The present invention relates to the proline rich transmembrane protein 2 (PRRT2) gene, and the identification of mutations and variations in PRRT2 that give rise to seizure and movement disorders. Accordingly, the present invention provides methods for the diagnosis or prognosis of such disorders by identifying alterations in the PRRT2 gene. Identification of alterations in the PRRT2 gene also enables the identification of subjects with an increased likelihood of having an offspring predisposed to such disorders. The present invention also provides an isolated nucleic acid molecule comprising an alteration in the PRRT2 gene, wherein said alteration produces a seizure and/or movement disorder phenotype. Also provided is an isolated PRRT2 polypeptide that comprises an alteration which produces a seizure and/or movement disorder phenotype. Furthermore, the present invention provides kit for diagnosing or prognosing a seizure and/or movement disorder in a subject, or for identifying a subject with an increased likelihood of having an offspring predisposed to a seizure and/or movement disorder, wherein the kit includes one or more components for testing for the presence of an alteration in the PRRT2 gene in the subject.