NEFL and Huntington disease: For stage discrimination, PENK (area under curve [AUC], 0.706; P = 0.0002) outperformed NfL (AUC, 0.661; P = 0.1596) with minimal gain from combining both (AUC, 0.714; joint P = 0.0007).<h4>Conclusions</h4>Lower baseline CSF PENK concentration predicted longitudinal striatal atrophy and CSF PENK outperformed CSF NfL in distinguishing HD-ISS stages 0 and 1, supporting its role as a striatum-specific biomarker with potential to enrich early-stage HD trial cohorts.