When a DSB happened, the histone 2A (H2A)X was rapidly phosphorylated at ser139 by PI3K- like kinase, including ATM (ataxia telangiectasia mutated)/ATR (ataxia telangiectasia and Rad3-related) and DNA-dependent protein kinase [23, 24]. The gene discussed is ATR; the disease is Telangiectasia.