In 2021, we published a study corroborating the significant elevation of salivary HO-1 in PD subjects compared to non-neurological control subjects and non-degenerative neurological controls (multiple sclerosis, epilepsy, essential tremor, stroke, nerve pain) though not compared to subjects with other neurodegenerative conditions (AD, mild cognitive impairment) [20]. Here, HMOX1 is linked to Cognitive impairment.