ATM and ataxia telangiectasia: Ataxia telangiectasia (AT; OMIM:208900), or Louis–Bar syndrome, is a rare autosomal recessive disease with an estimated incidence of 1/100,000–1/40,000, and is caused by the biallelic mutations in the ataxia telangiectasia mutated (ATM) gene located on chromosome 11q22–23 (1).