It is the second most frequent neurodegenerative pathology affecting about 1 in 500 people. It consists of a progressive disease of the nervous system characterized by the degeneration of the dopaminergic neurons of the substantia nigra responsible for movement control, which manifests itself in the form of movement disorders.
Parkinson's disease occurs when nerve cells or neurons in the basal ganglia, the area of the brain that controls movement, deteriorate and/or die. Normally, these neurons produce dopamine, so their destruction implies the production of less dopamine, which causes movement problems. However, the exact cause of the degeneration of these neurons is currently unknown. Some cases of Parkinson's appear to be hereditary and can be attributed to specific genetic changes, however, it is currently believed that it may be the result of a combination of genetic changes and environmental factors.
In addition to genetic predisposition, the following risk factors have been described:
- Gender: men are more likely to develop Parkinson's disease.
- Age: most people with Parkinson's develop the disease for the first time around the age of 60 and the risks increase with age. However, 5-10% have "early onset" disease that begins before age 50.
- Exposure to toxins. Constant exposure to herbicides and pesticides may slightly increase the risk of Parkinson's disease.
It presents a highly polygenic genetic architecture of a multitude of variants with small additive effects to the risk, onset and progression of the disease that contribute around 16-36% to its development, added to the effect of environmental factors. The study by meta-analysis of large cohorts of GWAS involving a total of more than 20000 Parkinson's disease cases and more than 415000 controls has revealed the significant association of 27 risk loci apparently related to dopaminergic neurotransmitter pathways and the development of different tissues including neuronal.
Signs and symptoms of Parkinson's disease can be variable among individuals. Early signs may be mild and go unnoticed. The rate of progression differs among people and even the initial symptoms are labeled as those of aging. Often, symptoms begin on one side of the body, and continue to worsen on that side, even after symptoms begin to affect both sides.
The symptoms most frequently associated with this disease are:
- Tremors in the hands, arms, legs, jaw or head.
- Stiffness of the limbs and trunk.
- Slowness of movement.
- Impaired balance and coordination, sometimes leading to falls.
People with Parkinson's often develop a parkinsonian gait that includes a tendency to lean forward, small quick steps as if rushing forward, and decreased arm swinging. They may also have trouble initiating or continuing movement. Other symptoms may include depression and other emotional changes, difficulty swallowing, chewing and speaking, urinary problems or constipation, skin problems and sleep disturbances.
Some cases of Parkinson's disease are inherited and may be caused by genetic changes, but in many cases, the disease is sporadic (not inherited). Because the specific cause of Parkinson's disease is unknown, proven ways to prevent it are also limited. Some research has suggested that regular physical exercise may reduce the risk of developing Parkinson's disease. Other studies indicate that consumption of caffeine from coffee, tea or cola drinks is associated with a lower risk, although there is currently insufficient evidence to indicate that consumption of caffeinated beverages has a protective effect against Parkinson's disease.
13.5 million variants
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Aaseth J et al. Prevention of progression in Parkinson's disease. Biometals. 2018;31(5):737-747.
Smeland OB et al. Genome-wide Association Analysis of Parkinson's Disease and Schizophrenia Reveals Shared Genetic Architecture and Identifies Novel Risk Loci. Biol Psychiatry. 2021 Feb 1;89(3):227-235.