Glossary

Basic explanations of Parkinson's words and terms.

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Note: All drugs and surgical therapies have side effects. While some information on side effects is provided here, this glossary is not - nor intended to be - a comprehensive source of side effect information. As with all treatment decisions, patients should work closely with their individual physicians to understand the potential benefits and side effects of all therapies included in their treatment regimen. For more information on PD treatments, please see Parkinson's 101.

Acetylcholinesterase inhibitors A class of drugs used to treat mild to moderate dementia in PD. These drugs increase brain levels of a neurotransmitter called acetylcholine, which helps neurons communicate with each other and is involved in memory, learning and thinking.

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. For more information please see the MJFF Viewpoint on Cell Replacement Therapy. (See also Embryonic stem cells, Stem cells, Umbilical cord-derived stem cells)

Aggregate A clumping of proteins inside body cells, which may be toxic. Aggregation of the protein alpha-synuclein is a hallmark of Parkinson's pathogenesis.

Agonist See Dopamine agonist

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

Alpha-synuclein A protein normally found in neurons, and present in high concentrations in Lewy bodies. A genetic mutation in this protein is the basis for a rare inherited form of Parkinson's disease.

Animal models Normal animals modified mechanically, genetically or chemically, used to demonstrate all or part of the characteristics of a disease. With models, researchers can study the mechanisms of a disease and test therapies.

Anticholinergic A class of drugs often effective in reducing the tremor of Parkinson's disease. They work by blocking the action of acetylcholine, a neurotransmitter in the brain. However, because acetylcholine is involved in memory, learning and thinking, anticholinergic drugs can bring about cognitive side effects including confusion or dementia.

Antiparkinsonian medication A medicine used to treat Parkinson's disease.

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.

Athetosis A movement disorder sometimes confused with PD that manifests in low, repetitive, involuntary movements, especially in the hands.

Autonomic dysfunction Any problem with the functioning of the autonomic nervous system, which controls bladder, bowels, sweating, sexual function and blood pressure.

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Basal ganglia A region deep within the brain consisting of large clusters of neurons responsible for voluntary movements such as walking and movement coordination. Many of the symptoms of Parkinson's disease are brought on by loss of or damage to dopamine neurons in this region, which encompasses the striatum, the subthalamic nucleus, and the substantia nigra. (See also Striatum, Subthalamic nucleus, Substantia nigra)

Bilateral surgery Surgery performed on both sides of the brain.

Biomarkers Specific, measurable physical traits used to determine or indicate the effects or progress of a disease or condition. For example, high blood pressure is a biomarker of potential cardiovascular disease. 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. (From the Greek brady, slow, and kinesia, movement.)

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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. (Please see the MJFF Viewpoint on Cell Replacement Therapy for more information.)

Central nervous system (CNS) A term referring to the brain and spinal cord.

Chorea A general term for movement disorders that can be confused with Parkinson's disease, which are characterized by involuntary, random, jerking movements of muscles in the body, face, or extremities.

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

Coenzyme Q10 The most common form of Coenzyme Q, a vitamin-like antioxidant. Results of the first placebo-controlled, multicenter clinical trial of the compound, published in October 2002, suggested that it might slow disease progression in patients with early-stage Parkinson's disease. The results have yet to be confirmed in a larger study.

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. (See also Dementia, Executive dysfunction)

Compulsions Irresistible impulses to act, regardless of the rationality of the motivation, or acts performed in response to such impulses. Some compulsive behaviors have been associated with dopamine agonists used to treat Parkinson's disease, though this association has not been conclusively established.

COMT inhibitor A drug that blocks an enzyme (catchol-O-methyltransferase) that breaks down dopamine. COMT inhibitors include entacapone and tolcapone. Tolcapone has been known to cause serious liver problems and has been withdrawn from the Canadian and European markets.

Creatine A naturally occurring amino acid that helps to supply energy to muscle cells. A preliminary clinical trial in 200 Parkinson's patients, published in February 2006, suggested that creatine may merit additional study.

CT (CAT) scan See Imaging

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DBS (Deep brain stimulation) Surgical procedure that uses a surgically implanted, battery-operated medical device called a neurostimulator - similar to a heart pacemaker and approximately the size of a stopwatch - to deliver electrical stimulation to targeted areas in the brain that control movement, blocking the abnormal nerve signals that cause tremor and PD symptoms. At present, the procedure is used primarily for patients whose symptoms cannot be satisfactorily controlled with medications. (See also Pallidotomy, Surgical Therapies, Thalamotomy)

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. (See also Cognitive dysfunction, Executive dysfunction)

Depression A mental state, and non-dopamine-responsive symptom of PD, characterized by feelings of despondency and a lack of ability to initiate activity. (See also Cognitive dysfunction) For more information on PD and depression, please see MJFF's Guide for the Newly Diagnosed.

Developmental biology The study of the process by which organisms grow and develop. Developmental biology studies in PD hold potential to identify therapeutic targets and new cell replacement strategies.

Diagnosis Identification or naming of a disease by its signs and symptoms.

DJ-1 A gene of unknown function implicated in rare inherited cases of Parkinson's disease.

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 PD 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. (See also Dopamine-non-responsive)

Dysequilibrium Unsteadiness or balance problems. A common problem in Parkinson's. (See also Dopamine-non-responsive)

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 PD.

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." (See also Dopamine-non-responsive)

Dystonia A movement disorder that may be confused with Parkinson's disease. Dystonia is characterized by abnormal and awkward posture or sustained movements of a hand, foot, or other part of the body; may be accompanied by rigidity and twisting.

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Embryonic stem cells Primitive (undifferentiated) cells from the embryo that have the potential to become a wide variety of specialized cell types. Embryonic stem cells are derived from embryos that develop from eggs that have been fertilized in an in vitro fertilization clinic and then donated for research purposes with informed consent of the donors. For more information please see the MJFF Viewpoint on Cell Replacement Therapy. (See also Adult stem cells, Stem cells, Umbilical cord-derived stem cells)

Environment The non-genetic surroundings, conditions or influences that affect an organism. These can be divided into physical, biological, social, cultural, and other factors and may play a role in the onset of various diseases, including PD. Environmental factors that have been inconclusively linked to PD risk include exposure to various pesticides and metals. For more information on environmental contributions to PD please see Parkinson's 101.

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.

Epidemiology The study of the patterns, causes, and control of disease in groups of people. Epidemiological studies can be used to better understand potential causes of PD.

Essential tremor A movement disorder that may be confused with Parkinson's disease. A fast tremor that is most pronounced when performing an action such as writing or bringing a hand to a target - as opposed to the resting tremor of PD, which is most pronounced when the limb is at rest.

Excitotoxicity Overstimulation of nerve cells by nerve impulses. Excitotoxicity often leads to cell damage or death, and 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. (See also Cognitive dysfunction, Dementia)

Exercise Physical activity undertaken in order to maintain or improve health. Preliminary evidence suggests that exercise may play an important role in treatment regimens for Parkinson's disease, and may even slow or stop disease progression. Research is ongoing to understand whether and how exercise confers neuroprotection. Please see Parkinson's 101 for more information on discussing an individualized exercise plan with your doctor.

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

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

Fatigue A common, poorly understood symptom of PD; a state in which one feels tired or exhausted, and the capacity for normal work or activity is reduced.

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.

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GDNF (Glial cell-derived neurotrophic factor) Part of a family of naturally occurring human growth factors (also known as trophic factors) known to nourish and foster the growth and development of dopamine-generating neurons. Several therapeutic approaches involving GDNF are currently under development. For more information please see the MJFF Viewpoint on Trophic Factors. (See also Neurturin, Trophic factors)

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. As of January 2007, three clinical gene therapy studies are under way for PD.

Genetic predisposition Any inherited genetic pattern that may make some individuals more prone than others to certain health conditions, disorders or diseases.

Genetics The branch of biology that deals with heredity, especially the mechanisms of hereditary transmission via DNA and the variation of inherited characteristics (genes) among similar or related organisms.

Globus pallidus A structure made up of nerve cells located deep in the brain affecting movement, balance, and walking. It is often used as a target for surgical procedures in PD, including pallidotomy or DBS.

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Heterogeneity From the Latin (hetero, different, and genus, kind), the variable appearance of a condition; the heterogeneity of Parkinson's disease refers to the fact that its symptoms and appearance vary widely from patient to patient.

Hypokinesia From the Greek (hypo, less, and kinesia, movement), a clinical term for the slow or diminished movement associated with Parkinson's disease.

Hypomimia From the Greek (hypo, less, and mimia, imitation or expression), a clinical term for the Parkinson's symptom more commonly known as facial masking - an immobile face with reduced blinking. (See also Facial masking)

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Imaging Any method used to produce a picture of internal body structures. Some imaging techniques commonly used in Parkinson's disease:

Inflammation The nonspecific immune response that occurs in reaction to any type of bodily injury. The reactions produced during inflammation and repair may be harmful or helpful. Work is ongoing to understand the role of inflammation in Parkinson's disease.

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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. (See also Sinemet)

Lewy bodies Abnormal protein clumps that accumulate in dead or dying dopamine-producing cells of the substantia nigra in Parkinson's disease. At autopsy, the presence of Lewy bodies is used to confirm a Parkinson's diagnosis. (See also Aggregate)

LRRK2 A gene implicated in up to one percent of Parkinson's disease cases. LRRK2 function as a kinase, an enzyme that modifies the function of proteins.

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MANF (mesencephalic astrocyte-derived neurotrophic factor) is a trophic factor that is still in the beginning stages of preclinical study. Early data suggests MANF is as effective in reducing behavioral deficits in preclinical Parkinson's disease models as GDNF. However, there is still a lot of work to do before we can fully assess the potential of MANF to effectively treat Parkinson's in people with the disease.

Microelectrodes Thin metallic tubes inserted into the brain and guided by stereotactic methods. They are connected to the operating room computer and used to measure the electrical signal from brain cells during surgical procedures, such as pallidotomy. (See also Stereotactic surgery)

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

Mitochondrial dysfunction Mitochondria are the "power plants" of the cell, generating energy needed for cell activity. Reduced or incorrect mitochondrial function has been implicated in oxidative stress that may play a role in PD.

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

Movement disorders Conditions including Parkinson's disease, many neurodegenerative, that prevent normal movement. Some are characterized by lack (or "poverty") 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.

Movement disorders specialist A neurologist with specific training in the subspecialty of movement disorders. Movement disorders specialists typically follow a greater number of patients with movement disorders, and are thus more experienced in the use of the various medications (and their combinations) as compared to a general neurologist, internist or general practitioner.

MRI (Magnetic resonance imaging) See Imaging

Multiple System Atrophy (Shy-Drager Syndrome) A movement disorder that may be confused with Parkinson's disease. It is a degenerative condition characterized by low blood pressure when standing. It may lead to parkinsonism, rigidity, ataxia, fainting, or incontinence.

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Neurobehavioral Having to do with the way the brain affects emotion, behavior, and learning. Parkinson's disease can include several neurobehavioral symptoms including depression and anxiety.

Neurodegeneration The slow death (degeneration) 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. (See also Movement disorders specialist)

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.

Neuropharmacology The branch of health science concerned with the study of drugs on the nervous system.

Neuroprotective/Neuroregenerative Providing protection to or stimulating the regrowth of any part of the body's nervous system. No currently available treatment for Parkinson's disease has been proven to provide a neuroprotective or neuroregenerative effect; all available PD treatments are symptomatic, meaning that they mask the symptoms while the underlying disease continues to progress. (See also Symptomatic)

Neurosurgeon A doctor who operates on the brain and central nervous system.

Neurotransmitter A specialized chemical messenger (e.g. dopamine, norepinephrine, serotonin) that sends messages from one nerve cell to another. Most neurotransmitters play different roles throughout the body, many of which are not yet known.

Neurturin A naturally occurring human growth factor (or trophic factor) in the same family as GDNF, known to nourish and foster the growth of dopamine-generating neurons. For more information please see the MJFF Viewpoint on Trophic Factors. (See also GDNF, Trophic factors)

Nicotine An alkaloid (nitrogen-containing chemical) made by the tobacco plant or produced synthetically that is one of the major chemicals in cigarettes. Epidemiological data have linked cigarette smoking to protection against Parkinson's onset. However, because of the grave health risks associated with smoking, no responsible physician would recommend it as a means of preventing PD.

Non-motor symptoms Poorly understood symptoms of Parkinson's that affect body systems other than movement. These include cognitive impairment, sleep problems and depression. These typically do not respond to dopamine replacement therapy.

NURR1 A gene that plays an important role in the early development of dopamine neurons.

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Olfactory dysfunction A reduced or impaired ability to detect odors, which can be an early sign of Parkinson's disease. Researchers are studying olfactory dysfunction as a possible avenue toward a biomarker, or molecular fingerprint, of Parkinson's disease. (See also Biomarkers)

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.

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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. Pallidotomy has become less commonly performed with the establishment of deep brain stimulation (DBS) surgery as a safe and effective surgical intervention for PD. (See also DBS, Surgical Therapies, Thalamotomy)

Palsy Antiquated term for paralysis or an uncontrollable shaking of the body. When he discovered Parkinson's disease, Dr. James Parkinson named it "the shaking palsy."

Parkin A gene, mutations in which have been associated with a familial form of Parkinson's disease. How loss of function of parkin leads to dopaminergic cell death is unclear. The current prevailing hypothesis is that the normal function of parkin is to help degrade one or more proteins toxic to dopaminergic neurons.

Parkinsonism Generic term referring to slowness and mobility problems that result from or look like Parkinson's disease. Several conditions that are not actually PD, including multiple system atrophy and progressive supranuclear palsy, as well as a number of medications, can result in parkinsonism and a misdiagnosis of Parkinson's disease.

Patient registry A database used to record cases of diseases of public health importance. Registries are a valuable epidemiological resource that can be used to calculate and monitor incidence rates and risk, as well as trends in incidence and mortality.

PET scan See Imaging

Physical therapy The use of exercises and physical activities to help condition muscles and restore strength and movement. Similar to exercise, certain forms of physical therapy may be useful to maintain balance and flexibility as part of an overall PD treatment regimen.

Pill-rolling Alternating movements of the thumb and forefinger that give the appearance of rolling a small object between the fingers; a characteristic slow tremor in the fingers of Parkinson's patients.

PINK1 A gene of unknown function implicated in rare cases of Parkinson's disease.

Postencephalitic parkinsonism A Parkinson's-like illness, cases of which followed the worldwide flu epidemic of 1918; also called von Economo encephalitis.

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.

Prognosis The expected future course of an illness.

Progressive Supranuclear Palsy (PSP) A movement disorder that can be mistaken for Parkinson's disease. PSP is a degenerative disease of unknown cause characterized by problems looking up and down, frequent falls and parkinsonism. It does not consistently respond to dopamine replacement therapy.

Protein handling Process by which cells regulate the expression, localization and degradation of proteins. Mishandling of proteins is of interest to Parkinson's researchers because it has been inconclusively linked to PD.

PWP Abbreviation for "People with Parkinson's" or "Person with Parkinson's."

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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. (See also Tremor)

Rigidity Abnormal stiffness in a limb or other body part. One of the cardinal clinical features of Parkinson's disease, rigidity is often most apparent when an examiner moves a patient's limb.

RNAi (RNA interference) A mechanism in which certain genes in an organism are "silenced" (turned off, so that their normal effects do not occur) by the introduction of small fragments of RNA whose sequence matches that of the gene in question. Researchers can use RNAi to test the functions of genes they are studying, and it may also form the basis of novel therapies to treat disease.

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SCNT (Somatic cell nuclear transfer) Technique in which a nucleus from a patient's body cell, such as a skin cell, is introduced into an unfertilized egg from which the original genetic material has been removed. The egg is then used to produce a blastocyst whose stem cells could be used to create tissue that would be compatible with that of the patient. This is called "therapeutic cloning." For more information please see the MJFF Viewpoint on Cell Replacement Therapy. (See also Adult stem cells, Embryonic stem cells, Stem cells, Umbilical cord-derived stem cells)

Serotonin A brain neurotransmitter that may be deficient in some cases of depression and whose potential role in PD is under investigation. (See also Neurotransmitter)

Shy-Drager Syndrome (Multiple System Atrophy) A degenerative condition that can be confused for Parkinson's disease, characterized by low blood pressure when standing. It may lead to parkinsonism, rigidity, ataxia, fainting, or incontinence.

Sinemet The brand name of the most commonly prescribed version of the drug levodopa, consisting of a combination of levodopa and carbidopa.

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. PD-associated speech disorders often can be alleviated by a specialized physical therapy regimen.

Sporadic Parkinson's disease The most common form of PD, accounting for upwards of 95 percent of cases, and arising from causes likely to include a combination of genetic and environmental factors. Sporadic PD is sometimes called idiopathic, meaning that the cause is unknown. Sporadic PD does not run in families, unlike other (much rarer) forms of Parkinson's disease. (See also Familial Parkinson's disease)

Stem cells Very immature cells with potential to differentiate into a wide variety of cells, including neurons. For more information please see the MJFF Viewpoint on Cell Replacement Therapy. (See also Adult stem cells, Embryonic stem cells, Umbilical cord-derived stem cells)

Stereotactic Refers to use of precise coordinates to identify deep structures of the brain. The coordinates may be obtained by fitting a patient's head with a special frame and conducting a CT scan or MRI. The position of the brain structures relative to the frame permits precise, three-dimensional localization of the deep brain structures. (See also Imaging)

Striatum The largest component of the basal ganglia, the striatum controls movement, balance, and walking. It is sometimes called the corpus striatum. Loss of dopamine in the striatum is responsible for many of the symptoms of Parkinson's disease. (See also Basal ganglia, Substantia Nigra)

Substantia nigra From the Latin for "black substance," the substantia nigra is a part of the basal ganglia that is rich in dopamine-producing nerve cells and the black pigment neuromelanin. In Parkinson's the loss of nerve cells from this region leads to a dopamine deficit and subsequently to Parkinson's symptoms. (See also Basal ganglia, Striatum)

Subthalamic nucleus (STN) A nerve center near the substantia nigra. The STN may be targeted for deep brain stimulation (DBS) to reduce Parkinson's symptoms. (See also Basal ganglia, Substantia nigra)

Surgical therapies Brain surgery that can supplant or supplement drug therapies for PD in some patients. Deep brain stimulation (DBS) is currently the most common surgery for PD. Other less frequently performed procedures include surgical lesion of the subthalamic nucleus and of the internal segment of the globus pallidus, a procedure known as pallidotomy. As in all aspects of their treatment regimen, patients considering surgery should work closely with their individual physicians to assess the risks and potential benefits of surgical intervention. (See also DBS, Pallidotomy, Thalamotomy)

Swallowing The reflexive muscular contraction that causes substances to pass from the mouth through the esophagus and into the body. Some people with advanced Parkinson's disease develop difficulty swallowing (also called dysphagia), which may become severe enough to require a change in diet. (See also Dysphagia)

Symptoms Any of a variety of changes in the body or its functions that indicate disease or phases of disease.

Symptomatic 1. Of or pertaining to the symptoms of a disease. 2. A term used by people with Parkinson's to describe the state in which they are strongly affected by the symptoms of their PD, and in which their medication or treatment regimen is providing little relief. 3. Pertaining to treatments that affect the symptoms of a disease, but not the underlying actions that cause the disease to progress. All currently available treatments for PD are symptomatic, meaning that they mask symptoms while the disease continues to progress. (See also Neuroprotective/Neuroregenerative)

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Thalamotomy A surgical procedure, now less commonly performed than it once was, in which cells in the thalamus are destroyed in an effort to eradicate debilitating tremors. (See also DBS, Pallidotomy, Surgical Therapies)

Thalamus A mass of gray matter (nerve cells) located deep in the brain that is responsible for motor control and serves as a relay center for sensory signals.

Therapeutic cloning See SCNT

Tremor Involuntary, uncontrollable, rhythmic movements (fast or slow) that may affect the hands, head, voice or other body parts. Resting tremor is one of the cardinal clinical features of Parkinson's disease. (See also Resting tremor)

Trigger event An external or environmental factor such as head trauma, stress or exposure to a toxin that may contribute to the development of a condition or disease.

Trophic factors Naturally occurring molecules that contribute to cell growth and survival. Neurotrophic factors, such as GDNF and neurturin, are trophic factors that affect nerve cells. For more information please see the MJFF Viewpoint on Trophic Factors. (See also GDNF, Neurturin)

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UCH-L1 A gene that provides instructions for making an enzyme called ubiquitin carboxyl-terminal esterase L1. This enzyme is found in nerve cells throughout the brain and is probably involved in the cell machinery that breaks down unwanted proteins. In rare familial instances of Parkinson's disease, mutations in UCH-L1 may increase risk of PD onset.

Umbilical cord-derived stem cells Undifferentiated cells taken from umbilical cord blood. These cells can be used in some research toward cell replacement therapies for regenerative medicine and tissue replacement after injury or disease. For more information please see the MJFF Viewpoint on Cell Replacement Therapy. (See also Adult stem cells, Embryonic stem cells, Stem cells)

Unilateral surgery Surgery performed on one side of the brain. (See also Bilateral surgery)

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Vitamins Various substances found in plants and animals that are required for life-sustaining processes. While anecdotal evidence suggests that taking certain vitamins may prevent or improve some symptoms of PD, no clinical trial to date has proved this.

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Wearing off Loss of effectiveness of Parkinson's medications between doses. If the effectiveness of a medication does not last until the next dose is due, it "wears off."

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Young-onset Parkinson's disease A rare form of Parkinson's disease characterized by onset of symptoms before age 40.

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