Mary J. Morrison

Complex karyotypic evolution in B-cell chronic lymphocytic leukemia

Cytogenetic analysis at diagnosis in a female patient with chronic B-cell leukemia showed a single abnormal clone with a 4p+ abnormality, 46,XX, -4, +der(4)t(4;?)(p16;?). Six additional clones evolved from this clone during the following 4 1/2 years and showed 3p+, 4p-, and 11q- chromosomes in addition to the 4p+ abnormality. Immunoglobulin heavy chain gene rearrangement studies showed two rearranged bands and a faint germline band. Following splenectomy, a strong germline and faint rearranged bands were seen, suggesting that the majority of cells were normal, whereas cytogenetic studies showed that the karyotypically abnormal cells were still present. The combination of cytogenetic and Ig gene rearrangement studies provides detailed information regarding the number of circulating normal and leukemic cells.

Methylation status of the 3rd exon of the c-MYC oncogene in B-cell malignancies

We examined the methylation status of the third exon of the MYC oncogene in 39 patients with B-cell malignancies. DNA was digested with MspI plus EcoRI or HpaII plus EcoRI and hybridised with a probe specific for the third exon of MYC. Thirty four patients showed complete methylation of the CCGG site. Four patients, one with chronic B-cell leukaemia and one with pro-lymphocytic leukaemia (PLL) and two with B-cell lymphoma showed partial hypomethylation of the CCGG site, while another patient with PLL showed complete hypomethylation of the CCGG site. These results suggest that hypomethylation of the MYC oncogene is infrequent in B-cell tumours but may be involved in the development of some cases of B-cell malignancies.

Hypermethylation of the M27β (DXS255) locus in chronic B-cell leukaemia

We have investigated the methylation status of the M27β (DXS255) locus in 21 female patients with chronic B‐cell leukaemia and in 20 normal controls. DNA was digested with PstI and then with the methylation sensitive enzyme HpaII and probed with the M27β probe. Eight patients (38%) showed hypermethylation of the M27β locus which was not seen in any of the normal controls. Hypermethylation of the M27β locus has also been found in acute myeloid leukaemia, acute lymphocytic leukaemia and lymphoma, suggesting that hypermethylation of the M27β locus is associated with the leukaemic process.

Translocation (2;14) associated with complex rearrangements of the Ig heavy chain in non-Hodgkin lymphoma

Cytogenetic analysis of a patient with non-Hodgkin lymphoma revealed the following karyotype: 49,XXX,t(2;14)(q21;q32),+4,+8,del(13)(q14q21). Southern blot analysis with an Ig region probe showed non-productive rearrangements indicative of a translocation involving the Ig locus. However, molecular cloning of the abnormal rearrangements did not show novel sequences derived from chromosome 2 but showed that the BCL-6 gene was juxtaposed to the IgH enhancer. Three further clones with abnormal rearrangements involving the Ig locus, particularly Iggamma3, were isolated. This suggests that the mature lymphoid cells, in this patient, were capable of undergoing indiscriminate switch cleavage and religation.

Elevated frequency of an ETS-1 restriction fragment polymorphism in chronic B-cell leukaemia.

We studied the frequency of an SstI polymorphism in 70 patients with chronic B-cell leukaemia (CLL) and 100 normal controls. There was a highly significant difference in the distribution of the three genotypes between the CLL patients and the normal controls (χ2= 13.46, 2 df, P<0.001). The C2 allele was found more frequently in CLL patients and may be a marker for a predisposition to develop CLL.

Elevated frequency of the C2 allele of the ETS-I oncogene in elderly subjects.

We studied the frequency of an Sst I polymorphism of the ETS-I oncogene in 122 elderly subjects (mean age 78.14 years) and 115 teenagers (mean age 16.9 years). No difference in the frequency of the three genotypes (C1C1, C1C2, C2C2) was found between the two groups. However, the C2 allele occurred more frequently in the elderly subjects (chi 2 = 5.49, P < 0.02). These data suggest that the presence of the C2 allele may be associated with survival to old age.

Elevated frequency of a SstI polymorphism of the Ets-1 oncogene in non-Hodgkin's lymphoma patients

We studied the frequency of a SstI polymorphism of the Ets-1 oncogene in 100 patients with non-Hodgkins lymphoma, 44 patients with Hodgkins disease, 49 patients with chronic myeloid leukemia, and 100 controls. There was no difference in the genotype frequency between the controls and patients with either Hodgkins disease or chronic myeloid leukemia. In contrast, there was a highly significant difference in the distribution of the three genotypes between the patients with non-Hodgkins lymphoma and the controls (X2 = 10.76, 2df, p = 0.004) with the C2 allele being more frequent in the lymphoma patients. Molecular cloning indicated that the polymorphic SstI site lay 304 bp from exon 7. This is the second association of the SstI polymorphism of the Ets-1 oncogene with a lymphoid disorder and suggests that the presence of the C2 allele is associated with a predisposition to develop a lymphoid malignancy.

Identification of three RFLPs at the HCK locus on chromosome 20

New HindIII, RsaI and TaqI restriction fragment length polymorphisms (RFLPs) within the haemopoietic cell kinase gene in chromosome band 20q11.2 are described. These RFLPs provide a useful marker for linkage analysis in proximal 20q.