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To determine the extent to which mutations in genes known to cause familial hemiplegic migraine (FHM) account for the disorder, the authors used a population-based approach through the Danish National Patient Register. In members of 42 families with FHM, they sequenced the exon and promoter regions of the CACNA1A and ATP1A2 genes. They also sought the Q1489K mutation in the SCN1A gene.
Mutations in the CACNA1A and ATP1A2 genes accounted for only 14% of the families; four novel and two known mutations in these genes were identified. This suggests that many more FHM genes remain to be found. Also notable were the penetrance rates for the identified mutations in the two genes of only 67% and 63%, respectively — far lower than previous estimates…