Genetic factors might be a cause of vitamin D deficiency, and the association of PD with single nucleotide polymorphisms (SNPs) in the VDR and vitamin D binding protein (VDBP/GC) have been investigated in PD, such as a possible cerebrospinal fluid (CSF) biomarker in PD [56,76,77,78,80]. Here, GC is linked to Parkinson disease.