The main abnormality that causes PD seems to be related to loss of certain nerve cells (neurons) in a part of the brain called the substantia nigra. However, we know that in fact it is a whole-brain disease, involving just about every area studied so far.
To date, it is unclear exactly why these cells die or deteriorate, although there are clues from genetic and environmental studies suggesting a multi-factorial origin. Normally, the substantia nigra cells produce a neurotransmitter known as dopamine, which is used to communicate with other parts of the brain. Dopamine allows smooth, coordinated function of the body's muscles and movement. When approximately 80% of the dopamine-producing cells are damaged, the symptoms of Parkinson Disease appear. PD diagnosis and treatment is often complicated.
Parkinson's Disease (PD) is found throughout the world and was described as early as 5000 B.C. in Ayurvedic texts in India. Up to 1.5 million people in the United States are believed to currently suffer with PD, with approximately 100,000 new cases diagnosed each year. Due to the demographics of aging in the U.S., these numbers will double by the year 2025.
Parkinson Disease affects both men and women in almost equal numbers. Although it shows no social, ethnic, economic or geographic boundaries, a recent study showed that PD is twice as prevalent in the U.S. as in other countries, due to a number of factors.
In the United States, it is estimated that up to 100,000 new cases are diagnosed each year, joining the 1.5 million Americans who currently have Parkinson Disease. While the average age of onset is 62, 15% of those diagnosed are under 50 and have a condition known as “Young-Onset PD.” We used to think it was associated with professions such as arc-welding or steel mill work, but more recent studies have not confirmed this; in fact, it seems to be more prevalent in engineers, accountants, and doctors, suggesting that these patients are more likely to seek help and be diagnosed.
Interestingly, there is a very clear familial or genetic association in only a small proportion of PD patients. For instance, if your twin gets PD, the likelihood you will get it is only about 5%. However, for patients with a strong family history of PD, there are about 20 different genes that seem to be strongly associated and make it much more likely that the carrier will eventually come down with PD.