Parkinson disease (PD) is a movement disorder (a general term used to describe problems with smoothness and ease of voluntary movement). In PD, the parts of the brain controlling smoothness and ease of movement slowly begin to lose proper function. The first symptoms often include a trembling hand, and slowness or stiffness in movement. Later symptoms include problems with balance. Parkinson disease is progressive. Medications can improve the symptoms, but cannot yet cure or reliably slow progression of the disorder. PD is often classified by the age when symptoms are first noticed: early-onset (before the age of 40) or late-onset (after the age of 40).
What causes Parkinson disease?
The exact cause of Parkinson disease is unknown. Scientists believe that both environmental and inherited factors are involved. The interaction between them is believed to be important. The general course of PD is known. In PD, neurons (specialized brain cells which conduct messages) that produce dopamine die off. Dopamine is a chemical needed by other nerve cells that control movement. As more and more of these neurons die, less dopamine is produced and voluntary movements become difficult to control.
The area of the brain most affected in PD patients is the substantia nigra, located in the brain stem. The neurons in this area have connections with other structures deep within the brain. Dopamine is sent through these connections. The substantia nigra and the deep-brain structures affected by PD are part of the brain called basal ganglia. A major function of the basal ganglia is to help with smooth voluntary movement.
How is Parkinson disease diagnosed?
The three classic signs of PD are tremor at rest, slowed voluntary movements (bradykinesia), and stiffness or rigidity. Less common symptoms include smaller handwriting (micrographia) and a softer speaking voice. Because other disorders can mimic PD, doctors base a diagnosis of PD on a neurological examination, as well as the presence and severity of symptoms.
The primary symptoms of PD are thought to be caused by a lack of dopamine in the brain. Therefore, if a person takes a medication such as L-dopa (Sinemet) which increases the amount of dopamine in the brain and symptoms improve, then a diagnosis of PD is supported.To date, there are no common laboratory or blood tests that will confirm the diagnosis of PD.
Who has Parkinson disease?
PD is one of the most common movement disorders and ranks only behind Alzheimer’s in frequency of neurological disorders. For example, in the United States it is twice as common as multiple sclerosis, another neurological condition. PD affects over 500,000 Americans, a number equivalent to the entire population of Washington D.C. One percent of the population of the United States over the age of 60 has PD. The majority of patients with PD are diagnosed between ages 50 and 75 years old. The average age of diagnosis is 61 years old. Early-onset PD (development of symptoms before age 40) accounts for only 5-10% of cases. The symptoms of people with early-onset PD generally develop more gradually than those of people with late-onset PD.
Is PD inherited?
To answer that one must understand that genes can cause disease in two different basic ways. The first is where a change in the DNA of a gene is so severe that it stops the normal function of the gene from occurring or creates a new function that is very damaging to the cell. This mutation is serious enough to cause a disease independently. These single gene diseases are called Mendelian disorders, after Gregor Mendel, the monk that first described the inheritance patterns we now know as genetic segregation, when he studied his famous peas. However, most common diseases that affect humans are due to a combination of factors, in which genes maybe the largest part. The gene variation here is not severe mutations, but variations in the genes that make us each of the individuals that we are. Certain combinations of these variations, perhaps with environmental exposures make people more predisposed or susceptible to a disease. We all know of things that run in my family whether it is cancer, heart disease, etc. The genetics that contribute to these common diseases is called complex genetics.
To date, several genes have been identified in which a severe mutation, by itself, causes Parkinson disease. These are alpha-synuclein, Parkin, LRRK2, PINK1, DJ1 and one variant of EIF4G1. No one knows for sure, but current estimates are that these “Mendelian”; disease genes account for only about 5% of PD. The genes for the rest of PD are complex. While the UM Udall Center works on all genes leading to PD, we concentrate on these complex genes, as they are the ones affecting the most people. The risk for siblings and offspring of a PD patient have been estimated to be 2-10 times that of the general population, suggesting that complex genes are important in PD.
What is the difference between Parkinson disease and Parkinsonism?
Parkinsonism is the general term used to describe a large number of movement disorders, of which PD is the most common form, with a specific group of symptoms. In general, any disease that has some of the symptoms of PD is included in the larger “parkinsonism” group.
What are the PD treatment options?
These are described well in many sites, and new options are continually changing. Individuals should consult their local physician, neurologist or movement disorder specialist for information for them.