Submicroscopic Deletions of Immunoglobulin Heavy Chain Gene (IGH) in Precursor B Lymphoblastic Leukemia with IGH Rearrangements.

Translocations leading to fusions between the immunoglobulin heavy chain gene (IGH) and various partner genes have been reported in B-cell precursor acute lymphoblastic leukemia (B-ALL). However, submicroscopic deletions within IGH in B-ALL have not been rigorously assessed. In this study, we investigated characteristics of IGH submicroscopic deletions, by FISH, in B-ALL with IGH rearrangements. FISH was performed by using commercially available IGH dual-color break-apart rearrangement probes (Abbott/Vysis, Downers Grove, IL, USA; Kreatech, Amsterdam, Netherlands). The study group included seven B-ALL patients with IGH rearrangements, observed by FISH. Among them, two exhibited deletion of the 5' variable region of IGH by FISH. The B-ALL in these two patients included two kinds of abnormal cells; one had an IGH rearrangement without any IGH submicroscopic deletion, while the other had an IGH submicroscopic deletion, which showed that one normal fusion signal and one 3' IGH signal were detected. Thus, submicroscopic deletion of the IGH 5' variable region may have occurred in either the native or rearranged chromosome 14. These findings indicate that B-ALL with IGH rearrangements may be accompanied by submicroscopic deletions of the IGH 5' variable region, which can be detected by FISH. The clinical significance of such deletions is unclear, but the loss of part of the IGH gene in B-ALL warrants further study.