Molecular Analysis Redefines 3 Human-Chromosome-14 Deletions

We have used a panel of 13 DNA markers in the distal region of chromosome 14q to characterize deletions in three patients determined cytogenetically to have a ring or terminally deleted chromosome 14. We have characterized one patient with a ring chromosome 14 [r (14) (p13q32.33)] and two with terminal deletions [del (14) (pter-->q32.3:)]. The two patients with cytogenetically identical terminal deletions of chromosome 14 were found to differ markedly when;characterized with molecular markers. In one patient, none of the markers tested were deleted, indicating that the apparent terminal deletion is actually due to either an undetected interstitial deletion or a cryptic translocation event. In the other patient, the deletion was consistent with the cytogenetic observations, The deleted chromosome was shown to be of paternal origin. The long-arm breakpoint of the ring chromosome was mapped to within a 350-kb region of the immunoglobulin heavy chain gene cluster (IGH). This breakpoint was used to localize markers D14S20 and D14S23, previously thought to lie distal to IGH, to a more proximal location. The ring chromosome represents the smallest region of distal monosomy 14q yet reported.