Levels of PDYN (Fig. 1G) and PENK (Fig. 1H) were significantly decreased in preHD (PDYN: MD = 0.614, 95% CI: 0.176–1.052, **P = 0.004, PENK: MD = 0.799, 95% CI: 0.229–1.369, **P = 0.004), early/mid HD (PDYN: MD = 0.537, 95% CI: 0.099–0.975, *P = 0.012, PENK: MD = 0.698, 95% CI: 0.128–1.268, *P = 0.012), and late HD compared with controls (PDYN: MD = 0.761, 95% CI: 0.323–1.199, ***P = 0.0003, PENK: MD = 1.021, 95% CI: 0.451–1.591, ***P = 0.0002). The gene discussed is PENK; the disease is Huntington disease.