Recombination between the postulated CCD/MHE/MHS locus and RYR1 gene markers.

Malignant hyperthermia (MH) susceptibility is considered a subclinical myopathy or a pharmacogenetic trait, and is believed to be closely associated with central core disease (CCD). Data support the notion that MH susceptibility is heterogeneous, with the ryanodine receptor I (RYR1) locus on chromosome 19 being one locus harboring a gene that can cause MH susceptibility. The gene for CCD is believed to reside in the locus on chromosome 19. In the family presented here, a girl has CCD, and several close relatives are MH susceptible (MHS). DNA studies conducted on available family members uncovered recombination between the MH susceptibility locus and RYR1 markers. Consequently, if one postulates that the CCD gene in this family resides in the same locus as the MH susceptibility gene, an additional CCD locus different from the RYR1 locus must also be postulated.