RYR1 and hyperkalemic periodic paralysis: Two patients had a prior suspected intraoperative MH event treated with dantrolene; two patients had prior genetic testing with a diagnostic ryanodine receptor (RyR1) abnormality; two patients had a first-degree relative with muscle contracture testing consistent with MHS; and two patients had underlying diagnoses either strongly linked (congenital minicore myopathy) or possibly associated (hyperkalemic periodic paralysis) with MHS.