RNF213 and multiminicore myopathy: However, since the c.14576G>A polymorphism in RNF213 greatly enhances the risk of MMD pathogenesis and that patients with this polymorphism show earlier disease onset and more severe clinical manifestations than MMD patients without the polymorphism [44], it is conceivable that the c.14576G>A polymorphism in RNF213 plays an important role in MMD pathogenesis.