Ataxia-telangiectasia (A-T) is a rare neurodegenerative disorder that presents with cerebral ataxia and oculocutaneous telangiectasia. Mutations in Ataxia-Telangiectasia Mutated (ATM) gene are prominently responsible for the condition. ATM gene encodes a serine/threonine protein kinase, a crucial component in DNA repair systems. Whole exome sequencing was performed on a nine year old male subject with clinical features of A-T. Alpha fetoprotein and immunoglobulins levels in the serum sample were also measured by biochemical testing. Sequencing test revealed c.7456C>T (p.Arg2486X) mutation in exon 50 of ATM gene in this patient. This mutation was previously described as a missense pathogenic variant that can lead to truncation or lack of protein. Here we report this variant in the Iranian population for the first time.