RYR1 and multiminicore myopathy: While the functional effects of RYR1 mutations associated with CCD, MHS and MmD are at least partially understood, the precise molecular mechanisms in the pathogenesis of SEPN1-related MmD remains unclear; a calcium-binding motif within the selenoprotein N protein suggests that intracellular Ca2+ handling may also be affected in this subgroup of MmD and points at a common pathway in the pathogenesis of core formation.