Without a known family history
Sporadic ALS
Most people with ALS have no known family history. Genetic factors can still play a role.
The science, made clearer
Understanding ALS
A closer look at the connections that move us.
Understand what changes, and what it means for daily life.
ALS & motor neuron diseaseSources & further reading
01 / The essentials
What is ALS?
Movement begins with a message.
ALS affects the nerve cells that carry it.
Amyotrophic lateral sclerosis (ALS) is a progressive disease that damages motor neurons in the brain and spinal cord. These cells help control muscles used for movement, speaking, swallowing, and breathing.
As motor neurons stop working, muscles receive less stimulation. Over time, they become weaker and may shrink. The pattern and pace of these changes differ from person to person.
ALS is a type of motor neuron disease (MND). You may also hear it called Lou Gehrig’s disease.
With a family history
Familial ALS
ALS can run in families. Inheritance and risk depend on the specific gene; genetic counseling can help explain what testing means.
Learn more: ALS Association — genetics and family history ↗
02 / The motor pathway
From intention
to movement.
Two connected groups of motor neurons carry messages from the brain to the muscles.
- 01
The brain sends a command
Upper motor neurons carry signals from the motor cortex toward the brainstem and spinal cord.
- 02
A motor neuron carries the signal
Lower motor neurons extend from the brainstem or spinal cord to muscles through long fibers called axons.
- 03
The muscle receives the message
At the neuromuscular junction, a chemical messenger helps the nerve activate a muscle fiber.
What changes in ALS
Motor neurons degenerate and connections to muscle can be lost. This loss of nerve supply is called denervation. It contributes to weakness and muscle wasting.
03 / A closer look
A small connection.
A vital role.
Follow a signal from a nerve cell to a muscle. Choose a view, or take the guided tour.
This close-up shows a lower motor neuron and its connections to muscle. ALS can also affect the upper motor neurons in the brain, described above.
- 1Electrical signal
The blue light travels along the nerve to its ending.
- 2Chemical messenger
Gold dots represent acetylcholine crossing the tiny gap.
- 3Muscle response
A connected fiber is activated and briefly shortens.
Nerve cell & axon
Myelin · insulating covering
Muscle fiber
Lost connection · gap shown
A working connection. The blue light represents an electrical signal in the nerve. At the nerve ending, gold dots represent acetylcholine, a chemical messenger. It crosses the tiny gap and triggers muscle activation; the connected fiber then shortens.
This simplified model shows one aspect of ALS. Colors, fiber counts and movement are illustrative; the junction gap is enlarged and signals are slowed down. Wasting happens over time. Switching views does not represent recovery or predict anyone’s disease course. Other changes, including muscle twitching, are not shown.
The connection, in motion
Watch the illustrated guide.
A quiet, close-up journey from the nerve cell to its connection with muscle.
30 seconds · Silent film with captionsRead the film transcript
- Motor neurons carry messages that help us move.
- Branching dendrites receive input. The cell body supports the neuron.
- An electrical signal travels along the axon.
- At the nerve–muscle junction, chemical messengers help activate a muscle fiber.
- In ALS, motor neurons degenerate and connections to muscle can be lost.
- Less nerve supply contributes to weakness and muscle wasting. The pattern and pace vary for each person.
04 / Signs & symptoms
Different beginnings.
Different experiences.
Symptoms often begin in one area. For some people, that means a hand or foot. For others, speech or swallowing changes appear first; breathing symptoms can also occur.
Muscle weakness
Tasks such as buttoning a shirt, writing, or climbing stairs become more difficult.
Twitching & cramps
Small involuntary muscle twitches, called fasciculations, and muscle cramps.
Speech & swallowing
Speech may become less clear, and chewing or swallowing may become harder.
Stiffness & movement
Muscle tightness, changes in walking, and increasing difficulty with daily activities.
Breathing changes
Breathing muscles can weaken, affecting breathing and the ability to cough effectively.
Involuntary laughing or crying
Pseudobulbar affect can cause episodes that do not match how a person feels.
Keep in mind
These symptoms have many possible causes. A symptom list cannot diagnose ALS; a neurologist evaluates the full pattern and tests for other conditions.
More than movement
ALS primarily affects the motor system. Senses such as sight and hearing are usually preserved. Some people also experience changes in thinking, language, or behavior, so those concerns deserve attention from the care team.
05 / How ALS progresses
Care evolves.
Every path is individual.
There is no single timetable. Symptoms, support needs, and decisions vary. These are examples of how care may change, not milestones everyone must follow.
Understanding new symptoms
Subtle weakness, fatigue, tripping, or speech changes may prompt neurological assessment. Care begins with understanding the diagnosis and planning support.
Adding practical support
Mobility aids, communication tools, nutrition support, and breathing assessments can help as needs change.
More support, personal choices
Some people need extensive help with movement, nutrition, or breathing. Options such as feeding tubes and ventilation are discussed with the care team in line with the person’s wishes.
06 / Common questions
A little more clarity.
What causes ALS?
ALS is complex, and for many people the exact cause is unknown. Genetic changes are involved in some cases, including some without a family history. Researchers continue to study how genetic and environmental factors contribute.
Is there a cure for ALS?
There is currently no cure. Treatments and multidisciplinary care can help manage symptoms, and some treatments can slow aspects of disease progression. The options depend on the individual, including genetic findings and local availability.
Explore research updates ↗Can ALS affect thinking or behavior?
Yes. Some people experience changes in thinking, language, or behavior. Some develop frontotemporal dementia. Others retain these abilities. Discuss new changes with the care team.
How quickly does ALS progress?
The pace varies widely. Some changes develop over months; others unfold over years. Population averages cannot predict an individual’s course. The care team can help plan around current needs and emerging changes.
Sources & further reading
National Institute of Neurological Disorders and StrokeALS overview ↗ The ALS AssociationGenetics & family history ↗ The ALS AssociationGenetic counseling ↗Educational information and conceptual illustrations. Your neurologist and care team can advise on your own circumstances.
ALS changes how the body works.
It does not change a person’s worth.