MOLECULAR CYTOGENETIC CHARACTERIZATION OF 17-ROB(13Q14Q) ROBERTSONIANTRANSLOCATIONS BY FISH, NARROWING THE REGION CONTAINING THE BREAKPOINTS

We have characterized 17 rob(13q14q) Robertsonian translocations, usin g six molecular probes that hybridize to the repetitive sequences of t he centromeric and short-arm regions of the five acrocentric chromosom es by FISH. The rearrangements include six de novo rearrangements and the chromosomally normal parents, five maternally and three paternally inherited translocations, and three translocations of unknown origin. The D21Z1/D13Z1 and D14Z1/D22Z1 centromeric alpha-satellite DNA probe s showed all rob(13q14q) chromosomes to be dicentric. The rDNA probes did not show hybridization on any of the 17 cases studied. The pTRS-47 satellite III DNA probe specific for chromosomes 14 and 22 was retain ed around the breakpoints in all cases. However, the pTRS-63 satellite III DNA probe specific for chromosome 14 did not show any signals on the translocation chromosomes examined. In 16 of 17 translocations stu died, strong hybridization signals on the translocations were detected with the pTRI-6 satellite I DNA probe specific for chromosome 13. All parents of the six de novo rob(13q14q), including one whose pTRI-6 se quence was lost, showed strong positive hybridization signals on each pair of chromosomes 14 and 13, with pTRS-47, pTRS-63, and pTR1-6. Ther efore, the translocation breakpoints in the majority of rob(13q14q) ar e between the pTRS-47 and pTRS-63 sequences in the pll region of chrom osome 14 and between the pTRI-6 and rDNA sequences within the pll regi on of chromosome 13.