SAMHD1 and Aicardi-Goutieres syndrome: Although one study failed to detect elevated retrotransposition of L1s in the hippocampus of an AGS patient with SAMHD1 mutations (Upton et al, 2015), more recent work using TREX1‐deficient neural cells generated from human embryonic stem cells has strongly implicated accumulating LINE‐1‐derived single‐stranded DNAs (ssDNAs) in type I IFN production and neurotoxicity (Thomas et al, 2017), consistent with a role for active LINE‐1s in AGS pathophysiology (Garcia Perez & Alarcon‐Riquelme, 2017).