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Is olfactory impairment in Parkinson disease related to phenotypic or genotypic characteristics?

From the Department of Neurology (D.V., S.M.v.R., M.V., J.M., J.J.v.H.), Leiden University Medical Center; and the Department of Neurology (S.B., H.W.B.) and the Section of Medical Genomics, Department of Clinical Genetics (M.G.M., Y.F., P.H.), VU University Medical Center, Amsterdam, the Netherlands.

Address correspondence and reprint requests to D. Verbaan, Department of Neurology, K5Q-92, Leiden University Medical Center, P.O. Box 9600, NL- 2300 RC Leiden, the Netherlands D.Verbaan{at}lumc.nl

Objective: To evaluate the relation between olfactory impairment (OI) and other impairment domains in Parkinson disease (PD) and the characteristics of OI in patients with certain genotypic characteristics.

Methods: In 295 nondemented patients with PD and 150 controls with a similar overall age and sex distribution, olfactory function was evaluated with the identification (ID) and discrimination (DIS) tests of the Sniffin’ Sticks. In patients, demographic and clinical characteristics were evaluated, and genetic analyses were performed.

Results: Of all patients, 61% had an impaired ID and 43% had an impaired DIS. No significant correlations >0.4 were found between olfactory scores and other demographic or clinical variables. Age and sex accounted for the 22% explained variance of the ID score regression model, whereas age, sex, and disease duration accounted for the 15% explained variance of the DIS score regression model. Parkin and DJ-1 mutation carriers (homozygous or heterozygous compound, n = 6) had normal ID scores. APOE 2 or APOE 4 carriers had no significantly different olfactory scores than noncarriers. The allele distribution of the alpha-synuclein (SNCA)-REP1 polymorphism in groups with an impaired or normal ID or DIS was comparable.

Conclusions: Olfactory impairment (OI) in Parkinson disease (PD) may be unrelated to other impairment domains of the disease, which may indicate that olfaction is an independent feature of PD. Parkin and DJ-1 mutation carriers had normal identification scores but the number of mutation carriers is too small to draw conclusions. The APOE genotype (APOE 2 or APOE 4 alleles) and SNCA-REP1 polymorphism do not seem to influence olfaction in PD.

GLOSSARY: AAO = age at onset; BDI = Beck Depression Inventory; DIS = discrimination test of the Sniffin’ Sticks; EOPD = early-onset PD; H&Y = Hoehn & Yahr; ID = identification test of the Sniffin’ Sticks; LDE = levodopa equivalent; LUMC = Leiden University Medical Center; MMSE = Mini-Mental State Examination; OI = olfactory impairment; PD = Parkinson disease; PIGD = postural instability gait difficulty; PROPARK = PROfiling PARKinson’s disease; SCOPA = SCales for Outcomes in PArkinson’s disease; SNPs = single nucleotide polymorphisms; UPSIT = University of Pennsylvania Smell IdentificationTest; VUMC = VU University Medical Center.

Supported by grants from the Prinses Beatrix Fonds (PBF, project no. WAR05-0120), the Netherlands Organization of Scientific Research (NWO, project no. 0940-33-021), the van Alkemade-Keuls Foundation, and the Dutch Parkinson’s Disease Society.

Disclosure: The authors report no disclosures.

Received May 28, 2008. Accepted in final form September 2, 2008.