Cytokinesis-block micronucleus assay by manual and automated scoring: calibration curves and dose prediction

The cytokinesis-block micronucleus assay in peripheral blood lymphocytes is one of the best standardized and validated techniques for individual radiation dose assessment. This method has been proposed as an alternative to the dicentric chromosome assay, which is considered the "gold standard" in biological dosimetry because it requires less time and cytogenetic expertise. Nevertheless, for application as a biodosimetry tool in large-scale nuclear or radiological accidents, the manually performed cytokinesis-block micronucleus assay needs further strategies (e.g., the automation of micronucleus scoring) to speed up the analysis. An essential prerequisite for radiation dose assessment is to establish a dose-effect curve. In this study, blood samples of one healthy subject were irradiated with seven increasing doses of x-ray (240 kVp, 1 Gy min⁻¹) ranging from 0.25-4.0 Gy to generate calibration curves based on manual as well as on automated scoring mode. The quality of the calibration curves was evaluated by determination of the dose prediction accuracy after the analysis of 10 blood samples from the same donor exposed to unknown radiation doses. The micronucleus frequencies in binucleated cells were scored manually as well as automatically and were used to assess the absorbed radiation doses with reference to the respective calibration curve. The accuracy of the dose assessment based on manual and automatic scoring mode was compared.

Laboratory intercomparison on the γ-H2AX foci assay

The focus of the study is an intercomparison of laboratories' dose-assessment performances using the γ-H2AX foci assay as a diagnostic triage tool for rapid individual radiation dose assessment. Homogenously X-irradiated (240 kVp, 1 Gy/min) blood samples for establishing calibration data (0.25-4 Gy) as well as blinded test samples (0.1-6.4 Gy) were incubated at 37°C for 2 and 24 h (repair time) and sent to the participants. The foci assay was performed according to protocols individually established in participating laboratories and therefore varied. The time taken to report dose estimates was documented for each laboratory. Additional information concerning laboratory organization/characteristics as well as assay performance was collected. The mean absolute difference (MAD) of estimated doses relative to the actual doses was calculated and radiation doses were merged into four triage categories reflecting clinical relevance to calculate accuracy, sensitivity and specificity. First γ-H2AX based dose estimates were reported 7 h after sample receipt. Estimates were similarly accurate for 2 and 24 h repair times, providing scope for its use in the early phase of a radiation exposure incident. Equal accuracy was achieved by scoring 20, 30, 40 or 50 cells per sample. However, MAD values of 0.5-0.7 Gy and 1.3-1.7 Gy divided the data sets into two groups, driven mainly by the considerable differences in foci yields between calibration and blind samples. Foci yields also varied dramatically between laboratories, highlighting reproducibility issues as an important caveat of the foci assay. Nonetheless, foci counts could distinguish high- and low-dose samples in all data sets and binary dose categories of clinical significance could be discriminated with satisfactory accuracy (mean 84%, ±0.03 SEM). Overall, the results suggest that the γ-H2AX assay is a useful tool for rapidly screening individuals for significant exposures that occurred up to at least 24 h earlier, and may help to prioritize cytogenetic dosimetry follow-up.

Comparison of established and emerging biodosimetry assays

Rapid biodosimetry tools are required to assist with triage in the case of a large-scale radiation incident. Here, we aimed to determine the dose-assessment accuracy of the well-established dicentric chromosome assay (DCA) and cytokinesis-block micronucleus assay (CBMN) in comparison to the emerging γ-H2AX foci and gene expression assays for triage mode biodosimetry and radiation injury assessment. Coded blood samples exposed to 10 X-ray doses (240 kVp, 1 Gy/min) of up to 6.4 Gy were sent to participants for dose estimation. Report times were documented for each laboratory and assay. The mean absolute difference (MAD) of estimated doses relative to the true doses was calculated. We also merged doses into binary dose categories of clinical relevance and examined accuracy, sensitivity and specificity of the assays. Dose estimates were reported by the first laboratories within 0.3-0.4 days of receipt of samples for the γ-H2AX and gene expression assays compared to 2.4 and 4 days for the DCA and CBMN assays, respectively. Irrespective of the assay we found a 2.5-4-fold variation of interlaboratory accuracy per assay and lowest MAD values for the DCA assay (0.16 Gy) followed by CBMN (0.34 Gy), gene expression (0.34 Gy) and γ-H2AX (0.45 Gy) foci assay. Binary categories of dose estimates could be discriminated with equal efficiency for all assays, but at doses ≥1.5 Gy a 10% decrease in efficiency was observed for the foci assay, which was still comparable to the CBMN assay. In conclusion, the DCA has been confirmed as the gold standard biodosimetry method, but in situations where speed and throughput are more important than ultimate accuracy, the emerging rapid molecular assays have the potential to become useful triage tools.

Abstract P3-06-01: ATM Heterozygosity as a Breast Cancer-Susceptibility Factor in the General Population

Background: Do ATM heterozygous (ATM-htz) carriers have an increased risk of developing breast cancer? Do they have an increased sensitivity to ionizing radiation (IR)? Definitive information does not yet exist to answer these questions. Case-control studies have suggested a link between single copy ATM gene mutation and increased breast cancer risk. Lymphoblasts and skin fibroblasts from ATM-htz carriers are less sensitive to IR than cells from Ataxia Telangiectasia (AT) patients, but more sensitive than cells from the general population. Because of the clinical and environmental implication of these aspects, large studies are in progress to better understand the interaction between ATM-htz and increased breast cancer risk or radio-sensitivity. However, to be performed on the general population rather than on the obligate ATM-htz carriers, i.e., the rare parents of children affected by AT, these studies must relay on the expensive sequencing of the entire ATM gene (approximately 160Kb of genomic DNA, a 13Kb transcript of 66 exons, and more than 400 unique mutations that extend across the full length of the gene). Materials and Methods: Based on a serendipitous discovery, we have development of a new, non-invasive, easy, quick, and inexpensive test to identify AT patients and, more interestingly, the ATM-htz carriers. In particular, we found that, in mitosis, p53 localizes at centrosomes, the cytoplasmic organelles that organize the interphase cytoskeleton and contribute to bipolar spindle formation during mitotic cell division. In addition, we demonstrated that ATM is required for p53 localization at centrosome. These findings allowed us to identify a particular phenotype of peripheral blood lymphocytes (PBL) from AT patients or their parents, the obligate ATM-htz that should allow to easily discriminate the ATM-htz carries in the general population with a very high statistical significance (P<0.001). We have employed this new test to assess the contribution of ATM heterozygosity in the risk to develop breast cancer. Results: The frequency of ATM-htz in breast cancer patients and in healthy individuals was assessed by our new test and compared with the Italian theoretical frequency (between 1.69 and 3.43%; Italian AT Registry). At present, we have found 6 ATM-htz out of 80 breast cancer patients (7.5%) and 1 ATM-htz out of 70 healthy donors (1.4%) supporting the proposed link between single copy ATM gene mutation and increased breast cancer risk. In addition, an initial individual evaluation of the 6 ATM-Htz patients showed the following common characteristics: 1) early onset of tumor appearance (37-42 years of age); 2) ER and PgR positive and HER negative breast cancers.

Discussion: Beside an accurate assessment of the relative contribution of ATM heterozygosity to tumor susceptibility, this study will open the possibility of performing large screening for ATM-htz carries in the general population for different clinical aspects, such as IR sensitivity, genetic counseling, cancer predisposition, or selection for specific targeted therapies.

Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P3-06-01.

The Fixion expansion nail in the surgical treatment of diaphyseal fractures of the humerus and tibia. Our experience

The authors present their experience in the application of a Fixion expansion intramedullary nail for the treatment of diaphyseal fractures of the humerus and tibia, in a total of 40 surgeries. The features of the nail are: stability and flexibility of the instrumentation, speed of surgery, minimal exposure to radiation. The results obtained up to now are encouraging; there are no significant problems either during or after surgery, and mean consolidation time is 3 months for fractures of the humerus, and 4 months for those of the tibia. The Fixion nail is a versatile type of instrumentation that is easy to use.

Alignment of the extensor apparatus of the knee by alar and tuberosity transposition in recurrent subluxation of the patella and in external patellar hypertension syndrome

In consideration of the multiple anatomical structures involved in recurrent subluxation of the patella and in external patellar hypertension syndrome, the authors propose an operation which allows for complete realignment of the extensor apparatus by transposition of the anterior tibial tuberosity, division of the external alar ligament, tightening of the internal alar ligament, and correction of the muscular insertions. In particular, removal of a capsulofascial band medially and its reimplantation into the external incision is proposed, thus avoiding the formation of retractive scar tissue. The long-term results, which were overall satisfactory, confirm the effectiveness of the operation proposed.