Neurodegenerative Disorders Revisited
Updated: Dec 13, 2021
Neurodegenerative diseases are incurable and are debilitating. Through various physiological pathways, the nerves degenerate and ultimately die. The most common of these neurodegenerative diseases are Alzheimer’s Disease (AD) and Parkinson’s Disease (PD). According to the Alzheimer’s organization, in 2020, over 6 million Americans were living with AD. AD and other dementias will cost the nation $355 BILLION in 2021, and by 2050, costs could top more than $1.1 TRILLION. One in three senior citizens (age 65 and older) will die from some form of dementia. Between 2000 and 2019, deaths from heart disease have decreased 7.3% while in the same timeframe, deaths from AD alone rose 145%. For patients diagnosed with dementia, typically AD is the most common form of dementia and vascular dementia is second. Symptoms of each form do overlap; however, the pathophysiology of the two diseases is somewhat different. With regard to genetic implications, research shows that those who have a parent or sibling with AD's are more likely to develop the disease than those who do not have a first-degree relative with AD. There is some evidence as well that a genetic variant of the apolipoprotein E (APOE) gene on chromosome 19 does increase a person's risk.
According to the National Institutes of Health (NIH), PD affects at least 500,000 people in the United States, although some estimates are much higher. For example, parkinsonsdisease.net reports an estimated one percent of the population over the age of 60 is afflicted with PD. A small percentage of people with PD (4 percent of all cases) are diagnosed before the age of 50. Based on the foregoing information, the number of Americans suffering from this disease could be considerably higher than 500,000, approaching nearly 1 million people! Additionally, approximately 60,000 Americans are diagnosed with PD each year. The average age of onset is about 60 years, and as a greater proportion of the U.S. population lives longer, disease prevalence is expected to increase. As reported on the PD website, every patient with PD does not experience the same problems. Having PD disease means to many afflicted with the disease as being aware, indeed self-conscious, of their own physical limitations and abnormalities. According to Healthline.com, most cases of Parkinson's are not hereditary. However, people who get early-onset PD are more likely to have inherited it. Having a family history of Parkinson's disease may increase the risk that a relative will get it the disease. However, there is a growing body of evidence that suggests that, like AD, PD may have a more causal relationship with genetics. For example, it has been suggested that certain genes (specifically PARK7, PINK1, or PRKN) may be involved. As reported by MedLine Plus if this is determined to be true, PD is inherited in an autosomal recessive pattern.
Regarding symptoms, AD and PD are both neurological illnesses. Both diseases are caused by damaged brain cells. Both conditions can involve dementia, as well as depression, anxiety, and sleep disturbances. Both conditions can lead to psychotic symptoms such as delusions and hallucinations. Anxiety is common to both PD and AD, and may require behavioral treatment, lowering of AD or PD medications, or addition of antidepressant or antianxiety medications, keeping in mind that both conditions leave patients vulnerable to medication side effects.
Treatment of moderate-to-severe AD for the immediate future is likely to involve several approaches, many of which have been covered by CureScience™ in other papers. To summarize, these approaches include the administration of memantine, cholinesterase inhibitors, vitamin E, as well as psychotropic medications if necessary to control noncognitive behavioral symptoms. Memantine represents the first NMDA-receptor antagonist for the treatment of moderate to severe AD. A double-blind, phase III clinical trial utilizing memantine has been completed, and while the evaluation is incomplete, initial results are encouraging. To be clear, numerous trials have been initiated to determine what new therapies and what novel variations to previously examined therapies provide more relief to the victims and their families.
With regard to advances in the treatment of PD, there are a number of therapeutic approaches, from pharmacological therapy to neurosurgical treatment or non-drug therapy. As A. Draoui et al. reported in a seminal review in 2020 in Revue Neurologique (Volume 176, Issues 7–8, September 2020, Pages 543-559), non-drug therapy focuses on relieving the symptoms and increasing the management effectiveness of symptoms that cannot otherwise provide relief using pharmacological therapy. Other non-conventional therapies have also been proposed such as sports and exercise, relaxation, occupational therapy, speech therapy and psychological support. However, there are numerous drugs reported that are either alone or in combination with other medications useful in treating this disease. These include Levodopa, the most effective PD medication, and a natural chemical that passes into your brain and is converted to dopamine; carbidopa, which protects levodopa from early conversion to dopamine outside your brain as well as dopamine agonists, glutamate antagonist, anticholinergics, COMT inhibitors, MAO-B inhibitors and other dopaminergic medications.
As reported by Yu et al. in Geriatrics (Published online 2021 Jan 26. doi: 10.3390/geriatrics6010010), neurodegenerative diseases are a group of diseases that are characterized by the progressive loss of neurons in the central and peripheral nervous systems. AD is the most common neurodegenerative disorder and form of dementia and is characterized by neuronal loss in the brain leading to cognitive decline and memory loss. As previously stated PD is the second most common neurodegenerative disorder, and it is characterized by neuronal loss in the substantia nigra. In contrast to AD, only a subset of PD patients develop dementia. However, in both diseases, patients experience a gradual worsening of their clinical condition as neuronal loss progresses, ultimately affecting their quality of life. Importantly, patients affected by neurodegenerative disorders often present with multiple age-related comorbidities. These observations have led several studies to investigate the hypothesis that individuals with neurodegenerative diseases exhibit heightened susceptibility to COVID-19. After evaluating numerous cases worldwide, Yu et al. concluded that a pre-existing diagnosis of dementia or AD predicted the largest risk of COVID-19 and mortality. However, while PD patients were found to be at heightened risk of SARS-CoV-2 infection, they did not exhibit mortality from COVID-19. This study as well as others supports the thesis that improved knowledge of these factors is critical to developing strategies to protect clinically vulnerable patients affected by neurodegenerative diseases during this pandemic.
Written By: Lawrence D. Jones, Ph.D.
Keywords: AD, Alzheimer’s, PD, Parkinson’s, COVID-19, Neurodegenerative Disease