USP8 and Parkinson disease: In particular, the COWAS interaction test identified significant effects on PD from genetically regulated co-expression between SNCA and DARS1 (P=1.21e-13), SNCA and ENSA (P=1.03e-08), SNCA and HCLS1 (P=5.50e-05), and SNCA and USP8 (P=3.64e-07).