Parkinson's disease is a chronic neurodegenerative disease that affects the central nervous system, specifically the areas of the brain responsible for movement control. It is a degenerative disease that affects approximately 1-3% of the population over 60 years of age and is influenced by different factors such as genetics.
Symptoms of Parkinson's disease
Parkinson's disease occurs when nerve cells in the basal ganglia, cells responsible for producing dopamine, deteriorate or die. Dopamine is involved in many functions including movement control. That is why patients with this disease present involuntary or uncontrollable movements among which the characteristic tremors of Parkinson's disease stand out.
Without sufficient dopamine, the direct circuit (responsible for the initiation and execution of voluntary movements) is not adequately activated, and the indirect circuit (responsible for suppressing involuntary or unnecessary movements) is not adequately inhibited, resulting in difficulties in initiating and controlling movements.
This is a progressive symptomatology based on:
- Stiffness
- Tremors
- Slowness in the initiation and execution of movements (bradykinesia).
- Difficulty in maintaining balance and posture.
What are the types of Parkinson's disease?
There are three very different types of Parkinson's disease in terms of the age of the patients:
- Late Onset Parkinson's: it is the most common. It occurs in 90% of Parkinson's cases and symptoms appear in people over 60. Only 10% of these cases are hereditary, the rest are due to genetic predispositions and exposure to environmental factors.
- Early Onset Parkinson's: occurs in only 5-10% of Parkinson's cases and is that which develops at less than 50 years of age. This form of Parkinson's is hereditary.
- Atypical juvenile Parkinson's: occurs during the 20s and is extremely rare. According to orphanet, there are only 6 families worldwide with this type of Parkinson's disease.
How do genetics affect Parkinson's?
Although there are monogenic forms (a single gene is responsible for the manifestation of the disease), most cases are the result of the complex interaction between phenotypic factors such as age or gender (more frequent in males), environmental factors such as exposure to certain toxins (pesticides) and genetic factors. In addition, an association has been seen between the presence of the ε4 allele of APOE (risk factor for Alzheimer's disease) and the susceptibility to develop Parkinson's disease.
Regarding the specific genes involved, numerous genes (either causal or susceptibility genes) are known. Among them we can find:
- Late Onset Parkinson's disease: variations in LRRK2, PARK, VPS35 and GBA genes.
- Early Onset Parkinson's: this type of Parkinson's has been associated with the genes LRRK2, PARK1, PARK2, PARK5, PARK6, PARK7, PARK8, VPS13C and PODXL.
- Atypical juvenile Parkinson's: in the few patients diagnosed with this type of Parkinson's, variations in the genes ATP13A2, PLA2G6, FBXO7, DNAJC6, SPG11, SPG15 and SYNJ1 have been seen.
Changes in the expression or presence of mutations in the PARK1 gene (also known as SNCA) are thought to have neurotoxic effects on dopaminergic neurons. This gene expresses the protein α-synuclein, whose monomers form fibrils and protofibrils that are toxic in dopamine-producing neurons, thus causing their death and reducing the amount of dopamine in the organism.
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