An inhibitor for use in the treatment or prevention of a disorder in a subject caused by the generation of repeat expansion transcripts, wherein the disorder is Myotonic Dystrophy type 1 or Myotonic Dystrophy type 2, and wherein the inhibitor is an inhibitor of CDK12 (cyclin-dependent kinase 12) comprising: (a) a compound of Formula or a pharmaceutically acceptable salt or solvate thereof: wherein: R 1 is H, -OH, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynl, C 1-6 haloalkyl, halogen, -CN, -OC 1-6 alkyl; R 2 is H, -OH, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynl, C 1-6 haloalkyl, halogen, -CN, -OC 1-6 alkyl or a five or 6 membered cycloaryl, cycloalkyl or heterocycl having one, two or three heteroatoms selected from O, S and N, for example benzene, morpholinyl, piperidine, piperazine; R 3 is C 3-6 cycloalkyl, for example cyclopropyl, wherein: R 4 is H, -OH, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynl, C 1-6 haloalkyl, halogen, -CN, -OC 1-6 alkyl; R 5 is H; -OH; C 1-6 alkyl; C 2-6 alkenyl; C 2-6 alkynl; C 1-6 haloalkyl; halogen; -CN; -OC 1-6 alkyl; C 1-6 alkyl-N-; a five or six membered cycloaryl, cycloalkyl or heterocycl having one, two or three heteroatoms selected from O, S and N and said cycloaryl, cycloalkyl or heterocycle being optionally substituted with a C 1-3 alkyl, for example N-methylpiperazinyl; or -OC 1-6 alkyl-N; wherein X is H or C 1-6 alkyl, and Y is H or C 1-6 alkyl; and wherein the alkyl groups are optionally substituted by one or more -OH groups; and R 6 is H, -OH, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynl, C 1-6 haloalkyl, halogen, -CN, -OC 1-6 alkyl; or (b) a compound of Formula or a pharmaceutically acceptable salt or solvate thereof: or (c) a compound of Formula or a pharmaceutically acceptable salt or solvate thereof: or (d) a compound of Formula or a pharmaceutically acceptable salt or solvate thereof: or (e) a compound of Formula (XIII) or a pharmaceutically acceptable salt or solvate thereof: or (f) a compound of Formula or a pharmaceutically acceptable salt or solvate thereof: (a) a compound of Formula or a pharmaceutically acceptable salt or solvate thereof: wherein: R 1 is H, -OH, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynl, C 1-6 haloalkyl, halogen, -CN, -OC 1-6 alkyl; R 2 is H, -OH, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynl, C 1-6 haloalkyl, halogen, -CN, -OC 1-6 alkyl or a five or 6 membered cycloaryl, cycloalkyl or heterocycl having one, two or three heteroatoms selected from O, S and N, for example benzene, morpholinyl, piperidine, piperazine; R 3 is C 3-6 cycloalkyl, for example cyclopropyl, wherein: R 4 is H, -OH, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynl, C 1-6 haloalkyl, halogen, -CN, -OC 1-6 alkyl; R 5 is H; -OH; C 1-6 alkyl; C 2-6 alkenyl; C 2-6 alkynl; C 1-6 haloalkyl; halogen; -CN; -OC 1-6 alkyl; C 1-6 alkyl-N-; a five or six membered cycloaryl, cycloalkyl or heterocycl having one, two or three heteroatoms selected from O, S and N and said cycloaryl, cycloalkyl or heterocycle being optionally substituted with a C 1-3 alkyl, for example N-methylpiperazinyl; or -OC 1-6 alkyl-N; wherein X is H or C 1-6 alkyl, and Y is H or C 1-6 alkyl; and wherein the alkyl groups are optionally substituted by one or more -OH groups; and R 6 is H, -OH, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynl, C 1-6 haloalkyl, halogen, -CN, -OC 1-6 alkyl; or R 1 is H, -OH, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynl, C 1-6 haloalkyl, halogen, -CN, -OC 1-6 alkyl; R 2 is H, -OH, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynl, C 1-6 haloalkyl, halogen, -CN, -OC 1-6 alkyl or a five or 6 membered cycloaryl, cycloalkyl or heterocycl having one, two or three heteroatoms selected from O, S and N, for example benzene, morpholinyl, piperidine, piperazine; R 3 is C 3-6 cycloalkyl, for example cyclopropyl, wherein: R 4 is H, -OH, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynl, C 1-6 haloalkyl, halogen, -CN, -OC 1-6 alkyl; R 5 is H; -OH; C 1-6 alkyl; C 2-6 alkenyl; C 2-6 alkynl; C 1-6 haloalkyl; halogen; -CN; -OC 1-6 alkyl; C 1-6 alkyl-N-; a five or six membered cycloaryl, cycloalkyl or heterocycl having one, two or three heteroatoms selected from O, S and N and said cycloaryl, cycloalkyl or heterocycle being optionally substituted with a C 1-3 alkyl, for example N-methylpiperazinyl; or -OC 1-6 alkyl-N; wherein X is H or C 1-6 alkyl, and Y is H or C 1-6 alkyl; and wherein the alkyl groups are optionally substituted by one or more -OH groups; and R 6 is H, -OH, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynl, C 1-6 haloalkyl, halogen, -CN, -OC 1-6 alkyl; or R 4 is H, -OH, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynl, C 1-6 haloalkyl, halogen, -CN, -OC 1-6 alkyl; R 5 is H; -OH; C 1-6 alkyl; C 2-6 alkenyl; C 2-6 alkynl; C 1-6 haloalkyl; halogen; -CN; -OC 1-6 alkyl; C 1-6 alkyl-N-; a five or six membered cycloaryl, cycloalkyl or heterocycl having one, two or three heteroatoms selected from O, S and N and said cycloaryl, cycloalkyl or heterocycle being optionally substituted with a C 1-3 alkyl, for example N-methylpiperazinyl; or -OC 1-6 alkyl-N; wherein X is H or C 1-6 alkyl, and Y is H or C 1-6 alkyl; and wherein the alkyl groups are optionally substituted by one or more -OH groups; and R 6 is H, -OH, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynl, C 1-6 haloalkyl, halogen, -CN, -OC 1-6 alkyl; or (b) a compound of Formula or a pharmaceutically acceptable salt or solvate thereof: or (c) a compound of Formula or a pharmaceutically acceptable salt or solvate thereof: or (d) a compound of Formula or a pharmaceutically acceptable salt or solvate thereof: or (e) a compound of Formula (XIII) or a pharmaceutically acceptable salt or solvate thereof: or (f) a compound of Formula or a pharmaceutically acceptable salt or solvate thereof: