Variation in the reported prevalence of Huntington's disease: a systematic review and guide to interpretation.

There is significant variation in the reported estimates of Huntington's disease (HD) prevalence in different settings. This systematic review was undertaken to describe and assess the sources of heterogeneity in estimated prevalence values, and to consider the role of quantitative synthesis in the context of such heterogeneity. Observational studies from which a prevalence estimate (point or period) or cumulative incidence of HD could be calculated between 1993 and 2024 were sought from Medline and Embase databases. The study features are described and the sources of heterogeneity are discussed. A meta-regression was conducted including predictor variables: continent, median age of population, number of years since 1993, case ascertainment method, and Healthcare Access and Quality Index score. 43 studies met the inclusion criteria. Significant clinical and methodological heterogeneity between studies is described, including differences in case definitions and ascertainment methods, and in the estimates of disease burden calculated. There were differences in the estimated point prevalence between regions and populations within regions, while the estimated point prevalence was shown to be increasing since 1993. Wide prediction intervals in the overall pooled point prevalence (95% prediction interval: 0.32-37.55 cases per 100,000), and the European pooled point prevalence (95% prediction interval: 1.64-19.18 cases per 100,000), indicate the scale of heterogeneity between studies and settings. While such heterogeneity currently limits the validity and utility of quantitative synthesis, developing an accepted consensus on the minimum standards and reporting requirements for HD prevalence studies could reduce the methodological heterogeneity between future studies, enabling more valid and meaningful quantitative synthesis in future.