AN INTERSTITIAL DELETION IN THE REARRANGED T-CELL RECEPTOR GAMMA-CHAIN LOCUS IN A CASE OF T-CELL ACUTE LYMPHOBLASTIC-LEUKEMIA

This report describes the cloning and sequencing of the breakpoint of a deletion of approximately 166 bp in the 5' region of a rearranged T-cell receptor gamma (TCRG) Vgamma2 gene from the disease cells of a patient with T-cell ALL. This abnormal rearrangement was not detected in a biopsy taken during clinical remission. Sequence analysis indicated that the deletion breakpoint occurred at a position immediately upstream of sequences found in the germline Vgamma2 gene that are closely related to known heptamer and nonamer recombination signal sequences. Furthermore, the rearrangement was found to have non-germline nucleotides (N-region) in between otherwise intact V and J segments. These data indicate that this structure may be the result of an aberrant rearrangement event in common with the frequently occurring chromosomal abnormalities found in T-cell ALL. This event could either be one directly associated with the leukaemic transformation or one occurring during normal lymphocyte development but which is coincidental with leukaemic transformation. This represents the first molecular genetic evidence for an abnormality specifically involving the TCRG locus in ALL.