What is Parkinson’s disease?
Parkinson’s disease is a neurodegenerative condition primarily affecting movement of the body although some patients may also experience other neurological dysfunction like dementia. It is one of the most common neurological conditions in the elderly particularly in developed nations. The term neurodegenerative means decline of the nervous system functions and with Parkinson’s disease it mainly affects the central nervous system – the brain. However, the exact cause and disease mechanism of Parkinson’s disease is not fully understood.
Parkinson’s disease is a slowly progressive disorder meaning that it gradually gets worse over a long period of time. The cause is largely unknown. Eventually there will be symptoms associated with the muscles – movement and coordination – such as resting tremor, muscle rigidity, slowness of movement called bradykinesia and postural instability. However, the effects of Parkinson’s disease along with the drugs used to treat it has a major psychosocial impact beyond just the physical symptoms.
Who gets Parkinson’s disease?
Parkinson’s disease is often seen as a neurological condition of the elderly. It affects less than 1% of adults over 40 years of age but this rises sharply to 10% of people over the age of 80 years. Parkinson’s disease very rarely occurs in a person before the age of 40 and the mean age of onset is about 57 years. Men are more likely to be affected with Parkinson’s disease than women.
A family history of Parkinson’s disease may increase the risk of developing the disease but it usually a minor factor. There is significant evidence to suggest that long term exposure to certain herbicides and pesticides may be a risk factor for the development of Parkinson’s disease even years or decades after last contact. The condition is less common in cigarette smokers possibly illustrating a neuroprotective effect of cigarette smoking. The same neuroprotective effect has been noticed with regards to caffeine use.
The Parkinson’s Brain
In Parkinson’s disease (PD) there is a gradual deterioration and loss of certain nerve cells in the brain. It mainly affects the nerve cells that are involved with regulation and control of movements. It is important to understand the anatomy and normal physiology within certain areas of the brain. There is a cluster of nerve cells in the brain known as the substantia nigra which seems to be more affected in Parkinson’s disease. In a healthy person, there is a sufficient amount of a chemical messenger (neurotransmitter) known as dopamine present within the substantia nigra.
Dopamine and Acetylcholine
Dopamine is transported from the substania nigra along the course of the nerve cells to the corpus striatum where these nerve cells end. It is here where dopamine and another chemical messenger known as acetylcholine controls the body movements. In Parkinson’s disease there is an imbalance of dopamine and acetylcholine. There is loss of dopamine in the substantia nigra and degeneration of dopamine nerve terminals in the corpus striatum. This is the most likely mechanism for Parkinson’s disease but symptoms only emerge once approximately 60 to 80% of these nerve cells dopaminergic neurons) are lost. In some rare cases, it is the overactivity of the acetylcholine nerve cells that appears to be the cause of Parkinson’s disease.
The presence of clumps of protein known as Lewy bodies in the brain of Parkinson’s disease patients indicates another possible component of the disease mechanism. It is important to note that the presence of Lewy bodies is not unique to Parkinson’s disease. These protein clumps have been found in several other neurological disorders. However, it is rare for Lewy bodies not to be present in the brain of Parkinson’s patients. It is therefore characteristic but not specific for Parkinson’s disease. The exact role of Lewy bodies in Parkinson’s disease has not as yet been fully established.
Certain herbicides and pesticides may play a significant role in the development of Parkinson’s disease. It is only with long term exposure to these substances that the possible role in Parkinson’s disease becomes apparent. Thus far it has been noted that the effects of certain substances (other than herbicides and pesticides) on mitochondrial pathways is similar to Parkinson’s disease. These other substances share a similar chemical structure with herbicides and pesticides thereby highlighting a possible role.
Free radicals are compounds that are unstable and can cause damage to cells. Some of these compounds are produced by cells itself during the utilization of energy. Usually a balance is maintained by the presence of antioxidants which counteract the effects of the free radicals. However, high levels of free radicals or low levels of antioxidants can cause damage to nerve cells. This may be further exacerbated by toxins (free radicals) in the environment that have an affinity for brain tissue.
Causes of Parkinson’s Disease
The exact cause of Parkinson’s disease is unknown and it is therefore termed idiopathic. It is believed that Parkinson’s disease is due to a combination of genetic and environmental factors. However, it is important to note that these factors are definitive causes of Parkinson’s disease but have been found to increase the risk of developing the condition.
- Genetics. Several genes have been identified as important contributors of Parkinson’s disease. It explains the incidence of PD among family members and ethnic groups. However, these genes are not significant factors in the majority of Parkinson’s patients. Neither is having these genes a definitive cause of Parkinson’s disease on its own and possibly an interplay of genetic and environmental factors may be responsible
- Advancing age, especially over the age of 60 years is a risk factor.
- Toxins such as herbicides and pesticides which are structurally similar to chemicals such as 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) – a substance known to have similar effects to those seen in Parkinson’s disease
- Oxidative stress as a result of free radicals like hydrogen peroxide that is not rapidly cleared from cells by antioxidants.
- Certain viruses which may not play a direct role in the progressive nature of Parkinson’s disease but rather serves as a trigger.