What is the state of Parkinson’s disease biomarkers?

Neurologists are always cautious when making a diagnosis of Parkinson’s disease (PD). This shouldn’t be the case because PD is not difficult to recognise-at least not most of the time. For one, PD has classical clinical signs- the trio of resting tremor, slow movements (bradykinesia), and stiffness (rigidity). For another, it is asymmetrical, starting and remaining worse on one side of the body.

All these features are however vague in the early stages of PD. To make matters worse, there are many other diseases that mimic PD. These include multiple system atrophy (MSA), progressive supranuclear palsy (PSP), Lewy body disease (LBD), corticobasal degeneration (CBD), and even SWEDDS (if it exists at all!). And always lurking in the shadows, waiting to catch the neurologist out, are dystonic tremor and essential tremor.

Marking Parkinson's. EMSL on Flikr. https://www.flickr.com/photos/emsl/4704802544
Marking Parkinson’s. EMSL on Flikr. https://www.flickr.com/photos/emsl/4704802544

 

These PD mimics challenge and intrigue neurologists in equal measure. They contribute to the delayed and missed diagnosis of PD in 20% of cases. Are there shortcuts out there to improve our diagnostic accuracy? A simple test perhaps? Maybe some biomarker? Here are 6 budding contestants.

1. Dopamine transporter (DAT) scans

Dopamine. John Lester on Flikr. https://www.flickr.com/photos/pathfinderlinden/211882099/in/photolist-jHXaD
Dopamine. John Lester on Flikr. https://www.flickr.com/photos/pathfinderlinden/211882099/in/photolist-jHXaD

DAT scans are now in general, even if not universal, use. They help to distinguish PD from conditions such as essential tremor or drug-induced Parkinsonism. DAT scans are however expensive, and they do not distinguish PD from many of its other mimics such as MSA, PSP, (you know the roll call). There are indications that DAT scans may be normal in cases of PD. We therefore clearly need better, cheaper (and newer!) PD biomarkers than DAT scans.

2. Cerebrospinal fluid (CSF) biomarkers

© Nevit Dilmen [CC BY-SA 3.0 or GFDL], via Wikimedia Commons
© Nevit Dilmen [CC BY-SA 3.0 or GFDL], via Wikimedia Commons
Perhaps the answer is in a spinal tap or lumbar puncture (LP). A lumbar puncture is a simple but dreaded test. It is however useful for giving us access to the cerebrospinal fluid (CSF) that bathes the brain and spinal cord. Analysis of the CSF often gives the game away in many neurological disorders. It is not surprising therefore that researchers looked at a panel of nine CSF biomarkers that may identify PD. The paper, published in the JNNP, suggests that there may be biomarker roles for neurofilament light chain (NFL), soluble amyloid precursor protein (sAPP), and α-synuclein (of course). CSF α-synuclein is the focus of another paper in BioMedCentral which reports that one form, oligomeric α-synuclein, is the one to watch out for.

Another set of CSF biomarkers is related to blood vessel formation (angiogenesis). I came across this in a paper in Neurology titled Increased CSF biomarkers of angiogenesis in Parkinson disease. The authors are referring to vascular endothelial growth factor (VEGF) and its receptors VEGFR-1 and VEGFR-2. Others are placental growth factor (PlGF), angiopoietin 2 (Ang2), and interleukin-8. Enough to keep researchers busy for a while.

3. Peripheral blood biomarkers

Even the most compliant patient would prefer to have a blood test rather than a spinal tap. Thankfully there are some blood-based biomarkers in the offing. One set are called α-synuclein blood transcripts (SNCA transcripts). The authors of an article published in the journal Brain report that SNCA transcripts are consistently reduced in the blood of people with early PD. The accompanying editorial however cautions on the utility of these SNCA transcripts because low levels are also seen in some people who do not have PD. The true value of SNCA transcripts may lie in their ability to predict cognitive decline, but how many people really want to know that?

Other potential blood based biomarkers mentioned are uric acid and epidermal growth factor (EGF).

4. Retinal optical coherence tomography (OCT)

CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=525623
CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=525623

Even better than blood and spinal fluid biomarkers would be something totally painless. And to the rescue comes retinal optical coherence tomography (OCT). OCT uses light waves to take pictures of the retina. This allows measurement of the size of different parts of the retina; the area of interest in PD is called the foveal pit. A paper in Movement Disorders reports that OCT is a sensitive marker of PD. The authors show that the foveal pit in PD has a unique form; it is shallow in the superior-inferior and the nasal-temporal slopes. Perhaps neurologists will soon be running to ophthalmologists, cap-in-hand, to save their blushes.

5. Salivary gland α-synuclein

Public Domain, https://commons.wikimedia.org/w/index.php?curid=1074079
Public Domain, https://commons.wikimedia.org/w/index.php?curid=1074079

 

Back to painful biomarkers I’m afraid, all in aid of clinching an early diagnosis you must understand. This time it’s salivary gland biopsy. Some eager researchers took biopsy samples of the submandibular salivary glands of people with early PD. They then looked for, and found, α-synuclein in about 75% of them. Their paper is published in Movement Disorders titled Peripheral Synucleinopathy in Early Parkinson’s Disease: Submandibular Gland Needle Biopsy Findings. Unfortunately  20% of control subjects without PD also had α-synuclein in their salivary glands. Could these people have pre-manifest PD? We must await larger and longer studies before we start needling away at the salivary glands of the worried-well.

6. Intestinal tract α-synuclein

What if the answer is not in the salivary glands? Then we should be really afraid because α-synuclein has popped up in …the intestines. A review paper in Movement Disorders describes this in the brilliantly titled Gut Feelings About α-Synuclein in Gastrointestinal Biopsies: Biomarker in the Making? Another paper published in PLOS One takes things further, reporting an association between intestinal α-synuclein with increased gut permeability. I’ll make no further comments on the gut; not with the threat of cameras and scopes going up all sorts of body openings.

α-synuclein staining of a Lewy body. By Marvin 101 - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=7533521
α-synuclein staining of a Lewy body. By Marvin 101Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=7533521

Below is a link to an open access article in Movement Disorders with more potential PD biomarkers

Are there any other biomarkers out there? Please leave a comment.

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Is neurology research finally breaking the resolve of MND?

Motor neurone disease (MND) is, to say the least, dreadful. It also doesn’t help that the terminology neurologists use adds to the distress. West of the Atlantic, amyotrophic lateral sclerosis (ALS) means MND but goes eastwards and it is only a subtype of MND. Thankfully, for most Americans at least, there is no confusion; it is simply Lou Gehrig disease.

By Goudey [Public domain], via Wikimedia Commons
By Goudey [Public domain], via Wikimedia Commons

MND however remains a conundrum for neurologists who are struggling to solve its puzzling riddles. MND researchers continue to toil and sweat, but their efforts are bearing fruits. Take for example the great strides that established the link between MND and the C9ORF72 gene. What are the promising prospects in the world of MND? Here are some.

Associations: Thiamine deficiency and Diabetes 

By Jynto [CC0], via Wikimedia Commons
By Jynto [CC0], via Wikimedia Commons
Should we be on the lookout for thiamine deficiency in patients with MND? This question is prompted by an article in the JNNP which shows an unexpectedly high frequency of laboratory, but not clinical, thiamine deficiency. Titled Thiamine deficiency in amyotrophic lateral sclerosis, the paper reported thiamine deficiency in about 28% of subjects with MND. The authors did not impute any causal association, and there is nothing to suggest that replenishing the thiamine improved outcomes. It is still worth thinking about because people with MND, as the paper emphasised, are at risk of thiamine deficiency.

Another reported association, more difficult to fathom, is the one between MND and diabetes mellitus. The report in the European Journal of Neurology is titled Association between diabetes and amyotrophic lateral sclerosis in Sweden. Why am I sceptical?

Risk factor: Human endogenous retrovirus K (HERV K) 

Retrovirus capsid. A J Cann on Flikr. https://www.flickr.com/photos/ajc1/3269017701/in/photostream/
Retrovirus capsid. A J Cann on Flikr. https://www.flickr.com/photos/ajc1/3269017701/in/photostream/

The cause for MND remains unknown. Risk factors however abound such as smoking and other environmental risk factors. You may now add human endogenous retrovirus K (HERV K) to that list. This is according to a recent paper in Science Translational Medicine titled Human endogenous retrovirus-K contributes to motor neuron disease. The authors report that HERV K is activated in some people with MND, and it is the envelope proteins that cause damage to tissues. The US National Institutes of Health (NIH) think this is an important development, and it released a press statement titled Dormant viral genes may awaken to cause ALS. Scary! Is this important, or just another risk factor? Only time will tell.

Pathology: Neuromuscular junction inflammation 

By Elliejellybelly13 - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=40798702
By Elliejellybelly13Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=40798702

This sounds almost sacrilegious- the thought that inflammation may really play a role in MND. And at the neuromuscular junction (NMJ), not the anterior horn cells. Well, some researchers are ready to commit blasphemy; publishing in Experimental Neurology, the authors showed evidence of inflammation in the muscles and NMJs of rat models of MND. They went further to show that injecting a growth factor called GDNF reduced this inflammation. Do I perceive a potential treatment pathway? Read all about it if you dare, its titled Macrophage-mediated inflammation and glial response in the skeletal muscle of a rat model of familial amyotrophic lateral sclerosis (ALS).

Treatment target: TDP-43 protein 

By Emw (Own work) [CC BY-SA 3.0 or GFDL], via Wikimedia Commons
By Emw (Own work) [CC BY-SA 3.0 or GFDL], via Wikimedia Commons
Will MND ever be a curable disease? A big question, but this is the vision of all the hard-working researchers in this field. What are the prospects for a cure? One group of researchers believe the answer is in preventing misfolding of TDP-43, the protein that plays an important role in MND. They set out their case in an article published in Neurotherapeutics titled TDP-43 Proteinopathy and ALS: Insights into Disease Mechanisms and Therapeutic Targets. And don’t worry, its free access. The bold abstract says it all: “we present the case that preventing the misfolding of TDP-43 and/or enhancing its clearance represents the most important target for effectively treating ALS”. The proof of the pudding….

Diagnostic test: Nerve ultrasound

By Oleg Alexandrov - self-made with MATLAB, Public Domain, https://commons.wikimedia.org/w/index.php?curid=3036844
By Oleg Alexandrov – self-made with MATLAB, Public Domain, https://commons.wikimedia.org/w/index.php?curid=3036844

Making the diagnosis of MND is not always (make that is hardly ever) straightforward. In the early stages, symptoms are vague, and clinical signs are non-specific. MND also has many mimics. One of such mimics is multifocal motor neuropathy (MMN). To distinguish this and other mimics from MND, neurologist rely on a test called nerve conduction study (NCS). Even this however is not always helpful.

Researchers have now reported that ultrasound may be more sensitive in distinguishing MND from MMN. Another sacrilegious thought! They published their paper in Journal of Neurology with a rather long title: Nerve ultrasound in the differentiation of multifocal motor neuropathy (MMN) and amyotrophic lateral sclerosis with predominant lower motor neuron disease (ALS/LMND). Could the diagnosis of MND really be this simple? I am concerned that there were only 16 subjects with MND in the study, all from one centre. Perhaps a randomised, multi-centre, trial will come to the rescue?

Diagnostic biomarker: Brain iron deposition 

By Oleg Alexandrov - self-made with MATLAB, Public Domain, https://commons.wikimedia.org/w/index.php?curid=3036844
By Oleg Alexandrov – self-made with MATLAB, Public Domain, https://commons.wikimedia.org/w/index.php?curid=3036844

Brain magnetic resonance imaging (MRI) is not a test neurologist rely upon to make the diagnosis of MND. Not anymore it seems, going by an article in American Journal of Neuroradiology. The paper is titled A Potential Biomarker in Amyotrophic Lateral Sclerosis. In the article, the authors assessed the amount of iron deposition in the brains of people with MND using the MRI techniques called SWI and DTI. Their findings suggest that the amount of iron in the motor cortex and motor tracts of the brain is a good guide to the presence of MND. If confirmed, this technique will help to reduce the long time it often takes before neurologists confirm their suspicions of MND to patients and their families.

Prognostic biomarker: Neurofilament light chain (NfL) 

Neurofilament and MBP. Dan O'Shea on Flikr. https://www.flickr.com/photos/dan_oshea/4079086197
Neurofilament and MBP. Dan O’Shea on Flikr. https://www.flickr.com/photos/dan_oshea/4079086197

The outcome of MND, poor as it often is, varies quite widely. This is influenced by several factors such as the type of MND, use of the medicine riluzole, and multidisciplinary care. New research suggests that neurofilament light chain (NfL) may be a more sensitive marker of prognosis. This is reported in an article published in Neurology titled Neurofilament light chain: A prognostic biomarker in amyotrophic lateral sclerosis. The authors demonstrated that patients with MND have much higher levels of NfL than those without the disease. Furthermore, subjects with MND who had the highest levels at the onset had a higher mortality hazard ratio. I think I know what that means.

Prognostic scale: ALS-MITOS predictive system

A paper in the JNNP has proposed a new predictive system for MND called ALS-MITOS, reportedly better than the more familiar ALSFRS-R. The report is titled The MITOS system predicts long-term survival in amyotrophic lateral sclerosis. Most practicing neurologists wouldn’t know the difference because they don’t to use such predictive systems. But MND researchers would be licking their lips at the prospect of a better measure of disease progression; it will make it much easier for them to show that their interventions really do work!

Treatment: Copper 

By Native_Copper_Macro_Digon3.jpg: “Jonathan Zander (Digon3)"derivative work: Materialscientist (talk) - Native_Copper_Macro_Digon3.jpg, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=7223304
By Native_Copper_Macro_Digon3.jpg: “Jonathan Zander (Digon3)”derivative work: Materialscientist (talk) – Native_Copper_Macro_Digon3.jpg, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=7223304

There are >100 mutations in the superoxide dismutase 1 (SOD-1), a gene known to cause MND. SOD-1 is an enzyme that binds both copper and zinc, and when defective it results in mutant copper (don’t worry, I’m just finding this out myself). Acting on this hypothesis, researchers came up with a crafty way of delivering normal copper into the central nervous system of  mice modelled with SOD-1 MND. Publishing in Neurobiology of Disease, the authors showed how they achieved this with CuATSM, a chemical that contains copper and currently used for PET scans. CuATSM is readily transported into the nervous system, delivering its copper as it does so.

The paper has a rather cumbersome title: Copper delivery to the CNS by CuATSM effectively treats motor neuron disease in SODG93A mice co-expressing the Copper-Chaperone-for-SOD. The result is however anything but. The technique extended the lives of the mice by an average of 18 months. Unbelievable it seems. Any doubts however vanished when, on stopping the treatment, the mice died within 3 months. The finding is exciting enough for Eureka Alert to run the story with the headline New therapy halts progression of Lou Gehrig’s disease in mice. ‘Halt’ sounds very much like ‘cure’, but lets put the brakes on and wait for confirmation in human trials .

Treatment: Gene therapy

Gene_therapy. 1Droid JamLos on Flikr. https://www.flickr.com/photos/jamlos/2734418031
Gene_therapy. 1Droid JamLos on Flikr. https://www.flickr.com/photos/jamlos/2734418031

Every recalcitrant disease is today threatened with gene therapy. Considering it has a long list of genetic risk factors, why should MND be any different? Research taking steps in this direction is therefore long overdue. One such step was published in Gene Therapy and is titled Healthy and diseased corticospinal motor neurons are selectively transduced upon direct AAV2-2 injection into the motor cortex. The authors report that they successfully transduced motor nerves of mice models of MND. In doing so they have set the stage for gene therapy in MND. I don’t claim to understand it all, but it sounds very much like they have set the ball rolling. Promising.

Treatment: Stem cell therapy

By Ryddragyn at English Wikipedia - Transferred from en.wikipedia to Commons., Public Domain, https://commons.wikimedia.org/w/index.php?curid=2148036
By Ryddragyn at English Wikipedia – Transferred from en.wikipedia to Commons., Public Domain, https://commons.wikimedia.org/w/index.php?curid=2148036

Where gene therapy goes, stem cell therapy seems to follow. And this comes from JAMA Neurology with a classic unwieldy academic title: Safety and Clinical Effects of Mesenchymal Stem Cells Secreting Neurotrophic Factor Transplantation in Patients With Amyotrophic Lateral Sclerosis. The content isn’t any easier to interpret, and I will not pretend I get it at all. I comfort myself that it’s all at the ‘open-label, proof of concept‘ stage, and only the very brainy brains need to delve further. But it seems to offer hope.

By Jim Campbell/Aero-News Network - http://www.flickr.com/photos/39735679@N00/475109138/ / http://mediaarchive.ksc.nasa.gov/detail.cfm?mediaid=31873, Public Domain, https://commons.wikimedia.org/w/index.php?curid=3655144
By Jim Campbell/Aero-News Network – http://www.flickr.com/photos/39735679@N00/475109138/ / http://mediaarchive.ksc.nasa.gov/detail.cfm?mediaid=31873, Public Domain, https://commons.wikimedia.org/w/index.php?curid=3655144

 

The sky is surely the limit. Here are a couple of other headlines if you wish to explore further:

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Will Smith and chronic traumatic encephalopathy?

"Will-smith-userbox" by Walmart Stores (Original image) - File:Will Smith 2011, 2.jpg. Licensed under CC BY 2.0 via Wikimedia Commons.
Will-smith-userbox” by Walmart Stores (Original image) – File:Will Smith 2011, 2.jpg. Licensed under CC BY 2.0 via Wikimedia Commons.

No, Will Smith has not developed chronic traumatic encephalopathy (CTE). He is however playing Nigerian-born Bennett Omalu in an upcoming film, Concussion. The Nigerian-born and trained forensic pathologist was the first to report an association between repeated head trauma and the neurodegenerative disease CTE. He relates his story in this interview.

It will be interesting to see the film portrays the great lengths the National Football League (NFL) went to discredit the hero but here is a trailer:

https://www.youtube.com/embed/Qk-1TLVUPZk” target=”_blank”>

And talking of Nigerian doctors and the movies, Danny Glover will be playing a part in 93 days, a film about the action of a few dedicated doctors to stop the spread of the deadly ebola virus in Nigeria, Africa’s most populated country.

https://www.youtube.com/embed/zOnBCfEtIs4” target=”_blank”>

The heroine of the story is however Dr Stella Adadevoh, the brave doctor who lost her life to the virus but saved a nation. This link tells her story.

What has Ebola got to do with Neurology? I thought it was a cause of viral encephalitis but apparently not going by this statement from The Encephalitis Society