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.

False Homozygosity Results in HLA Genotyping due to Loss of Chromosome 6 in a Patient with Acute Lymphoblastic Leukemia / 대한진단검사의학회지

Loss of heterozygosity (LOH) in chromosome 6p has been reported in a number of tumors and some hematologic malignancies, including ALL. LOH in chromosome 6p, on which the HLA genes are located, can give rise to false homozygosity results in HLA genotyping of patients with hematologic malignancies. Here we report false homozygosity results in HLA genotyping due to the loss of whole chromosome 6 in the neoplastic cells of a patient with ALL. A 33-yr-old Korean female patient was admitted for the evaluation of leukocytosis detected during a workup for headache. Her initial white blood cell count was 336.9x109/L with 84% of blasts in the differential count. Precursor-B lymphoblastic leukemia was diagnosed from a subsequent bone marrow study. HLA high-resolution genotyping of the patient was requested at the time of diagnosis for possible hematopoietic stem cell transplantation. Homozygosity results (A*02:01, B*54:01, C*08:01, DQB1*04:01) were obtained, except for the DRB1 locus (DRB1*04:05, DRB1*11:01), in sequence-based typing. Conventional karyotyping of bone marrow metaphase cells revealed chromosomal abnormalities, with loss of multiple chromosomes including chromosome 6, and reduplication of the remaining chromosomes: 29,X,+X,+8,inv(9)(p11q13),+10,+14,+18,+21[15]/58,idemX2[3]/46,XX,inv(9)[2]. LOH at the HLA region was suspected and HLA genotyping was repeated with the peripheral blood in remission state after induction chemotherapy. All 5 HLA loci were typed as heterozygous (A*02:01, A*02:06, B*40:01, B*54:01, C*03:04, C*08:01, DRB1*04:05, DRB1*11:01, DQB1*03:01, DQB1*04:01). To avoid false HLA typing results in patients with hematologic malignancies, clinicians, as well as laboratory personnel, need to be aware of such problems and take appropriate precautions.