Alzheimer’s disease (AD) is a neurodegenerative disease that leads to progressive declines in memory and cognitive abilities and is the most common type of dementia, which is irreversible. The disease can, however, begin to develop well before symptoms of dementia manifest themselves in the preclinical and prodromal stages. Identifying individuals in these stages has been difficult, and as a result, many estimates of AD typically focus on estimating the prevalence of AD once dementia has set in.
Given the irreversible nature of dementia, interventions targeting AD during these stages present a tremendous opportunity to mitigate the progression of AD to its more severe stage. Thus, it is crucial to understand the size and risk factors along the AD continuum, defined by preclinical AD and prodromal AD and AD dementia.
A recent meta-analysis by Gustavsson and colleagues, published in the journal Alzheimer’s & Dementia, aimed to shed some light on the issue by estimating the global prevalence of preclinical and prodromal AD. The study evaluated all literature published in the past ten years and identified 55 articles reporting prevalence estimates of AD at any disease stage, with or without biomarker confirmation.
In the US, the authors estimated that as many as 28.4 million individuals over the age of 50 are on the Alzheimer’s continuum, with 20 million and 5.6 million having preclinical AD and prodromal AD, respectively. Such an estimate is much higher than the approximately 2.3 million individuals over 60 projected to be diagnosed with AD, and another roughly 2.3 million individuals with mild cognitive impairment in the US this year, according to GlobalData.
While the inclusion of the 50–59 age group in Gustavsson’s estimate accounts for some of this difference, estimates of individuals on the AD continuum were lowest in this age group and thus did not significantly impact the discrepancy. Therefore, including individuals with preclinical and prodromal AD in prevalence estimates suggests that millions of individuals in the US are at risk of AD dementia, many of whom do not know they are at risk due to the difficulty of diagnosing preclinical and prodromal AD.
While, in many instances, individuals in the AD continuum will not develop AD, the large size of this group, coupled with an ageing US population, has significant implications for AD treatment and prevention. This presents an opportunity to expand the current research and increase healthcare systems’ focus on populations at the earliest stages of the disease. Such a focus should aim at elucidating factors that may influence the progression of AD, like socioeconomic, racial and gender disparities, and aim at screening individuals earlier and more routinely. In doing so, prevention and mitigation strategies can be more effectively distributed and reduce the overall burden of AD.