Correlation between the availability of dopamine transporter and olfactory function in healthy subjects

This is a nice article which showcases how making data available prevents unnecessary replication and expense. The Parkinson's Progression Markers Initiative 'dumped' (in a good way) a large proportion of the data in ~400 PD patients and ~200 controls online for researchers in the field to devour.

Here the authors confirm findings that up to now have only been available in small numbers of participants and they demonstrate the relationship between smell test scores and striatal binding. Age, as it is in so many exposure-outcome associations, was an important confounding factor. However, even after taking account of age in the analysis there was a clear association between sense of smell and binding ratio on DAT-SPECT. 

Interesting to me was the fact that age had a stronger relationship with caudate binding compared with putaminal binding, whereas olfaction was equally associated with caudate and putaminal binding. I guess one could raise questions about the legitimacy of using linear analysis methods when the distribution of smell data is clearly non-normal, but a pragmatic approach must be taken in some instances and if they transformed the smell data here they would ceased to have meaning...

Eur Radiol. 2017 Nov 21. doi: 10.1007/s00330-017-5147-7. [Epub ahead of print]
Pak K, Kim K, Lee MJ, Lee JM, Kim BS, Kim SJ, Kim IJ.

https://link.springer.com/article/10.1007%2Fs00330-017-5147-7

OBJECTIVES: Olfactory dysfunction in Parkinson's disease is usually prodromal to other symptoms. In this study, we aimed to explore the association of olfactory function with the availabilities of striatal dopamine transporter (DAT) in healthy subjects.

METHODS: Data used in the preparation of this article were obtained from Parkinson's Progression Markers Initiative database ( www.ppmi-info.org/data ). The study population consisted of healthy controls with screening 123I-FP-CIT single photon emission tomography (SPECT). University of Pennsylvania Smell Identification Test (UPSIT) was assessed to evaluate the olfactory function.

RESULTS: Totally, 181 healthy subjects (117 male, 64 female) with 123I-FP-CIT SPECT data were included in this study. Specific binding ratios (SBRs) of the caudate nucleus (rho = -0.4217, p < 0.0001), putamen (rho = -0.2292, p = 0.0019), and striatum (rho=-0.3425, p < 0.0001) showed a reduction with ageing. SBRs of the caudate nucleus, putamen, and striatum were positively correlated with UPSIT (rho = 0.3716, p < 0.0001; rho = 0.3655, p < 0.0001; rho = 0.3880, p < 0.0001). After controlling for age by partial correlation, SBRs of the caudate nucleus, putamen, and striatum showed an influence on UPSIT (rho = 0.3288, p < 0.0001; rho = 0.3374, p < 0.0001; rho = 0.3511, p < 0.0001).

CONCLUSION: Olfactory function is associated with the availability of striatal DAT independent of age in healthy subjects.

KEY POINTS: • Olfactory dysfunction in Parkinson's disease is prodromal to other symptoms. • The availability of dopamine transporter showed a reduction with ageing. • Olfactory function is associated with the availability of dopamine transporter.