The Biomarkerization of Alzheimer’s Disease: From (Early) Diagnosis to Anticipation?

Abstract

AbstractThe idea that disease can exist without symptoms has recently been boosted by the increasing number of molecular biomarkers. This also spurred controversy about the desirability of early diagnosis. Biomarkers’ role in early diagnosis and definition of disease, as well as the controversies this raises, are particularly noticeable in the domain of Alzheimer’s disease (AD). This chapter analyses how the introduction of biomarkers in the AD field has reshaped the conceptualization of ‘AD’. We begin by reconstructing and analysing the subsequent versions of criteria to diagnose AD, issued by the National Institute of Ageing and the Alzheimer’s Association (NIA-AA). This reconstruction is then used to show how biomarker research induces a gradual shift from an ‘ontological’ to a ‘physiological’ mode of approaching disease, which also has several implications beyond the field of AD. Firstly, it helps to see that biomarker testing affects both individuals with and without symptoms. Moreover, it shows that the search for a more specific diagnosis may result in an explosion of heterogeneity rather than diminish it. Finally, it suggests that the value of biomarkers for healthcare practice may lie in their capacity to anticipate on disease trajectory, rather than in a more precise and earlier diagnosis.