The prodromes of Parkinson's

Following on nicely from our last post, we are delighted to publicise our latest peer-reviewed publication.

This will come out in a special edition of the European Journal of Neuroscience, dedicated to the memory of Tom Isaacs. Tom was the founder and leader of the Cure Parkinson's Trust - a truly dynamic leader and a real disruptive presence (in all the right ways) within  Parkinson's research. We are honoured to have our names and our ideas as testimonial to him in this way.

It is clear that Parkinson's is more of an umbrella condition than one single entity. For instance, some people have significant tremor, while others have none. Some progress very slowly, and a decade from diagnosis have barely any more symptoms - others progress more quickly. For many Parkinson's affects mainly movement while others have many non-motor symptoms. It is likely (although not yet proven) that these different subtypes of Parkinson's have a different underlying process causing them.

It therefore stands to reason that the earliest phases are also different. In our article we lay out the evidence that Parkinson's that comes from people with a particular kind of sleep disorder (REM sleep behavioural disorder), smell loss, and genetic forms do all look different. The evidence is not bomb-proof, but in Predict-PD we will be able to shed light on both the sleep disorder, smell loss and try and pick apart differences in the general population.

To see the article, please see the journal website. Please also remember to talk to friends and family to read more about the study and sign up themselves: www.predictpd.com

RNR

The Importance of being Picky

This week the UCL Institute of Neurology who ran the randomised trial of the diabetes drug, Exenatide as a disease modifying treatment for Parkinson’s, have published a paper looking at particular groups who may benefit more from the treatment. 

The tenet of clinical trials is that you specify who can enter the trial, and you give one group the intervention (in this case drug) of interest, and you give another group something else (in this case placebo), and see which does better against a pre-specified list of measures. This implies a ‘winner-takes-all’ outcome that is beyond reproach. Either the new drug did better than no drug, or it didn’t – end of discussion. 

This approach is important. New drugs are met with excitement, clinicians want it to work, scientists have often spent years suggesting that it will, and patients are desperate for it to work. Therefore rigid and robust tests with a categorical ‘winner’ help to provide an unbiased outcome.

However, the disadvantage is that the baby can get thrown out with the bathwater. The randomised clinical trial, when done well is a robust and unbiased tool for making a judgement. However, it is not ‘perfect’. No matter how good the design of the study, there will be flaws and biases that are both explicit and hidden, and there is always the issue of ‘generalisability’ – how well the recruited volunteers represent the patient in clinic.

The UCL team have continued to look at the data. For a future trial, are there some people that are likely to do better from this treatment, and are the some people that will never respond. This is key and at the heart of this endeavour is the understanding that a ‘One-size-fits-all’ approach in Parkinson’s will never work.

As Exenatide, and other compounds, are proven to be safe for people with Parkinson’s, great care will need to be taken to ensure that the right people are chosen for trials of effectiveness. This will entail careful analysis and subgroup analyses of early studies.

In this analysis, it seems that people with a shorter duration of disease and less impact of disease (in other words, milder disease) may get more benefit from Exenatide. This fits closely with the hypothesis that lies at the heart of PREDICT-PD: very early identification of Parkinson’s will allow effective disease modification that may be enough to proactively prevent the onset of motor symptoms.

RNR

onlinelibrary.wiley.com/doi/pdf/10.1111/ejn.14096

Athauda D, Maclagan K, Budnik N, Zampedri L, Hibbert S, Aviles-Olmos I, et al. Post hoc analysis of the Exenatide-PD trial - factors that predict response. Eur J Neurosci. 2018 Aug 2.

Exenatide, a glucagon-like peptide-1 agonist and a licensed treatment for Type 2 diabetes significantly reduced deterioration in motor symptoms in patients with Parkinson's disease in a randomised, placebo-controlled trial. Additionally, there were trends favouring the exenatide group in assessments of non-motor symptoms, cognition and quality of life. The aim of this exploratory post-hoc analysis was to generate new hypotheses regarding (1) whether candidate baseline factors might predict the magnitude of response to exenatide and (2) whether the beneficial effects of exenatide reported for the overall population are consistent in various subgroups of patients. Univariate and multivariate analyses were conducted to determine possible predictors of motor response to exenatide in this cohort. Potential treatment by subgroup interactions for changes in; motor severity, non-motor symptoms, cognition and quality of life after 48-weeks treatment with exenatide were evaluated among post-hoc subgroups defined by age, motor phenotype, disease duration, disease severity, BMI and insulin resistance. In the subgroup analyses, exenatide once-weekly was associated with broadly improved outcome measures assessing motor severity, non-motor symptoms, cognition and quality of life across all subgroups, however tremor-dominant phenotype and lower MDS-UPDRS Part-2 scores predicted greatest motor response to exenatide and there was an indication that patients with older age of onset and disease duration over 10 years responded less well. While patients with a range of demographic and clinical factors can potentially benefit from exenatide once-weekly, these data support an emphasis towards recruiting patients at earlier disease in future planned clinical trials of GLP-1 receptor agonists in PD. This article is protected by copyright. All rights reserved.

Remedies from the natural world

An article caught my eye this week as several comments received on this blog and in clinic relate to ‘natural’ remedies for Parkinson’s. To provide some background, my therapeutic philosophy is a common one: I will only prescribe or endorse treatments that have gone through robust, unbiased, reproducible testing, and where the benefits outweight the risks. I also believe that there are undoubtedly treatments that have the power to radically alter diseases that are under our noses in the natural world, and once they are identified, purified and tested, will revolutionise medicine. Exenatide is a perfect example: originally derived from the saliva of the Gila monster, this is now a powerful drug against diabetes and may even have the ability to halt or slow Parkinson’s. 

This article looks at whether blackberry juice can reduce levodopa-induced dyskinesia. The first thing to point out was that they didn’t test it in humans with Parkinson’s disease, this experiment involved the MPTP mouse model of Parkinson’s. Mice were given the same amount of levodopa and then different groups were given increasing doses of blackberry juice. The good news is that there was some benefit on the extra movements associated with ‘dopamine overdose’. However, this was mainly seen in the 15mL/kg group. To put this into a human context (assuming that it works as well in humans with Parkinson’s as mice with MPTP induced parkinsonism, which is a very  big assumption, a human would have to drink over a litre of pure blackberry juice per day to have less dyskinesia. 

Science is a journey of increments. These positive results may yield a useful weapon for people with Parkinson’s, but plenty of work needs to be done. I highly recommend blackberries, especially ones forraged on a nice walk in the woods, but I wouldn’t suggest they’re going to make your Parkinson’s better just yet.

RNR

Effects of blackberry (Morus nigra) fruit juice on levodopa-induced dyskinesia in a mice model of Parkinson's disease.

Fahimi Z¹, Jahromy MH¹.

J Exp Pharmacol. 2018 Jul 4;10:29-35. doi: 10.2147/JEP.S161782. eCollection 2018.

Abstract

BACKGROUND AND OBJECTIVE: 

Levodopa-induced dyskinesia (LID) is a movement disorder that occurs due to levodopa consumption for a long period to attenuate Parkinsonism. Plants have been the basis for medical treatments in human history and still widely practiced. Blackberry (Morus nigra) is one of the fruits rich in anthocyanin. The present study examined the effect of blackberry fruit juice on LID in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced Parkinson's disease in mice.

MATERIALS AND METHODS: 

In this study, 42 male mice were used, which were divided into six groups equally: one control group and five groups receiving MPTP injection. After confirmation of Parkinsonism in MPTP groups, one group was preserved without treatment and four other groups were treated with levodopa (50 mg/kg ip). After the onset of LID (2 weeks), one group was kept without additional treatment and three other groups were treated with three different doses of blackberry fruit juice (5, 10, and 15 mL/kg) with levodopa orally for 7 days. Abnormal involuntary movement scale (AIMS) and cylinder behavioral test were carried out according to the schedule. The collected data were analyzed using the SPSS software with the significant level of P<0.05.

RESULTS: 

Parkinson's disease was confirmed with AIMS test on the fourth day after MPTP injection. The onset of LID was observed after 2 weeks of levodopa treatment using both behavioral tests. The result of administration of M. nigra fruit juice for 1 week showed that this addition is useful in hindering LID. These effects were more pronounced at doses 10 and 15 mL/kg with nearly the same results on attenuating AIMS. Low dose of the fruit juice does not seem to affect LID significantly.

CONCLUSION: 

M. nigra fruit juice is effective to attenuate LID in an MPTP-induced Parkinson mice model.

Is the horizon getting closer ?

Week after week we talk about the need for a disease modifying drug in Parkinson’s, and week after week we hope to reassure you, dear reader, (as well as ourselves) that this Holy Grail is getting ever closer. 

This week marks the publication of a study that may mark a turning point in this journey. Prothena Pharmeceuticals have run a study looking at the safety and tolerability of a new compound (excitingly called PRX002/RG7935). This is a compound that sticks to the toxic protein that is understood to cause the brain cell loss in Parkinson’s – α-synuclein. Once it sticks to this substance, it ‘flags’ the body’s immune system to come and clear up the mess. This, we think, reduces the amount of the α-synuclein that is floating around and causing damage. 

In this study 80 participants with mild-moderate Parkinson’s were given one of six different doses of this medicine or salt-water (placebo) through a ‘drip’. They attended once a month and the infusion lasted 1-2 hours. Neither the participants nor the investigators knew how much (if any) of the drug they were getting. They received three infusions in total.

I must stress that this study wasn’t designed to see if this did anything at all for their Parkinson’s. The study was too small, and too short for any changes to be detected. The primary purpose of this study was to evalute whether the medicine was safe and tolderable, with secondary objectives of studying what happens to the drug when it is in the body.

Overall, of the 55 participants that had any strength of the medicine, 50 completed the study, and 5 did not manage all 24 weeks of the study. 1 stopped because their Parkinson’s worsened, 1 decided to withdraw (reason not stated), 2 (both in the highest dose group) stopped because of side effects, and 1 also in the highest group withdrew. I also note that 3 out of 25 getting placebo also withdrew.

This study is a vital step. After extensive laboratory testing, a compound like this will be given to a very small number of totally healthy volunteers to ensure it is safe in humans. Then it will be given to a small number of volunteers with the condition to make sure it is safe in the ‘target’ population and to determine a range of safe doses, which is this study. Then it will be given to a moderately large sample to see if there are any suggestions of positive effects and to refine the ideal dose, and finally it will undergo a large study of affected individuals where the investigators (and cruicially the funders) hope to find that it has a true benefit.

All the participants in this study had had Parkinson’s for around 3 years (although this was as much as 15 years) and was moderately advanced. We hope that in future studies, the investigators take people with the earliest possible disease duration and learn lessions from the Alzheimer’s journey. 

This compound has been being studied in the earliest stages of the research process for around 10 years. The next stage of the path for this compound, the PASADENA trial, started almost exactly 1 year ago, and will be running until February 2021. I would expect results to come out towards the end of 2021, and then (hopefully) a phase 3 study will start which will take several more years to run and analyse. If all these steps are successful, we may be in a position to prescribe this medication in around 7-10 years from now.

RNR

Safety and Tolerability of Multiple Ascending Doses of PRX002/RG7935, an Anti-α-Synuclein Monoclonal Antibody, in Patients With Parkinson Disease: A Randomized Clinical Trial.

JAMA Neurol. Published online June 18, 2018. doi:10.1001/jamaneurol.2018.1487

Joseph Jankovic, MD; Ira Goodman, MD; Beth Safirstein, MD; Tonya K. Marmon, DrPH; Dale B. Schenk, PhD; Martin Koller, MD, MPH; Wagner Zago, PhD; Daniel K. Ness, DVM, PhD; Sue G. Griffith, MD, PhD, MRCP; Michael Grundman, MD, MPH; Jay Soto, BS; Susanne Ostrowitzki, MD, PhD;Frank G. Boess, PhD; Meret Martin-Facklam, PhD; Joseph F. Quinn, MD; Stuart H. Isaacson, MD; Omid Omidvar, MD; Aaron Ellenbogen, DO;Gene G. Kinney, PhD

Importance:Aggregated α-synuclein is believed to be central to the pathogenesis of Parkinson disease (PD). PRX002/RG7935 (PRX002) is a humanized monoclonal antibody designed to target aggregated forms of α-synuclein, thereby inhibiting neuron-to-neuron transfer of presumed pathogenic forms of α-synuclein, potentially resulting in neuronal protection and slowing disease progression.

Objective:To evaluate the safety and tolerability of multiple intravenous infusions of PRX002 in patients with idiopathic PD.

Design, Setting, and Participants:Multicenter, randomized, double-blind, placebo-controlled, multiple ascending-dose trial at 8 US study centers from July 2014 to September 2016. Eligible participants were aged 40 to 80 years with mild to moderate idiopathic PD (Hoehn and Yahr stages 1-3).

Interventions:Participants were enrolled into 6 ascending-dose cohorts and randomly assigned to receive PRX002 (0.3 mg/kg, 1.0 mg/kg, 3.0 mg/kg, 10 mg/kg, 30 mg/kg, or 60 mg/kg) or placebo. Participants received 3 intravenous infusions every 4 weeks of PRX002 or placebo and were monitored during a 24-week observational period.

Main Outcomes and Measures:Safety and tolerability assessments included physical and neurological examinations, laboratory tests, vital signs, and adverse events. Pharmacokinetic parameters included maximum PRX002 concentration, area under the curve, and half-life.

Results:Of the 80 participants, most were white (97.5%; n = 78) and male (80%; n = 64); median (SD) age was 58 (8.4) years. PRX002 was generally safe and well tolerated; no serious or severe PRX002-related treatment-emergent adverse events (TEAEs) were reported. The TEAEs experienced by at least 5% of patients receiving PRX002, irrespective of relatedness to study drug, were constipation (9.1%; n = 5), infusion reaction (7.3%; n = 4), diarrhea (5.5%; n = 3), headache (5.5%; n = 3), peripheral edema (5.5%; n = 3), post-lumbar puncture syndrome (5.5%; n = 3), and upper respiratory tract infection (5.5%; n = 3). No antidrug antibodies were detected. Serum PRX002 levels increased in an approximately dose-proportional manner; mean terminal elimination half-life was similar across all doses (10.2 days). Rapid dose- and time-dependent mean reductions from baseline vs placebo in free serum α-synuclein levels of up to 97% were seen after a single infusion at the highest dose (F78,284 = 1.66; P = .002), with similar reductions after 2 additional infusions. Mean cerebrospinal fluid PRX002 concentration increased with PRX002 dose and was approximately 0.3% relative to serum across all dose cohorts.

Conclusions and Relevance:Single and multiple doses of PRX002 were generally safe and well tolerated and resulted in robust binding of peripheral α-synuclein and dose-dependent increases of PRX002 in cerebrospinal fluid, reaching cerebrospinal fluid concentrations that may be expected to engage extracellular aggregated α-synuclein in the brain. Findings support the design of an ongoing phase 2 clinical study (NCT03100149).

Trial Registration:ClinicalTrials.gov Identifier: NCT02157714.

To D or not to D, that is the question

At medical school we learned about the role that vitamin D has in bone metabolism, including its transformation from a less active form made by the kidneys to the more active form, which requires adequate sunlight on the skin. Low levels would lead to rickets in children, and osteomalacia in adults. Northern climes were associated with fair skin to allow more of the active vitamin D to be made in the ‘weaker’ sunshine, and that between October and March, even the fairest skinned amongst us would be unable to get enough natural sunshine (I was at medical school in Sheffield).

Since then however, there seems to have been some “mission creep”. Vitamin D now has been associated with countless conditions that seem to have nothing to do with calcium and phosphate turnover. Low levels are associated with worse response to TB treatment; vitamin D supplements are given in the community to people with non-specific aches, pains and low levels of depression; low vitamin D increases your risk of stroke and heart attack.

The brain diseases are involved too. People with MS are exhorted to take on extra vitamin D; low vitamin D levels are associated with a higher incidence of dementia. There is clearly much we have to learn about this intruiging compound, and its functions are clearly much more complex than has previously been thought.

What about Parkinson’s disease? There are several ongoing studies of prodromal Parkinson’s disease – research identifying people who have the underlying process that causes PD, but haven’t yet developed the full motor manifestations that are necessary for the clinical diagnosis. PREDICT-PD is one (and although we are partial, we think it's the best one), but the PRIPS study in Europe and the PARS study in North America are also very well designed studies that are reporting key discoveries in the fight against Parkinson’s.

An article this week reported on the levels of vitamin D in participants of the PARS study. The authors compared those thought to be at high risk of PD based on poor smell and abnormal DaT scans (a kind of brain scan that looks at dopamine transporters) and found no differences between the two groups.

At the moment, therefore, there is no justification for recommending taking vitamin D supplements to reduce your risk of PD. On the other hand, as many of our blog posts have highlighted, getting out and about, and doing some exercise in the sunshine, or even taking a nice holiday to escape the brisk British November greyness, might well do you good!

RNR

https://www.ncbi.nlm.nih.gov/pubmed/28984598

J Alzheimers Dis. 2017;60(3):989-997. doi: 10.3233/JAD-170407.

Vitamin D and the Risk of Dementia: The Rotterdam Study.

Licher S^1,2, de Bruijn RFAG², Wolters FJ^1,2, Zillikens MC³, Ikram MA^1,2,4, Ikram MK^1,2.

Author information

Abstract

BACKGROUND:

Vitamin D has gained interest as a potentially modifiable risk factor for dementia because of its putative neuroprotective effects. However, longitudinal studies examining the association between vitamin D and dementia have provided inconsistent results.

OBJECTIVE:

To determine the relationship of serum vitamin D with prevalent and incident dementia in the general population.

METHODS:

Within the prospective Rotterdam Study, we measured serum 25-hydroxyvitamin D concentrations between 1997 and 2001 using electrochemiluminescence-immunoassay in 6220 participants 55 years or older. We assessed dementia at baseline and continuously during follow-up until 1 January 2015. We used appropriate regression models to determine the relationship of vitamin D with prevalent and incident dementia, including Alzheimer's disease (AD). We adjusted models for age, sex, and season of blood collection. Additionally, we adjusted for ethnicity, education, cardiovascular risk factors, serum calcium, kidney function, depression, outdoor-activity and APOEɛ4 carriership.

RESULTS:

At baseline, 127 of 6,220 participants had dementia, of whom 97 had AD. Lower vitamin D concentrations were associated with a non-significantly higher prevalence of dementia (adjusted OR, per SD decrease 1.20, 95% CI 0.95;1.52), but not with AD (adjusted OR: 0.97, 95% CI 0.74;1.29). Among 6,087 non-demented participants with 68,884 person-years of follow-up, 795 participants developed dementia, of whom 641 had AD. Lower vitamin D concentrations were associated with higher risk of dementia (adjusted HR, per SD decrease 1.11, 95% CI 1.02;1.20) and AD (adjusted HR: 1.13, 95% CI 1.03;1.24).

CONCLUSION:

Lower serum vitamin D concentrations are associated with a higher incidence of dementia.

Unrecognised vitamin D deficiency is common in Parkinson disease: a report from the Harvard Biomarker Study

The headline findings from this study are dramatic: patients with PD are nearly twice as likely as age matched controls to be deficient in vitamin D. Although this study does not reveal much regarding a possible causal role for vitamin D in PD, the results are clinically relevant.

An association between PD and low vitamin D levels has previously been reported in smaller observational studies (Sato et al., 1997; Evatt et al., 2008; Knekt et al., 2010) - although none of these found a correlation between vitamin D levels and disease severity. Further evidence for a causal role of vitamin D in PD come from genetic studies which have shown polymorphisms in the vitamin D receptor to be associated with increased risk of developing PD (Scherzner et al., 2007; Butler et al., 2011; Kim et al., 2005). Furthermore, in animal models of PD, vitamin D appears to have a neuroprotective effect (Wang et al., 2001). Taken together, this evidence points towards a link between vitamin D and Parkinson's disease, but up until now the studies have been small and subject to limitations.

This large case-control study provides new support for the existence of a relationship between PD and low vitamin D3 levels. Patients with PD were found to be nearly twice as likely as age matched controls to be deficient in vitamin D3 (17.6% vs 9.3%, p=0.002) and the degree of deficiency is correlated to the severity and duration of disease. However, after adjusting for age, sex, race and vitamin D3 supplementation the association between PD and vitD3 deficiency was only just statistically significant (p=0.047). As Raja Mahana points out in a response to the article, there was no adjusting for multiple statistical tests, which, if performed, may have tipped this value over the edge of the 95% cutoff for statistical significance (Mahana, 2013).

In addition, importantly, no significant association was found with total vitamin D levels, suggesting that vitamin D2 levels were not changed in patients with PD (they may even have been higher). The authors offer no explanation for these seemingly conflicting results - in fact, they do not mention this in their discussion at all.

This failure to discuss important negative findings, combined with the borderline statistical significance and the lack of correction for multiple comparisons mean this study should be treated with a degree of scepticism.

Further limitations include:

1. Confounding - some additional, unmeasured factors may account for the association
2. Generalisability - patients and controls were drawn entirely from two hospitals in a small area of Massachusetts and are therefore not representative of all patients with Parkinson's disease. Further studies in minority populations that may be at even higher risk of vitamin D deficiency are necessary.
3. Correlation does not imply causation - the association found in this study could be explained if vitamin D deficiency accelerates PD pathology or if PD predisposes to vitamin D deficiency, because of a reduced tendency to go outdoors (sunlight is needed for the body to synthesise vitamin D).

Therefore it is impossible to make any claims about whether vitamin D deficiency causes Parkinson's Disease or whether Parkinson's Disease results in vitamin D deficiency from the results of this study alone.

Nonetheless, this study does show that patients with PD are at a considerably increased risk of vitamin D deficiency, whether as a result of confounding/reverse causality or not. The issues of confounding and reverse causality are only really important for scientists trying to understand whether low vitamin D has a causal role in PD. From a clinical viewpoint, all that really matters is that patients with PD have an increased risk of being vitamin D deficient and this, combined with an increased risk of falls and fractures, makes patients with PD an important population in which to consider testing of vitamin D levels and supplementation (Dobson et al, 2013).

Ding H, Dhima K, Lockheart K et al. (2013). Unrecognized vitamin D3 deficiency is common in Parkinson disease Neurology DOI: 10.1212/WNL.0b013e3182a95818

Abstract: Unrecognized vitamin D3 deficiency is common in Parkinson disease

Objective: To conclusively test for a specific association between the biological marker 25-hydroxy-vitamin D3, a transcriptionally active hormone produced in human skin and liver, and the prevalence and severity of Parkinson disease (PD).

Methods: We used liquid chromatography/tandem mass spectrometry to establish an association specifically between deficiency of 25-hydroxy-vitamin D3 and PD in a cross-sectional and longitudinal case-control study of 388 patients (mean Hoehn and Yahr stage of 2.1 6 0.6) and 283 control subjects free of neurologic disease nested in the Harvard Biomarker Study.

Results: Plasma levels of 25-hydroxy-vitamin D3 were associated with PD in both univariate and multivariate analyses with p values 5 0.0034 and 0.047, respectively. Total 25-hydroxy-vitamin D levels, the traditional composite measure of endogenous and exogenous vitamin D, were deficient in 17.6%of patients with PD compared with 9.3% of controls. Low 25-hydroxy-vitamin D3 as well as total 25-hydroxy-vitamin D levels were correlated with higher total Unified Parkinson’s Disease Rating Scale scores at baseline and during follow-up.

Conclusions: Our study reveals an association between 25-hydroxy-vitamin D3 and PD and suggests that thousands of patients with PD in North America alone may be vitamin D–deficient. This finding has immediate relevance for individual patients at risk of falls as well as public health, and warrants further investigation into the mechanism underlying this association.

Additional references:

  

Butler MW, Burt A, Edwards TL, Zuchner S, Scott WK, Martin ER, Vance JM, Wang L (2011) Vitamin D receptor gene as a candidate gene for Parkinson disease. Ann Hum Genet 75: 201-210

Dobson R, Yarnall A, Noyce AJ, Giovannoni G (2013) Bone health in chronic neurological diseases: a focus on Multiple sclerosis and Parkinsonian syndromes. Pract Neurol 13: 70-79

Evatt ML, Delong MR, Khazai N, Rosen A, Triche S, Tangpricha V (2008) Prevalence of vitamin d insufficiency in patients with Parkinson disease and Alzheimer disease. Arch Neurol 65: 1348-1352

Kim JS, Kim YI, Song C, Yoon I, Park JW, Choi YB, Kim HT, Lee KS (2005) Association of vitamin D receptor gene polymorphism and Parkinson's disease in Koreans. J Korean Med Sci 20: 495-498

Knekt P, Kilkkinen A, Rissanen H, Marniemi J, Sääksjärvi K, Heliövaara M (2010) Serum vitamin D and the risk of Parkinson disease. Arch Neurol 67: 808-811

Mehanna R (2013) Is Parkinson's disease associated with deficit in Vitamin D? Neurology

Sato Y, Iwamoto J, Honda Y (2011) Amelioration of osteoporosis and hypovitaminosis D by sunlight exposure in Parkinson's disease. Parkinsonism Relat Disord 17: 22-26

Scherzer CR, Eklund AC, Morse LJ, Liao Z, Locascio JJ, Fefer D, Schwarzschild MA, Schlossmacher MG, Hauser MA, Vance JM, Sudarsky LR, Standaert DG, Growdon JH, Jensen RV, Gullans SR (2007) Molecular markers of early Parkinson's disease based on gene expression in blood. Proc Natl Acad Sci U S A 104: 955-960

Wang JY, Wu JN, Cherng TL, Hoffer BJ, Chen HH, Borlongan CV, Wang Y (2001) Vitamin D(3) attenuates 6-hydroxydopamine-induced neurotoxicity in rats. Brain Res 904: 67-75