To investigate how FAN1 expression might modify HD onset and progression, we introduced wild-type (WT) or variant FAN1 isoforms in a tetracycline (Tet)-inducible green fluorescent protein (GFP) expression cassette into FAN1 knockout U20S osteosarcoma cells (31) (FAN1−/−; Supplementary Material, Fig. S1). The gene discussed is FAN1; the disease is Huntington disease.