Recombinants of intrachromosomal transposition of subtelomeres in chromosomes 1 and 2: A cause of minute terminal chromosomal imbalances

Abstract

Two cases of submicroscopic recombinants of intrachromosomal transposition of telomeres, one each from chromosome 1 and 2 are described. Meiotic crossing-over would generate the recombinants from these reciprocal rearrangements. In both cases, which were detected by FISH with subtelomeric probes, there is a minute deletion of the qter region and a second presence of the pter subtelomeric region on the respective qter, i.e., a duplication of 1pter or 2pter respectively. The deletion on 2qter (case 2) was confirmed by microsatellite inheritance and was of paternal origin, but in case 1 there was no detectable 1q deletion other than of the subtelomeric probe, and parental origin could not be determined. The present case 2 with del(2qter)/dup(2pter) shares many features with reported cases of simple deletion (2qter) but did not have features of Albright hereditary osteodystrophy, which are seen in half of such deletion patients. The clinical features present in case 1 were similar to those of the previously reported case of a submicroscopic 1qter deletion but also to cases with microscopically visible 1qter deletions, presumably because of gene enrichment in subtelomeric regions. Recombinants of such intrachromosomal subtelomere transpositions detected by subtelomeric probes may comprise up to 10% of submicroscopic pter or qter deletion cases. Other cases of this unusual mechanism may be detected with more common use of subtelomeric probes. It is suggested the bouquet associations of telomeres in early meiosis may facilitate such unusual rearrangements.