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Genetic Variant Predetermines Risk of Cognitive Decline in Parkinson’s, Research Suggests

genetic variant

Researchers have found that Parkinson’s patients whose cognitive ability is intact, but who have a specific genetic variant, have significantly less gray matter in the regions of their brain that are related to dementia.

The study with that finding, “Reduced gray matter volume in cognitively preserved COMT 158Val/Val Parkinson’s disease patients and its association with cognitive decline,” was published in Brain Imaging and Behavior.

Several mutations in the COMT gene have been associated with the risk of developing Parkinson’s disease. This gene provides instructions for making catechol-O-methyltransferase (COMT), an enzyme that helps break down certain chemical messengers like dopamine.

The most common alteration in the DNA sequence that makes up the COMT gene is the Val158Met mutation in which a valine (Val) is replaced by a methionine (Met) at position 158. Val and Met are both amino acids, also known as the protein’s building blocks.

Every individual has two copies of each gene, one inherited from each parent. Therefore, a person can have two Val’s in the same position at both COMT gene copies (also known as the Val/Val genotype), a Val in one gene and a Met in the other (Val/Met genotype), or two Met’s (Met/Met genotype). Scientists use the word “genotype” to describe a person’s genetic constitution.

Changes in COMT’s molecular structure, lead to high (Val/Val), intermediate (Val/Met) and low (Met/Met) enzymatic activity.

The Val158Met mutation in the COMT gene has been associated with an increased risk of cognitive decline in Parkinson’s disease, particularly in people with greater COMT activity. When this happens, there is too much neurotransmitter degradation, thus leading to reduced levels of dopamine and affecting basic brain functions such as motor coordination and memory.

Evidence suggests a correlation between cognitive impairment, one of Parkinson’s non-motor features, and reduced gray matter volume.

The brain is composed of gray and white matter. The first consists of cell bodies — the control center of neurons — while the latter is made up of nerve cell projections, known as axons or fibers, connecting distinct parts of gray matter.

A Spanish team of researchers used magnetic resonance imaging (MRI), a non-invasive imaging technology, to investigate a possible structural brain compromise in Parkinson’s patients with highly active COMT activity that could explain their increased risk for subsequent cognitive impairment.

The study included 120 newly diagnosed Parkinson’s patients with normal cognition (who were not previously treated for the disease) and 48 healthy controls from the Parkinson’s Progression Markers Initiative database.

Results showed that there was a widespread, significant reduction in cerebral gray matter volume in patients with the Val/Val genotype. They observed alterations in the fronto-subcortical and posterior-cortical brain regions, where motor and cognitive functions originate.

Gray matter volume at some of the identified regions was associated with cognitive decline in a four-year follow-up period, suggesting that gray matter volume reduction during the early stages of disease predisposes Val/Val patients to cognitive impairment.

Nonetheless, gray matter volume analysis at one-year follow-up was not increased in Val/Val subjects, in comparison to Val/Met and Met/Met participants, indicating a somewhat stable atrophy in the Val/Val subset and that those brain changes might already be present prior to diagnosis.

The team believes their research “sparks the need to further characterize the association between a modified COMT enzymatic effect and a structural brain compromise in the early stages of [Parkinson’s disease].”

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New Imaging Technique May Aid Early-Stage Diagnosis of Parkinson’s, Study Says

brain imaging

A new imaging agent can efficiently reach the brain and bind toxic amyloid aggregates during early-stage Parkinson’s and Huntington’s disease, a study has found.

This opens a new approach to diagnose and evaluate the effectiveness of treatments for these neurodegenerative diseases.

The article, “ScFv-conjugated superparamagnetic iron oxide nanoparticles for MRI-based diagnosis in transgenic mouse models of Parkinson’s and Huntington’s diseases,” was published in Brain Research.

It is widely accepted that misfolded amyloidogenic proteins, alpha-synuclein, mutant Huntington protein, and amyloid-beta, are toxic species that play a role in the development of neurodegenerative diseases including Parkinson’s, Huntington’s, and Alzheimer’s diseases.

However, there are currently no conclusive diagnoses for the early stages of these neurodegenerative diseases.

Despite the differences in the makeup of amyloidogenic proteins and their associated diseases, these misfolded aggregates assembled from distinct amyloid proteins share general common structural features and mechanisms of toxicity. Therefore, antibodies targeting each specific misfolded amyloidogenic protein can be powerful tools for early diagnosis and treatment of several neurodegenerative diseases.

Over the past decade, molecular imaging — the visualization, characterization, and measurement of biological processes at the level of cells and molecules in humans and other living systems — has become a thriving field and offers potential tools for disease diagnosis.

Magnetic resonance imaging (MRI) techniques represent one of the best non-invasive molecular imaging methods and hold great promise for studying the brain.

The use of nanoparticles — tiny molecules — also is attracting increased attention due to their unique capacity to facilitate diagnostics and therapeutics. Among all types of nanoparticles, biocompatible superparamagnetic iron oxide nanoparticles (SPIONs) have attracted a great deal of attention for therapeutic delivery applications.

SPIONs consist of magnetic cores made of iron oxides coated with a biocompatible polymer that can be targeted to the required area through external magnets. The coating acts to shield the magnetic particle from the surrounding environment and also can be used to attach different types of molecules to increase their targeting capacity. These molecules then act as attachment points for the coupling of therapeutic molecules or antibodies to be delivered to the organ of interest.

SPIONs have been shown to penetrate the blood-brain barrier — a lining of cells that protect the brain from circulating molecules capable of damaging and disrupting neural function. When joined with an antibody that recognized amyloid-beta, SPIONs were successfully used to diagnose Alzheimer’s using MRI.

Although recent advances in molecular imaging techniques have improved the ability to diagnose other neurodegenerative diseases, Parkinson’s is still diagnosed mainly by a doctor’s observation based on motor symptoms including slowness of movement (i.e., bradykinesia), resting tremors, and muscular rigidity. For these reasons, researchers wanted to investigate whether SPIONs could be used to target amyloidogenic proteins in Parkinson’s disease and Huntington’s disease.

The team developed an amyloidogenic-targeted molecular MRI probe called W20-SPIONs. This imaging probe consists of an amyloidogenic-specific antibody known as W20 joined to SPIONs.

The researchers showed that these W20-SPIONs were stable, non-toxic, and specifically recognized alpha-synuclein oligomers in human cells and mice. Oligomers consist of a few units (or monomers) and are suggested to be the most toxic form of amyloid.

When applied to mouse models of Parkinson’s and Huntington’s, W20-SPIONs crossed the blood-brain barrier and specifically bound to the brain regions with amyloidogenic proteins, giving an MRI signal and distinguishing between mice with neurodegenerative disease from healthy controls.

These results indicate that W20-SPIONs have potential in early-stage diagnosis of Parkinson’s and Huntington’s disease and open a new strategy for assessing the effectiveness of new treatments for neurodegenerative diseases.

“In our study, W20-SPIONs showed sufficient signal sensitivity, good biostability, and no potential toxicity in vitro and in vivo, which also had the capacity of specially targeting oligomers in the brain,” researchers wrote.

“This evidence supports that W20-SPIONs were a successful oligomer-targeted MRI probe for early diagnostics of Parkinson’s and Huntington’s disease. Identification of reliable biomarkers of disease progression will play a key role in the diagnosis of neurodegenerative diseases, and also be important for the development and assessment of disease-modifying treatments,” they added.

Future studies will be required to show the safety and effectiveness of W20-SPIONs in the early-stage diagnosis of Parkinson’s disease and other neurodegenerative diseases in human patients.

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