Extending the Spectrum of Nonmotor Symptoms with Olfaction in Premotor Huntington's Disease: A Pilot Study

The aim of this pilot study was to investigate change of olfactory functions in Huntington's disease (HD).

HD is a neurodegenerative disease characterized by motor, cognitive, and behavioral abnormalities. There are several studies reporting olfactory dysfunction in manifest and some studies in premanifest HD carriers, and a recent neuropathological study demonstrated HD-specific protein aggregation in the anterior olfactory nucleus in HD patients. In this study, we wanted to assess olfactory functions as a possible early nonmotor symptom of HD mutation carriers without disease-specific motor symptoms and HD patients.

All participants had genetic confirmed HD and were prospectively recruited during their routine control in a specialized outpatient clinic of the Medical University of Innsbruck, Department of Neurology, Austria. Healthy controls (HCs) were caregivers from patients. They were only included if they were younger than 70 years, scored more than 24/30 points on the Mini Mental State Examination, and had no other disease compromising olfactory function. Furthermore, all participants were tested on the Sniffin' sticks 16-items identification test.

We included 23 patients with manifest HD, 13 HD mutation carriers, and 19 HCs. Mutation carriers showed significant impaired odor identification compared to HCs (p < 0.001), as well as Huntington's patients compared with both mutation carriers (p = 0.003) and HCs (p < 0.001).

The results of this pilot study suggest that olfactory dysfunction may be an early nonmotor symptom of HD and could be a potential marker to assess disease progression.