Ataxia telangictasia mutated (ATM) is involved in DNA repair pathway and cell-cycle checkpoints. ATM alterations were found in medulloblastomas, gliomas, but not in astrocytoma. The polymorphism D1853N was reported in healthy individuals and medulloblastomas. We could observe this polymorphism, heterozygously, in a proband affected with astrocytoma and traced it through her pedigree. We propose the three-hit hypothesis as a triangle initiators includes D1853N as a first predisposing hit, IVS 38- 63T → A as a second hit deriving from the first somatic evolution before differentiation and IVS 38- 30 A → G as a third hit through the development of an astrocytoma. In addition, the D1853N polymorphism was occurred in different allele from IVS 38- 63T → A and IVS 38- 30 A → G.