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Tay-Sachs vs. Spinal Muscular Atrophy: Comparing Late-Onset Forms

Posted on March 29, 2022
Medically reviewed by
Evelyn O. Berman, M.D.
Article written by
Eli Sachse, RN

Spinal muscular atrophy (SMA) and Tay-Sachs disease are neurodegenerative, autosomal recessive conditions. This means both conditions affect the nerves in our body and are passed on genetically, from parents to children. Parents don’t need to have the conditions in order to pass them on — they are carriers.

SMA and Tay-Sachs have different classifications or forms. Some people experience severe symptoms early in life, and others have mild symptoms later in life. The late-onset forms (when symptoms usually don’t appear until later in life) of each condition are SMA types 3, 4, and Finkel and late-onset Tay-Sachs disease (LOTS), also known as adult or chronic Tay-Sachs.

How Do You Know if You Have Late-Onset SMA or LOTS?

If your health care provider or neurologist suspects you have late-onset SMA or LOTS, they may perform various physical tests, and the diagnosis is generally confirmed by blood tests.

Both conditions can be diagnosed by genetic testing, a type of blood test. Genetic testing can also be performed by testing samples of amniotic fluid or the placenta in a pregnant parent. This is usually performed after parents with SMA or Tay-Sachs in their family history have been advised to do so by a genetic counseling professional, after undergoing carrier screening.

People who have SMA often have a difference in their SMN1 gene, causing their bodies to lack a protective protein, which leads to neuron (nerve cell) death over time. As mentioned, SMA is usually diagnosed by genetic testing.

Tay-Sachs can also be diagnosed by testing a person’s blood for an enzyme called hexosaminidase. This enzyme breaks down a certain compound in our bodies that can damage neurons. People with Tay-Sachs have differences in their hexosaminidase alpha-subunit gene, which prevents their bodies from creating this enzyme. Someone missing this enzyme from their blood may be suspected of having Tay-Sachs.

How Are the Conditions Different?

The main difference between SMA and Tay-Sachs is that with SMA, only motor neurons are affected. These are specialized neurons that control our muscles. This is why people with SMA can experience problems with not only the muscles we use for moving our bodies but also those used for swallowing and breathing. People with SMA usually have normal intelligence.

People with Tay-Sachs, on the other hand, can experience neuron degeneration in every part of their nervous system, including the brain. This deterioration can lead to many cognitive dysfunction and impairments, including memory problems, difficulty solving problems or concentrating, depression, psychosis including schizophrenia, and dementia.

Tay-Sachs has been found to affect people of Ashkenazi Jewish ancestry in particular. It is unclear if SMA affects people of different ethnic groups with a greater prevalence than the general population.

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How Are the Conditions Similar?

SMA and Tay-Sachs have many similar clinical features. A person with either of these conditions later in life might experience muscle shrinking (atrophy) and weakness, trouble speaking (dysarthria) or swallowing (dysphagia), and tremors or twitching. As a result, people with these conditions may find assistive technologies or interventions to be helpful. For example, walkers, wheelchairs, or medications for muscle spasms may be beneficial. People with SMA or Tay-Sachs may also need assistive technologies for communication, adaptive tools for eating, or modified meals.

Neither of these late-onset conditions necessarily shorten someone’s life span. Some people may experience more complications than others, such as pneumonia related to a weakened ability to breathe or cough. Others may have few complications of the disease.

When Do Late-Onset SMA and LOTS Begin Affecting the Body?

Symptoms of SMA type 3 (also known as Kugelberg-Welander disease or juvenile type) can manifest anywhere from early childhood to early adulthood. SMA type 4 and Finkel type usually appear after age 30. Muscle weakness or tremors are the main symptoms of adult-onset SMA.

LOTS is a rare type of Tay-Sachs. Symptoms can manifest anywhere from childhood to adulthood, ranging greatly in severity. In people with this condition, muscle symptoms sometimes present first. They may experience muscle spasms, weakness, trouble with balance (ataxia), or seizures. Other times, cognitive symptoms are noticed first, such as psychiatric or intellectual difficulties.

Both conditions usually cause progressive degeneration of abilities — symptoms often worsen over time.

Treatments for SMA and Tay-Sachs

There is no cure for SMA or Tay-Sachs. Recent research has developed different treatments for SMA, which appear to slow the progress of the disease. More research is being done in clinical trials. Nusinersen (Spinraza), onasemnogene abeparvovec-xioi (Zolgensma), and risdiplam (Evrysdi) are gene therapies that are treatment options for SMA. There is no medical treatment for Tay-Sachs that can delay or halt its progression. However, treatments to replace the missing enzyme and remove the nerve-damaging compounds, as well as gene therapy, are being researched.

In both cases, medications and assistive technologies are useful to treat symptoms. For example, people with Tay-Sachs experiencing seizures may be prescribed anticonvulsants to prevent them. People with SMA who have muscle contractions and spasms may be prescribed muscle relaxants. Those with either condition who are experiencing difficulty breathing or eating may need equipment such as BiPAP (bilevel positive airway pressure), other breathing aids, or a feeding system that bypasses the mouth.

Individuals with either condition are recommended to work closely with their team of health care providers. These people include physical therapists, occupational therapists, speech-language pathologists, assistive technologists, and others to develop a personalized plan for their activities. The plan helps people maintain and maximize their strength, mobility, and functional abilities. This team can also help advise and guide families in using adaptive technologies, such as wheelchairs, standing devices, and speech-generating devices.

Talk With Others Who Understand

On mySMAteam, the social network for people with SMA, more than 1,400 members come together to ask questions, give advice, and share their stories with others who understand life with SMA.

Have you been diagnosed with SMA later in life? Share your experience in the comments below, or start a conversation by posting on your Activities page.

All updates must be accompanied by text or a picture.
Evelyn O. Berman, M.D. is a neurology and pediatric specialist and treats disorders of the brain in children. Review provided by VeriMed Healthcare Network. Learn more about her here.
Eli Sachse, RN is a registered nurse living in California. He has written about health topics for Sonoma Medicine and Microcosm Publishing. Learn more about him here.

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