TK2 and spinocerebellar ataxia type 31: Spinocerebellar ataxia type 31 (SCA31) is a neurological disease caused by insertion of a 2.5 to 3.8 kb repeat that includes the long TGGAA stretch present in a common intronic region of BEAN1 (brain expressed associated with NEDD4-1) and thymidine kinase 2 (TK2) genes [39,40,45].