Remarkably, A‐T BOs recapitulate the microcephaly phenotype previously reported in A‐T patients (Nissenkorn et al., 2011), and chemical inhibition of cGAS and STING via aspirin (Dai et al., 2019) or H‐151 (Haag et al., 2018), respectively, rescued both BO size defects and entry into cellular senescence. Here, CGAS is linked to microcephaly.