To examine the specific consequences of the RNF213 p.R4810K founder mutation, Hitomi et al. (2013a) recently developed induced pluripotent stem cell (iPSC)-derived endothelial cell (EC) lines from three MMD patients (two of whom were homozygous for p.R4810K), one unaffected heterozygous subject, and two control subjects. This evidence concerns the gene RNF213 and multiminicore myopathy.