Physical characteristics of a person with Down's syndrome include small and short head, flat nasal bridge, reddish cheeks, dry lips, large, protruding tongue, small ears, epicanthal folds, and short neck. Mental retardation and hypotonia are also major symptoms, the degree of which varies with individuals. There is also a high incidence of congenital heart diseases and duodenal atresia. With good support, persons with this syndrome can develop their full potential. An Alzheimer-like dementia often occurs in the fourth and fifth decades and leads to a shortened life expectancy. The chromosomal abnormality is diagnostic. In 95% of cases, trisomy 21 is present (one extra chromosome 21), and in the rest which has the usual 46 chromosomes present, there is an abnormal translocation involving chromosome 21.