RESUMEN
Telomeric translocations are uncommon: Fluorescence in situ hybridisation with TTAGGG repeats as the probe was used to search for derivative chromosomes with telomeric repeats at the break-point junction in a sample of 16 translocations with at least one terminal breakpoint and ascertained through an aneuploid patient. There were 11 cases (8 autosomal and 3 X;Y translocations) with a de novo/unknown origin in the study group and 5 control familial rearrangements. At least 20 metaphases showing a clear telomeric signal on the relevant chromosomes(s) were analysed in each individual. All 16 translocations appeared to be reciprocal events as interstitial telomeric sequences were not found. The lack of telomeric translocations in this sample may be related, among other factors, to the relative absence of tertiary monosomies which are the most suitable candidates. These data and previously published information indicate that telomeric translocations are uncommon and differ from reciprocal exchanges in several relevant ways such as an exclusive unbalanced occurrence; a consistent de novo origin and therefore a non-significant recurrence risk; restricted malsegregations, namely 3:1 tertiary monosomy and adjacent-1; a yield of "pure" imbalances, and a proneness to exhibit a jumping behaviour.
Asunto(s)
Aberraciones Cromosómicas/genética , Aberraciones Cromosómicas Sexuales/genética , Telómero/genética , Translocación Genética/genética , Cromosoma X , Cromosoma Y , Trastornos de los Cromosomas , Sondas de ADN , Pruebas Genéticas , Hibridación Fluorescente in Situ , Secuencias Repetitivas de Ácidos Nucleicos/genética , Factores de RiesgoRESUMEN
Seventeen patients presenting with either de novo or familial supernumerary marker (mar) 15 chromosomes were shown by fluorescent in situ hybridization techniques (FISH) to have markers derived from and composed entirely of chromosome 15 material. Using a combination of conventional cytogenetics, FISH, Southern blotting and multiplex polymerase chain reaction (PCR) methods, it was possible to sub-classify the 17 mar(15)s into six distinct morphological and molecular groups. Analysis of DNA and metaphase spreads from the probands and their parents using probes and primers from the pericentromeric and Prader-Willi/Angelman syndromes critical regions (PWS/AS), clearly differentiated between marker 15s which included the PWS/AS critical regions and those which did not. A direct correlation between the presence of the PWS/AS region in the mar(15) and severe mental retardation was observed. Based on these results, a system of classification of supernumerary marker 15 chromosomes is proposed.