Many of the better known age-related neurodegenerative conditions involve aggregates of damaged or misfolded proteins, but there are other similarities as well. This is too be expected, given that aging is at root caused by a small variety of forms of molecular damage. This damage spirals out into a much larger set of secondary and later consequences, ultimately leading to the wide variety of age-related diseases. Simple processes acting in a complex system, such as human biochemistry, tend to produce complex outcomes. Thus if starting at the point of any two age-related diseases, dig far enough back into their roots and you will arrive at shared origins. Somewhat in that vein, this open access review paper looks over some of the commonalities in Alzheimer's disease and Parkinson's disease:
Alzheimer's disease and Parkinson's disease are two common neurodegenerative diseases of the elderly people that have devastating effects in terms of morbidity and mortality. The predominant form of the disease in either case is sporadic with uncertain etiology. The clinical features of Parkinson's disease are primarily motor deficits, while the patients of Alzheimer's disease present with dementia and cognitive impairment. Though neuronal death is a common element in both the disorders, the postmortem histopathology of the brain is very characteristic in each case and different from each other. In terms of molecular pathogenesis, however, both the diseases have a significant commonality, and proteinopathy (abnormal accumulation of misfolded proteins), mitochondrial dysfunction and oxidative stress are the cardinal features in either case.
These three damage mechanisms work in concert, reinforcing each other to drive the pathology in the aging brain for both the diseases; very interestingly, the nature of interactions among these three damage mechanisms is very similar in both the diseases. In the case of Alzheimer's disease, the peptide amyloid beta (Aβ) is responsible for the proteinopathy, while α-synuclein plays a similar role in Parkinson's disease. The expression levels of these two proteins and their aggregation processes are modulated by reactive oxygen radicals and transition metal ions in a similar manner. In turn, these proteins - as oligomers or in aggregated forms - cause mitochondrial impairment by apparently following similar mechanisms. Understanding the common nature of these interactions may, therefore, help us to identify putative neuroprotective strategies that would be beneficial in both the clinical conditions.
Alzheimer’s and Parkinson’s disease are both neurological diseases that cause progressive damage to the brain, resulting in a decline in neurocognitive function. While Parkinson’s disease is known for affecting movement and function and Alzheimer’s disease is known for affecting cognition, they are a bit more complex than that.
Below, we provide an overview of Alzheimer’s and Parkinson’s disease with a comparison of key similarities and differences.
Dementia
Dementia is an umbrella term used to describe a group of symptoms associated with a decline in memory, reasoning, thinking, or other cognitive functions. These symptoms may include a decline in memory, poor reasoning and judgment skills, changes in thinking or problem-solving abilities, and changes in language and communication abilities.
Many of the following conditions, including Alzheimer’s and Parkinson’s disease, can cause dementia:
Alzheimer’s Disease
Alzheimer’s disease is the most common cause of dementia, accounting for approximately 60% to 80% of all dementia cases. Most commonly, Alzheimer’s disease is characterized by beta-amyloid plaques and neurofibrillary tangles resulting from abnormal tau hyperphosphorylation.
These plaques, tangles, and the loss of neuronal connections cause progressive damage to the brain, starting in parts of the brain responsible for memory (entorhinal cortex and hippocampus). As the disease progresses, this damage continues to spread to other regions of the brain, such as parts of the cerebral cortex responsible for reasoning, language, and social behavior.
Parkinson’s disease is a progressive neurodegenerative disease that is most commonly known for affecting function and movement, though it also affects cognition, particularly as the disease progresses. Parkinson’s disease primarily impacts dopaminergic, or dopamine-producing, neurons in a specific area of the brain known as the substantia nigra. Dopamine is a key neurotransmitter that transmits signals between neurons and plays a crucial role in movement and motor control.
The lack of dopamine makes it challenging for the brain to coordinate muscle movements and can also contribute to mood and cognitive issues later in the disease course. Patients with Parkinson’s disease also lose nerve endings that produce norepinephrine, a chemical messenger of the sympathetic nervous system responsible for controlling a wide range of functions in the body, such as blood pressure and heart rate.
Alzheimer’s and Parkinson’s Disease: Similarities and Differences
Similar cognitive and functional impairments are observable in both diseases. However, different proportions, varying manifestations along the disease continuums, and different rates of occurrence set the two apart.
Generally speaking, Parkinson’s patients will show early signs of functional impairment and in later stages may experience cognitive impairment, such as memory and thinking issues, if they develop dementia. According to the National Parkinson’s Foundation, recent studies that followed Parkinson’s patients over the course of the disease estimate that 50% to 80% of people with Parkinson’s disease eventually develop dementia. Conversely, earlier symptoms of Alzheimer’s patients may be more biased towards cognitive impairment, with functional impairments observed in later stages of the disease.
Characteristic/SymptomAlzheimer's DiseaseParkinson's DiseaseAverage age of onset- Early-onset: Before age 60
- Late-onset: After mid-60s
- Early-onset: Before age 50
- Late-onset: 50-65
Neuropathological hallmarks- Tau hyperphosphorylation, beta-amyloid plaques, neurofibrillary tangles, cerebral amyloid angiopathy, glial responses, neuronal loss, synaptic loss
- Key proteins: beta-amyloid and tau
- Nigral degeneration, brainstem Lewy bodies, alpha-synucleinopathy
- Key proteins: alpha-synuclein
Established risk factors- Advanced age
- Female sex
- Genetics
- Poor lifestyle habits (e.g. poor diet, lack of exercise, poor sleep, smoking, etc.)
- Vascular conditions (e.g. stroke, heart disease, high blood pressure, diabetes, high cholesterol)
- Head trauma
- Hearing loss
- Advanced age
- Male sex
- Genetics
- Environmental factors (e.g., exposure to toxins)
- Head trauma
Significant memory loss- Possible years after disease onset
Challenges with spatial relationships between objects or with sense of directionDecline in thinking abilities that interfere with Activities of Daily Living- Possible years after disease onset
Difficulty with planning or problem-solvingChanges in moodLanguage problemsFluctuations in cognitive abilities, attention, and alertnessChallenges with balancingRapid eye movement sleep behavior disorderHallucinationsSevere sensitivity to medications used to treat hallucinationsChanges in movement, including gait changes and tremorsAltoida: Pioneering AI-Enabled Precision Diagnosis
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What are the similarities and differences between Alzheimer and Parkinson disease?
Alzheimer's and Parkinson's Disease: Similarities and Differences. Similar cognitive and functional impairments are observable in both diseases. However, different proportions, varying manifestations along the disease continuums, and different rates of occurrence set the two apart.
Is Alzheimer's disease and Parkinson's disease same?
Alzheimer's disease (AD) and Parkinson's disease (PD) are generally considered to be separate and distinct disease entities. However, a considerable amount of evidence demonstrates that these disorders share common clinical and neuropathologic features and that overlap between the two conditions is extensive.
What are the similarities between Alzheimer's and dementia?
Alzheimer's disease has been said to be a “type” of dementia and a “cause” of dementia. Dementia covers symptoms such as memory loss and a decline in reasoning ability. Alzheimer's accounts for between 60 and 80 percent of dementia cases. Sometimes it is difficult to see a clear distinction between the two.
What is are similarities between the Parkinson's disease and Huntington's disease?
Parkinson's disease and Huntington's disease both involve the central nervous system. As a result, they affect how brain cells work, leading to symptoms such as tremors, limb stiffness, difficulty walking or talking, and cognitive or thinking problems.
