A compound of formula, or a pharmaceutically acceptable salt thereof, wherein R 1 represents a hydrogen or fluorine atom or a trifluoromethyl group; R 2 represents a group -X-Y-R 3; X and Y each independently represent a bond, an oxygen atom or a group - C, -S n, -C NR 4, -S 2 NR 4, -NR 4, or -CR 4 R 5 -, provided that X and Y cannot both simultaneously represent a bond and provided that if X and Y are both other than a bond, then at least one of X and Y represents -CR 4 R 5 -; n is 0, 1 or 2; each R 4 independently represents a hydrogen atom or a C 1 -C 6 alkyl or C 1 -C 6 haloalkyl group; each R 5 independently represents a hydrogen atom, a C 1 -C 6 alkyl or C 1 -C 6 haloalkyl group or =CH-; R 3 represents a 3- to 10-membered saturated or unsaturated carbocyclic or heterocyclic ring system, the ring system itself being optionally substituted by at least one substituent selected from halogen, hydroxyl, cyano, oxo, C 1 -C 6 alkyl, C 2 -C 6 alkenyl, C 1 -C 6 haloalkyl, C 1 -C 6 hydroxyalkyl, C 1 -C 6 alkoxy, C 1 -C 6 haloalkoxy, C 1 -C 6 alkylthio, C 1 -C 6 alkylsulphinyl, C 1 -C 6 alkylsulphonyl, C 1 -C 6 alkylcarbonyl, C 1 -C 6 alkylcarbonyloxy, C 1 -C 6 alkoxycarbonyl, amino, -CON(R 6) 2, C 1 -C 6 alkylamino, di-(C 1 -C 6 alkyl)amino, C 3 -C 6 cycloalkyl, C 3 -C 6 cycloalkyloxy, C 3 -C 6 cycloalkylmethyl, - p -(CH 2) q -O-R 7 and a 4- to 6-membered saturated or unsaturated heterocyclic ring (optionally substituted with at least one substituent selected from C 1 -C 4 alkyl and C 1 -C 4 alkoxy); each R 6 independently represents a hydrogen atom or a C 1 -C 6 alkyl group; p is 0 or 1; q is 1, 2, 3 or 4; and R 7 represents a C 1 -C 6 alkyl group; for use in the prevention or treatment of an ataxic disorder. R 1 represents a hydrogen or fluorine atom or a trifluoromethyl group; R 2 represents a group -X-Y-R 3; X and Y each independently represent a bond, an oxygen atom or a group - C, -S n, -C NR 4, -S 2 NR 4, -NR 4, or -CR 4 R 5 -, provided that X and Y cannot both simultaneously represent a bond and provided that if X and Y are both other than a bond, then at least one of X and Y represents -CR 4 R 5 -; n is 0, 1 or 2; each R 4 independently represents a hydrogen atom or a C 1 -C 6 alkyl or C 1 -C 6 haloalkyl group; each R 5 independently represents a hydrogen atom, a C 1 -C 6 alkyl or C 1 -C 6 haloalkyl group or =CH-; R 3 represents a 3- to 10-membered saturated or unsaturated carbocyclic or heterocyclic ring system, the ring system itself being optionally substituted by at least one substituent selected from halogen, hydroxyl, cyano, oxo, C 1 -C 6 alkyl, C 2 -C 6 alkenyl, C 1 -C 6 haloalkyl, C 1 -C 6 hydroxyalkyl, C 1 -C 6 alkoxy, C 1 -C 6 haloalkoxy, C 1 -C 6 alkylthio, C 1 -C 6 alkylsulphinyl, C 1 -C 6 alkylsulphonyl, C 1 -C 6 alkylcarbonyl, C 1 -C 6 alkylcarbonyloxy, C 1 -C 6 alkoxycarbonyl, amino, -CON(R 6) 2, C 1 -C 6 alkylamino, di-(C 1 -C 6 alkyl)amino, C 3 -C 6 cycloalkyl, C 3 -C 6 cycloalkyloxy, C 3 -C 6 cycloalkylmethyl, - p -(CH 2) q -O-R 7 and a 4- to 6-membered saturated or unsaturated heterocyclic ring (optionally substituted with at least one substituent selected from C 1 -C 4 alkyl and C 1 -C 4 alkoxy); each R 6 independently represents a hydrogen atom or a C 1 -C 6 alkyl group; p is 0 or 1; q is 1, 2, 3 or 4; and R 7 represents a C 1 -C 6 alkyl group;