Linkage Disequilibrium Responsible for Association Between Susceptibility to the Malignant Hyperthermia Syndrome (MHS) and PHI Types in Danish Landrace Pigs

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Abstract
Danish Landrace pigs from elite herds and production herds were subjected to PHI (phosphohexose isomerase) typing and to the halothane test for susceptibility to the malignant hyperthermia syndrome (MHS). The Phi locus and the Hal locus for halothane reactivity are closely linked. Susceptibility to MHS was highly significantly associated with the PHI types within both materials. The magnitude of the .chi.2 [significance of association] values based on the total number of individuals was partly due to the fact that the individuals studied comprised groups of full and half sibs, and partly due to linkage disequilibrium between the 2 loci. This is deduced from the close relationship which exists between the strength of an association (r), (.chi.2) and the magnitude of the coefficient of linkage disequilibrium (D). The D value of 0.071 based on production herds was significantly different from 0; the D value of 0.038 based on individuals representing elite herds was not significant. Since the estimated D values for both materials represent positive maximum values, the observed associations are caused mainly by linkage disequilibrium. The linkage disequilibrium is related to an observed association between PHI types and meat quality.