Huntington’s disease, a neurodegenerative condition, stems from a mutation in the HTT gene sequence in which a trio of nucleotides, cytosine, adenine and guanine (referred to as CAG), becomes repeated to abnormal lengths. HTT codes for the protein huntingtin, which is abundant in the brain but has a poorly understood function. Despite three decades of research since its discovery, the mechanism linking HTT mutations to Huntington’s disease remains unclear. Writing in Cell, Handsaker et al.¹ report single-cell analyses suggesting that neuronal toxicity emerges only after decades of CAG-repeat expansions in HTT, potentially offering a wide therapeutic window.