Olfaction in Homozygous and Heterozygous SYNJ1 Arg258Gln Mutation Carriers

Hyposmia is a common nonmotor symptom in Parkinson's disease (PD) and has been variably detected in monogenic parkinsonism. SYNJ1 has been recently identified as the gene defective in a novel form of autosomal-recessive, early-onset atypical parkinsonism, designed as PARK20. To assess olfaction in PARK20, we administered the University of Pennsylvania Smell Identification Test (UPSIT) in four groups of subjects: SYNJ1 homozygous (HOM = 3) and heterozygous (HET = 4); sporadic PD (PD = 68); and healthy control subjects (CTR = 61). A linear regression model was constructed to assess the association between raw UPSIT score (outcome) and group (HOM, HET, PD, and CTR), adjusting for age, gender, and current smoking status. Likewise in PD patients, odor identification is impaired in homozygous SYNJ1 mutation carriers. Although the limited sample size precludes definite conclusions about olfaction in SYNJ1-related parkinsonism, our findings suggest new insights into PARK20 phenotype and pathophysiology.