Importance: Reliable prevalence estimates are lacking for young-onset dementia (YOD), in which symptoms of dementia start before the age of 65 years. Such estimates are needed for policy makers to organize appropriate health care. Objective: To determine the global prevalence of YOD. Data Sources: The PubMed, Embase, CINAHL, and PsycInfo databases were systematically searched for population-based studies on the prevalence of YOD published between January 1, 1990, and March 31, 2020. Study Selection: Studies containing data on the prevalence of dementia in individuals younger than 65 years were screened by 2 researchers for inclusion in a systematic review and meta-analysis. Data Extraction and Synthesis: Prevalence estimates on 5-year age bands, from 30 to 34 years to 60 to 64 years, were extracted. Random-effects meta-analyses were conducted to pool prevalence estimates. Results were age standardized for the World Standard Population. Heterogeneity was assessed by subgroup analyses for sex, dementia subtype, study design, and economic status based on the World Bank classification and by meta-regression. Main Outcomes and Measures: Prevalence estimates of YOD for 5-year age bands. Results: A total of 95 unique studies were included in this systematic review, of which 74 with 2 760 379 unique patients were also included in 5-year age band meta-analyses. Studies were mostly conducted in Europe and in older groups in Asia, North America, and Oceania. Age-standardized prevalence estimates increased from 1.1 per 100000 population in the group aged 30 to 34 years to 77.4 per 100000 population in the group aged 60 to 64 years. This gives an overall global age-standardized prevalence of 119.0 per 100000 population in the age range of 30 to 64 years, corresponding to 3.9 million people aged 30 to 64 years living with YOD in the world. Subgroup analyses showed prevalence between men and women to be similar (crude estimates for men, 216.5 per 100 000 population; for women, 293.1 per 100 000 population), whereas prevalence was lower in high-income countries (crude estimate, 663.9 per 100 000 population) compared with upper-middle-income (crude estimate, 1873.6 per 100 000 population) and lower-middle-income (crude estimate, 764.2 per 100 000 population) countries. Meta-regression showed that age range (P <.001), sample size (P <.001), and study methodology (P =.02) significantly influenced heterogeneity between studies. Conclusions and Relevance: This systematic review and meta-analysis found an age-standardized prevalence of YOD of 119.0 per 100000 population, although estimates of the prevalence in low-income countries and younger age ranges remain scarce. These results should help policy makers organize sufficient health care for this subgroup of individuals with dementia. Study Registration: PROSPERO CRD42019119288.
Bibliographical noteFunding Information:
Funding/Support: This study was supported by the Gieskes-Strijbis Foundation, Alzheimer Netherlands, and the Dutch Young-Onset Dementia Knowledge Centre.
reported receiving grants from Gieskes-Strijbis Foundation, Alzheimer Netherlands, and Dutch Young-Onset Dementia Knowledge Centre during the conduct of the study. Dr Peetoom reported receiving grants from Gieskes-Strijbis fonds/ Gieskes-Strijbis fund, Alzheimer Netherlands, and Kenniscentrum Dementie op Jonge Leeftijd/ Knowledge Center Young-Onset Dementia during the conduct of the study. Dr Bakker reported receiving grants from Gieskes Strijbis, Alzheimer Netherlands, and Kenniscentrum Dementie op Jonge Leeftijd during the conduct of the study. Dr van der Flier reported receiving grants from ZonMW, NWO, CVON, Alzheimer Netherlands, Gieskes-Strijbisfonds, Combinostics, Fujifilm, Roche, AVID, Health–Holland, Topsector Life Sciences & Health, EU-JPND, Stichting Dioraphte, Stichting Equilibrio, Pasman Stichting, Biogen, Life-MI, Philips, Novartis NL, Neurocast, and ADX-Neuroscience outside the submitted work; has been an invited speaker at Boehringer Ingelheim, Biogen MA Inc, Danone, Eisai, and WebMD Neurology (Medscape); is a consultant for Oxford Health Policy Forum CIC, Roche, and Biogen MA Inc; served on the advisory board for Biogen MA Inc.; is associate editor at Alzheimer’s Research & Therapy; and all funding is paid to her institution. Dr de Vugt reported receiving grants from Alzheimer Netherlands, Gieskes Strijbes Fund, and Dutch Knowledge Center Young Onset Dementia during the conduct of the study. Dr Parlevliet reported coauthorship of the Cross-Cultural Dementia screening test. Dr Radford reported receiving grants from Australian National Health and Medical Research Council 510347 & 1103312 and RW & JG Fellowship in Aboriginal Health & Ageing during the conduct of the study. Dr Broe reported receiving grants from Australian National Health and Medical Research Council Chief Investigator B during the conduct of the study. Dr Smith reported receiving grants from Australian National Health Medical Research Council during the conduct of the study. Dr Subramaniam reported receiving grants from Ministry of Health Singapore and Temasek Foundation during the conduct of the study. No other disclosures were reported.
© 2021 American Medical Association. All rights reserved.