High population incidence of the 15p marker D15Z1 mapping to the short arm of one homologue 14

Abstract

We have read with interest the paper by Smeets et al. (1991), reporting a "Frequent occurrence of translocation of the short arm of chromosome 15 to other D-group chromosomes" . We have per formed a similar population study of 100 subjects using the satellite-III probe D15Z1 obtained f rom the same source (Higgins et al. 1985), which is in fact a repetit ive human 1.8 kb KpnI sequence and not an alphoid sequence. Under high stringency conditions, this p robe has previously been thought to map exclusively to the DA/DAPI-pos i t ive juxta centromeric heterochromatic region of 15p, but 12 of our 100 subjects showed an additional hybridization spot on an acrocentric chromosome other than 15 (Fig. 1). In contrast to the observation by Smeets et al. (1991) we found the additional hybridization restricted to the p arm of one homologue 14, as identified by pre-G-banding, co-hybridization with the whole chromosome pBS14 and pBS15 probes, sequential D A / D A P I staining and D15Z1 hybridization. None of our cases showed hybridization to the p arm of chromosome 13. It will be interesting to see if this represents a true population difference between the British and the Dutch, or is merely due to chance variation. Family studies (two families) demonstrated that the 14p marker is an inherited character. The high incidence of this marker obviously restricts the value of D15Z1 as a diagnostic tool for the identification of 15p, particularly when used in interphase. We are still uncertain about the origin of this common constitutional marker . We suggest that it is premature to call it a chromosomal translocation, implying chromosome breakage and rearrangement. To-date there are no reasons to believe that this heritable polymorphism could not have originated by other means, e.g., selective amplification of sequences common to 15p and 14p.