SNCA and Parkinson disease: The MeSH strategy used in PubMed and PMC was: (("saliva"[MeSH Terms] OR "saliva"[All Fields]) AND ("alpha-synuclein"[MeSH Terms] OR "alpha-synuclein"[All Fields] OR ("alpha"[All Fields] AND "synuclein"[All Fields]) OR "alpha synuclein"[All Fields])) AND ("parkinson disease"[MeSH Terms] OR ("parkinson"[All Fields] AND "disease"[All Fields]) OR "parkinson disease"[All Fields] OR ("parkinson's"[All Fields] AND "disease"[All Fields]) OR "Parkinson’s disease"[All Fields]).