Hunger hormone levels in blood may reveal dementia type

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Age \> 60 years * Subject or carer / legal representative is willing to sign consent document Specific criteria for each group; Parkinson's Disease * PD diagnosed by a movement disorder specialist and meets the diagnosis of PD * MoCA \> 26/30 * No evidence of cognitive symptoms causing functional impairment Parkinson's Disease Dementia * PD diagnosed by a movement disorder specialist * Duration of motor symptoms \> 1 year * Meets MDS task force criteria for PDD * MoCA \< 21/30 Dementia with Lewy Bodies * Meets criteria for probable DLB as defined by the 4th report of the DLB consortium Alzheimer's Disease * Meets criteria for probable AD dementia (consistent with NIA/AA core clinical criteria for probable AD dementia) Exclusion Criteria: * Age \< 60 years * Current major depression * Use of anti-psychotic medication * Type I or Type II diabetes mellitus (DM) (excluding diet-controlled DM) * Tobacco use * BMI \<15.0 kg/m2 * BMI \> 30 kg/m2 * Comorbid gastrointestinal disease i.e. includes Coeliac, active Inflammatory Bowel Disease (Colitis), evidence for active gastric ulcers within the last 12 months, but excludes gastroesophageal reflux and hiatus hernia. * \>5 kg weight change over the preceding 3 months (determined by researcher from previous clinic visit and discussion with partner/carer) * Significant active comorbidity * Difficult venous access * Vagotomy Additional disease specific exclusions; * Parkinson's Disease exclusion criteria * Evidence of dementia or mild cognitive impairment * Deep brain stimulation (DBS) * Use of Duodopa Parkinson's Disease Dementia exclusion criteria * Dementia within 12 months of diagnosis of PD * DBS Dementia with Lewy bodies exclusion criteria * Onset of motor Parkinsonism symptoms greater than 12 months prior to dementia diagnosis Alzheimer's dementia exclusion criteria * Presence of PD, PDD, DLB, or Frontotemporal Dementia (FTD) Controls exclusion criteria * Evidence of parkinsonism * Evidence of dementia or mild cognitive impairment * MoCA \<26/30