Two-tier analysis of histone H2AX phosphorylation allows the identification of Ataxia Telangiectasia heterozygotes

Background and purpose: Ataxia Telangiectasia (A-T) heterozygotes constitute 0.36-1% of the general population. They have a higher risk of developing several types of cancer and may be more likely to Suffer side-effects following radiotherapy than the general population. Their identification is both labor- and time-consuming and the sensitivity and specificity of the methods employed has not been evaluated. This paper describes a new approach to the identification of A-T heterozygotes based on a two-tier analysis of histone H2AX phosphorylation. Materials and methods: We compared the T-cell phenotype after exposure to 2 Gy in nine obligate A-T heterozygotes and 17 normal donors. Examined end points were histone H2AX phosphorylation by flow cytometry 1 h after irradiation (kinase proficiency) and the residual gamma-H2AX foci by confocal microscopy 72 h after irradiation (DSB repair proficiency). Results: The sequential use of these two methods results in 100% positive predictive Value (PPV), 67% negative predictive value (NPV), 78% sensitivity, and 100% specificity. The overall hit rate, i.e. the ratio between the true positives Plus the true negatives and the total number of observations was 85%. Conclusions: A-T heterozygotes can be identified by analysing irradiated T-cell H2AX phosphorylation level and residual gamma-H2AX foci. (C) 2009 Elsevier Ireland Ltd. All rights reserved. Radiotherapy and Oncology 92 (2009) 133-137