Pedigrees of all four families showing cosegregation of phenotype and genotype. These pedigrees are coded to indicate in vitro contracture test and mutation status. In all families except for C, all known genotypes were concordant with the phenotype. Circles represent females and squares males; diagonal line through symbol = deceased; diagonal arrows indicate clinical reaction. (A) Family A; (B) family B; (C) family C. Here, one individual was discordant between genotype (variant +) and phenotype (MHN). For this individual and his MHE father, the additional boxes provide details of in vitro contracture test and creatine kinase results; (D) family G. C = tension at 2 mm caffeine; CK = creatine kinase concentration in international units per liter (U/l; normal <205); H = tension at 2% halothane; MH = malignant hyperthermia; MHE = MH equivocal; MHN = MH negative; MHS = MH susceptible; R = onset time for ryanodine contracture test.