SMARCA4 and ataxia telangiectasia: Individuals with AT/RT-SMARCA4 are younger in age, more likely to be carriers of germline mutations and have shorter overall survival.4 Moreover, DNA methylation studies show that AT/RT-SMARCA4 does not classify in any of the known AT/RT subgroups and should be regarded as a distinct entity.4 There is inadequate knowledge regarding the specific mechanisms involved in AT/RT-SMARCA4 development, making it increasingly difficult to treat.