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Tay-Sachs disease

Definition

Tay-Sachs disease is a deadly disease of the nervous system passed down through families.

Causes, incidence, and risk factors

Tay-Sachs disease occurs when the body lacks hexosaminidase A, a protein that helps break down a chemical found in nerve tissue called gangliosides. Without this protein, gangliosides, particularly ganglioside GM2, build up in cells, especially nerve cells in the brain.

Tay-Sachs disease is caused by a defective gene on chromosome 15. When both parents carry the defective Tay-Sachs gene, a child has a 25% chance of developing the disease. The child must receive two copies of the defective gene -- one from each parent -- in order to become sick. If only one parent passes the defective gene to the child, the child is called a carrier. He or she won't be sick, but will have the potential to pass the disease to his or her own children.

Anyone can be a carrier of Tay-Sachs, but the disease is most common among the Ashkenazi Jewish population. About 1 in every 27 members of the Ashkenazi Jewish population carries the Tay-Sachs gene.

Tay-Sachs has been classified into infantile, juvenile, and adult forms, depending on the symptoms and when they first appear. Most people with Tay-Sachs have the infantile form. In this form, the nerve damage usually begins while the baby is still in the womb. Symptoms usually appear when the child is 3 to 6 months old. The disease tends to get worse very quickly, and the child usually dies by age 4 or 5.

Late-onset Tay-Sachs disease, which affects adults, is very rare.

Symptoms

• Deafness
• Decreased eye contact, blindness
• Decreased muscle tone (loss of muscle strength)
• Delayed mental and social skills
• Dementia
• Increased startle reaction
• Irritability
• Listlessness
• Loss of motor skills
• Paralysis or loss of muscle function
• Seizures
• Slow growth

Signs and tests

If Tay-Sachs disease is suspected, the doctor will perform aphysical examination and take a family history. Additional tests may include:

• Enzyme analysis of blood or body tissue for hexosaminidase levels
• Eye examination (reveals a cherry-red spot in the macula)

Treatment

There is no treatment for Tay-Sachs disease itself, only ways to make the patient more comfortable.

Support Groups

The stress of illness may be eased by joining support groups whose members share common experiences and problems. See Tay-Sachs - support group.

Expectations (prognosis)

Children with this disease have symptoms that get worse over time. They usually die by age 4 or 5.

Complications

Symptoms appear during the first 3 to 10 months of life and progress to spasticity, seizures, and loss of all voluntary movements.

Calling your health care provider

Go to the emergency room or call the local emergency number (such as 911) if your child has a seizure of unknown cause, if the seizure is different from previous seizures, if the child has difficulty breathing, or if the seizure lasts longer than 2 - 3 minutes.

Call for an appointment with your health care provider if your child experiences a seizure lasting less than 2 - 3 minutes or has other noticeable behavioral changes.

Prevention

There is no known way to prevent this disorder. Genetic testing can detect if you are a carrier of the gene for this disorder. If you or your partner are from an at-risk population, it is recommended that you undergo testing before starting a family. Testing the amniotic fluid can diagnose Tay-Sachs disease in the womb.

References

Johnston MV, Neurodegenerative Disorders of Childhood. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics. 18th Ed. Philadelphia, Pa: Saunders Elsevier; 2007: chap 599.