Studies have also explored α‐syn in various forms of PD within the gut,50 submandibular glands,51 skin,52 and retina53 for reflecting α‐syn as a definitive PD biomarker. While blood α‐syn species, neurofilament light chain, and lysosomal enzymes could supplement CSF findings, these have yet to show accuracy for following disease progression, and thus strongly supports the need for validation by other measurements.42, 54, 55, 56. This evidence concerns the gene NEFL and Parkinson disease.