Mortality associated with Down's syndrome in the USA from 1983 to 1997: a population-based study

Down's syndrome is the most frequently identified cause of mental retardation, but information about mortality and comorbidity in people with Down's syndrome is limited.

We used data from US death certificates from 1983 to 1997 to calculate median age at death and standardised mortality odds ratios (SMORs) for common medical disorders in people with Down's syndrome.

Of 17897 people reported to have Down's syndrome, median age at death increased from 25 years in 1983 to 49 years in 1997, an average increase of 1.7 years per year studied (p<0.0001). Median age at death was significantly lower in black people and people of other races than in white people with Down's syndrome. As expected, death certificates with a diagnosis of Down's syndrome were more likely to list congenital heart defects (SMOR 29.1, 95% CI 27.8-30.4), dementia (21.2, 19.6-22.7), hypothyroidism (20.3, 18.5-22.3), or leukaemia (1.6, 1.4-1.8) than were those that did not report Down's syndrome. By contrast, malignant neoplasms other than leukaemia were listed on death certificates of people with Down's syndrome less than one-tenth as often as expected (0.07, 0.06-0.08). A strikingly low SMOR for malignancy was associated with Down's syndrome at all ages, in both sexes, and for all common tumour types except leukaemia and testicular cancer.

Identification of factors responsible for the racial differences recorded could facilitate further improvement in survival of people with Down's syndrome. Reduced exposure to environmental factors that contribute to cancer risk, tumour-suppressor genes on chromosome 21, or a slower rate of replication or higher likelihood of apoptosis in Down's syndrome cells, could be possible reasons for paucity of cancer in people with Down's syndrome.