Young Onset Dementia Affects Almost 4 Million Worldwide

The global age-standardized prevalence of young-onset dementia (YOD; ages 30 to 64) was 119.0 per 100,000 population, a meta-analysis found.

“Using the United Nations world population of 2019, this projects to 3.9 million people aged 30 to 64 years living with YOD worldwide,” wrote Sebastian Köhler, PhD, of Maastricht University in the Netherlands, and colleagues from the Young-Onset Dementia Epidemiology Study Group in JAMA Neurology.

“Age-standardized prevalence was lower in the U.S. than in Europe, similar in women and men, highest in upper–middle-income countries, and highest for Alzheimer’s disease (AD), followed by vascular dementia and frontotemporal dementia,” they added. “Register based studies reported lower prevalence estimates than cohort studies.”

However, “estimates of the prevalence in low-income countries and younger age ranges remain scarce,” they acknowledged.

Köhler and colleagues included 95 studies from PubMed, Embase, CINAHL, and PsycInfo databases published between January 1990 and March 2020. Meta-regression identified age range, sample size, and methodology-influenced heterogeneity between studies.

Most studies were from Europe, Asia, North America, and Oceania. Studies included those reporting on the prevalence of AD (n=20), vascular dementia (n=13), and frontotemporal dementia (n=12). Studies on Lewy body and Parkinson’s disease dementia (n=4) and alcohol-related dementia (n=3) were not included in the meta-analysis.

Age-standardized prevalence estimates increased from 1.1 per 100,000 population in the group 30-34 years old to 77.4 per 100,000 population in the group 60-64 years old. Prevalence per 100,000 in the other brackets was 1.0 for ages 35-39; 3.8 for ages 40-44; 6.3 for ages 45-49; 10.0 for ages 50-54; and 19.2 for ages 55-59.

Subgroup analyses for YOD in the global population showed:

• Similar prevalence for men and women (crude estimates for men and women were 216.5 versus 293.1 per 100,000, respectively).
• Lower prevalence in high-income versus upper-middle and lower-middle income countries (crude estimates per 100,000 of 663.9, 1,873.6, and 764.2, respectively).
• Prevalence was highest per 100,000 for AD (41.1), followed by vascular dementia (14.9) and frontotemporal dementia (2.3).

Despite the highest prevalence for AD overall, for lower age ranges — until age 50 — vascular dementia prevalence was highest, followed by frontotemporal dementia and AD, the authors said. “However, these analyses were based on few studies, so interpreting these prevalence estimates with caution is warranted,” they wrote.

“The major take-home message of this analysis of all-cause dementia in the age range of 30 to 64 years is that YOD is about one-twentieth as common as [late-onset dementia] LOD and that most cases occur from 45 to 64 years of age,” noted David Knopman, MD, of Mayo Clinic in Rochester, Minnesota, in an accompanying editorial. “In the age range 30 to 44 years, dementia is exceedingly rare. The prevalence of YOD worldwide is consistent across continents, with the caveat that Africa and parts of Asia are represented sparsely in the meta-analysis.”

“At one time in the not-too-distant past, [YOD] was considered a disease, whereas later-onset dementia (LOD) was considered the inevitable consequence of aging,” Knopman added. “We now reject such a formulation, but within that misguided dichotomy is a recognition of the dramatic differences in prevalence and incidence of YOD compared with LOD.”

The most referenced studies on the prevalence of YOD report estimates from 42.3 to 54.0 per 100,000 population, Köhler and co-authors noted. “People with YOD were identified retrospectively with a register-based approach, so underreporting was likely,” they wrote.

Both identifying and accurately diagnosing YOD is more difficult than it is for LOD. “The rarity of prevalent dementia in younger patients makes traditional case finding by active surveillance prohibitively expensive,” Knopman observed. Epidemiological case finding relies heavily on passive surveillance methods, including medical record reviews, he noted.

“The acknowledged disadvantage of passive surveillance for dementia is the lack of control of diagnostic methods across numerous clinicians, raising the possibility of undercounting or overcounting cases owing to misdiagnosis (e.g., YOD as a psychiatric disorder or vice versa) or of noncontact by the young patient with dementia with the medical system,” Knopman wrote.

In the present study, Köhler and colleagues also reported YOD prevalence rates for a standardized European population (159.4 per 100,000) and United States population (114.7 per 100,000).

The reported difference in prevalence estimates “is owing to a difference in the age structure of the populations, rather than a difference in the risk of YOD,” Köhler and colleagues wrote. “Because the prevalence of YOD increases with age, prevalence of YOD is higher in the older European Standard Population than the younger World Standard Population and United States Standard Population. Unfortunately, we lacked data for age standardization for other parts of the world.”

“A clear definition of YOD is lacking, and our cutoff at 65 years of age remains arbitrary,” the authors acknowledged. “According to the World Alzheimer Report, only one-third to one-half of the people living with dementia receive a routine clinical diagnosis. Hence, the reported estimates should be seen as a lower boundary of the true young onset dementia prevalence.”

Other limitations include limited information on dementia associated with Parkinson’s disease, Lewy body dementia, and ethnicity, which were not included in the analysis.

1. The global age-standardized prevalence of young-onset dementia (ages 30 to 64) was 119.0 per 100,000 population, a meta-analysis found.

2. Age-standardized prevalence was lower in the U.S. than in Europe, similar in women and men, highest in upper–middle-income countries, and highest for Alzheimer’s disease, followed by vascular dementia and frontotemporal dementia.

Paul Smyth, MD, Contributing Writer, BreakingMED™

Cat ID: 130

Topic ID: 82,130,730,130,33,361,192,925