Olfactory dysfunction in Parkinsonism caused by PINK1 mutations

Hyposmia is a common nonmotor feature of Parkinson's disease (PD) and has been variably detected in monogenic Parkinsonisms. To assess olfactory dysfunction in PINK1-related Parkinsonism, we evaluated olfactory detection threshold, odor discrimination, and odor identification in five groups of subjects: sporadic PD (n = 19), PINK1 homozygous (n = 7), and heterozygous (n = 6) parkinsonian patients, asymptomatic PINK1 heterozygous carriers (n = 12), and Italian healthy subjects (n = 67). All affected subjects and all healthy heterozygotes but one resulted hyposmic, with most patients in the range of functional anosmia or severe hyposmia. Detection threshold was more preserved and discrimination more impaired in patients with PINK1 mutations than in PD cases. Alterations of detection and discrimination were observed also in PINK1 asymptomatic heterozygotes. On the contrary, odor identification appeared to be mostly related to the disease status, as it was impaired in nearly all patients (including PD and PINK1 cases) and preserved in healthy heterozygotes. Our data indicate that olfactory dysfunction is common in PINK1 Parkinsonism and consists typically in defective odor identification and discrimination. A milder olfactory deficit, mostly involving discrimination, can be found in asymptomatic heterozygotes, possibly indicating an underlying preclinical neurodegenerative process.