Here, we carry out the first large screening study of the three main paroxysmal dyskinesia genes [the total coding regions of SLC2A1 and PRRT2 and exons one and two (the only exons in which mutations have been previously identified) of PNKD] in a large referral series of 145 paroxysmal movement disorders and in a further 53 genetically undefined patients with episodic ataxia or familial hemiplegic migraine. Here, SLC2A1 is linked to familial hemiplegic migraine.