Sex differences in the incidence and prevalence of young‐onset Alzheimer's disease: A meta‐analysis

OBJECTIVES: The lifetime incidence of Alzheimer's disease is higher in women than in men, but it remains unclear if similar sex differences exist in young‐onset Alzheimer's disease (YOAD). This systematic review test the hypothesis that women have a higher prevalence and incidence of YOAD than men. METHODS: We searched Pubmed and Embase (inception to 11 June 2020) for original publications of population‐based observational studies with data on the prevalence and/or incidence of YOAD, defined as a medical diagnosis of Alzheimer's disease before the age of 65 years. Data on cross‐sectional and/or prospective numbers, percentages, incidences, and incidence rates (in person‐years) were derived from included studies. Quality assessment was done using the Nottingham Ottawa Scale. Meta‐analyses were done to test the hypothesis that women have a higher prevalence and incidence of YOAD than men. RESULTS: After screening of 3252 titles, 12 articles were included. The pooled prevalence was 0.4% (confidence interval [CI] = 0.1–2.1) in women and 0.2% (CI = 0–1.2) in men (six studies, relative risk [RR] = 1.54, CI = 0.69–3.44, I (2) = 38%). The pooled incidence was 0.02% (CI = 0.01–0.08) in women and 0.01% (CI = 0–0.05) in men (five studies, RR = 1.50, CI = 0.91‐2.48, I (2) = 0%). The incidence rates per 100,000 person‐years ranged from 0 to 132 in women and from 0 to 42 in men. CONCLUSIONS: Given the low prevalence and wide CIs, no firm conclusions can be drawn. Large‐scale studies are required to verify that women are more likely than men to develop YOAD.