There are a number of studies now, including PREDICT-PD which are profiling healthy people thought to be at risk of Parkinsons. PARS is one of the key studies in the field and has previously reported poorer cognition in their high risk group - people who have both smell loss and evidence of dopamine deficit on imaging.
The study has now published longitudinal data on cognition in the group of participants with smell loss. Of 10 participants who went on to develop Parkinsons there were poorer overall cognitive scores and executive function scores at baseline. An analysis of the association between dopamine deficit on imaging and cognition showed that reduction in dopamine predicted poorer attention and processing speed over time.
The results overall are borderline in terms of statistical significance but that's not necessarily surprising. We know that smell loss is non-specific and a risk factor for other neurological diseases so all the participants analysed here are likely to perform worse than the general population. The numbers are also probably too small to show statistically significant changes. I think the association between dopamine and poorer attention is interesting, suggesting that this domain of cognition (rather than executive function changes) may be particularly sensitive for tracking changes in Parkinsons risk over time.
-Anna
https://www.ncbi.nlm.nih.gov/pubmed/29063713
Weintraub D, Chahine LM, Hawkins KA, Siderowf A, Eberly S, Oakes D, Seibyl J, Stern MB, Marek K, Jennings D; PARS Investigators.
The study has now published longitudinal data on cognition in the group of participants with smell loss. Of 10 participants who went on to develop Parkinsons there were poorer overall cognitive scores and executive function scores at baseline. An analysis of the association between dopamine deficit on imaging and cognition showed that reduction in dopamine predicted poorer attention and processing speed over time.
The results overall are borderline in terms of statistical significance but that's not necessarily surprising. We know that smell loss is non-specific and a risk factor for other neurological diseases so all the participants analysed here are likely to perform worse than the general population. The numbers are also probably too small to show statistically significant changes. I think the association between dopamine and poorer attention is interesting, suggesting that this domain of cognition (rather than executive function changes) may be particularly sensitive for tracking changes in Parkinsons risk over time.
-Anna
https://www.ncbi.nlm.nih.gov/pubmed/29063713
Mov Disord. 2017 Oct 24. doi: 10.1002/mds.27189. [Epub ahead of print]
Cognition and the course of prodromal Parkinson's disease.
Weintraub D, Chahine LM, Hawkins KA, Siderowf A, Eberly S, Oakes D, Seibyl J, Stern MB, Marek K, Jennings D; PARS Investigators.
BACKGROUND:
Prospective data on cognition in prodromal Parkinson's disease are limited. The objectives of this study were to assess in prodromal PD (1) if baseline cognition predicts conversion to clinical PD, (2) if baseline dopamine transporter binding predicts longitudinal changes in cognition, and (3) if impaired olfaction predicts future cognitive decline.
METHODS:
Prodromal
participants were 136 hyposmic individuals enrolled in the Parkinson
Associated Risk Study. We examined baseline neuropsychological test
performance in PD converters versus nonconverters and the association
between baseline dopamine transporter binding and change in cognition. An additional 73 normosmic individuals were included in analyses of the relationship between hyposmia and cognitive decline.
RESULTS:
In
prodromal participants, baseline cognitive scores did not significantly
predict conversion, but converters performed numerically worse on 5 of
the 6 cognitive domains assessed, with the greatest differences in
executive function/working memory (0.68 standard deviation lower) and
global cognition
(0.64 standard deviation lower). Lower baseline dopamine transporter
binding predicted greater future decline in processing speed/attention
(P = 0.02). Hyposmia predicted greater future decline in language
(P = 0.005) and memory (P = 0.01) abilities.
CONCLUSIONS:
Given hyposmia in the general population predicts cognitive decline, the role of cognition
in predicting conversion in prodromal PD needs to be assessed in large
cohorts followed long-term. The dopamine system may be associated with
changes in processing speed/attention in individuals at risk for PD. ©
2017 International Parkinson and Movement Disorder Society.
Hyposmia - loss of sense of smell - is reversible in some cases. It has been shown that a daily oral intake of ~2.4gm E-304 (palmitoyl ascorbate) can reverse the total loss of sense of smell. This gives rise to the supposition that it is the conduction of signals from the olfactory epithelium that is faulty and not the epithelial sensors themselves.
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