Definition:

Sporadic and familial hemiplegic migraines (SHM and FHM) are rare paroxysmal disorders characterized by motor aura and headache. The distinction is based on whether at least one first or second degree relative is also affected, otherwise the diagnostic criteria are similar. The majority of FHM families have a mutation in one of the ion channels CACNA1A, ATP1A2 and SCN1A. SHM is sometimes caused by a de novo mutation in one of the genes. However, at least a quarter of the large families affected and most sporadic cases do not have a mutation in the three genes known to be implicated in this disorder, suggesting that other genes are still to be identified.