In fibroblasts of AGS patients with RNase H2 or SAMHD1 deficiency, defective ribonucleotide excision repair or depletion of dNTP pools, respectively, cause chronic low-level DNA damage leading to constitutive activation of p53 and type I IFN19, 20, raising the question as to how DNA damage signalling may be linked to type I IFN activation in TREX1 deficiency. This evidence concerns the gene TREX1 and Aicardi-Goutieres syndrome.