Clinical Manifestations

The most easily recognizable features of Down syndrome derive from abnormalities in growth of the cranium and face. These include a short, relatively broad head (brachycephaly), hypoplastic maxilla, upslanting palpebral fissures, epicanthal folds, increased neck skin, small ears, and flattened nasal bridge. Common postcranial anomalies include a wide space between the first and second toe, abnormal finger and palm dermatoglyphs (in particular, the occurrence of single palmar creases), and shortened distal long bones. About 80 percent of children with Down syndrome are hypotonic and 90 percent are hyperflexible. There are also variably associated major organ anomalies, the most important being congenital heart disease (CHD), which occurs in 30 to 50 percent of all children with Down syndrome. In addition, metabolic and hormonal systems are variably affected and include, among others, carbohydrate metabolism, deficient absorption of vitamin A, elevated serum uric acid, and abnormal serotonin metabolism.

In an extensive recent survey of 1,341 children with Down syndrome born between 1952 and 1981 in British Columbia, Patricia Baird and Adel Sadovnick (1987) reported survival rates up to 30 years of age in 50 percent for those with CHD, but nearly 80 percent for those without CHD. The survival rate for the latter group, however, was less than that for a comparison group of mentally retarded individuals without Down syndrome.

Children with Down syndrome experience abnormal physical and cognitive development. Birth weight and length are near normal, but the growth rate in the first 3 years of life is significantly slower than normal, and most children are less than the fifth percentile in height by the time they are 3 years of age. Growth rate during childhood is near normal, but the adolescent growth spurt is often absent (Cronk et al. 1988). Deficient growth differentially affects distal segments of the long bones. Whereas some early developmental milestones are normal, more marked delays in walking, talking, and other motor and cognitive skills usually become apparent by the end of the first year of life. Mild to moderate mental retardation (IQ: 30 to 67) is commonly present by childhood. Recent innovations in early intervention and new special education programing allow individuals with Down syndrome to hold jobs as adults in sheltered work situations.

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