Parkinson's Disease

- Overview

Parkinson’s disease (PD) is a degenerative neurological disease that affects movement, coordination, and balance. Named for James Parkinson, the English doctor who identified it in 1817, PD afflicts nearly 10 million people worldwide. Although most people respond well to treatment, PD is a progressive disorder that worsens over time. 

PD destroys nerve cells, or neurons, in a part of the brain stem known as the substantia nigra. It’s a crescent-shaped hub in the midbrain that produces an essential type of chemical called a neurotransmitter. Neurotransmitters help bridge gaps between the nerve cells, allowing them to communicate with one another and pass nerve signals from the brain to the rest of the body. 

Dopamine is a key neurotransmitter that helps with muscle movement, mood, and motivation. Lack of dopamine is the primary cause of Parkinson’s motor symptoms. Dopamine normally helps control muscle coordination, balance, and walking. 

PD progresses slowly, often starting with tremors (shaking) on one side of the body, slowed movement, rigid muscles, halting gait, balance problems, speech or writing changes, and difficulty smiling or blinking.

- Causes 

Researchers have not yet discovered the causes of PD. Scientists think PD arises from a complex interplay of genetic and environmental factors. No single factor likely causes PD on its own. Although we still don’t know precisely what causes the disease, some factors increase an individual’s risk of developing Parkinson’s disease. Risk factors include:

• The disorder is diagnosed mainly in people over the age of 60. The single most significant risk factor for PD is advancing age.
• Men are more likely than women to develop the disorder. PD usually begins with slow or rigid movement in men, while tremor is usually the dominant symptom in women.
• Genetic factors include a mutation in specific genes — LRRK2 and GBA — that raises the risk of developing PD. Several other gene variants have been linked to PD. Mutations in the mitochondria, the parts of your cells that generate energy, may also play a role in PD.
• Environmental triggers include toxic chemicals. Low-level exposure to some agricultural pesticides may be related to PD.
• Brain inflammation may play a crucial role in the development of PD.
• Head injuries increase the risk of PD.

- Genetics

PD can strike one or more family members, but it is rarely inherited directly. Only about 2% of PD cases appear to be related to an inherited mutation. However, people of specific ethnic backgrounds -- Ashkenazi Jews, North Africans, and Basques -- are more likely to suffer from PD.

Changes in the LRRK2 gene (a mutation known as G2019S) account for 15-20% of cases in Ashkenazi Jews and 40% of cases in North African Arab-Berbers. Other changes in LRRK2 that raise the risk of PD have been found in people of Chinese descent.