused by the presence of an extra chromosome 21 in the G group or, in a small percentage of cases, by the translocation of chromosome 14 or 15 in the D group and chromosome 21 or 22. Down syndrome occurs in approximately 1 in 600 to 650 live births and is associated with advanced maternal age, particularly over 35 years of age. The incidence is as high as 1 in 80 for offspring of women above 40 years of age. In cases caused by translocation, which is a genetic aberration that is hereditary rather than a chromosomal aberration caused by nondisjunction during cell division, the incidence is not associated with maternal age. The condition can be diagnosed prenatally by amniocentesis. A mosaic variant, in which there is a mixture of trisomy 21 and normal cells, causes fewer physical defects and less severe cognitive impairment, depending on the degree of mosaicism. Also called trisomy 21. See also nondisjunction. ▪ OBSERVATIONS: Infants with the syndrome are small and hypotonic, with characteristic microcephaly, brachycephaly, a flattened occiput, and typical facies with a characteristic slant to the eyes, depressed nasal bridge, low-set ears, and a large, protruding tongue that is furrowed and lacks a central fissure. The hands are short and broad with a transverse palmar or simian crease; the fingers are stubby and show clinodactyly, primarily of the fifth finger. The feet are broad and stubby with a wide space between the first and second toes and a prominent plantar crease. Other anomalies associated with the disorder are bowel defects, congenital heart disease (primarily septal defects), chronic respiratory infections, visual problems, abnormalities in tooth development, and susceptibility to acute leukemia. ▪ INTERVENTIONS: The health care problems that affect physical health must be addressed. However, other issues can affect social and school success. A coordinated team approach will assist the individual with Down syndrome, and the caregivers, to achieve a maximal level of function and the best quality of life possible. ▪ PATIENT CARE CONSIDERATIONS: The most significant feature of the syndrome is cognitive impairment which varies considerably. The average IQ is in the range of 50 to 60, so that the child is generally trainable and in most instances can be reared at home. The mortality rate is high within the first few years, especially in children with cardiac anomalies. Those who survive tend to be shorter than average and stocky in build; they show delayed or incomplete sexual development and can live to middle or old age, although adults with Down syndrome are prone to respiratory infections, pneumonia, and lung disease.
