Salivary α-Synuclein as a Candidate Biomarker of Parkinsonism in 22q11.2 Deletion Syndrome

Background: 22q11.2 deletion syndrome (22q11.2DS) has been linked to an increased risk of early-onset Parkinson's disease. However, the pathophysiological mechanisms underlying parkinsonism remain poorly understood. Objective: The objective is to investigate salivary total alpha-synuclein levels in 22q11.2DS patients with and without parkinsonian motor signs. Methods: This cross-sectional study included 10 patients with 22q11.2DS with parkinsonism (Park+), ten 22q11.2DS patients without parkinsonism (Park-), and 10 age and sex-comparable healthy subjects (HS). Salivary and serum alpha-synuclein levels were measured using enzyme-linked immunosorbent assay. Results: Salivary total alpha-synuclein concentration was significantly lower in Park (+) patients than in Park (-) patients and HS (P = 0.007). In addition, salivary alpha-synuclein showed good accuracy in discriminating Park (+) from Park (-) patients (area under the curve = 0.86) and correlated with motor severity and cognitive impairment. Conclusion: This exploratory study suggests that the parkinsonian phenotype of 22q11.2DS is associated with a reduced concentration of monomeric alpha-synuclein in biological fluids.