Familial hemiplegic migraine (FHM), is rare, usually autosomal dominant, and characterised typically by attacks beginning with unilateral paraesthesia and weakness lasting for around 30–60 min, and followed by severe pulsatile, often contralateral, headache lasting for several hours. Three genetic subgroups have been identified, FHM1–3. FHM1 is due to mutations in the gene CACNA1A encoding …