Breast cancer at Hiroshima and Nagasaki

A calculation is made of the incidence of breast cancer at Hiroshima and Nagasaki using the dosimetry of Straume and Dobson. Gamma rays cause a mutation in a critical gene. Using a two hit theory, an estimate of the number of target cells and a time period of 24 years, an estimate of the probability of carcinogenesis is obtained which is in good agreement with observation.     

X-ray or gamma-ray leukemogenesis at Hiroshima and Nagasaki

Because of the uncertainty in dosimetry at the Japanese cities, I have recalculated the probability of x-ray or gamma-ray leukemogenesis using the revised doses given by the Livermore group. The theory is of the two hit type. The first hit damages DNA repair capability of base damage. The second hit causes derepression of a two repressor system. Inactivation of the first repressor permits synthesis of the second which will repress the expression of the leukocyte maturation gene. In comparing the observed data, I convert data expressed as mortality per year to leukemia incidence. I also supply evidence of the lack of the importance of chromosomal aberration and consider CML, AML, and ALL data lumped together. Agreement between theory and observation is good.     

Aging in Hiroshima and Nagasaki Atomic Bomb Survivors: Speculations Based upon the Age-Specific Mortality of Persons with Malignant Neoplasms

Evaluation of 1639 malignant tumors from 3067 autopsies of members of the Extended Life Span Study Sample reveals that death occurs earlier in those persons most heavily irradiated ([unk]100 rad) compared with those persons who were less exposed. This effect is particularly pronounced in the younger age categories and among females and is not attributable to a specific neoplasm. Assuming that a positive correlation exists between aging and the age-specific mortality of persons with neoplasms, it is concluded that this response is consistent with other observations which suggest the presence of accelerated or precocious aging in the most heavily irradiated group of survivors.     

Heritability of baseline and induced micronucleus frequencies

The scoring of micronuclei (MN) is widely used in biomonitoring and mutagenicity testing as a surrogate marker of chromosomal damage inflicted by clastogenic agents or by aneugens. Individual differences in the response to a mutagenic challenge are known from studies on cancer patients and carriers of mutations in DNA repair genes. However, it has not been studied to which extent genetic factors contribute to the observed variability of individual MN frequencies. Our aim was to quantify this heritable genetic component of both baseline and radiation-induced MN frequencies. We performed a twin study comprising 39 monozygotic (MZ) and 10 dizygotic (DZ) twin pairs. Due to the small number of DZ pairs, we had to recruit controls from which 38 age- and gender-matched random control pairs (CPs) were generated. For heritability estimates, we used biometrical modelling of additive genetic, common environmental, and unique environmental components (ACE model) of variance and direct comparison of variance between the sample groups. While heritability estimates from MZ to DZ comparisons produced inconclusive results, both estimation methods revealed a high degree of heritability (h(2)) for baseline MN frequency (h(2) = 0.68 and h(2) = 0.72) as well as for the induced frequency (h(2) = 0.68 and h(2) = 0.57) when MZ were compared to CP. The result was supported by the different intraclass correlation coefficients of MZ, DZ and CP for baseline (r = 0.63, r = 0.31 and r = 0.0, respectively) as well as for induced MN frequencies (r = 0.79, r = 0.74 and r = 0.0, respectively). This study clearly demonstrates that MN frequencies are determined by genetic factors to a major part. The strong reflection of the genetic background supports the idea that MN frequencies represent an intermediate phenotype between molecular DNA repair mechanisms and the cancer phenotype and affirms the approaches that are made to utilise them as predictors of, for example, cancer risk.     

Fluorescent chromosome polymorphisms: frequencies and segregations in a Dutch population

A study of the frequencies and segregation behaviour of fluorescent chromosome polymorphisms within a Dutch population is presented. The polymorphism patterns for chromosomes 1, 3, 4, 9, 13, 14, 15, 16, 21 and 22 were scored from 221 (108 female and 113 male) individuals with normal karyotype. Males and females were both found to carry an average of 4 polymorphic chromosomes per person, and approximately half of these were present in chromosomes No. 3 and 13. There was no significant difference between the frequencies per chromosome for the two sexes, and the data for chromosomes 3, 4, 14, 21 and 22 fitted a Hardy-Weinberg distribution. However, for chromosomes 13 and 15 an excess of heterozygotes and a lack of homozygotes was observed. Although the segregation behaviour of most chromosomes studied appeared to be mendelian, the segregation of chromosome No. 13 showed a lack of homozygotes without polymorphism. Possible mechanisms accounting for this effect are discussed.     

Comparison of hprt variant frequencies and chromosome aberration frequencies in lymphocytes from radiotherapy and chemotherapy patients: a prospective study

The autoradiographic 6-thioguanine-resistant mutant lymphocyte assay and a chromosome aberration assay were used to determine the time-course of appearance and persistence of elevated frequencies of hprt variants and dicentric chromosomes in patients receiving x-irradiation therapy. Twelve cancer patients, treated with 180-200 cGy/day, 5 days/wk, for 3-7 wk, were studied before treatment, at various weekly intervals during treatment, and after treatment. The hprt mutation assays were done with frozen/thawed lymphocytes isolated from aliquots of the same blood samples used for the chromosome aberration assays. The hprt variant frequencies (Vfs) of only 4 of the 7 patients assayed at 2 wk of treatment were elevated over pre-treatment Vfs, but during the 3rd and 4th weeks of treatment there were significant (P less than 0.01) 5- to 15-fold increases in all Vfs. By 6-32 wk after treatment Vfs had fallen to levels only slightly higher than the mean pre-treatment Vf. The frequencies of cells with dicentric chromosomes were significantly increased (P less than 0.01) after 1 wk of radiotherapy, continued to increase during therapy, and remained elevated after treatment. Five multiple sclerosis patients were also studied before and at 2 and 4 wk intervals after treatment with monthly i.v. doses of 750 mg/m2 of cyclophosphamide (CP). There were no significant elevations in chromosome aberrations at these post-treatment sample times. Previous assays for hprt mutants, done with aloquots of the same blood samples (Ammenheuser et al.: Mutat Res 204:509-520, 1988), had shown 8- to 20-fold increases in Vfs 2 wk after the 1st CP treatment. Our results demonstrate the complementary nature of these two human monitoring assays and emphasize the importance of careful selection of optimal sampling times.     

The relationship between induced mutation frequency and chromosome dosage in established mouse fibroblast lines

The frequencies of induced mutation to ouabain (OUA) and 6-thioguanine (6TG) resistance were compared in two established mouse fibroblast lines with different doses of the active X chromosome. The activity states of the X chromosomes were determined by DNA replication studies. Mutation frequency to 6TG^R, an X-linked recessive phenotype, was inversely related to dosage whereas OUA^R, a codominant phenotype, occurred with equal frequency in both lines. 6TG^R clones isolated from the line containing a majority of cells with two active X chromosomes were monosomic for the active X chromosome. Enzyme activity studies of these cytologically monosomic lines yielded results that were consistent with the presence of a single active X chromosome. The findings strongly support the hypothesis that mutation frequency is dependent on gene dosage.     

G-Banding analysis of radiation-induced chromosome damage in lymphocytes of hiroshima A-bomb survivors

Summary The present report describes the G-band analysis of somatic chromosomes in lymphocytes from 63 A-bomb survivors in Hiroshima to determine the type and frequency of radiation-induced chromosome aberrations. (1) The cells with stable-type chromosome aberrations (Cs cells) predominated among the aberrant cells, and showed a dose-dependent increase. All stable chromosome aberrations were classified into nine categories: reciprocal translocations, translocations of complex type, insertions, complex exchanges, peri- and paracentric inversions, terminal and interstitial deletions, and unidentified rearrangements. The frequencies of aberrations were found to increase with increasing dose for all aberration categories. Reciprocal translocations predominate in all dose ranges and among the chromosome aberrations classified. (2) The linear model was fitted to test the dose-response relationship for Cs cell frequencies. Employing a constant neutron RBEs of 10, an estimated linear slope of 15.2%/Sv was obtained for DS86 bone marrow dose with an intercept of 2.9% at dose 0. (3) Statistical analysis of data on 3,370 break sites showed good correlations betweens relative DNA content and the distribution of chromosome breaks involved in translocations, although the involvement of chromosome 1 is significantly higher.     

Comparison of AluI-induced frequencies of dicentrics and translocations in human lymphocytes by chromosome painting.

It has been shown repeatedly that following irradiation of human lymphocytes in the G0 stage, more translocations are induced than dicentrics. To check the role of DNA double-strand breaks (DSB) alone for the induction of symmetrical and asymmetrical chromosome aberrations, the frequencies of induced exchange aberrations by the restriction enzyme AluI were analyzed. The enzyme was introduced into cells using the pellet pipetting technique. Frequencies of induced translocations and dicentrics were determined using a chromosome painting assay with chromosome-specific DNA libraries for chromosomes 1, 4 and X (representing 16.8% of the human genome). The number of translocations detected was approximately 3-fold higher than the number of dicentrics, indicating that the increased frequency of translocations compared with dicentrics found in irradiated human lymphocytes does not result from DNA lesions other than DSB but from differential processing of DSB.     

Spontaneous and 3-aminobenzamide-induced sister-chromatid exchange frequencies estimated by ring chromosome analysis

Ring chromosomes offer an opportunity to measure sisterchromatidexchange (SCE) frequencies without the use of an agent to differentiatesister chromatids: SCE frequencies can be determined from thenumber of dicentric rings formed in cells from a cell line carryinga monocentric ring chromosome. Ash is a pseudotetraploid Chinesehamster ovary cell line in which 40% of metaphase cells havea large ring chromosome. We have used this cell line to investigatethe spontaneous rate of SCE by determining the rate of dicentricring formation and have compared this with the rate of lossof the ring chromosomes over time. In the absence of both [³H]thymidineand bromodeoxyuridine, the spontaneous rate of SCE in Ash cellswas 0.12 SCEs/ring/cell cycle; this rate was increased by bromodeoxyuridine,by the polyfunctional alkylating agent mitomycin C, and by thepoly(ADP-ribose) polymerase inhibitor 3-aminobenzamide. Thisindicates that spontaneous SCE occurs in this line and thatnot all 3-amino-benzamide-induced SCEs are dependent upon incorporatedbromodeoxyuridine. Ring chromosomes were not lost over timeas rapidly as predicted by the SCE frequencies observed. Non-disjunctionof the dicentric ring, or anaphase bridge breakage followedby reunion to form one or two monocentric rings, are the mostlikely explanations for this discrepancy. ¹To whom correspondence should be addressed     

Effects of age and gender on micronucleus and chromosome nondisjunction frequencies in centenarians and younger subjects

Studies have shown a significant increase in chromosome aneuploidy with age. The aim of this study was to elucidate whether the age-related changes in the level of hypoploidy correlate with the occurrence of micronuclei (MN) and chromosome nondisjunction (ND) in men and women. We analyzed cytokinesis-blocked (binucleated) lymphocytes treated with cytochalasin B, from 127 donors varying in gender and age including 53 centenarians. Fluorescent in situ hybridization with probes specific for several autosomes (1, 4, 6, 8, 20) and for the sex chromosomes was applied to analyze the chromosomal content of MN and to analyze the frequency of reciprocal loss and gain due to ND in binucleated interphase cells. The general level of MN in Giemsa-stained preparations was higher in women and in both genders increased with age until approximately 70 years and ranged, depending on age group, from 0.5 to 1.4% in men and from 0.9 to 1.8% in women. Gender-related differences were mostly observed in the younger age groups (< or =50 years), with an almost two-fold difference between men and women (P < 0.005). Frequencies of autosome-positive MN in both genders and of sex chromosome-positive MN in men were comparable and remained unchanged in older groups. The frequency of X-positive MN in women was higher than the average frequency of autosome-positive MN and continued to increase until the oldest age. The frequency of NDs involving the analyzed chromosomes was on average two-fold higher in women than in men. In both genders, the frequency of NDs increased with age and was, on average, an order of magnitude higher than that of cells with MN, consistent with the previous reports that the efficiency of elimination of micronucleated cells is higher than of the cells presenting chromosome ND.