A cryptic splice site mutation in RYR1 intron 101 was identified in a severely affected isolated case from a consanguineous Tunisian family with MmD and ophthalmoplegia [22], resulting in a marked depletion of the normal RYR1 transcript, probably explaining the severe phenotype; both parents were asymptomatic carriers. This evidence concerns the gene RYR1 and ophthalmoplegia.