Adult stem cells
Undifferentiated cells, found in a differentiated tissue, that can renew themselves and - with certain limitations - differentiate to yield all the specialized cell types of the tissue from which they originated.

Akinesia
Inability to move ("freezing") or difficulty in beginning or maintaining a body motion.

Antioxidant
A chemical compound or substance that inhibits oxidation - damage to cells' membranes, proteins or genetic material by free radicals (the same chemical reaction that causes iron to rust). Some studies have linked oxidative damage to Parkinson's.

Ataxia
A movement disorder marked by loss of balance and decreased coordination.

Bioethics
A discipline dealing with the ethical implications of biological research and applications especially in medicine.

Biomarkers
Specific, measurable physical traits used to determine or indicate the effects or progress of a disease or condition. No validated biomarker of Parkinson's disease currently exists.

Blood-brain barrier
A thin layer of tightly packed cells separating the central nervous system from the body's blood stream. This layer is crucial to protecting the brain from foreign substances, but also blocks some potentially therapeutic treatments from entering the brain via orally administered drugs.

Bradykinesia
One of the cardinal clinical features of Parkinson's disease, the slowing down and loss of spontaneous and voluntary movement.

Cell replacement therapy
A strategy aiming to replace cells damaged or lost by disease or injury with healthy new cells. Cell replacement for Parkinson's disease aims to replace with new cells the dopamine-producing cells in the brain that are progressively lost in PD.

Clinical trials
Organized studies that test the value of various treatments, such as drugs or surgery, in human beings.

Cognitive dysfunction
The loss of intellectual functions (such as thinking, remembering, and reasoning) of sufficient severity to interfere with daily functioning. The term cognitive dysfunction includes dementia and executive dysfunction, and may also encompass changes in personality, mood, and behavior. Cognitive dysfunction in Parkinson's disease typically does not respond to dopamine replacement therapy.

DBS (deep brain stimulation)
Surgical procedure that uses a surgically implanted medical device called a neurostimulator - similar to a heart pacemaker - to deliver electrical stimulation to targeted areas in the brain that control movement, blocking the abnormal nerve signals that cause tremor and Parkinson's disease symptoms.

Dementia
A decline in memory and/or intellectual functioning severe enough to interfere with social or occupational functioning. Some Parkinson's patients experience dementia, generally at later stages of disease progression. This symptom does not typically respond to dopamine replacement therapy.

Depression
A mental state, and non-dopamine-responsive symptom of Parkinson's disease, characterized by feelings of despondency and a lack of ability to initiate activity.

Dopamine
A neurotransmitter chemical produced in the brain that helps control movement, balance, and walking. Lack of dopamine is the primary cause of Parkinson's symptoms.

Dopamine agonist
A class of drugs commonly prescribed in Parkinson's disease that combines with dopamine receptors to mimic dopamine's actions in the brain. Dopamine agonists stimulate dopamine receptors and produce dopamine-like effects.

Dopamine-non-responsive
Refers to symptoms of Parkinson's disease characterized by a lack of improvement when treated with current dopamine-replacement therapies. These symptoms include cognitive dysfunction, gait and posture dysfunction, sleep disorders and depression, and others.

Dysarthria
Slurred or otherwise impaired speech. A common problem in Parkinson's.

Dysequilibrium
Unsteadiness or balance problems. A common problem in Parkinson's.

Dyskinesia
Involuntary, uncontrollable, and often excessive movements that are a common side effect of many drugs used to treat Parkinson's disease. These movements can be lurching, dance-like or jerky, and are distinct from the rhythmic tremor commonly associated with Parkinson's disease.

Dysphagia
Difficulty swallowing. A common problem in Parkinson's that increases the risk of inhaling food or liquids into the airways, which in its later stages can lead to a condition known as "aspiration pneumonia."

Embryonic stem cells
Primitive (undifferentiated) cells from the embryo that have the potential to become a wide variety of specialized cell types.

Environment
The non-genetic surroundings, conditions or influences that affect an organism.

Enzyme
A protein that catalyzes or speeds up chemical reactions. Enzymes are critical to a wide range of healthy cell activities, and alterations in their function may play a role in Parkinson's disease.

Executive dysfunction
Difficulty sustaining "executive functions," higher-order processes that enable us to plan, sequence, initiate, and sustain our behavior toward a given goal, incorporating feedback and making adjustments along the way. Some people with Parkinson's experience executive dysfunction or other forms of cognitive impairment, which do not respond to dopamine replacement therapy.

Facial masking
A symptom experienced by some people with Parkinson's, in which the face is immobile with reduced blinking.

Familial Parkinson's disease
A rare form of Parkinson's disease that runs in families, in which genetics is believed to play an important role. This form may account for less than five percent of Parkinson's cases worldwide.

Festination
A quickening of steps and shuffling after starting to walk.

Freezing
Abrupt and temporary inability of Parkinson's patients to move that frequently occurs at a boundary such as a door or when exiting a car.

Gene therapy
A novel approach to treat, cure or prevent disease by changing the expression of a person's genes. In Parkinson's disease, this research primarily seeks to repair or restore the function of dopaminergic neurons in the brain.

Hypokinesia
A clinical term for the slow or diminished movement associated with Parkinson's disease.

Lesion
An area of cell damage or cell death.

Levodopa
Also called L-dopa, the most commonly administered drug to treat Parkinson's symptoms. Levodopa helps restore levels of dopamine, a chemical messenger in the brain responsible for smooth, coordinated movement and other motor and cognitive functions.

Micrographia
Small, cramped handwriting that is a symptom for many Parkinson's patients.

Monoamine oxidase inhibitors (MAO)
Drugs that enhance the effect of dopamine by preventing enzymes from breaking them down.

Movement disorders
Conditions that prevent normal movement. Some are characterized by lack of movement, some by excessive movement. Besides Parkinson's, conditions categorized as movement disorders include essential tremor, multiple system atrophy, progressive supranuclear palsy, Huntington's disease, Tourette's syndrome and cerebral palsy.

Neurodegeneration
The slow death of certain brain systems in conditions such as Parkinson's disease, Alzheimer's disease and Lou Gehrig's disease (ALS).

Neurologist
A physician specializing in diseases and disorders of the brain, spinal cord, nerves, and muscles,including stroke, Parkinson's disease, epilepsy, Alzheimer's disease, and muscular dystrophy.

Neuroprotection
Neuroprotection is the mechanisms and strategies used to protect against neuronal injury or degeneration in the central nervous system (CNS) following acute disorders (e.g. stroke or nervous system injury/trauma) or as a result of chronic neurodegenerative diseases (e.g. Parkinson's, Alzheimer's, Multiple Sclerosis).

Neuron 
A nerve cell used to transmit information within the central nervous system. Parkinson's disease involves death of and/or damage to dopamine neurons.

Neurotransmitter
A specialized chemical messenger (e.g. dopamine, norepinephrine, serotonin) that sends messages from one nerve cell to another.

Olfactory dysfunction
A reduced or impaired ability to detect odors, which can be an early sign of Parkinson's disease.

On-Off phenomenon
Sudden loss of activity of levodopa lasting minutes to hours after a brief period of effectiveness. The term also sometimes refers to a cyclical response to medication where the patient can function adequately at times but is too stiff and immobile to function at other times.

Pallidotomy
A surgical procedure in which lesions are produced in the globus pallidus region of the brain in an effort to lessen Parkinson's symptoms such as tremors, rigidity, and bradykinesia.

Postural instability and gait dysfunction
Uncontrollable problems with standing or walking, or impaired balance and coordination, which are symptoms of Parkinson's disease for some patients and do not respond to dopamine replacement therapy.

Progressive disease
The signs and symptoms of the disease become worse over time.

Resting tremor
One of the cardinal clinical features of Parkinson's disease, an unwanted and uncontrollable movement that affects a limb when it is at rest and stops for the duration of a voluntary movement.

Rigidity
Abnormal stiffness in a limb or other body part. One of the cardinal clinical features of Parkinson's disease.

Sleep disorders
Chronic troubles with the amount, duration or quality of sleep an individual experiences. Some people with Parkinson's experience sleep disorders as a symptom. This symptom typically does not respond to dopamine replacement therapy.

Speech disorders
Symptoms that affect up to 90 percent of individuals with Parkinson's disease at some time in the course of their disease, and that commonly include reduced volume, monopitch, hoarseness, a breathy voice quality and/or imprecise articulation.

Stem cells
Very immature cells with potential to differentiate into a wide variety of cells, including neurons.

Tremor
Involuntary, uncontrollable, rhythmic movements (fast or slow) that may affect the hands, head, voice or other body parts.