LRRK2 and Parkinson disease: Possible reasons for the negative SAA results include inaccuracy in the Parkinson’s diagnosis (around 50% of the initial PD diagnosis in untreated subjects are wrong53), the sensitivity (82.6%) and specificity (88.2%) of CSF α-synuclein SAA at the time point of the initial diagnosis in other cohorts54,55 and the possible presence of genetic variants such as LRRK2. LRRK2 patients show less α-synuclein pathology and significantly fewer positive SAA results56.