Low frequency of p57KIP2 mutation in Beckwith-Wiedemann syndrome.

Beckwith-Wiedemann syndrome (BWS) is an autosomal dominant disorder of increased prenatal growth and predisposition to embryonal cancers such as Wilms tumor. BWS is thought to involve one or more imprinted genes, since some patients show paternal uniparental disomy, and others show balanced germ-line chromosomal rearrangements involving the maternal chromosome. We previously mapped BWS, by genetic linkage analysis, to 11p15.5, which we and others also found to contain several imprinted genes; these include the gene for insulin-like growth factor II (IGF2) and H19, which show abnormal imprint-specific expression and/or methylation in 20% of BWS patients, and p57KIP2, a cyclin-dependent kinase inhibitor, which we found showed biallelic expression in one of nine BWS patients studied. In addition, p57KIP2 was recently reported to show mutations in two of nine BWS patients. We have now analyzed the entire coding sequence and intron-exon boundaries of p57KIP2 in 40 unrelated BWS patients. Of these patients, only two (5%) showed mutations, both involving frameshifts in the second exon. In one case, the mutation was transmitted to the proband's mother, who was also affected, from the maternal grandfather, suggesting that p57KIP2 is not imprinted in at least some affected tissues at a critical stage of development and that haploinsufficiency due to mutation of either parental allele may cause at least some features of BWS. The low frequency of p57KIP2 mutations, as well as our recent discovery of disruption of the K(v)LQT1 gene in patients with chromosomal rearrangements, suggest that BWS can involve disruption of multiple independent 11p15.5 genes.

Lack of imprinting of three human cyclin-dependent kinase inhibitor genes.

Genomic imprinting is an epigenetic modification in the germline leading to parental allele-specific gene expression in somatic cells. We have previously found that imprinted genes can be abnormally expressed or silenced in tumors and that the cyclin-dependent kinase inhibitor (CKI) CDKN1C (p57KIP2) is normally imprinted, with preferential expression of the maternal allele. Here we analyze the imprinting status of three additional CKIs, the abnormal expression and/or chromosomal localization of which has been implicated in human malignancy: CDKN1A, CDKN1B, and CDKN2C. Allele-specific expression was examined by reverse transcription-PCR, using primers that span transcribed polymorphisms as well as exon/intron boundaries, to distinguish cDNA products from genomic DNA. Biallelic expression was observed for all three genes in both fetal and adult tissues. Thus, genomic imprinting is not a generalized feature of CKIs.

Molecular residual disease status at the end of chemotherapy fails to predict subsequent relapse in children with B-lineage acute lymphoblastic leukemia.

PURPOSE: We have investigated whether the extent of residual leukemia in the marrows obtained at the completion of chemotherapy can predict subsequent relapse in children with B-lineage acute lymphoblastic leukemia (ALL). PATIENTS AND METHODS: Marrow samples of 24 patients were examined for residual disease at the end of treatment using a quantitative method based on the polymerase chain reaction (PCR) amplification of the complementarity determining region-3 of the immunoglobulin heavy chain. RESULTS: Of the 15 patients who remain in continuous bone marrow remission (range, 41 to 98 months), 14 had no detectable leukemic cells; one patient had a very low level (one in approximately 335,000 marrow cells) of residual leukemic cells that underwent clonal evolution. Among the nine patients who had a marrow relapse after the completion of treatment, eight patients whose relapses occurred 4 to 54 months from the end of therapy had no detectable leukemic cells, whereas only the one patient who relapsed 2 months after the completion of therapy had detectable residual disease. CONCLUSION: These observations indicate that the absence of detectable residual leukemia by PCR at the end of chemotherapy is not sufficient to assure that the patient is cured and suggest that frequent serial monitoring is required for the early prediction of relapse off therapy.

Residual disease at the end of induction therapy as a predictor of relapse during therapy in childhood B-lineage acute lymphoblastic leukemia.

PURPOSE: More than 95% of children with B-lineage acute lymphoblastic leukemia (ALL) achieve a clinical remission after the induction phase of chemotherapy (first 28 days) as evaluated by morphologic criteria. However, relapse occurs in approximately 30% of these children. The objective of this study was to determine whether the outcome of patients in clinical remission at the end of induction therapy could be predicted using a highly sensitive method to detect residual disease. PATIENTS AND METHODS: All children diagnosed with B-lineage ALL at the Children's Hospital of Philadelphia during a 2-year period were eligible. The extent of residual leukemia was quantitated in remission marrow samples obtained at the end of induction therapy in 44 children using a phage clonogenic assay in association with complementarity-determining-region 3 (CDR3)-polymerase chain reaction (PCR). RESULTS: Residual disease was a significant predictor of outcome independent of WBC count, age, or sex. The estimated relapse-free survival (RFS) during therapy was 50.4% (+/- 12.6%) for patients with high residual disease (> or = 0.6% leukemia cells among total marrow B cells) versus 91.9% (+/- 5.5%) for those with lower levels (P < .002). There were no significant differences in off-treatment RFS between patients with high or low residual disease who completed therapy in continuous remission (P = .82). The overall estimated RFS was 32.3% (+/- 11.6%) for patients with high residual disease versus 62.6% (+/- 10.7%) for patients with lower levels of residual leukemia cells, with a median follow-up of 5.3 years for patients in continuous remission (P < .008). CONCLUSION: PCR detection of high residual disease at the end of induction therapy identifies patients at increased risk for relapse during therapy.

Predominance of fetal type DJH joining in young children with B precursor lymphoblastic leukemia as evidence for an in utero transforming event.

The presence of N sequences in the complementarity determining region 3 (CDR3) of the rearranged immunoglobulin H chain is developmentally regulated: N regions are generally present in the DJH joinings of adult B cells but are often absent in fetal B cells. Analysis of the CDR3 in 61 B precursor acute lymphoblastic leukemias indicated that 87.5% of the leukemias obtained from children < or = 3 yr old lacked N regions at the DJH junction. In contrast, in children > 3 yr old, only 11.1% of the leukemias lacked N regions at this junction, a frequency similar to what we have observed in B cells from children and adults. These findings suggest that the majority of leukemias presenting within the first 3 yr of age arise from an in utero transforming event.

The pattern of joining (JH) gene usage in the human IgH chain is established predominantly at the B precursor cell stage.

Preferential utilization of JH and D genes has been demonstrated in the rearranged IgH chain in human peripheral B cells. We report here that the same hierarchy of JH gene usage is observed in leukemic cells arrested in the B precursor stage of differentiation. Specifically, JH4 and JH6 accounted for 42.9% and 35.7%, respectively, of the JH gene usage in the leukemias compared with an expected frequency of 16.7% assuming unbiased gene usage. Within the D gene families, the DN1 gene appears to be overutilized in both populations, representing about 15% of the total gene usage compared with an expected frequency of 3.2%. Because 21 of the 36 leukemias contained only nonproductive IgH rearrangements, the preferential gene usage could not have arisen from pre-B cells that have undergone clonal selection after a productive rearrangement but before surface Ig expression. Nonproductive rearrangements exhibited the biased gene usage seen for productive rearrangements. These findings suggest that a recombination bias favoring certain segments may be the actual mechanism responsible for the apparent preferential utilization of JH and D genes.

VH gene rearrangement events can modify the immunoglobulin heavy chain during progression of B-lineage acute lymphoblastic leukemia.

The presence of multiple VHDJH joinings in upwards of 30% of acute lymphoblastic leukemias (ALL) suggests a relative instability of the rearranged immunoglobulin heavy chain (IgH) gene, but the mechanisms involved are not completely understood. An investigation of the structure of the VHDJH joinings using complementarity determining region (CDR)3 polymerase chain reaction (PCR) in 12 leukemias at both diagnosis and relapse indicates that this instability may increase as a function of time. In only one of seven cases in which relapse occurred within 3 years from diagnosis was a new VHDJH joining identified and this coexisted with the original diagnostic joining. Most strikingly, new VHDJH joinings were identified in four of five cases in which relapse occurred more than 5 years from diagnosis. In this latter population, the instability of the joinings was generated from VH----VH gene replacement events in two cases, since the new joinings retained the original DJH sequences and partial N region homology at the VHD junction, and probably in a third case from a VH gene rearrangement to a common DJH precursor. Furthermore, in five of 23 (21.7%) additional cases studied at diagnosis, subclones were identified that had similar modifications of the VH-N region. These data indicate that VH gene replacement events and VH gene rearrangements to a common DJH joining contribute to the instability of the VHDJH joining in ALL. This phenomenon should be taken into consideration in those methodologies that exploit IgH rearrangements for detection of minimal residual disease.

Preferential utilization of specific immunoglobulin heavy chain diversity and joining segments in adult human peripheral blood B lymphocytes.

We have examined at the molecular level the CDR3 and adjacent regions in peripheral blood B lymphocytes of normal individuals. A total of 111 sequences (12-28 sequences from six individuals) were obtained after cloning of the polymerase chain reaction-amplified segments into plasmids or phage. The average length of the VDJ joining was 109 nucleotides, with a range from 79 to 151. Approximately 75% of the sequences were in frame when translated into amino acids. Among the JH segments, JH4 was found most frequently (in 52.5% of the sequences), and JH1 and JH2 segments the least frequently (approximately 1% of the clones). A polymorphic JH6 gene with a one-codon deletion accompanied by a base change was present in two of six patients. Preferential breakpoints were found for JH2, JH3, JH4, and JH5, although the breakpoints of JH6 were distributed more heterogenously. In approximately 90% of the cases, significant homology of the D regions with published D sequences was found. Preferential usage of a particular coding frame was observed in in-frame sequences utilizing DA, D21/9, and DM1 segments. However, in general, all coding frames of germline D genes were used to generate CDR3s. Eight sequences that have a DN1-like D sequence with two base changes at the same positions were identified, suggesting the likely existence of a new germ line D gene belonging to the DN families. Using probes specific for a particular CDR3, the frequency of a specific B cell clone in the peripheral blood of normal individuals was estimated to be at most as high as 1/20,000.

Minimal residual disease in childhood B-lineage lymphoblastic leukemia. Persistence of leukemic cells during the first 18 months of treatment.

BACKGROUND: Whether patients in clinical remission for acute lymphoblastic leukemia (ALL) continue to harbor leukemic cells is not known, because methods of detecting residual malignant cells have not been sufficiently sensitive. This information might be useful for predicting recurrence and determining the duration of therapy. METHODS: Using a sensitive new method--identifying complementarity-determining region III sequences with the polymerase chain reaction--we estimated the number of residual leukemic cells in the bone marrow of eight children with B-lineage lymphoblastic leukemia before and after remission. RESULTS: Induction chemotherapy produced a 3-to-4-log reduction in the number of leukemic cells. In all samples obtained up to 18 months after diagnosis, however, 0.004 to 2.6 percent of bone marrow nucleated cells were residual leukemic cells. Among the four patients studied more than 18 months after diagnosis, three had no detectable leukemic cells in marrow samples. Despite this, one of them, who was no longer receiving therapy, had a central nervous system relapse. In one patient receiving maintenance chemotherapy, there was a 60-fold increase in leukemic cells three months before bone marrow relapse. CONCLUSIONS: The complete disappearance of leukemic cells (or their reduction below our method's threshold of detection, 1 in 100,000 cells) may be necessary to achieve a cure of ALL. The quantification of residual leukemic cells in serial marrow aspirates during therapy may allow the early detection of relapse.

Point mutations in both transforming and non-transforming codons of the N-ras proto-oncogene of Ph+ leukemias.

The distribution and frequency of point mutations in the first and second coding exons of the N-ras proto-oncogene was examined in 6 cases of Philadelphia positive (Ph+) hemopoietic malignancies. To increase the detection sensitivity of the mutations and to estimate more accurately the frequency of abnormal alleles in the hemopoietic cell population, a polymerase chain reaction (PCR)/shotgun cloning/double stranded DNA sequencing method was used. Mutations activating the ras oncogenes involving codon 61 were observed in 5 out of 6 cases; in one of these cases (CML3), mutation at codon 61 involved a two base transition. Mutations involving codon 59 were also observed in one case (CML1). In longitudinal studies of 3 cases of chronic myelogenous leukemia samples obtained at the time of initial diagnosis and 5 to 7 years later, a multiplicity of mutations were detected at the time of initial diagnosis prior to any therapy. In one case (CML3), a mutation in codon 61 detected at diagnosis was still present 5 years later, in a second case (CML1) a mutation in codon 61 appeared during the course of the disease and persisted for at least one year, and in the third case (CML2) a mutation in codon 61 was present at diagnosis but absent 5 years later. In one instance (CML1) a mutation in codon 59 was present at the time of initial diagnosis but was not detectable in later samples. Several other point mutations leading to aminoacid changes were scattered predominately through the second exon but were not consistently detected in longitudinal studies on cells from the same patient. The data suggest that there is considerable genetic instability in the 2nd exon of N-ras in the myeloid leukemias but in every case a small subset of cells contains the mutations and these cells do not have a proliferative advantage.