HTT and Huntington disease: Moreover, three different ASOs have been studied in clinical trials for HD; one of them, in phase III, consists in a nonallele-specific ASO targeting both wild-type and mutant HTT RNAs, in which no pathogenic effect caused by wild-type HTT protein deficiency was detected [220], and the remaining are in phase I/II and they specifically target mutant HTT, using single nucleotide polymorphisms associated with the disease haplotype [226].