Tay-Sachs Disease

Conditions Basics

What is Tay-Sachs disease?

Tay-Sachs is a rare disease that is passed down through some families. A person with Tay-Sachs has gene changes that prevent the body from making any or enough of an enzyme called hexosaminidase A (Hex A). This enzyme breaks down fatty compounds. Without it, fatty compounds build up in the nerve cells of the brain and cause damage.

There are three forms of Tay-Sachs:

• Infantile Tay-Sachs. This is the most common form. It develops soon after a baby is born and causes death early in childhood.
• Juvenile Tay-Sachs. This affects children ages 2 and older and progresses more slowly than the infantile form. Children don't live beyond their mid-teens.
• Late-onset Tay-Sachs. This is very rare and can start between puberty and the mid-30s. It is a milder form of Tay-Sachs. Some people who have this form may live a normal lifespan.

What causes it?

Tay-Sachs can occur when parents pass on a changed gene to their child.

• A baby who gets the changed gene from both parents will have the disease.
• A baby who gets the changed gene from only one parent will be a carrier. This means that the child will have one gene that produces Hex A and one that doesn't. The child will have enough Hex A and won't get the disease. But the child can pass the changed gene on to their children.

The juvenile and late-onset forms of Tay-Sachs are also caused by a changed gene from both parents.

The changed gene that causes Tay-Sachs disease is more commonly found in people of Ashkenazi Jewish descent. About 1 out of 30 people in this population is a carrier of the disease. People who have family from the Quebec Bas-St-Laurent or Gaspésie regions or New Brunswick territories, or have a family history of the disease are also more likely to carry the changed gene.^{footnote 1}

What are the symptoms?

Each form of Tay-Sachs disease has different symptoms.

Infantile Tay-Sachs

With infantile Tay-Sachs, a baby looks healthy at birth. A doctor may see a red spot on the child's retina. But symptoms increase over time. By 6 months of age, babies start losing the ability to see, hear, and move. By 2 years of age, a child may have seizures and no longer respond to their surroundings.

Juvenile Tay-Sachs

Juvenile Tay-Sachs occurs in children 2 years of age or older. Symptoms progress more slowly than they do in infantile Tay-Sachs. A child may have seizures and may lose the ability to walk and communicate.

Late-onset Tay-Sachs

In late-onset Tay-Sachs (LOTS), early symptoms such as clumsiness or mood changes may be minor or seem "normal" and go unnoticed. Later symptoms may include difficulty walking, slurred speech, or mental health problems. The symptoms depend on how much Hex A the body makes.

How is it diagnosed?

If you or your doctor thinks that your child has Tay-Sachs disease, your doctor will do a physical exam and a blood test to check the level of an enzyme called Hex A. A genetic test may be needed to be sure the disease is Tay-Sachs.

How is Tay-Sachs disease treated?

The focus of treatment for Tay-Sachs disease is to control symptoms and make your child as comfortable as possible. There is no cure. It may be helpful to seek counselling or find support from others who are going through the same thing you are.

If you have late-onset Tay-Sachs disease (LOTS), treatment also focuses on controlling symptoms. The treatment you receive, such as medicine for depression, depends on the symptoms you have.

It may be overwhelming to learn that your child has Tay-Sachs. It's important that you care for yourself as well as your child. Talk to your doctor about:

• Your concerns and the help you'll need for your child.
• A support group in your area.
• Family counselling to help each member cope with the disease.

As the disease gets worse, your child will need more care. Encourage your child to be as active as possible for as long as possible. Give your child your love and affection.

You may not be able to care for your child without help. Talk with your doctor about groups that can help you.

Who should be tested?

If you are thinking about having a child, experts recommend that:^{footnote 1}

• Both you and your partner get a screening test if you are both of Ashkenazi Jewish descent, or have a family history of the disease. If both of you test positive as carriers, genetic counselling may help you with making choices.
• You or your partner get a screening test if either of you is of Ashkenazi Jewish descent, has family from the Quebec Bas-St-Laurent or Gaspésie regions or New Brunswick territories, or has a family history of the disease. If one of you tests positive for being a carrier, the other partner should be tested.

Carriers of the Tay-Sachs gene changes can pass the changed gene to their children even though the carriers don't have the disease. If both you and your partner are carriers, there is a 1-out-of-4 chance (25%) that any child you have will have Tay-Sachs disease.