Meiotic drive at the myotonic dystrophy and the cone-rod dystrophy loci on chromosome 19q13.3

The apparently conflicting observations of a high new mutation rate at the myotonic dystrophy (DM) locus on chromosome 19q13.3 and of a founder effect for DM chromosomes led researchers to invoke the influence of meiotic drive at this locus. Two studies (Carey et al. 1994; Gennarelli et al. 1994) suggested such an effect in male meioses, whereas one study (Shaw et al. 1995) found evidence for segregation distortion in female meioses. In the October 1996 issue of the Journal, Leeflang et al. demonstrated convincing evidence that, if such an effect exists in male meioses, it must operate postejaculation, presumably influencing sperm motilityor sperm survival. In so doing, the authors also reviewed the literature both supporting and opposing the influence of the action of meiotic drive at the DM locus. However, they appear to have missed a report from our laboratory (Evans et al. 1994) of a similar observation for dominant cone-rod dystrophy (CORD2), a form of retinal degeneration that also maps to chromosome 19q. The data from the study of the CORD2 locus suggest segregation distortion in female meioses. The most recent locus refinement for CORD2 (Bellingham et al., in press) places it in an interval 0.8-2.4 Mb distal to the DM locus, on the metric FISH map of Gordon et al. (1995). Is it not possible that the close proximity of these two loci, both of which apparently have such an unusual pattern of inheritance, is more than a coincidence?