Clinical Context

Dementia is usually a disease of the old and very old, but certainly not every patient with dementia is 65 years old or older. A previous study by Kvello-Alme and colleagues, published in the May 2019 issue of the Journal of Alzheimer's Disease, examined patients referred for possible young-onset dementia (YOD) before age 65 years in a single center in Norway to assess the prevalence of early dementia.^[1]

Researchers found 390 patients with YOD and compared this group with persons without dementia in the center's catchment area. The overall prevalence of YOD was 76.3 cases per 100,000 at-risk adults between the ages of 30 to 65 years. Middle age was associated with a higher prevalence of YOD, and the respective prevalence among adults between 45 and 65 years of age was 163.1 cases per 100,000 adults.

More than half of cases of YOD were a result of Alzheimer's disease, with the next most common etiologies being frontotemporal dementia and alcohol-related dementia. There was a slight preponderance of men vs women with YOD.

These data are valuable in understanding the effect of a major illness that is frequently unrecognized, but there remains controversy regarding the prevalence of YOD. The present systematic review and meta-analysis address this issue.

Study Synopsis and Perspective

The global prevalence of YOD is significantly higher than previously thought.

Results of a large meta-analysis show that at this time, 3.9 million individuals are living with YOD. Among these patients, symptoms of the memory-robbing disease start before age 65 years.

Recent global YOD estimates have ranged from 42.3 to 54.0 per 100,000 population, the researchers note. However, the new study, which included 74 global studies with almost 2.8 million participants, shows that the global age-standardized prevalence of YOD is 119.00 per 100,000 among individuals aged 30 to 64 years; there was little difference in prevalence between men and women. On the basis of the latest population estimates, these new prevalence data imply that there are approximately 175,000 persons with YOD in the United States.

Although the new global estimate of YOD is higher than previously thought, "it is probably an underestimation owing to lack of high-quality data. This should raise awareness for policy makers and health care professionals to organize more and better care for this subgroup of individuals with dementia," the investigators, with first author Stevie Hendriks, MSc, from Maastricht University, the Netherlands, and the Young-Onset Dementia Epidemiology Study Group, write.

The study was published online July 19 in JAMA Neurology.^[2]

YOD is exceedingly rare in those aged 30 to 63 years (1.1 per 100,000) but is more prevalent at ages 60 to 64 years (77.4 per 100,000), the authors note.

"Our findings fit the general observation that prevalence of dementia increases exponentially from 60 years of age onward," they write.

The prevalence of YOD was similar in men and women, lower in the United States than in Europe, highest in upper-middle-income countries, and highest for Alzheimer's disease, followed by vascular dementia and frontotemporal dementia.

Monitoring the prevalence of YOD is "essential" to adequately plan and organize health services, the investigators note.

In addition, to ensure more accurate prevalence estimates in the future, "efforts should be made to conduct more cohort studies and to standardize procedures and reporting of prevalence studies. In addition, more data are needed from low-income countries as well as studies that include younger age ranges," they add.

In an accompanying editorial, David S. Knopman, MD, from the Department of Neurology, Mayo Clinic, Rochester, Minnesota, notes that the study provides new insights into an "underappreciated problem."^[3]

YOD is a "particularly disheartening diagnosis because it affects individuals in their prime years, in the midst of their careers, and while raising families," Dr Knopman writes.

"Most dementia care is geared for older patients, and as a consequence, services are rarely available to address the needs of someone diagnosed with dementia in their 50s who has dependent children at home and a spouse who must continue working. Understanding the prevalence and incidence of YOD is a first step in addressing this challenge," Dr Knopman adds.

He notes that the authors of this analysis have "done a service to the dementia community by collecting and analyzing the dozens of individual studies of YOD.

"The product, a rationally derived estimate of dementia prevalence across the population aged 30 to 64 years, provides a basis for initiating more efforts to improve methods for timely diagnosis and to address the unique needs of patients with YOD," Dr Knopman concludes.

JAMA Neurol. Published online July 19, 2021.

Clinical Implications

• A previous study found that the overall prevalence of young-onset dementia was 76.3 cases per 100,000 at-risk adults between the ages of 30 to 65 years. Being aged 45 to 65 was associated with a much higher rate of young-onset dementia. More than half of cases of young-onset dementia were caused by Alzheimer's disease, with the next most common etiologies being frontotemporal dementia and alcohol-related dementia.
• In the current study, the global age-standardized prevalence of young-onset dementia was 119.0 cases per 100,000 population between the ages of 30 and 64 years.
• Implications for the healthcare team: Young-onset dementia is rare, but the healthcare team should remain alert for symptoms of dementia as reported by patients or people close to them.

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