Some genes that impact CAG instability, such as Fanconi Anemia Associated Nuclease 1 (Fan1) and MutL Protein Homolog 1 (Mlh1), as well as Neurofilament Light Chain (Nfl), a marker of disease severity, and cyclic-AMP-regulated phosphoprotein (Darpp32), which is inversely correlated with mHtt accumulation, have been found to be dysregulated in HD [1,22,23]. This evidence concerns the gene FAN1 and Huntington disease.