Parkinson's Disease in the Amish Community

Parkinson’s disease (PD) is the second most common neurodegenerative disorder after Alzheimer’s disease, affecting approximately 120 per 100,000 individuals in the United States. Parkinson’s disease is a disease that affects the way a person moves. It occurs when there is a problem with certain types of nerve cells within your brain. These certain nerve cells make a chemical called dopamine. Dopamine sends signals to the part of the brain that controls movement and allows the muscles to move smoothly and do what you want them to. However, with Parkinson’s disease, the nerve cells break down. Without these nerve cells, the body can no longer produce dopamine. Therefore, a person with Parkinson’s disease has trouble with their movement. Parkinson’s disease is progressive, which means it gets worse over time. This usually happens slowly over a long period of many years. There are four main symptoms of Parkinson’s disease. This includes tremors, stiff muscles, slow movement, and problems with balancing and walking. Tremors in the body are usually the first symptom of Parkinson’s disease. The cause of PD is unknown, although older age and smoking habit appear to be established risk factors.

The article I chose is called “A Genome-wide Scan in an Amish Pedigree with Parkinsonism.” The researchers of this study wanted to identify the PD genes in an eight generation Amish pedigree with apparent autosomal dominant Parkinsonism with incomplete penetrance. Autosomal dominance is a gene on one of the non-sex chromosomes that is always expressed, even if only one copy is present. However, since it has incomplete penetrance, it means that even if the individuals have the genes that would express Parkinson’s disease, not all would express it.

So far, seven genes have been identified in familial PD cases: α—synuclein (PARK1, PARK4), Parkin (PARK2), UCH-L1 (PARK5), PINK1 (PARK6), DJ-1 (PARK7), LRRK2 (PARK8), and ATP13A2 (PARK9).

Individuals who were being screened had to go through an interview with a board of genetic counselors. They were screened for a history of encephalitis, dopamine-blocking medication exposure within one year before diagnosis, symptoms of normal pressure hydrocephalus, or a clinical course with unusual features suggestive of atypical or secondary Parkinsonism. Participants were also evaluated for a history of exposure to substances known or suspected to cause Parkinsonism, including heavy metals or pesticides. Individuals with a positive symptom history of PD as well as unaffected individuals were personally examined by a board-certified neurologist with subspecialty training in movement disorders. Participants were classified as affected, unaffected or unclear, using published diagnostic criteria based on clinical history and neurologic examination.

Affected individuals had at least two cardinal signs of PD (tremors, slow movement, or rigidity) and no atypical features of Parkinsonism. Individuals with unclear status had only 1 sign of PD, a history of atypical clinical features, or both. Unaffected individuals had no signs of PD.

The severity of signs and symptoms was evaluated by the Unified Parkinson’s Disease Rating Scale. To figure out the genotypes of the individuals, DNA samples were prepared from whole blood using standard methods and stored using a bar-coded system. The genomic screen was conducted using a preselected set of 364 markers conducted in multiplex sets of two to three markers per sample.

What they found in this screening is that there were some genetic factors for why this pedigree has PD, but there is also evidence of environmental factors causing this disorder. This surprised the researchers because they believed with the inbreeding in this type of community; Parkinson’s disease would be from a result of genetic factors.

I thought this article is interesting because my husband is half Amish. Also, both my husband and his father are showing signs of Parkinson’s disease. It helped me better understand what exactly Parkinson’s disease is and where he could possibly be getting the disease from.

Citation: Lee, S., Murdock, D., McCaughley, J., Haines, J. (2008). A Genome-wide Scan in an Amish Pedigree with Parkinsonism. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2764120/?tool=pubmed
Christina M. Strubhar