1/6. A case of elevated spontaneous micronucleus frequency derived from chromosome 2.This work tested the hypothesis that the content of spontaneous micronuclei in lymphocytes in an apparently healthy normal human subject, who exhibited an unusually high micronucleus frequency, was non-random. Several dna probes were used in fluorescent in-situ hybridization (FISH), beginning with a probe generated from the subject's micronuclei. Micronuclei obtained from peripheral blood lymphocytes by microdissection were subjected to random amplification of polymorphic DNA (RAPD-PCR), and a unique PCR product was then used to isolate a cosmid clone from a human genomic library. This clone hybridized to chromosome 2. Subsequently, commercial probes were included in FISH analyses of micronuclei from the subject and age- and sex-matched controls. No significant differences were found between subject and controls in the percentages of micronuclei hybridizing with a centromere probe for the x chromosome or a painting probe for chromosome 3. However, the subject had a very highly significant increase (p<0.0001) in chromosome 2 in micronuclei over a level that might be expected to be present by chance. Characterization of micronuclei may be a promising tool in studies of mechanisms of inherited or induced chromosome instability. The strength of the strategy employed in this study is that, by characterizing the chromosomes present in micronuclei, this work has advanced from an observation of chromosomal instability to a foundation for study of the mechanism underlying the observation. ( info) |
2/6. Micronuclei in peripheral blood lymphocytes as a possible cancer risk biomarker: a cohort study of occupationally exposed workers in croatia.AIM: To describe the cohort of Croatian workers monitored for micronuclei in peripheral blood lymphocytes and validate predictive value of micronuclei for the risk of cancer development. methods: Between 1985 and 1999, peripheral blood lymphocytes were analyzed with in vitro micronucleus assay in a cohort of 200 subjects occupationally exposed to genotoxic agents. The follow-up for cancer incidence and mortality was performed through the Croatian National Cancer Registry and records of occupational medicine physicians. Micronucleated cell frequency values were compared by Kruskal-Wallis test. RESULTS: The median micronucleated cell frequency value in the cohort was 49 (range, 30-79) per thousand cells. Micronucleated cell frequency was significantly higher in men than in women, which could be attributed to the different distribution of exposures. Micronucleated cell frequency increased with age for both sexes. smoking habit had no influence on micronucleated cell frequency. The follow-up identified four cases of cancer. Three of them belonged to the highest micronucleated cell frequency tertile. CONCLUSION: Due to a small number of cancer cases, the predictive value of micronuclei for the risk of cancer development in the cohort of Croatian workers was not estimated, but 4 identified cases were more than expected in a similar non-exposed group. The Croatian cohort will contribute to the pooled analysis of the current European study of predictive value of micronuclei for the risk of cancer development. ( info) |
3/6. Chromosome instability in ICF syndrome: formation of micronuclei from multibranched chromosomes 1 demonstrated by fluorescence in situ hybridization.We report on a new patient with immunodeficiency, centromeric heterochromatin instability, and facial anomalies (the ICF syndrome). Studies with traditional cytogenetic methods demonstrate that aberrations in this syndrome primarily involve the centromeric regions of chromosomes 1 and 16. We applied fluorescence in situ hybridization (FISH) using "painting" probes for chromosomes 1 and 16 to document the progression of centromeric instability from simple decondensation aberrations to the subsequent formation of complex multibranched chromosomes 1, and finally to the interphase aberrations of nuclear projections and micronuclei involving both chromosomes 1 and 16. The loss of the large multibranched chromosome 1 configurations from the cells as micronuclei suggests that the centromeric aberrations subsequently interfere with normal chromosome movement at anaphase in ICF syndrome. Circular areas of counterstained chromatin were observed by FISH in the micronuclei corresponding to the intertwined segments of centromeric heterochromatin seen involving multibranched chromosomes 1 in the patient's G-banded chromosome study. The current hypothesis of recessive inheritance for this disorder suggests that the chromosomal aberrations are not a causative event in this syndrome; however, the chromosome aberrations are clearly an important basic diagnostic criterion. ( info) |
4/6. Effect of in vivo exposure to iodine-131 on the frequency and persistence of micronuclei in human lymphocytes.The validity of the micronucleus test as a biomarker of chromosome damage in dividing mammalian cells is well established. This assay was used to study the response of peripheral lymphocytes of a 34-yr-old male patient following treatment with 131I ablative radiation therapy following a total thyroidectomy. Coincidentally, 8 mo before diagnosis, the patient had provided a blood sample for an in vitro study of micronucleus induction following exposure to graded doses of x-rays. The background frequency in the unexposed culture showed a mean count of 6.0 micronuclei per 1000 binucleated (first division) lymphocytes, while mean values of 18.5, 29.0, 41.0, 61.0 and 75.5 micronuclei/1000 cells were observed following x-ray doses of 5, 10, 15, 20, and 25 cGy, respectively. These data fit a nonthreshold, linear dose-response function (y = 2.78x 3.71; r = .99). Eight months after the in vitro x-ray study, the subject was diagnosed with thyroid cancer. Surgery was performed, and 5 wk later the patient received 1.78 GBq (48 mCi) of 131I as adjuvant radiation therapy. blood was drawn 11 d after the radiation treatment and at monthly intervals thereafter to analyze the frequency and persistence of micronuclei. The first posttreatment sample showed 35.5 micronuclei per 1000 binucleate cells. Based on the linear dose-response equation from the earlier study, the sixfold increase in micronucleus frequency suggests a dose to the peripheral blood of approximately 11 cGy. The cytogenetic dose estimate compares to approximately 30 cGy using a new model based on external whole-body counting data. Nine consecutive monthly samples have been analyzed to date. Although the micronucleus count has fluctuated (four- to sixfold above background), the frequency after 8 mo is equivalent to the first posttreatment sample. Data show that radiation-induced cellular lesions persist for months following relatively brief radiation exposure to a medical isotope. Results of this study support the conclusion that the lymphocyte micronucleus test is a rapid, sensitive, and perhaps quantitative biomarker of low-dose (< 25 cGy) radiation exposure. ( info) |
5/6. Centromeric instability of chromosome 1 resulting in multibranched chromosomes, telomeric fusions, and "jumping translocations" of 1q in a human immunodeficiency virus-related non-Hodgkin's lymphoma.BACKGROUND. acquired immunodeficiency syndrome-related non-Hodgkin's lymphomas are associated with the B-cell chromosomal translocation t(8;14)(q24; q32). The most common secondary chromosome aberrations in these patients involve 1q and are believed to be associated with tumor progression. A mechanism for the origin of these 1q aberrations has not been demonstrated. To their knowledge, the authors report the first human immunodeficiency virus (hiv)-positive patient to have centromeric decondensation and multibranched chromosome aberrations of chromosomes 1 and 16 resulting in telomeric associations and "jumping translocations" of 1q. methods. Tumor cells from peritoneal fluid of an hiv-positive patient were cultured for 24, 48, and 72 hours and analyzed by both conventional G-banding and fluorescence in situ hybridization. RESULTS. G-band analysis showed a stemline with t(8;14)(q24;q32), but also showed the progression from centromeric decondensation to multibranched chromosome configurations of chromosomes 1 and 16. The interchange and duplications of chromosome arms resulted in the gain of extra copies of 1q material on a number of different chromosomes, but also the loss of 16q in at least one sideline and the formation of micronuclei. fluorescence in situ hybridization analysis demonstrated that micronuclei predominantly involved chromosome 1 and, to a lesser extent, chromosome 16. CONCLUSIONS. The cytogenetic findings in this unique case suggest that immunodeficiency may be a factor involved in centromeric instability, multibranching, and the progression to the subsequent formation of telomeric fusions and multiple unbalanced translocations of 1q (jumping translocations). The striking similarity of the centromeric instability in this patient to those with ICF syndrome (variable immunodeficiency, centromeric heterochromatin instability, and facial anomalies) suggests hypomethylation as the etiologic mechanism for the chromosome instability. ( info) |
6/6. Acute radiodermatitis from accidental overexposure to x-rays.Approximately 2 weeks after accidental overexposure to X-ray radiation, a worker developed acute radiodermatitis on fingers of both hands. Exposure simulation indicated that total ionizing radiation absorbed by his fingers amounted to about 20 Gy. After 2 years, acute radiodermatitis evolved to chronicity of lesions with presence of atrophic skin, teleangiectasia, alopecia, and dyskeratosis on three right-hand fingers. Cytogenetic dosimetry of peripheral blood lymphocytes, performed 2 months after acute radiation, showed an increase of micronuclei (7% vs. 1 /- 0.4% according to laboratory reference data). The increase was ascribed to the high dose of ionizing radiation absorbed by circulating lymphocytes in the vessels of overexposed tissues. The cytogenetic examination was repeated 27 months after acute irradiation; it was found that the percentage of micronuclei had been restored to within reference levels. The possibility of using cytogenetic dosimetry, following acute partial exposure to x-rays, not just as an indicator of previous exposure, but also as an indicator of the absorbed radiation dose is examined. Lastly, the possible stochastic effects that may set in on the skin of the affected fingers and the need for periodically monitoring the evolution of chronic skin lesions, are discussed. ( info) |