**Abstract**

The DNA damage response (DDR) is a concerted response involving a myriad of pathways that cells elicit in the presence of DNA injuries. Patients bearing mutations in DDR genes have an increased cancer incidence derived from their diminished ability to respond to DNA damage, and the consequent increase in mutations. Intriguingly, mutations in ATM, the chief DDR regulator, can cause ataxia telangiectasia, a neurodegenerative disorder characterized by progressive loss of movement coordination, weak immune system, and increased cancer risk. The relationship between ATM and neural system development and degeneration remains to be fully elucidated and will be discussed in this chapter.

**Keywords:** ATM, DNA damage response, ataxia telangiectasia, neurodegeneration
