SAMHD1 and Aicardi-Goutieres syndrome: While RNase H2 appears to facilitate, rather than inhibit, LINE-1 retrotransposition [32,36], cell lines with RNase H2 mutations also have significantly reduced overall levels of genomic DNA methylation, compared to cell lines derived from TREX1 or SAMHD1 AGS patients [37], suggesting that silencing of genomic regions (usually correlated with stable DNA methylation) is impaired in cells lacking fully functional RNase H2.