Abstract: The present invention relates to an aptamer characterized in that it has the ability to distinguish conformers of F-type ?-Syn fibres of the ?-Syn (?-Syn) protein from conformers of R-type ?-Syn fibres, and in that it comprises a sequence specific for modified ribonucleic acid (RNA) having at least 85% identity with a sequence chosen from SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID NO: 4, SEQ ID NO: 5, SEQ ID NO: 6 and SEQ ID NO: 7, preferably chosen from SEQ ID NO: 1 and SEQ ID NO: 2. The present invention also relates to a composition or a kit comprising at least one of these aptamers, and also to the uses thereof in vitro. The present invention also relates to a method for diagnosing synucleinopathies, as well as to a method for stratification, monitoring, prognosis and evaluation of the efficacy of a synucleinopathy treatment, comprising the use of at least one aptamer and/or a composition and/or a kit mentioned above.