Parkinson’s disease is a progressive neurodegenerative disorder that affects the nervous system and, predominately, the dopamine-producing neurons in the substantia nigra (Parkinson’s Foundation). In physical aspect, this disorder mainly affects an area called the substantia nigra, as well as several other areas within the brain. The substantia nigra is an area in the brain that controls balance and movement. Parkinson’s disease also affects the sufferer’s cognitive abilities in addition to physical capabilities. As stated on the Genetics Home Reference, Parkinson disease is caused by a set of complex interactions between environmental and genetic factors. Not only can Parkinson disease brought on by interaction with external factors, it can also be linked genetically within families, meaning the internal factors. Approximately fifteen percent of people with Parkinson disease have familial history of Parkinson’s (GHR). Parkinson’s disease often shows itself after the age of fifty. This is referred to as late-onset disease. When Parkinson’s shows itself before the age of twenty it is referred to as early-onset, or juvenile-onset Parkinson disease. It has also been shown that Parkinson’s affects more males than it does females (Miller, Cronin-Golomb). There are also differences in how Parkinson’s affects men and women in clinical characteristics like depression and rigidity (Miller, Cronin-Golomb). Generally speaking though, Parkinson disease affects more than one million people in North America (GHR). In the United States, approximately thirteen of one hundred-thousand people have Parkinson’s. Additionally, sixty-thousand new cases are diagnosed each year (GHR).
Diagnosing Parkinson disease often contains two major parts; identifying symptoms and genetic testing. Often times Parkinson disease is first noticed by symptoms. As previously mentioned, Parkinson disease has effects on both the physical and cognitive abilities of the sufferer. For physical aspects, one of the major areas affected is the substantia nigra. The substantia nigra is located in the midbrain, which is at the part of the brainstem nearest to the center of the brain. The substantia nigra controls balance and movement. This control slowly dissipates to the point that the body begins trembling and shaking while at rest. This is also referred to as a tremor and is one of the first symptoms of Parkinson’s. These tremors often originate in one side of the body, usually starting in the hand. As the disease progresses, these tremors begin to affect the arms, legs, feet, torso, and face (GHR). Other physical symptoms include rigidity/ stiffness of the limbs and torso, bradykinesia (slow movement), akinesia (inability to move), and postural instability (impaired balance /coordination (GHR). As with the tremors, all of these symptoms progress in severity with time. In order to be diagnosed with Parkinson’s, you must have two of the four main symptoms previously mentioned present (Parkinson’s Foundation). Other symptoms of Parkinson disease can be noticed cognitively. Some individuals that suffer from Parkinson’s can develop psychiatric conditions (GHR). Depression and hallucinations can be seen, as well as an increased risk of developing dementia. Dementia causes a weakening of judgment and memory, as well as other intellectual functions (GHR). Another way to identify and diagnose Parkinson disease is through genetic testing. Genetic testing for Parkinson’s is a more recent capability. These tests can be run on the parkin and PINK1, PARK7, SNCA and LRRK2 genes (National Human Genome Research Institute). Genetic testing is widely available to all today through companies like 23andMe. 23andMe is a genetic testing kit where you order a kit, collect and submit a saliva sample, and send it to their labs where the researchers for 23andMe examine your genome. After examining your genome, these researchers formulate a report of your health risks, which includes how likely it is that you may develop Parkinson Disease. While these at home kits could be good indicators of health conditions, like Parkinson’s, they will not be as accurate as a test conducted in a hospital. If there are individuals and families that wish to learn more, it is recommended that they should seek advice from a Genetics Health Professional (NHGRI).
As with many disorders, Parkinson disease has genes that are paired with specific inheritance patterns. These patterns are called autosomal dominant and autosomal recessive and differ depending on what gene has been altered (GHR). Autosomal dominant patterns mean one copy of an altered gene in each cell sufficient enough to cause the disorder (GHR). This means that in most cases, an affected person has one parent that also has the condition. Autosomal recessive patterns mean that two copies of the gene in each cell are altered. With this inheritance pattern, often times the parents of an individual with the autosomal recessive Parkinson disease each carry a copy of the altered gene but do not show signs or symptoms of Parkinson’s. Genes that are associated with the autosomal dominant pattern are SNCA and LRRK2. SNCA or synuclein alpha is a gene that provides the instructions for making a small protein called alpha-synuclein (GHR). This protein is abundant in the brain, but is also found in small amounts in the heart, muscles, and other tissues. In the brain it is mostly found at the tips of nerve cells in the presynaptic terminals (GHR). These presynaptic terminals allow for communication between neurons using neurotransmitters. These transmitters are critical for brain functions. The purpose of alpha-synuclein is not well understood at this time (GHR). Studies suggest that it plays an important role in keeping an adequate supply of synaptic vessels. It may also regulate the release of dopamine which is key in the start and stop of involuntary and voluntary movements (GHR). The statement, “These findings above suggest a specific speed and a spread of neuropathological involvement in patients with SNCA mutations. Moreover, a correlation emerged between the incidence of non-motor symptoms and disease severity.”, which is found in A53T in a parkinsonian family: a clinical update of the SNCA phenotypes shows that the SNCA gene is also being linked to symptoms we can see, as well as the rate of progression. The LRRK2 gene, which stands for leucine rich repeat kinase 2, also provides instructions for producing a protein. The difference is that this gene instructs production of the protein dardarin. A segment of this protein is defined as a leucine-rich region due to it containing large quantities of an amino acid known as leucine. Proteins with these leucine-rich regions play a role in transmitting signals and helping to assemble the cytoskeleton (GHR). It is also shown that dardarin has an enzyme function noted as kinase activity. Kinase activity aids in the phosphorylation of certain proteins.