Introduction
The life expectancy of a person with Down syndrome has significantly increased. In 1900, the life expectancy of a person with Down syndrome was around 9 years. By 1950, that had increased to around 26 years. By 1983, the life expectancy was 28 years, and by the mid-2010s, it increased further to 53 years. Today, the life expectancy for white adults with Down syndrome living in the United States is around age 60 years.[1][2][3][4] Thus, in the last 40 years, life expectancy has more than doubled.
Although there has been significant improvement in overall life expectancy, there are still racial and ethnic differences. Fortunately, these disparities appear to be decreasing. For individuals with Down syndrome who are non-Hispanic blacks or American Indians/Alaska natives, the mean life expectancy in 1950 was 22 years (compared to 26 years in non-Hispanic whites, Hispanics, and Asian/Pacific Islanders). The median life expectancy in 1950 for individuals with Down syndrome who were non-Hispanic blacks or American Indians/Alaska natives was 2 years (compared to 4 years in non-Hispanic whites, Hispanics, and Asian/Pacific Islanders).[5] In 2010, the mean life expectancy for non-Hispanic blacks or American Indians/Alaska natives was 50 years (compared to 54 years in non-Hispanic whites, Hispanics, and Asian/Pacific Islanders).[5] The median life expectancy in 2010 for individuals with Down syndrome who were non-Hispanic blacks or American Indians/Alaska natives was 57 years (compared to 58 years in non-Hispanic whites, Hispanics, and Asian/Pacific Islanders).[5] These between-group differences in life expectancy are attributed to differences in childhood survival, and they are decreasing.[5]
The increase in life expectancy across all ethnic groups is largely attributed to advances in treatments for congenital heart disease and improvements in general health.[2] Approximately 50% of infants with Down syndrome are born with congenital heart disease.[6] Open heart surgery to treat congenital heart defects became available in the 1960s and 1970s.[7] However, infants and children with Down syndrome and congenital heart disease were not initially offered these surgeries. Over time, societal attitudes changed such that these children were referred for surgery, and it was found that they tolerated the surgeries well.[7] It is now standard of care to offer surgical repair to children with congenital heart disease and Down syndrome who otherwise meet criteria for surgery.[7] In fact, up to 10% of all children undergoing cardiac surgery have Down syndrome.[7] Surgical correction has markedly reduced the mortality related to congenital heart disease and increased overall life expectancy.[6][8]
While the life expectancy of individuals with Down syndrome has dramatically increased, it appears to now be leveling off. The most significant contributor to this plateau appears to be Alzheimer’s disease.[9] Individuals with Down syndrome are disproportionately affected by Alzheimer’s disease and are impacted at younger ages. Most (>90%) will have symptomatic disease by their 60s, whereas in individuals aged 65 and older without Down syndrome, only 11% of women and 9% of men are affected.[10][11] The average age of diagnosis of Alzheimer’s disease in individuals with Down syndrome is approximately 55 years, whereas in the non-Down syndrome population, symptoms typically begin in the mid-60s or later.[12] Alzheimer’s disease is fatal, and there are currently no medications proven to stop, slow, or prevent it in individuals with Down syndrome.[10] It seems that life expectancy in this population will not increase until new approaches to treating Alzheimer’s disease are developed.[9]
As the life expectancy of individuals with Down syndrome has increased, the number of people living with Down syndrome has also risen. In the United States, there has been a four-fold increase in the Down syndrome population between 1950 and 2010, from 49,923 to 206,366. At the same time, the total US population only doubled, from 151,325,798 to 308,745,538.[13] The number of persons aged 20 and above with Down syndrome also increased sevenfold during that same period, from 13,368 to 117,763. As of 2008, Down syndrome is no longer considered a “rare disease”, which is defined in the United States as affecting less than 200,000 people.[5]
Besides an increase in adults living with Down syndrome, in the United States the live birth prevalence of Down syndrome is rising.[5] While the availability of prenatal testing has led to an increase in selective pregnancy termination, this has been counteracted by the effect of increasing maternal age, which greatly increases the chance of having a pregnancy with a fetus with Down syndrome.[5] As such, the live birth prevalence of Down syndrome in the United States has increased from 1 in 990 in 1980, to 1 in 813 in the 2000’s and 1 in 775 in 2018.[5]
The population growth for different ethnic groups in the US varies. Population growth is the largest in Asian/Pacific Islanders and Hispanics.[5] Population data are also available for Europe, New Zealand, and Australia.[14][15] While the proportion of individuals with Down syndrome is increasing in the US and Australia, other countries are seeing a decrease, which is attributed to prenatal testing and selective pregnancy termination.