Chromosome 21-Encoded microRNAs (mRNAs): Impact on Down's Syndrome and Trisomy-21 Linked Disease.

Down's syndrome (DS; also known as trisomy 21; T21) is caused by a triplication of all or part of human chromosome 21 (chr21). DS is the most common genetic cause of intellectual disability attributable to a naturally-occurring imbalance in gene dosage. DS incurs huge medical, healthcare, and socioeconomic costs, and there are as yet no effective treatments for this incapacitating human neurogenetic disorder. There is a remarkably wide variability in the 'phenotypic spectrum' associated with DS; the progression of symptoms and the age of DS onset fluctuate, and there is further variability in the biophysical nature of the chr21 duplication. Besides the cognitive disruptions and dementia in DS patients other serious health problems such as atherosclerosis, altered lipogenesis, Alzheimer's disease, amyotrophic lateral sclerosis (Lou Gehrig's disease), autoimmune disease, various cancers including lymphoma, leukemia, glioma and glioblastoma, status epilepticus, congenital heart disease, hypotonia, manic depression, prostate cancer, Usher syndrome, motor disorders, Hirschsprung disease, and various physical anomalies such as early aging occur at elevated frequencies, and all are part of the DS 'phenotypic spectrum.' This communication will review the genetic link between these fore-mentioned diseases and a small group of just five stress-associated microRNAs (miRNAs)-that include let-7c, miRNA-99a, miRNA-125b, miRNA-155, and miRNA-802-encoded and clustered on the long arm of human chr21 and spanning the chr21q21.1-chr21q21.3 region.

Comparison of aneuploidies of chromosomes 21, X, and Y in the blood lymphocytes and sperm of workers exposed to benzene.

Benzene is a primary industrial chemical and a ubiquitous environmental pollutant that causes human leukemia and maybe other malignancies. Occupational exposure to benzene has been associated with increased chromosomal aneuploidies in blood lymphocytes and, in separate studies, in sperm. However, aneuploidy detection in somatic and germ cells within the same benzene-exposed individuals has never been reported. To compare aneuploidies in blood lymphocytes and sperm within the same individuals exposed to benzene, a cross-sectional study was conducted in 33 benzene-exposed male workers and 33 unexposed workers from Chinese factories. Air benzene concentrations in the exposed workers ranged from below the detection limit to 24 ppm (median, 2.9 ppm) and were undetectable in the unexposed subjects. Aneuploidies of chromosomes 21, X, and Y in blood lymphocytes were examined by multicolor fluorescence in situ hybridization and were compared to the previously reported aneuploidies in sperm. The results showed that benzene exposure was positively associated with the gain of chromosome 21 but not sex chromosomes in blood lymphocytes. This was in contrast to analysis of sperm, where the gain of sex chromosomes, but not chromosome 21, was significantly increased in the exposed workers. Furthermore, a significant correlation in the gain of sex chromosomes between blood lymphocytes and sperm was observed among the unexposed subjects, but not among the exposed workers. The findings suggest that benzene exposure induces aneuploidies in both blood cells and sperm within the same individuals, but selectively affects chromosome 21 in blood lymphocytes and the sex chromosomes in sperm.

t(3;21)(q26;q22) in myeloid leukemia: an aggressive syndrome of blast transformation associated with hydroxyurea or antimetabolite therapy.

BACKGROUND: The t(3;21)(q26;q22) translocation is associated with myeloid leukemias and results in a chimeric oncoprotein containing AML1/RUNX1 variably fused to EAP, MDS1, and/or EVI1. METHODS: The current study describes what to the authors' knowledge is the first large case series reported to date of 26 t(3;21)(q26;q22)-associated leukemias, in which 24 cases arose after chemotherapy. Conventional G-band karyotyping and flow cytometry immunophenotyping were performed. Reverse transcriptase-polymerase chain reaction (RT-PCR) was performed to detect fusion transcripts between AML1 and EAP, MDS1, or EVI1, followed by DNA sequencing. RESULTS: In all 16 patients with chronic myeloproliferative disorders, including 14 with chronic myelogenous leukemia (CML), the occurrence of t(3;21) heralded myeloid blast transformation. Fifteen (93%) patients had been previously treated with hydroxyurea. Eight patients with chronic myeloproliferative disorders (CMPD) were found to have t(3;21) with t(9;22) as the sole cytogenetic abnormality; in 5 other patients this was accompanied by trisomy 8. Among 10 cases of t(3;21)-associated acute myeloid leukemia, 8 were secondary tumors after chemotherapy for other neoplasms that had been treated with regimens including fludarabine and 5-fluorouracil in 3 patients each and etoposide in 2 patients. The immunophenotype of the blasts in all 22 tested cases was similar, with uniform expression of myeloid markers and CD34 and variable expression of CD7 and CD9, but minimal morphological myeloid maturation. Dysplastic micromegakaryocytes and bone marrow fibrosis were observed predominantly in CMPD cases. RT-PCR followed by DNA sequencing showed that the AML1-/MDS1-/EVI1 (AME) fusion transcript was detected in all 5 cases assessed. Among the patients with CMPD, 8 died of disease (at a median of 6.5 mos) and 5 achieved disease remission with bone marrow transplantation. Among patients with acute myeloid leukemia/myelodysplastic syndrome, 7 died of disease (at a median of 2 mos) and 2 had persistent leukemia with short follow-up. CONCLUSIONS: Activation of AME through t(3;21) defines a highly aggressive, therapy-related leukemic blast syndrome. Prior treatment with hydroxyurea or other antimetabolites is implicated as a contributory cause.

21q22 balanced chromosome aberrations in therapy-related hematopoietic disorders: report from an international workshop.

The International Workshop on the relationship between prior therapy and balanced chromosome aberrations in therapy-related myelodysplastic syndromes (t-MDS) and therapy-related acute leukemia (t-AL) identified 79 of 511 (15.5%) patients with balanced 21q22 translocations. Patients were treated for their primary disease, including solid tumors (56%), hematologic malignancy (43%), and juvenile rheumatoid arthritis (single case), by radiation therapy (5 patients), chemotherapy (36 patients), or combined-modality therapy (38 patients). 21q translocations involved common partner chromosomes in 81% of cases: t(8;21) (n = 44; 56%), t(3;21) (n = 16; 20%), and t(16;21) (n = 4; 5%). Translocations involving 15 other partner chromosomes were also documented with involvement of AML1(CBFA2/RUNX1), identifying a total of 23 different 21q22/AML1 translocations. The data analysis was carried out on the basis of five subsets of 21q22 cases, that is, t(8;21) with and without additional aberrations, t(3;21), t(16;21), and other 21q22 translocations. Dysplastic features were present in all 21q22 cases. Therapy-related acute myeloid leukemia (t-AML) at presentation was highest in t(8;21) (82%) and lowest in t(3;21) (37.5%) patients. Cumulative drug dose exposure scores for alkylating agents (AAs) and topoisomerase II inhibitors indicated that t(3;21) patients received the most intensive therapy among the five 21q22 subsets, and the median AA score for patients with secondary chromosome 7 aberrations was double the AA score for the entire 21q22 group. All five patients who received only radiation therapy had t(8;21) t-AML. The median latency and overall survival (OS) for 21q22 patients were 39 and 14 months (mo), compared to 26 and 8 mo for 11q23 patients, 22 and 28 mo for inv(16), 69 and 7 mo for Rare recurring aberrations, and 59 and 7 mo for Unique (nonrecurring) balanced aberration (latency P < or = 0.016 for all pairwise comparisons; OS, P < or = 0.018 for all pairwise comparisons). The percentages of 21q22 patients surviving 1 year, 2 years, and 5 years were 58%, 33%, and 18%, respectively. Noticeable differences were observed in median OS between 21q22 patients (n = 7) receiving transplant (BMT) (31 mo) compared to 21q22 patients who received intensive non-BMT therapy (n = 46) (17 mo); however, this was nonsignificant because of the small sample size (log-rank, P = 0.33). t-MDS/t-AML with balanced 21q22 aberrations was associated with prior exposure to radiation, epipodophyllotoxins, and anthracyclines, dysplastic morphologic features, multiple partner chromosomes, and longer latency periods when compared to 11q23 and inv(16) t-MDS/AML Workshop subgroups. In general, patients could be divided into two prognostic risk groups, those with t(8;21) (median OS, 19 mo) and those without t(8;21) (median OS, 7 mo) leukemia (log-rank, P = 0.0007).

Incidence of sperm aneuploidy in relation to semen characteristics and assisted reproductive outcome.

OBJECTIVE: To evaluate the incidence of sperm aneuploidy in men screened for infertility and identify any eventual relation with assisted reproductive outcome. DESIGN: Controlled prospective study. SETTING: University hospital-based IVF program. PATIENT(S): Infertile couples who were screened for sperm aneuploidy and evaluated for IVF treatment. INTERVENTION(S): Fluorescence in situ hybridization was used to identify chromosomes 18, 21, X, and Y. The assisted reproductive techniques of IVF and intracytoplasmic sperm injection were used for infertility treatment. MAIN OUTCOME MEASURE(S): The incidence of sperm aneuploidy, semen parameters, fertilization rate, pregnancy characteristics, and rate of neonatal malformations were determined. RESULT(S): Oligozoospermic and teratozoospermic men had a significantly higher incidence of chromosomal abnormalities than men with normal semen parameters (2.7% vs. 1.8%). The increased frequency of sperm aneuploidy did not appear to affect pregnancy losses or the occurrence of neonatal malformations. CONCLUSION(S): Suboptimal semen samples had a higher incidence of aneuploidy. In this study, the increased frequency of chromosomal abnormalities did not have a direct effect on the fertilization rate, pregnancy characteristics, or neonatal outcome.

[Chromosome translocations and leukemias induced by inhibitors of topoisomerase II anticarcinogenic drugs]. / Translocations chromosomiques et leucémies induites par les médicaments anticancéreux inhibiteurs de la topo-isomérase II.

The treatment of cancer with alkylating drugs or topoisomerase II inhibitors can be responsible for the development of myelodysplastic syndromes and acute myelogenous leukemia. Alkylating agents such as melphalan and cisplatinum mainly produce damages at chromosomes 5 and 7 whereas topoisomerase II inhibitors-induced lesions essentially affect chromosomes 11 and 21. Rearrangements of the MLL gene at band 11q23 are frequently observed in human de novo myeloid and lymphoid leukemia as well as in leukemia or myelodysplasia secondary to therapy with drugs targetting topoisomerase II such as the epipodophyllotoxins. A relationship between the treatment with etoposide on teniposide and the development of translocations of the MLL gene has been clearly evidenced. The potential molecular basis of the chromosomal rearrangements implicating topoisomerase II and its inhibitors are discussed. The chemical structure of the inhibitors, their mechanism of action and the genes targetted by these drugs are presented. DNA cleavages induced directly by topoisomerase II inhibitors or by the drug induced apoptotic cellular response are responsible for nonrandom chromosomal aberrations and contribute to leukemogenesis.

Increased translocations and aneusomy in chromosomes 8 and 21 among workers exposed to benzene.

Chromosome aberrations in peripheral blood lymphocytes have been used for many years to monitor human populations exposed to potential carcinogens. Recent reports have confirmed the validity of this approach by demonstrating that elevated levels of chromosome aberrations in lymphocytes are associated with subsequent increased cancer risk, especially for increased mortality from hematological malignancies including acute myeloid leukemia (AML). We postulated that this approach could be improved in two ways: (a) by detecting oncogenic disease-specific aberrations; and (b) by using chromosome painting so that many more metaphases could be analyzed. Numerical and structural aberrations in chromosomes 8 and 21 are commonly observed in AML. In the present study, we painted chromosomes 8 and 21 in lymphocyte metaphases from 43 healthy workers exposed to benzene, an established cause of AML, and from 44 matched controls. To examine dose-response relationships the workers were divided into two groups at the median exposure level, a lower-exposed group (< or = 31 ppm; n = 21), and a higher-exposed group (> 31 ppm; n = 22). Benzene exposure was associated with significant increases in hyperdiploidy of chromosomes 8 (1.2, 1.5, and 2.4 per 100 metaphases; P < 0.0001) and 21 (0.9, 1.1, and 1.9 per 100 metaphases; P < 0.0001). Translocations between chromosomes 8 and 21 were increased up to 15-fold in highly exposed workers (0.01, 0.04, and 0.16 per 100 metaphases; P < 0.0001). In one highly exposed individual, these translocations were reciprocal and were detectable by reverse transcriptase-PCR. These data indicate a potential role for t(8;21) in benzene-induced leukemogenesis and are consistent with the hypothesis that detection of specific chromosome aberrations may be a powerful approach to identify populations at increased risk of leukemia.

Preferential sensitivity of acrocentric chromosomes to the aneugenic effect of colchicine.

In order to evaluate the predisposition to the aneuploidy-inducing agent colchicine (Col) on lymphocytes from trisomic 21 patients compared with their parents and with a control group of subjects without trisomic children, we performed the micronucleus (MN) assay associated with C-banding, CREST staining, and nucleolar organizing region (NOR)-banding. According to our results Col behaves as an aneugenic agent independently of the population studied for CREST and C-banding. The Col-induced MN exhibited a clear majority (> 80%) of positive NOR-MN, meaning that they contain a NOR region transcriptionally active or inactive. The same data were observed in trisomic 21 individuals, their parents, and the control group, without significant differences between them. These results seem to suggest a preferential effect of the aneugen Col on acrocentric chromosomes in all of the three groups studied.

Use of tissue culture models to study environmental-genetic interactions relevant to neurodegenerative diseases.

1. Clonal cell lines, primary cultured neurones and transgenic animals expressing mutant genes linked to familial forms of neurodegenerative diseases provide models in which to examine the interaction between expression of a predisposing gene and exposure to neurotoxic chemicals. Methods of establishing these models are reviewed. 2. Mutations in the gene encoding Cu/Zn-superoxide dismutase (SOD-1) have been identified in cases of familial amyotrophic lateral sclerosis linked to chromosome 21. We report that in clonal lines of PC12 cells, the cytotoxicity of a glutathione-depleting epoxide, styrene oxide, varied with SOD activity in a manner similar to that previously demonstrated for redox cycling chemicals. These preliminary data suggest that either low or high SOD-1 activities may be associated with greater toxicity of a variety of neurotoxic chemicals and their metabolites.

Transient expression of trisomy 21 and monosomy 7 following cyclosporin A in a patient with aplastic anemia.

We present a patient with severe idiopathic aplastic anemia with no previous chromosomal abnormalities who developed trisomy 21 and monosomy 7 during treatment with intravenous (i.v.) cyclosporine. The abnormal karyotype disappeared when the drug was changed to the oral form. This cytogenetic aberration, previously unreported in association with cyclosporine, may reflect either a direct drug effect or the emergence of a hidden myelodysplastic cell clone subject to preferential survival during immunosuppression.