HTT and Huntington disease: Nuclease-deficient Cas9 protein (dCas9) epigenetic editing for targeted gene regulation is a promising therapeutic approach for HD through downregulation of the causative gene, HTT. A screen of several dCas9 variants with expanded PAM recognition was fused to KRAB and DNMT3A/L to assess the ability to downregulate total HTT. Surprisingly, only SpdCas9 could significantly downregulate HTT, while expanded PAM recognition variants dxCas9 and dCas9-VQR were less efficient or unable to reduce HTT expression.