*The Role of the DNA Damage Response in Ataxia-Telangiectasia Syndrome DOI: http://dx.doi.org/10.5772/intechopen.84902*

radiation. Lack of ATM permits these mutations to escape cell cycle checkpoints control and be transmitted to daughter cells, further contributing to tumorigenesis. This process can continue unchecked, as the genomic instability that it produces does not trigger apoptosis when ATM is absent or dysfunctional.

One of the most common malignancies in A-T patients is breast cancer [132]. Even heterozygous individuals bearing debilitating mutations in just one of the ATM genes also have increased breast cancer incidence. While many DDR components are likely to participate in breast cancer tumorigenesis, the loss of the direct control that ATM exerts over BRAC1 is likely one of the major contributing factors. Lymphomas of B-cell origin and leukemia of T-cell origin are also very common in A-T patients, as unrepaired programmed DSBs persisting in developing T and B cells can often be the substrate of translocations [133].
