New study highlights global prevalence of young-onset dementia

A new systematic review and meta-analysis presented at AAIC 2021 has hinted at a high prevalence of young-onset dementia (YOD) worldwide.

“Our findings should raise awareness in healthcare professionals, researchers, and policy makers because they show that a significant number of people are newly affected by YOD every year,” said study author Stevie Hendriks, MSc, from Maastricht University, Maastricht, the Netherlands.

The authors conducted a systematic search of observational population studies on YOD incidence and prevalence published between January 1990 and March 2020. Of the 95 studies in the systematic review, 74 studies, comprising 2,760,379 individuals, were included in the meta-analysis. The studies were primarily from Europe with a few among older age groups from North America, Asia, and Oceania.

The age-standardized prevalence rate of YOD, where onset of dementia occurs before age 65 years, increased from 1.1 per 100,000 population among those aged 30–34 years to 77.4 per 100,000 population among those aged 60–64 years. This corresponded to an overall global age-standardized prevalence rate of 119.0 per 100,000 population aged 30–64 years. [AAIC 2021, abstract 50895; JAMA Neurol 2021;doi:10.1001/jamaneurol.2021.2161]

The age-standardized prevalence rate differed by location, with a rate of 159.4 and 114.7 per 100,000 population in Europe and the US, respectively.

The results translated to 3.9 million people aged 30–64 years living with YOD globally, of whom 0.5 million live in Europe and 200,000 live in the US. An estimated 350,000 people develop YOD globally every year.

“Pooled analyses within 5-year age bands showed an increased prevalence with age,” said the authors. “[However, the overall prevalence] is probably an underestimation owing to lack of high-quality data.”

The authors noted substantial between-study heterogeneity, with meta-regression analysis showing that age range (p<0.001), sample size (p<0.001), and study methodology (p=0.02) significantly influenced heterogeneity.

In subgroup analysis, YOD prevalence did not differ between men and women (crude estimate 216.5 vs 293.1 per 100,000 population).

In the 60–64-years age band, YOD prevalence was lower in high-income countries* compared with upper-middle-income and lower-middle-income countries (crude estimate 663.9, 1873.6, and 764.2 per 100,000 population, respectively).

The age-standardized prevalence of Alzheimer’s disease was 41.1 per 100,000 population worldwide, with 54.1 and 31.8 per 100,000 population in Europe and the US, respectively. The age-standardized prevalence of vascular dementia was 14.9 per 100,000 population worldwide, 19.5 and 14.3 per 100,000 population in Europe and the US, respectively. The age-standardized prevalence of frontotemporal dementia (FTD) was 2.3 per 100,000 population worldwide, 2.9 and 2.3 per 100,000 in Europe and the US, respectively.

According to the authors, FTD is often underdiagnosed or misdiagnosed, suggesting the prevalence here may be underestimated. In general, no conclusions can be drawn on the dementia subtypes due to lack of pathological data.

More research needed in this important group

“YOD is a particularly disheartening diagnosis because it affects individuals in their prime years, in the midst of their careers, and while raising families. [Furthermore,] most dementia care is geared for older patients,” said Dr David Knopman from Mayo Clinic, Rochester, Minnesota, US, in an editorial. “Understanding the prevalence and incidence of YOD is a first step in addressing this challenge,” he said. [JAMA Neurol 2021;doi:10.1001/jamaneurol.2021.1760]

“This [study] shows the need for investment in tailored healthcare for this special patient group and more research into how we can best support but also prevent and treat YOD,” Hendriks pointed out.

The authors called for further study into determining the sex differences in the prevalence of various YOD subtypes. Insufficient data prevented determination of difference in prevalence by ethnicity, also a potential subject for future research.

“[M]ore data are needed from low-income countries as well as studies that include younger age ranges,” they said. “[E]fforts should [also] be made to conduct more cohort studies and to standardize procedures and reporting of prevalence studies.”

“The major take-home message of this analysis … is that YOD is about one-twentieth as common as late-onset dementia and that most cases occur [at age 45–64 years],” said Knopman.