A five-year-old boy with psychomotor retardation, microcephaly, bilateral cataracts, hearing impairment and hypospadia with microphallus was found to have multiple cell lines from peripheral blood: 46,XY/46,XY, -13,+r(13)/46, Xy, -13, +dic r(13) in the ratio of 35%/61%/4% by trypsin-Giemsa, and C-bandings. Using fluorescence in situ hybridization (FISH) with biotin-labeled alpha-satellite probe (D21Z1/D13Z1) and fluorescence staining (FITC), we confirmed that the ring originated from chromosome 13. To elucidate changes in the chromosome ends in the ring originated from chromosome 13. To elucidate changes in the chromosome ends in the ring formation, we used human telomere-specific probes for FISH study; it showed an absence of telomeres on the ring chromosome, although Ag-NOR staining was positive. These findings yielded different breaking points on the ends of both the short and long arms of chromosome 13 from those reported in the literature.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