There are various diseases that impair movement. Movement disorders may be caused by injuries, autoimmune diseases, infections and effects of certain medicinal drugs but are primarily caused by nerve diseases. Most of these diseases are chronic—persisting over long periods—and progressive where symptoms grow worse as time goes by. One such movement disorder that is both chronic and progressive and caused by nerve disease is the Parkinson’s disease.
The Disease and its Causes Parkinson’s disease, also called paralysis agitans or the shaking palsy, is a degenerative disorder of the central nervous system first described by James Parkinson in 1817. It is characterized by tremors, rigidity or the stiffness of the limbs and trunk, the slowness of movement called bradykinesia, and postural instability. However, as the disease progresses, patients may develop difficulty completing simple tasks, even in walking and talking.
Not all patients who suffer these symptoms have Parkinson’s disease as Parkinson’s disease is the most common form of Parkinsonism—a group of conditions with similar symptoms and features as the disease. The disease usually manifests itself during the later stage of life, typically at the age of 60 and above. Parkinson’s disease appears to be hereditary although most cases appear sporadic—that is, the disease does not seem to run in the family—and may have been caused by genetic mutations. However, it may have other causes such as exposure to environmental factors and free radicals.
The primary cause is attributed to the impairment of nerve cells in the substantia nigra. Neurons in the substantia nigra produce a chemical known as dopamine—a chemical messenger responsible for transmitting signals to produce smooth, purposeful movement such that the loss of the chemical results in abnormal nerve firing patterns within the brain that impairs movement. There are various genetic evidences presented for the development of Parkinson’s disease. Some researches show that “first degree relatives of the familial [Parkinson’s disease] patients are more vulnerable to [the disease] than the general population.
” Tang et al. explained that “genetic analysis has shown that over 100 genes are correlated with the etiology and pathology of [Parkinson’s disease]. ” Tang et al. identified some of the genetic mutations responsible for the development of Parkinson’s disease that are included in the Mutation Database for Parkinson’s Disease. For example, the LRRK2 G2019S is said to be a common pathogenic mutation found in 5-7 percent and 1-2 percent of familial and sporadic Parkinson’s disease respectively worldwide.
Genetic mutations found in the PARK2, PINK1, SNCA, UCHL1, PARK7, CYP2D6, MAPT, MAOB and APOE are also attributed to the development of the disease. The disease has not been properly documented until 1817. Today, it is estimated that 500,000 people in the United States alone suffer from the disease. Some scientists believe that Parkinson’s disease was uncommon before the Industrial Revolution and the increased number of patients may be attributed to the presence of environmental toxins produced by technological advancement.
MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine), a chemical byproduct created in the synthesis of illicit drugs, is also linked in the development of Parkinsonism in drug abusers. Gao et al. demonstrated that MPTP and an inflammogen lipopolysaccharide “synergistically induced a progressive and selective degeneration of dopaminergic neurons. ” Others held that the use of common garden pesticides and insecticides increases the risk of developing Parkinson’s disease although a link has yet to be established.
Exposure to carbon monoxide, cyanide, manganese and certain tranquilizers as well as exposure to some viruses, suffering head injuries and stroke are also said to cause the disease. Other scientists believe that free-radicals that have the potential to damage cell or molecules produced in the cells can cause the development of Parkinson’s disease. In summary, scientists now believe that Parkinson’s disease “results from a combination of genetic susceptibility and exposure to environmental factors that trigger the disease. ”