New linkage data for the X-linked types of muscular dystrophy and G6PD variants, colour blindness, and Xg blood groups.

Six families in which Duchenne muscular dystrophy (DMD) and G6PD or deutan colour blindness are segregating are reported. The sum of the lod-scores of these families together with three published previously indicates that the DMD locus is far from the G6PD:deutan cluster. The lod-scores of two families with Becker muscular dystrophy (BMD) informative for the G6PD locus together with those of one family previously studied by Emery, Smith, and Sanger (1969) suggest that the BMD locus could be at a measurable distance from this cluster. The maximum likelihood estimate of the recombination fraction is 0·27 and the 90% confidence limits are 0·17 and 0·40. This difference in linkage estimates for DMD and BMD suggests that the BMD and the DMD genes are located at two different loci on the X chromosome. Five more families with DMD and two with BMD informative for Xg blood groups support the conclusion of other authors that there is no hint of linkage between the loci for Xg and for the X-linked forms of muscular dystrophy.