Tightly clustered 11q23 and 22q11 breakpoints permit PCR-based detection of the recurrent constitutional t(11;22).

Palindromic AT-rich repeats (PATRRs) on chromosomes 11q23 and 22q11 at the constitutional t(11;22) breakpoint are predicted to induce genomic instability, which mediates the translocation. A PCR-based translocation-detection system for the t(11;22) has been developed with PCR primers flanking the PATRRs of both chromosomes, to examine the involvement of the PATRRs in the recurrent rearrangement. Forty unrelated carriers of the t(11;22) balanced translocation, plus two additional, independent cases with the supernumerary-der(22) syndrome, were analyzed to compare their translocation breakpoints. Similar translocation-specific junction fragments were obtained from both derivative chromosomes in all 40 carriers of the t(11;22) balanced translocation and from the der(22) in both of the offspring with unbalanced supernumerary-der(22) syndrome, suggesting that the breakpoints in all cases localize within these PATRRs and that the translocation is generated by a similar mechanism. This PCR strategy provides a convenient technique for rapid diagnosis of the translocation, indicating its utility for prenatal and preimplantation diagnosis in families including carriers of the balanced translocation.