ATM and LIG4 syndrome: Interestingly, the levels of spontaneous DSB and MN observed in DEMETER fibroblasts corresponding to a HBLR phenotype were found similar to those observed in fibroblasts deriving from the highest hyper-radiosensitivity syndromes, namely ataxia telangiectasia (AT), caused by ATM mutations and LIG4 syndrome, caused by LIG4 mutations [40].