Breakpoints at 11q23 in infant leukemias with the t(11;19)(q23;p13) are clustered.

We have analyzed a series of nine infant leukemias that carry a t(11;19)(q23;p13). They had the morphologic features of acute lymphoblastic leukemia (ALL) and expressed markers typical of B-cell progenitor ALL or pre-B ALL; one coexpressed myeloid markers in addition to lymphoid markers (biphenotypic). Two probes (P/S4 and 98.40) subcloned from a yeast artificial chromosome (YAC) known to span the breakpoint in the t(4;11) were used to investigate DNA isolated from the leukemic cells of these patients. A total of approximately 15 kb of genomic DNA in the vicinity of the probes was examined by conventional Southern blot analysis using a series of restriction enzymes. In eight of the nine cases, the breakpoint could be mapped to an approximately 10-kb BamHI fragment disclosed by hybridization to the P/S4 probe.