Atypical Teratoid Rhabdoid Tumor (ATRT) is an embryonal CNS tumor of early childhood with a poor prognosis, characterized by biallelic inactivation of SMARCB1 (or, less commonly, SMARCA4), a core component of the SWI/SNF chromatin remodeling complex [12, 50]. The gene discussed is SMARCB1; the disease is atypical teratoid rhabdoid tumor.