RYR1 and multiminicore myopathy: The marked clinical variability of MmD is reflected in genetic heterogeneity: Recessive mutations in both the selenoprotein N (SEPN1) [13] and the skeletal muscle ryanodine receptor (RYR1) gene [17,23-25,32] have been recently identified in clinically distinct subgroups; most reports of dominant inheritance predate molecular resolution of the condition [9,33-38] and may have been due to dominant mutations in the RYR1 gene or other genes giving rise to cores on muscle biopsy.