Doubling Of Life Expectancy Over Past Two Decades For People With Down’s Syndrome
A US population study in this week’s issue of THE LANCET reports how life expectancy of people with Down’s syndrome has doubled since the early 1980s. The study also highlights the unexpected finding that Down’s syndrome appears to reduce the risk of many forms of cancer.
Down’s syndrome (characterised by three copies of chromosome 21) occurs in around one in every 800 live births. It is the most frequently identified cause of mental retardation, but information about illness and causes of death in people with Down’s syndrome is limited. Quanhe Yang and colleagues from the Centers for Disease Control and Prevention, Atlanta, USA, used data from US death certificates from 1983 to 1997 to calculate the average age at death and standardised mortality odds ratios (SMORs) for common medical conditions in around 17,900 people with Down’s syndrome.
Life expectancy almost doubled from 1982 to 1997, the average age at death increasing from 25 to 49 years. People from non-white races were more likely to die younger than white people with Down’s syndrome. There were substantially increased SMORs for characteristic Down’s syndrome disorders including congenital heart defects, dementia, hypothyroidism, and leukaemia. By contrast, cancers other than leukaemia and testicular cancer were listed on death certificates of people with Down’s syndrome less than one-tenth as often as expected.
Quanhe Yang comments: “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 [programmed-cell death] in Down’s syndrome cells, could be possible reasons for paucity of cancer in people with Down’s syndrome.”
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