Development of a sensitive PCR to detect allele loss in a model hematopoietic neoplasm

Finer delineation and transcript map of the 7q31 locus deleted in myeloid neoplasms

Acquired complete and partial deletions of chromosome 7 are associated with several malignancies. In acute myelogenous leukemia (AML) and preleukemic myelodysplasia (MDS), loss of chromosome 7 portends a poor clinical outcome. The identity of a classical leukemia suppressor gene, however, has been elusive. Previously, we defined a candidate suppressor locus of approximately 6 Mb in the 7q31 interval. Here we report an island of retention of heterozygosity within this interval in a case of monosomy 7. Allelotyping of AML cell lines revealed that ML3 and HEL cells, karyotypically diploid for chromosome 7, are hemizygous for all the 7q31 loci, implicating loss of the wild type and duplication of the remaining chromosome 7. Based on the completed genomic sequence of chromosome 7, we have generated a transcript map of the critical region of loss (between the D7S525 and D7S2502 loci). Notably, a recently characterized tumor suppressor gene, DOCK4, and an evolutionarily conserved zinc finger gene, ZNF277, localize to this interval, head to head, within <0.5 kb of each other. Thus, the reagents generated in this study will be valuable in elucidating the role of loss of 7q31 loci in the pathogenesis of AML.

Deletions of chromosome 5q13.3 and 17p loci cooperate in myeloid neoplasms

Nonrandom interstitial deletions and monosomy of chromosomes 5, 7, and 17 in refractory myelodysplasia (MDS) and acute myelogenous leukemia (AML) suggest a multistep pathway that culminates in aggressive clinical course. Because cytogenetic studies frequently identify chromosome 5 and 17 deletions within a single clone, we searched for allele loss for 5q loci and TP53 gene mutations in the same leukemic samples. Cosegregating deletions of chromosomes 5 and 17 were found to specifically include the 5q13.3 interval between the lociD5S672 and D5S620/D5S626, a locus hypothesized to harbor a tumor suppressor gene1 and the TP53 gene on 17p. A rare patient with secondary refractory MDS and an unbalanced translocation [der(5;17)], which resulted in deletions of the 5q13.3-qter and 17p loci, provided clues on the sequence of genetic alterations. Serial molecular analysis of this patient revealed a dysplastic clone with der(5;17), which gave rise to a leukemic clone on acquiring an inactivating mutation of TP53. Our findings are consistent with functional cooperation between a putative tumor suppressor gene at 5q13.3 that contributes toward the progression of early stages of MDS, and the TP53 gene when mutated, causes transformation to AML.

5q- in a child with refractory anemia with excess blasts: similarities to 5q- syndrome in adults

A 19-month-old boy was referred to our institution because of chronic macrocytic anemia and severe thrombocytopenia. At age 17 months, he had developed petechiae. He had a leukocyte count of 4.4 x 10(9)/L, hemoglobin concentration of 7.9 g/dL, packed cell volume of 21%, mean corpuscular volume of 101 fL, and platelet count of 19 x 10(9)/L. At the time of referral, a bone marrow aspirate and biopsy revealed myelodysplastic changes that included megakaryocytic hyperplasia with hypolobated megakaryocytes, megaloblastoid erythropoiesis, 12% blast cells, and bone marrow fibrosis; the diagnosis was refractory anemia with excess blasts (RAEB). Cytogenetic analysis showed the following abnormalities: 47, XY, inv(3)(p21q25), del(5)(q22q31), +21/46, XY. By dinucleotide polymorphism analysis, the 5q22-q31 loci were normal in peripheral blood granulocytes. Because of severe thrombocytopenia that became refractory to platelet transfusions and because of possible progression to leukemia, the patient received an unrelated-donor bone marrow transplant. Recovery was complicated by a visceral fungal infection, but the patient now has normal, fully reconstituted bone marrow function. This patient is the youngest to be reported with RAEB and a 5q- anomaly accompanied by thrombocytopenia, megakaryocytic hyperplasia with hypolobated megakaryocytes, and macrocytic anemia with megaloblastoid erythropoiesis, similar to "5q- syndrome" in adults.

Molecular anatomy of chromosome 7q deletions in myeloid neoplasms: evidence for multiple critical loci

Complete or partial deletions of the long arm of chromosome 7 (7q- and -7) are nonrandom abnormalities seen in primary and therapy-induced myelodysplasia (MDS) and acute myelogenous leukemia (AML). Monosomy 7, occurring as the sole cytogenetic anomaly in a small but significant number of cases, may denote a dominant mechanism involving critical tumor suppressor gene(s). We have determined the extent of allele loss in cytogenetically prescreened MDS and AML patients for microsatellite markers from chromosome 7q22 and 7q31. Whereas >80% of these cases revealed allele loss for the entire region, a rare case of the 7q- chromosome showed allele loss for only the proximal 7q31.1 loci flanked by the markers D7S486 and D7S2456, and a case of monosomy 7 revealed allele loss for loci at both 7q31 and 7q22 with retention of sequences between these sets of loci. Furthermore, a case of AML with no cytogenetic anomaly of chromosome 7 revealed a submicroscopic allelic imbalance for a third distal locus, D7S677. These findings suggest the presence of three distinct critical loci that may contribute alone or in combination to the evolution of MDS and AML. The data also provide molecular evidence for unbalanced translocation with noncontiguous deletions, as an alternate mechanism underlying monosomy 7.

Physical mapping of the minimal region of loss in 5q- chromosome

Acquired interstitial loss of all or part of the long arm of human chromosome 5 (5q-) is an anomaly that is seen frequently in patients with preleukemic myelodysplasia and acute myelogenous leukemia. Loss of a critical region of overlap at band 5q31.1 in all of these cases, with various cytogenetic breaks, signifies the existence of a key negative regulator of leukemogenesis. Previous studies have defined the proximal and distal ends of the critical region to reside between the genes for IL9 and EGR1, respectively. In this report, we describe a yeast artificial chromosome contig spanning this myeloid tumor suppressor locus. The combined order of the polymorphic loci is centromere-IL9-(D5S525-D5S558-D5S89-D5S526 -D5S393)-D5S399-D5S396-D5S414-EGR1 and telomere. The physical distance between the IL9 and EGR1 genes is estimated to be < 2.4 Mb. Here we report the utility of these polymorphic loci by detecting a submicroscopic deletion of 5q31; an acute myelogenous leukemia patient with a three-way translocation, t(5;18;17)(q31;p11;q11), as the sole anomaly revealed allele loss of the D5S399 and D5S396 loci.