Hexosaminidase A Deficiency - Tay-Sachs Disease

Tay-Sachs disease is a genetic disorder that causes an early breakdown of the nervous system. Most people born with this disease do not survive past their third birthday.

What is going on in the body?

Tay-Sachs disease is caused by an enzyme defect. An important enzyme, hexosaminidase A, is not completely formed. Because of this enzyme defect, the body cannot break down a protein that is normally found in cells of the body. When this happens, the protein accumulates in the nerve cells. Then, the nerve cells swell up and degenerate, causing a breakdown of the nervous system.

What are the causes and risks of the disease?

A defective gene causes the enzyme defect that leads to Tay-Sachs disease. The gene is autosomal recessive in character. Autosomal means that the gene is on one of the 22 pairs of non-sex chromosomes. Recessive means that there must be two copies of the gene for the disease to exist.

Tay-Sachs disease is most common among Jews of Eastern European origin, specifically Ashkenazi Jews. Among this group, the carrier frequency is 1 in 30. Among non-Jews the carrier frequency is 1 in 300.

What are the signs and symptoms of the disease?

Children born with this disease have:

Most children die when they are between the ages of 2 and 4 years.

How is the disease diagnosed?

A parent or healthcare provider may think an infant has a problem after observing the child. When the disease is suspected, hexosaminidase A is measured in blood or other tissue. If the enzyme is deficient, diagnosis is confirmed. DNA testing is possible for Tay-Sachs disease. Diagnosis before birth is possible through amniocentesis.

What can be done to prevent the disease?

The enzyme defect that causes Tay-Sachs disease is present from the time of conception. There is no way to prevent the disease in children who have already been born.

What are the long-term effects of the disease?

The first signs of Tay-Sachs disease is the "startle reflex." This sign is present by the time a child is 6 months old. Shortly after the appearance of the "startle reflex," affected children are unable to roll over. They gradually lose their ability to make purposeful movements. By the time they are 1 year old, affected children begin to have seizures and lose their vision. By the time they are 2 years old, they enter a vegetative state and are unable to respond to their environments. Most children do not survive past their third birthday.

What are the risks to others?

Parents who have had an affected child with Tay-Sachs disease are at risk to have other affected children. One in four pregnancies for such parents is expected to result in an affected child. Genetic counseling is useful for relatives of affected children.

What are the treatments for the disease?

There is no treatment for Tay-Sachs disease. Affected children are kept comfortable and are provided good nutrition. They may receive medication for their seizures. Eventually, all affected children must be fed through a gastrostomy tube.

What are the side effects of the treatments?

All medications have side effects, including allergic reactions. There are no other significant side effects to treatments for Tay-Sachs disease.

What happens after treatment for the disease?

Most children with Tay-Sachs disease die between the ages of 2 and 4 years.

How is the disease monitored?

There is no useful way to monitor Tay-Sachs disease. Its progress can be documented by observation, but not changed.

Author:Ronald J. Jorgenson, DDS, PhD, FACMG
Date Written:
Editor:Smith, Elizabeth, BA
Edit Date:07/06/00
Reviewer:Eileen McLaughlin, RN, BSN
Date Reviewed:08/06/01

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