ATM and ataxia telangiectasia: Ataxia‐telangiectasia is a rare autosomal‐recessive disorder caused by mutations in the ATM gene on chromosome 11q22.3 (MIM 208900).1 The ataxia telangiectasia‐mutated (ATM) protein is a serine‐threonine protein kinase, which phosphorylates more than 700 substrates and is a key player in the cellular response to double‐stranded DNA damage.2 The clinical and genetic features of ataxia‐telangiectasia vary, and two forms of the disease have been described.