Current estimate of Down Syndrome population prevalence in the United States

Abstract

Objective: To calculate a reliable estimate of the population prevalence of Down syndrome in the US.

Study design: The annual number of births of infants with Down syndrome were estimated by applying published birth prevalence rates of Down syndrome by maternal age to US data from the Centers for Disease Control and Prevention for the years for which births by maternal age were available (1940-2008). Death certificate data for persons with Down syndrome were available for the years 1968-2007. We estimated the number of people with Down syndrome on January 1, 2008, using a life table approach based on proportions of deaths by age. Monte Carlo sampling was used to create 90% uncertainty intervals (UIs) for our estimates.

Results: We estimated the January 1, 2008, population prevalence of Down syndrome as approximately 250700 (90% UI, 185900-321700) based on proportions of deaths by age from the most recent 2 years (2006-2007) of death certificate data. This estimate corresponds to a prevalence of 8.27 people with Down syndrome per 10000 population (90% UI, 6.14-10.62).

Conclusion: Our estimate of Down syndrome prevalence is roughly 25%-40% lower than estimates based solely on current birth prevalence. The results presented here can be considered a starting point for facilitating policy and services planning for persons with Down syndrome.

Keywords: CDC; Centers for Disease Control and Prevention; UI; Uncertainty interval.

Figure 1

Birth and death estimates for the US population and persons with Down syndrome for 1909–2007. In both panels, blue corresponds to the US population and red corresponds to the population of persons with Down syndrome. Solid lines indicate 50th percentile estimates from Monte Carlo sampling for both the US and Down syndrome data. Dashed lines indicate 90% UIs; UIs are absent from the US data because they are too narrow. A, Total births by year for 1909–2008. Although the US and Down syndrome curves are mostly parallel, there is a notable dip in the births of infants with Down syndrome in the 1970s owing to fewer births among women in their 30s and 40s. Both curves show an increase in births during the 1946–1964 baby boom, followed by a decline in the 1970s. This decline was primarily among older women, possibly related to the advent of the birth control pill in 1960, which enabled them to prevent additional pregnancies. Fewer births among older women translated to even fewer births of infants with Down syndrome. B, Total deaths by year for 1900–2007. There is a spike in both populations in 1918, corresponding to the international influenza pandemic. DS, Down syndrome.

Figure 2

Mean, median, and 25th and 75th percentiles for age at death in persons with Down syndrome, 1900–2007. The mean and median age at death for persons with Down syndrome have increased significantly over the past 40 years. In 2007, the mean and median ages at death were 47.3 and 53 years, respectively, reflecting a 3.75–fold increase in average life expectancy since 1970.

Figure 3

Number of persons with Down syndrome in the US on January 1, 2008, by age. Estimates for the numbers of persons with Down syndrome alive at January 1, 2008, are plotted by their age. The solid curve indicates the 50th percentile estimate, and the dashed curves are 90% UIs (5th and 95th percentiles). There is a notable increase in the number of persons aged 35–60 years (born in 1947–1972), which can be explained by the 1946–1964 baby boom and the increased life expectancy in older individuals with Down syndrome.