Epistemic injustice suffered by patients with rare diseases, poorly understood diseases, and underdiagnosed diseases, and the epistemic advantage granted by these diseases.

Fricker (Epistemic Injustice. Power and the Ethics of Knowing, Oxford University Press, Oxford, 2007) coined the term epistemic injustice to refer to the downgrading of credibility of speakers provoked either by prejudices-which she labeled testimonial injustice-or by a gap in interpretative resources that account for a given phenomenon-which she referred to as hermeneutical injustice. This paper reviews the existing literature on how patients with rare diseases, poorly understood diseases, and underdiagnosed diseases are questioned by the healthcare practitioners who assist them in order to explore how they suffer from both these types of epistemic injustice. At the same time, the paper argues that the very epistemic marginalization suffered by these patients actually grants them some epistemic advantages over patients with better-known diseases, and even some meta-epistemic advantages-that is, a deeper understanding of how the very taxonomy that marginalizes or excludes them is, to some extent, a sociocultural construction. The paper therefore applies the notion of "epistemic advantage", coined by contemporary standpoint theorists, to the field of healthcare.