Hyposmia correlates with SNCA variant and non-motor symptoms in Chinese patients with Parkinson's disease

Background Hyposmia plays an important role in the early and differential diagnosis of Parkinson's disease (PD); however its underlying mechanism is poorly understood. The aim of the present study is to explore the clinical phenotypic and genotypic correlation of hyposmia in Chinese PD patients. Methods Olfactory function evaluated by 16-item odor identification test from Sniffin’ Sticks (SS-16) of 218 Chinese Han PD patients and 110 healthy controls was compared. 186 patients also had the genetic information of two positive GWAS-linked SNCA loci (rs11931074, rs894278) previously validated in our center. The associations of hyposmia with SNCA variants and disease phenotypic characteristics including motor symptoms (UPDRS motor score) and other common NMSs (clinical possible RBD-cpRBD, depression and chronic constipation) were analyzed. Results Nearly 39.9% (n = 87) of PD reported subjective complaints of hyposmia, while 60.1% (n = 131) patients had objective hyposmia (SS-16 < 8.3). Patients with hyposmia had older age (p = 0.001), later onset age (p = 0.020), higher SCOPA-AUT scores (p = 0.011), higher percentage of chronic constipation (p = 0.001) and cpRBD (p = 0.003). Binary logistic regression analysis revealed that ageing (OR = 1.058; 95%CI: 1.012–1.106; p = 0.013), chronic constipation (OR = 2.072; 95%CI: 1.157–3.710; p = 0.014) and cpRBD (OR = 2.234; 95%CI: 1.040–4.797; p = 0.039) were independent influential factors of hyposmia in Chinese PD patients. Subgroup analysis of patients with both clinical and genetic results demonstrated that after adjusting for age, sex, chronic constipation and cpRBD, rs11931074 TT genotype may increase the risk of hyposmia in PD (OR = 3.24 95% CI = 1.23–8.51, p = 0.017) compared to GG genotype via an additive model. Conclusions Age, cpRBD, chronic constipation and SNCA rs11931074 may correlate with hyposmia in Chinese PD patients.