The genetic basis of migraine: how much do we know?
Migraine with and without aura is thought to be genetically complex with aggregation in families due to a combination of environmental and genetic tendencies. Twin studies are most important in establishing the multifactorial nature of migraine with heritability approaching 50%. Familial hemiplegic migraine (FHM) on the other hand is an autosomal dominant, highly penetrant, though rare form of migraine with strong genetic tendency. Fifty percent of families with FHM are linked to chromosome 19p13 and mutations demonstrated for some in a brain expressed calcium channel alpha 1A subunit, CACNL1A4. Other FHM loci have been identified on chromosome 1q and further genetic heterogeneity is likely. The exact role of the mutated calcium channel in the pathway leading to hemiplegic migraine is yet to be established. Changes in the electrophysiologic properties of the mutated forms of the CACNL1A4 calcium channel expressed in heterologous systems help establish the functional significance of the mutations and suggest that chromosome 19p-linked FHM, an episodic disorder, represents a CNS channelopathy. Additional candidate genes causative for migraine might include other calcium channel subunits and related proteins important for neuronal membrane stability. Delineating the cascade of biochemical events leading to hemiplegic migraine will serve as a model for understanding the pathophysiology of more common forms of migraine. The evidence suggesting that some families of migraine with and without aura might also be related to the chromosome 19p locus, chromosome Xq28 locus, or DRD2 receptor polymorphisms is reviewed.
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