15p

We describe a subtle translocation t(8;11)(p23.2;p15.5) ascertained after two induced abortions in the same sibship because of the discovery of fetal hydrops on ultrasound examination. Initial cytogenetic studies performed on cultured amniotic fluid cells were considered as normal in both fetuses. High resolution banding analysis and FISH studies performed on the parents' chromosomes revealed a paternal translocation t(8;11)(p23.2;p15.5). Retrospective FISH analysis of both fetuses showed that they carried the same chromosomal imbalance including a distal monosomy 8pter and a distal trisomy 11pter. The phenotypes of the fetuses were re-examined and found to be compatible with Beckwith-Wiedemann syndromes (BWS). FISH analysis using an IGF2 probe demonstrated the presence of three copies of the IGF2 gene. This study highlights the value of searching for subtle chromosome rearrangements in families with recurrent unexplained multiple malformation syndromes discovered prenatally. Also, it contributes to a better delineation of the prenatal phenotype of BWS. Finally, it sheds new light on the aetiology of non-immune hydrops fetalis.Close

We report on a patient with neurosensory deafness, cataract and moderate mental retardation showing a constitutional mosaicism with the predominant cell line consisting of a 45,XY,-13,-15,+t(13;15) translocation of the Robertsonian type. By means of fluorescence in situ hybridization (FISH) using a panel of acrocentric pericentromeric probes and various banding techniques, the breakpoints in the translocation were determined at 13q12.1 and 15p13 respectively. Five other cell lines were present, at low percentage, one of them showing a t(13;15) tandem translocation. Interstitial telomeric sequences could be detected at the translocation fusion sites in both the Robertsonian and tandem translocations. The mosaicism appears therefore to be a consequence of chromosomal instability involving the t(13;15) fusion region of the predominant cell line, and related to the presence of interstitial telomeric sequences. The present observation suggests that in the pericentromeric 13q12 region, a gene involved in neurosensory deafness may be located.Close

A fetus was prenatally diagnosed as having a Y(nfqs) chromosome which was inherited from the father. With the QFQ technique, the Yqh was observed to be nonfluorescent and contained cytological satellites which were attached to the terminal long arm. The satellites were positively stained by the Ag-NOR technique suggesting that the NORs were active. A battery of DNA probes was used to characterise the Y(nfqs). Hybridisation experiments using a chromosome 15 specific classical satellite DNA probe (D15Z1) and a Yq telomere DNA probe showed that the additional satellited material on Yq originated from 15p, and that the Yq terminal region had been lost. This is the first reported case in which the origin of cytological satellites on Yq has been determined by FISH, but this does not imply that all satellited Y chromosomes are derived from 15p. However, the clinical significance of this Y(nfqs) chromosome remains obscure.Close

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A telomere YAC clone containing the most distal 115 kb of chromosome arm 4p has been previously isolated. This clone is of particular interest as it spans a potential candidate region for the Huntington disease gene. The YAC was subcloned into a phage vector, and a high-resolution restriction map extending to within 13 kb of the telomere was constructed. In situ hybridization of the YAC to human metaphase spreads gives a peak of hybridization on 4pter but also an increase in the number of signals close to several other telomeres. Where possible, these results were investigated further by the hybridization of probes from the YAC to somatic cell hybrids containing single human chromosomes. This analysis indicates that the most telomeric 60 kb of chromosome arm 4p is homologous to telomeric regions on 13p, 15p, 21p, and 22p. The extent of this homology makes it less likely that the mutation for Huntington's disease is located within the telomere YAC clone.Close