Background: While medical advancements and increased awareness have improved the life expectancy of individuals with Down syndrome (DS), studies on cohort-specific differences in mortality risk and long-term survival outcomes among individuals with DS remain limited. We assessed cohort differences in survival probabilities and mortality risk among individuals with DS born 1967–2018, using Norwegian national registry data.

 

Methods: Utilizing the Medical Birth Registry of Norway linked with additional registries, we included 3,014,455 eligible individuals. Kaplan–Meier survival curves and mortality rates were employed to examine birth cohort differences in survival probability between individuals with DS and the rest of the population up to age 40 years. A flexible parametric survival model was used to identify mortality risk factors among individuals with DS.

Results: Among 3,014,455 individuals, 3,484 (1.2 per 1000) were diagnosed with DS. Across birth cohorts, the most significant survival gap occurred in early childhood (less than 5 years) when compared to individuals without DS. Mortality rates for individuals with DS were consistently higher than the rest of the population across all birth cohorts. In analyses of follow-up birth to age 40 years, individuals born from 1967 to 1976 demonstrated the highest mortality risk (HR: 6.35) followed by those born from 1977 to 1986 (HR: 3.83) and from 1987 to 1996 (HR: 2.31) compared to those born between 2007 and 2018. Low birth weight (< 2,500 g) was associated with increased mortality risk (HR: 1.47) compared to those born with birth weight of 2500 g or more. Individuals born into households with income below the median showed a higher mortality risk (HR: 1.41) compared to those from higher-income households. Having one or more siblings also correlated with increased mortality risk (HR: 1.46) compared to having none. In sub-analyses restricted to follow-up from birth to five years, birth year remained a significant predictor of mortality risk for individuals with Down syndrome (DS). Compared with those born between 2007 and 2018, highest mortality risk was observed for births from 1967 to 1976 (HR: 6.18), 1977 to 1986 (HR: 3.61), and 1987 to 1996 (HR: 2.06). Low birth weight (HR: 1.66) and having one or more siblings (HR:1.56) was also showed a greater mortality risk. For the follow-up period from ages 6 to 40 years, those born into lower-income households experienced increased mortality risk (HR: 2.16).

Conclusions: This study found that individuals with DS experience significantly lower survival, particularly (with the largest gap) in early childhood. Being born in earlier birth cohort, low birth weight, lower household income, and having siblings were associated with higher mortality risk among individuals with DS. These findings underscore the need for targeted interventions (and support) to improve survival outcomes for individuals with DS.

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