- hexosaminidase A deficiency
- GM2-gangliosidosis, type I
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 fourth birthday.
What is going on in the body?
Tay-Sachs disease is caused by an enzyme defect. An important enzyme, beta-hexosaminidase A, is not completely formed. Because of this enzyme defect, the body cannot break down fatty materials that is are normally found in cells of the body. When this happens, the fatty materials 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 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 after that time.
How is the disease diagnosed?
A parent or healthcare professional may suspect that an infant has a problem after observing the child. Hexosaminidase A can then be measured in blood or other tissue. If the enzyme is deficient, the diagnosis of Tay-Sachs disease is confirmed. DNA testing is possible for this condition. Diagnosis before birth is possible through amniocentesis.
Long Term Effects
What are the long-term effects of the disease?
The first sign of Tay-Sachs disease is an exaggerated "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 the child is one year old, he or she begins to have seizures and lose vision. By 2 years old, the child usually enters a vegetative state and is unable to respond to the environment. Most children do not survive past their fourth 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 should receive medication to prevent or control seizures. Eventually, all affected children must be fed through a feeding tube to the stomach.
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.
Buyse ML: Birth Defects Encyclopedia. Blackwell Scientific Publications, 1990.
Goodman RM and Motulsky AG: Genetic Disorders among Ashkenazi Jews. Raven Press, 1979.
Scriver CS et al: The Metabolic and Molecular Basis of Inherited Disease. McGraw-Hill, 1995.