Genetic Disorders and the Fetus. Группа авторов

A later report from the Paris Registry of Congenital Anomalies (2001–2005) noted a “fairly stable prevalence of Down syndrome (7.1 per 10,000 livebirths) over time.”¹¹¹ A Scottish study aimed to assess the impact of prenatal diagnosis on the prevalence of Down syndrome from 1980 to 1996. Both births and pregnancy terminations were included. Pregnancy terminations for Down syndrome rose from 29 percent to about 60 percent.¹¹² In contrast, the prevalence of Down syndrome noted by the Dutch Paediatric Surveillance Unit in 2003 was 16 per 10,000 livebirths, exceeding earlier reports and thought to reflect an older maternal age cohort.¹¹³ In the United States, a prevalence rate of 8.27 per 10,000 was reported in 2013 with an estimated 250,700 individuals.^{114, 115} In Europe, the 2009–2012 prevalence rate was 10.2 per 100,000 livebirths.¹¹⁶ In Japan, the estimated prevalence rate approximates 22 per 10,000 births.¹¹⁷ Many more babies with Down syndrome are born to women under rather than over 35 years of age. There is some evidence that the risk of having Down syndrome offspring in very young mothers is increased,^118–121 but not in twin pregnancies.¹²²

The special problems and associated defects in Down syndrome are well known, as is the increasing life expectancy. Studies from Japan,¹²³ Denmark,¹²⁴ England,¹²⁵ Australia,¹²⁶ and Canada¹²⁷ highlight the increased life expectancy with Down syndrome. Baird and Sadovnick¹²⁷ reported a large study of 1,610 individuals with Down syndrome identified in more than 1,500,000 consecutive livebirths in British Columbia from 1908 to 1981. They constructed survival curves and a life table for Down syndrome (Table 1.2) and for the general population.¹²⁸ Their estimates show that 44.4 percent and 13.6 percent of liveborn individuals with Down syndrome will survive to 60 and 68 years, respectively, compared with 86.4 percent and 78.4 percent of the general population. In another report,¹²⁹ the authors have analyzed the causes of death in Down syndrome, highlighting congenital defects and cardiovascular and respiratory illnesses as the most important. A UK population prevalence study noted a median life expectancy of 58 years in 2011.¹³⁰

Table 1.2 Life expectancy with Down syndrome, between 1908–1981, to age 68 years.

Age	Total	Survival at start of age interval (percent)
5	1,020	81.05
10	841	78.40
20	497	75.34
30	91	72.12
40	136	69.78
50	57	60.68
55	31	53.96
60	16	44.44
68	1	13.57

      Source: Baird and Sadovnick 1989.¹²⁷ With permission from John Wiley and Sons.

      Additional studies of mortality rates in individuals with Down syndrome revealed that those up to about 35 years of age were little different from others with intellectual disability. Thereafter, however, mortality rates in Down syndrome doubled every 6.4 years, compared with 9.6 years for other intellectually disabled individuals.¹²⁹ Life tables constructed by these authors indicated a life expectancy of 55 years for a 1‐year‐old patient with Down syndrome and mild/moderate developmental delay and a life expectancy of 43 years for a 1‐year‐old patient with Down syndrome more profoundly affected.

A study from the CDC focused on the death certificates of 17,897 individuals with Down syndrome born between 1983 and 1997.¹³¹ These authors reported that the median age at death for those with Down syndrome increased from 25 years in 1983 to 49 years in 1997 (Figure 1.2).

Figure 1.2 Median age at death of people with Down syndrome by sex (upper), by racial group (middle), and with or without congenital heart defects (CHD) by racial group (lower).

      Source: Yang et al. 2002.¹³¹ Reproduced with permission of Elsevier.

      A 2009 Australian study found an overall survival figure for Down syndrome of 90 percent to at least 5 years of age.¹³² The known comorbidities of Down syndrome^{116, 133–149} and earlier onset Alzheimer disease¹³³ cast a longer shadow. In individuals with Down syndrome over 40 years of age, increasing neuropsychological dysfunction and loss of adaptive skills have been noted.¹⁴⁹ Between 50 and 70 percent develop Alzheimer disease by 60 years of age,¹³⁹ and up to 84 percent of those with dementia develop seizures.¹³⁶ People with Down syndrome who are APOEε4 carriers and/or have multiple comorbid disorders are at an increased risk of both dementia and death.¹⁵⁰ A French study between 1979 and 1999 found a sixfold decreased risk of death from urological cancer in those with Down syndrome.¹⁴⁶ People with Down syndrome have an overall decreased incidence of solid tumors.¹⁵¹

Table 1.3 reflects the common associated defects and complications that occur in Down syndrome, some of which can be anticipated, monitored, prevented, and treated.^132–165 A EUROCAT population‐based register study between 2000 and 2010 in 12 countries analyzed 7,044 livebirths and fetal deaths with Down syndrome. That report¹⁵² noted that 43.6 percent of births with Down syndrome had congenital heart disease while 15 percent had another congenital malformation. The National Society of Genetic Counselors published valuable guidelines for communicating both prenatal and postnatal diagnoses of Down syndrome.¹⁶⁶

Table 1.3 Defects and complications associated with Down syndrome^132–165.

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Defect or complication	Prevalence (percent)
Neurologic
Intellectual disability	100
Hypotonia	100
Alzheimer disease and dementia	68–80
Sleep disorders	65
Autism	7–16