Parkinson's Disease
Parkinson's disease is about far more than a tremor, and it starts with a shortage of one brain chemical.
By Greg Goodwin · Published November 4, 2026
Cheat Sheet
- Cell loss: by the time symptoms appear, most people have lost 60 to 80% or more of the dopamine-producing cells in the substantia nigra (NINDS).
- Age: the average age of onset is the early to mid-60s; a small percent have early-onset disease that begins before age 50.
- Sex: Parkinson's affects more men than women.
- Lewy bodies: abnormal clumps of the protein alpha-synuclein found in damaged brain cells of most people with the disease.
- Genes: SNCA was the first gene linked to Parkinson's, and GBA1 variants are the most common genetic risk factor.
- Diagnosis: no single test is definitive; skin and spinal fluid tests can detect alpha-synuclein but cannot tell it apart from multiple system atrophy or Lewy body dementia.
The 60-Second Version
Parkinson's disease is a disorder of the nervous system that affects movement and gets worse over time. It happens when nerve cells in parts of the brain weaken, become damaged, and die, most importantly in an area called the substantia nigra, whose neurons make the chemical messenger dopamine. Dopamine helps produce smooth, purposeful movement, so when it runs short, people can notice shaking, stiffness, slowness, and balance trouble. Symptoms differ from person to person, including when they start and how fast they progress, and many of them have nothing to do with movement. There is no cure yet, but medicines and, for some people, surgery can help them move more easily. This page is general information, not medical advice, and diagnosis and treatment decisions belong with a clinician.
The Long Version
The Dopamine Story
Most Parkinson's symptoms arise when brain cells weaken, become damaged, and die in the substantia nigra, an area whose neurons produce dopamine. NINDS says research shows that by the time symptoms appear, most people have lost 60 to 80% or more of those dopamine-producing cells. People with the disease also have damage to cells that make norepinephrine, a messenger involved in automatic body functions such as keeping blood pressure steady, and its loss is thought to explain some non-movement symptoms like fatigue. In most people, damaged brain cells contain Lewy bodies, clumps of a protein called alpha-synuclein. Researchers do not yet know why Lewy bodies form or how they affect the disease.
Four Classic Motor Signs
NINDS lists four common symptoms. Tremor often begins in a hand and has a rhythmic back-and-forth motion, sometimes called pill rolling, and it is most obvious at rest; some people never develop one. Rigidity, or muscle tightening, affects most people and can feel like steady "lead pipe" resistance or short, jerky "cogwheel" movements. Bradykinesia means the body moves more slowly, and it may come with fewer facial expressions. Postural instability brings balance problems that raise the risk of falls. Many people also develop a stooped posture with less arm swing and small, shuffling steps, and some freeze when starting to walk or find their steps getting faster and faster.
Beyond Movement
Parkinson's reaches well past the muscles. NINDS notes that depression or anxiety can appear in the early stage, even before movement problems begin. Sleep problems are common, including trouble staying asleep, vivid dreams, and in some people acting out dreams, a pattern called REM sleep behavior disorder. Other possible symptoms include urinary and digestive problems, constipation, speech changes such as a quiet or flat voice, trouble swallowing in later stages, oily or dry skin, pain, and fatigue. Some people develop problems with thinking and memory, and some develop Parkinson's disease dementia. A sudden blood pressure drop on standing, called orthostatic hypotension, can cause dizziness or fainting.
Who Gets It and Why
For most people the cause is unknown. NINDS says risk appears to come from both genes and environmental factors. The average age of onset is the early to mid-60s, and chances rise with age, though a small percent of people have early-onset disease before 50. It affects more men than women, and having close relatives with it raises risk. Exposure to some pesticides and other pollutants, such as through farming or landscaping, is also linked to higher risk. On the genetic side, SNCA was the first gene linked to the disease, variants in GBA1 are the most common genetic risk factor, and changes in DJ-1, PINK1, and PRKN can cause rare early-onset forms.
Diagnosis and Treatment
There is no single test that can definitively diagnose Parkinson's. Doctors consider medical history and a neurological exam, may use lab tests and brain imaging to rule out other disorders, and may use a dopamine transporter scan. Two newer tests, one on small skin samples and one on spinal fluid, detect alpha-synuclein but cannot distinguish Parkinson's from similar conditions. There is no cure, but the main medicine, levodopa, usually combined with carbidopa, can ease movement symptoms without stopping the disease from progressing. Deep brain stimulation is usually considered after medicines stop working well, and exercise such as walking, dancing, cycling, or yoga can also help, NINDS says.
Why People Care
Most people picture the tremor, but Parkinson's also touches sleep, mood, digestion, and thinking, so understanding the full picture helps patients, families, and friends. It is also an active research area with new diagnostic tools. This is general information, not medical advice.
Glossary
- Substantia nigra
- A brain area whose neurons produce dopamine and where cells weaken and die in Parkinson's disease.
- Dopamine
- A chemical messenger that sends signals in the brain to produce smooth, purposeful movements.
- Bradykinesia
- Slowness of movement, even in simple everyday actions that usually happen automatically.
- Lewy bodies
- Abnormal clumps of the protein alpha-synuclein found in damaged brain cells.
- Deep brain stimulation
- A surgical treatment in which a thin wire in the brain delivers electrical signals, powered by a battery pack under the collarbone.
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