This paper focuses on the causation of diseases, particularly on the idea of a "genetic cause" taking Alzheimer's Disease (AD) as an example. We (1) provide some historical information and a synopsis of the current knowledge on the etiology and pathogenesis of AD, (2) analyse some conceptual problems related to the notion of "genetic disease", (3) elaborate on the alleged (genetic) cause of AD, and (4) place the discussion on the cause of AD in a broader philosophical context, paying attention to a constructivist perspective, the notions of causal connection and causal selection, and to some practical and normative consequences of our analysis. We conclude (a) that AD is not a specific disease entity with one specific cause, (b) that the idea of a single (sufficient) cause can still function as a heuristic tool in AD research and practice, and (c) that a "belief" in causation can go together with the notions of multicausality and probability.