Collectively, we have shown that HPgV is present in the CNS and whole blood of patients with PD, that patients with HPgV nucleic acids in the brain have more advanced NFT pathology and complexin-2 protein levels, and that those with HPgV nucleic acids in the whole blood have higher IGF-1 and lower pS65-ubiquitin concentrations in the plasma. Here, CPLX2 is linked to Parkinson disease.