Down Syndrome Abstract
of the Month: May 2002
Mortality associated with Down's syndrome in the USA from 1983 to 1997: a population-based study.
Yang Q, Rasmussen SA, Friedman JM.
Lancet 2002 Mar 23;359(9311):1019-25
National Center on Birth Defects and Developmental Disabilities, Centers for Disease Control and Prevention, Atlanta, GA, USA.
Abstract:
BACKGROUND: 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. METHODS: 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. FINDINGS: Of 17,897 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. 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, dementia, hypothyroidism, or leukaemia 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. 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. INTERPRETATION: 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.
My comments: There are some inherent difficulties in this kind of study. A study based on death certificates reflects the attending physician's opinion and may not be complete or accurate. Also, assuming the birth rate in the US of live babies with DS is approximately 1 in 1000 (based on a previous study) and that birth rate equals death rate, then this study would have only reported about 60% of the expected deaths of people with DS. However, this study does give us some very interesting information.
Median age of death (not the average age) was 25 years in 1983 and 49 years in 1997. The biggest change was a large decrease in the number of children with DS dying under 5 years of age, which occurred in the early 1990s. The change in median age of death could be due to a number of factors, such as de-institutionalization of children with DS; but the change may most likely be due to increased access to medical care, especially cardiac surgery.
For children under 10 years of age, the presence of a congenital heart defect made a significant difference in higher mortality rates. This difference greatly decreased in the early 1990s, but still persists.
In people with DS over 30 years, respiratory infections such as influenza and pneumonia were most often cited on the death certificates, along with aspiration. Dementia was often cited in the 40 to 60 year range.
Racial distribution of the death certificates was 87% white, 11% black, and 2% others, which corresponded very well to the racial breakdown of all US death certificates for that period. There were significant differences in the median age of death between the white and black groups, as was reported widely in the news media in March of this year. The reasons for these differences aren't known, but could be influenced by access to insurance and/or health professionals.
Children with DS under 10 years of age were over 3 times more likely to have leukemia listed as a diagnosis on the death certificate than those children without DS. This association decreased with age until 40 years of age, when the association disappeared completely. The only solid tumor that showed up greater than the general population was testicular cancer, mostly in the 20 to 39 year age range. For al other tumors, there were significantly fewer occurrences than in the general population, which corresponds to previous statistical studies on cancer and people with DS.