Recently, neurofilament light (NfL), the smallest and most abundant subunit in the heteropolymer neurofilament structural protein complex, has emerged as a potential biofluid marker for neurodegenerative disorders, including HD [4–9], due to its exclusively neuronal expression, and release into the extracellular space following axonal degeneration or neuronal damage [10,11]. The gene discussed is NEFL; the disease is Huntington disease.