Huntington's vs. ALS: What Are the Differences?

Huntington's disease (HD) and amyotrophic lateral sclerosis (ALS) are progressive neurodegenerative (nerve-dying) diseases that affect movement. Apart from this broad similarity, HD and ALS are separate conditions.

Huntington's disease is an inherited condition associated with uncontrolled movements, psychiatric disturbances, and cognitive decline. ALS, also known as Lou Gehrig's disease, is associated with muscle weakness and (eventually) complete paralysis. The vast majority of ALS cases are not inherited.

This article reviews the key differences between Huntington's disease and ALS, including their unique causes, symptoms, diagnosis, and treatment.

Symptoms

The symptoms of Huntington's disease and ALS worsen over time, although they differ in type and how fast they progress.

Huntington's Disease Symptoms

The symptoms of Huntington's disease typically become noticeable between ages 30 and 50. The condition lasts around 15 to 20 years, from the start of symptoms to full-time care dependency and death.

Symptoms are motor (movement-related), cognitive, and psychiatric. They commonly include:

• Chorea (uncontrollable movements in the face, trunk, arms, or legs)
• Impaired coordination
• Emotional disturbances, including irritability, depression, anxiety, anger, and apathy (lack of interest)
• Hallucinations (seeing or hearing things that are not there) and delusions (false beliefs)
• Cognitive decline (e.g., reduced ability to multitask)
• Weight loss from difficulties swallowing and eating
  

ALS Symptoms

ALS is most likely to strike between the ages of 55 and 75. The disease's hallmark symptom is muscle weakness, leading to complete paralysis and death within a matter of years.

The weakness of ALS classically begins in an arm or leg before spreading throughout the entire body. Over time, people lose their ability to dress, bathe, walk, eat, and breathe independently.

Besides physical impairment, cognitive and behavioral dysfunction, like difficulties with problem-solving, apathy, and depression, may arise in ALS, especially as the disease progresses.

Causes

A critical difference between Huntington's disease and ALS is its cause. Huntington's disease is caused by a genetic abnormality, whereas the cause of ALS is largely unknown.

What Causes Huntington's Disease?

Huntington's disease is caused by a specific genetic mutation (change in DNA sequence) in HTT, a gene that codes for the protein huntingtin. The abnormal protein that results from the altered gene causes nerve cells within certain areas of the brain (e.g., basal ganglia) to die.

Huntington's disease is an autosomal dominant disorder. If either parent has Huntington's disease, their child has a 50% chance of inheriting the mutated gene and developing it.

What Causes ALS?

ALS involves the death of motor neurons (nerve cells that control muscle movement) within a person's brain and spinal cord.

Unlike Huntington's, ALS does not usually run in families, although there is a genetic component. Over 50 genes are identified as being linked to ALS.

Interestingly, many of these genes are involved in RNA metabolism. RNA is a molecule within living cells that creates proteins using cells' genetic information. As such, scientists believe that mechanisms like RNA misprocessing and the proteins produced not folding correctly may be involved in the nerve cell death seen in ALS.

Besides genetics, various environmental factors may increase a person's chances of developing ALS. Some of these factors are:

• Exposure to lead, electromagnetic fields, agricultural chemicals, or heavy metals
• Head trauma
• Smoking
• Intense physical activity

Diagnosis

The diagnosis of Huntington's disease can be confirmed with a single genetic blood test. For ALS, the diagnosis requires a bit more detective work.

Huntington's Disease Diagnosis

A person's symptoms and family history may provide the first clues to Huntington's disease. A genetic blood test that checks for the presence of the HTT mutation can then confirm the diagnosis. 

The HTT gene mutation is found on chromosome 4 and is associated with increased CAG repeats.

Huntington's disease develops when increased CAG repeats are present. Usually, people have less than 26 CAG repeats. Those with 36 to 39 CAG repeats may or may not manifest the disease, whereas those with 40 or more repeats definitely will.

ALS Diagnosis

A diagnosis of ALS is achieved by assessing a person's symptoms and performing a neurological exam.

Various tests will be ordered to help confirm the diagnosis. Some of these diagnostic tests include:

• Magnetic resonance imaging (MRI) is a noninvasive imaging test that uses strong magnets and radio waves to create detailed pictures of the body.
• Electromyography (EMG) and nerve conduction studies measure electrical activity in your muscles and nerve cells while they're active and at rest.
• Blood tests help rule out mimicking conditions, such as thyroid disease, vitamin B12 deficiency, human immunodeficiency virus (HIV), and some forms of cancer.

Treatment

Both Huntington's disease and ALS are fatal, incurable diseases. Treatments generally focus on managing specific symptoms, preventing complications, and maintaining comfort and quality of life.

Huntington's Disease Treatment

There are several treatments, especially prescription medications, that can help individuals living with Huntington's disease manage their symptoms.

Examples of such medications include:

• Xenazine (tetrabenazine) and Austedo (deutetrabenazine) are approved for treating Huntington-associated chorea.
• Antipsychotic drugs, such as Risperdal (risperidone), help control hallucinations and delusions.
• Antidepressants, such as a selective serotonin reuptake inhibitor (SSRI) or a tricyclic antidepressant, help treat depression, which is very common in Huntington's disease.

In addition to medication, rehabilitation therapies, including exercise therapy, speech therapy, and swallow therapy, are often integral components of treatment plans.

Counseling from a psychologist about coping with the physical, cognitive, and psychiatric changes imposed by the disease is also essential, as are family and social support.

ALS Treatment

As with Huntington's disease, therapies for ALS are primarily supportive. They often include:

• Physical therapy helps maintain muscle strength and mobility for as long as possible.
• Speech therapy assists in communication, often with the use of special devices as the disease progresses.
• Nutritional support with a feeding tube to help stabilize body weight and prevent malnutrition.
• Breathing care, often through noninvasive ventilatory support (oxygen delivered through a tight-fitting mask) may be needed.
  

Three ALS drugs are approved by the Food and Drug Administration (FDA): Rilutek (riluzole), Radicava (edaravone), and Relyvrio (sodium phenylbutyrate-taurursodiol). These drugs are intended to slow the disease down and, possibly, prolong survival.

Prevention

The only way to prevent Huntington's disease in future generations is to not have children if you know you have the gene for the condition. People with a parent who has Huntington's can have a genetic test to see if they also have Huntington's. If the gene is not present, they will not transmit the condition to their children.

While there is currently no definitive way to prevent ALS, limited research suggests that eating certain foods, such as whole-grain bread, citrus fruits, and raw vegetables, may protect you against developing ALS. Clinical trials looking into other possible ALS preventive factors are also underway.

Summary

Huntington's disease and ALS are progressive, neurodegenerative diseases that differ vastly in cause, symptoms, diagnosis, and treatment.

Huntington's disease is inherited, caused by a faulty gene that can be passed down from a parent. The disease affects the body and mind, causing uncontrolled movements and psychiatric and cognitive problems. ALS primarily affects the muscles causing progressive weakness and eventual paralysis. With ALS, the cause remains unknown in most cases.

Treatments for Huntington's disease and ALS aim to maintain the person's quality of life for as long as possible. Of note, there are three FDA-approved drugs intended to help slow ALS down. No such drugs exist yet for Huntington's disease.

A Word From Verywell

If you or a loved one has been diagnosed with a neurodegenerative condition like Huntington's disease or ALS, know that it's natural to feel a whirlwind of emotions. You might exhibit anxiety, despair, anger, or even emotional numbness. These feelings can ebb and flow as you navigate the various challenges of living with such a disease.

While being diagnosed with HD or ALS is distressing, know that you are not alone. A trained therapist or psychologist, along with your healthcare provider, can help you cope with the disease's difficulties and maintain a positive and hopeful mindset.