Tay-Sachs disease

Definition

Tay-Sachs disease is a genetic disorder caused by a missing enzyme that results in the accumulation of a fatty substance in the nervous system. This disease causes disability and death.

Description

Gangliosides are fatty substances necessary for the proper development of the brain and nerve cells (nervous system). Under normal conditions, gangliosides are continuously broken down, so that an appropriate balance is maintained. In Tay-Sachs disease, the enzyme necessary for removing excess gangliosides is missing. This situation allows gangliosides to accumulate throughout the brain and is responsible for the disability associated with the disease.

Demographics

Tay-Sachs disease is particularly common among Jewish people of Eastern European and Russian (Ashkenazi) origin. About one out of every 2,500 to 3,600 babies born to Ashkenazi Jewish couples have the disease. In the general population about one out of every 320,000 babies born has Tay-Sachs disease. Approximately one in 30 Ashkenazi Jews is a carrier of the gene that causes the disease. Tay-Sachs is also more common among certain French-Canadian, Pennsylvania Dutch, and Cajun families.

Causes and symptoms

Tay-Sachs is caused by a defective gene. Genes are located on chromosomes and serve to direct specific developments and processes within the body. The genetic defect in Tay-Sachs disease results in the lack of an enzyme called hexosaminidase A. Without this enzyme, gangliosides cannot be broken down. They build up within the brain, interfering with nerve functioning. Because Tay-Sachs is a recessive disorder, only people who receive two defective genes (one from the mother and one from the father) will actually have the disease. People who have only one defective gene and one normal gene are called carriers. They carry the defective gene and thus the possibility of passing the gene and/or the disease onto their offspring.

When a carrier and a non-carrier have children, none of their children will actually have Tay-Sachs. The statistical probability is that 50 percent of their children will be carriers themselves. When two carriers have children, their children have a 25 percent chance of having normal genes, a 50 percent chance of being carriers of the defective gene, and a 25 percent chance of having two defective genes. Only the individual with two defective genes actually has the disease.

Classic Tay-Sachs disease strikes infants around the age of six months. Up until this age, the baby appears to develop normally. When Tay-Sachs begins to show itself, the baby stops interacting with other people and develops a staring gaze. Normal levels of noise startle the baby to an abnormal degree. By about one year of age, the baby has very weak, floppy muscles and may be completely blind. The head is quite large. Children with Tay-Sachs also have other symptoms, such as loss of peripheral (side) vision, inability to breathe and swallow, and paralysis as the disorder progresses. Seizures become a problem between ages one and two, and the baby usually dies by about age four.

A few variations from this classical progression of Tay-Sachs disease are possible:

• Juvenile hexosaminidase A deficiency: Symptoms appear between ages two and five; the disease progresses more slowly, with death by about 15 years.
• Chronic hexosaminidase A deficiency: Symptoms may begin around age five or may not occur until between 20 and 30 years of age. The disease is milder. Speech becomes slurred. The individual may have difficulty walking due to weakness, muscle cramps , and decreased coordination of movements. Some individuals develop mental illness. Many have changes in intellect, hearing, or vision.

When to call the doctor

If the child has any noticeable problems that might be associated with Tay-Sachs disease or appears to stop developing normally after a period of normal development, the doctor should be consulted.

Diagnosis

Examination of the eyes of a child with Tay-Sachs disease reveals a characteristic cherry-red spot at the back of the eye in an area called the retina. Tests to determine the presence and quantity of hexosaminidase A can be performed on the blood, specially treated skin cells, or white blood cells. A carrier has about half the normal level of hexosaminidase A present, while an individual with the disease has no hexosaminidase A at all.

Treatment

Providing good, supportive care and treating the symptoms as they arise is the only way to treat Tay-Sachs; there is no way to treat the disease itself.

Prognosis

The prognosis for a child with classic Tay-Sachs disease is death. Because the chronic form of Tay-Sachs was discovered near the end of the 2000s, prognosis for this type of the disease was, as of 2004, not completely known.

Prevention

There is no known way to prevent Tay-Sachs disease. It is, however, possible to identify carriers of the disease and provide them with genetic counseling and appropriate information concerning the chance of their offspring having Tay-Sachs disease. When the levels of hexosaminidase A are half the normal level, a person is a carrier of the defective gene. Blood tests of carriers reveal reduction of hexosaminidase A.

When a woman is already pregnant, tests can be performed on either the cells of the fetus (amniocentesis ) or the placenta (chorionic villus sampling) to determine whether the baby will have Tay-Sachs disease.

Parental concerns

If parents are thinking of having a child and believe they might be carriers of Tay-Sachs, they should be screened so that they can assess their options. Children born with infantile Tay-Sachs, even with the best available care, usually die before the age of five. Children born with juvenile Tay-Sachs usually die before the age of 15.

KEY TERMS

Ganglioside —A fatty (lipid) substance found within the brain and nerve cells.

Resources

BOOKS

Behrman, Richard E., Robert M. Kliegman, and Hal B. Jenson. Nelson Textbook of Pediatrics, 17th ed. Philadelphia: Saunders, 2004.

Desnick, Robert, and Michael M. Kaback, eds. Tay-Sachs Disease. San Diego, CA: Academic, 2001.

ORGANIZATIONS

March of Dimes Birth Defects Foundation. 1275 Mamaroneck Avenue, White Plains, NY 10605. Web site: <www.modimes.org>.

National Tay-Sachs and Allied Diseases Association. 2001 Beacon Street, Suite 204, Brighton, MA 02135. Web site: <www.ntsad.org>.

Tish Davidson, A.M.

Tay-Sachs disease

Definition

Tay-Sachs disease is a genetic disorder caused by a missing enzyme that results in the accumulation of a fatty substance in the nervous system. This results in disability and death.

Description

Gangliosides are a fatty substance necessary for the proper development of the brain and nerve cells (nervous system). Under normal conditions, gangliosides are continuously broken down, so that an appropriate balance is maintained. In Tay-Sachs disease, the enzyme necessary for removing excess gangliosides is missing. This allows gangliosides to accumulate throughout the brain, and is responsible for the disability associated with the disease.

Tay-Sachs disease is particularly common among Jewish people of Eastern European and Russian (Ashkenazi) origin. About one out of every 3,600 babies born to Ashkenazi Jewish couples will have the disease. Tay-Sachs is also more common among certain French-Canadian and Cajun French families.

Causes and symptoms

Tay-Sachs is caused by a defective gene. Genes are located on chromosomes, and serve to direct specific development/processes within the body. The genetic defect in Tay-Sachs disease results in the lack of an enzyme, called hexosaminidase A. Without this enzyme, gangliosides cannot be degraded. They build up within the brain, interfering with nerve functioning. Because it is a recessive disorder, only people who receive two defective genes (one from the mother and one from the father) will actually have the disease. People who have only one defective gene and one normal gene are called carriers. They carry the defective gene and thus the possibility of passing the gene and/or the disease onto their offspring.

When a carrier and a non-carrier have children, none of their children will actually have Tay-Sachs. It is likely that 50% of their children will be carriers themselves. When two carriers have children, their children have a 25% chance of having normal genes, a 50% chance of being carriers of the defective genne, and a 25% chance of having two defective genes. The two defective genes cause the disease itself.

Classic Tay-Sachs disease strikes infants around the age of six months. Up until this age, the baby will appear to be developing normally. When Tay-Sachs begins to show itself, the baby will stop interacting with other people, and develop a staring gaze. Normal levels of noise will

startle the baby to an abnormal degree. By about one year of age, the baby will have very weak, floppy muscles, and may be completely blind. The head will be quite large. Patients also present with loss of peripheral (side) vision, inability to breath and swallow, and paralysis as the disorder progresses. Seizures become a problem between ages one and two, and the baby usually dies by about age four.

A few variations from this classical progression of Tay-Sachs disease are possible:

• Juvenile hexosaminidase A deficiency. Symptoms appear between ages two and five; the disease progresses more slowly, with death by about 15 years.
• Chronic hexosaminidase A deficiency. Symptoms may begin around age five, or may not occur until age 20-30. The disease is milder. Speech becomes slurred. The individual may have difficulty walking due to weakness, muscle cramps, and decreased coordination of movements. Some individuals develop mental illness. Many have changes in intellect, hearing, or vision.

Diagnosis

Examination of the eyes of a child with Tay-Sachs disease will reveal a very characteristic cherry-red spot at the back of the eye (in an area called the retina). Tests to determine the presence and quantity of hexosaminidase A can be performed on the blood, specially treated skin cells, or white blood cells. A carrier will have about half of the normal level of hexosaminidase A present, while a patient with the disease will have none.

Treatment

There is no treatment for Tay-Sachs disease.

Prognosis

Sadly, the prognosis for a child with classic Tay-Sachs disease is certain death. Because the chronic form of Tay-Sachs has been discovered recently, prognosis for this type of the disease is not completely known.

Prevention

Prevention involves identifying carriers of the disease and providing them with appropriate information concerning the chance of their offspring having Tay-Sachs disease. When the levels of hexosaminidase A are half the normal level a person is a carrier of the defective gene. Blood tests of carriers reveals reduction of Hexosaminidase A.

When a woman is already pregnant, tests can be performed on either the cells of the baby (amniocentesis) or the placenta (chorionic villus sampling) to determine whether the baby will have Tay-Sachs disease.

Resources

BOOKS

Behrman, Richard, ed. Nelson Textbook of Pediatrics. Philadelphia: W. B. Saunders, 1996.

PERIODICALS

Motulsky, Arno G. "Screening for Genetic Disease." New England Journal of Medicine, 336, no. 18 (May 1, 1997): 1314+.

Rosebush, Patricia I. "Late-Onset Tay-Sachs Disease Presenting as Catatonic Schizophrenia: Diagnostic and Treatment Issues." Journal of the American Medical Association 274, no. 22 (December 13, 1995): 1744.

ORGANIZATIONS

Late Onset Tay-Sachs Foundation. 1303 Paper Mill Road, Erdenheim, PA 19038. (800) 672-2022.

March of Dimes Birth Defects Foundation. National Office. 1275 Mamaroneck Avenue, White Plains, NY 10605. (888) 663-4637. resourcecenter@modimes.org. <http://www.modimes.org>.

National Tay-Sachs and Allied Diseases Association, Inc. 2001 Beacon Street, Suite 204, Brighton, MA 02146. (800) 906-8723. Fax: 617-277-0134. NTSAD-Boston@worldnet.att.net. <http://www.ntsad.org>.

Laith Farid Gulli, MD

Tay-Sachs Disease

Definition

Tay-Sachs disease is a genetic disorder caused by a missing enzyme that results in the accumulation of a fatty substance in the nervous system. This results in disability and death.

Description

Gangliosides are fatty substances necessary for the proper development of the brain and nerve cells (nervous system). Under normal conditions, gangliosides are continuously broken down, so that an appropriate balance is maintained. In Tay-Sachs disease, the enzyme necessary for removing excess gangliosides is missing. This allows gangliosides to accumulate throughout the brain, and is responsible for the disability associated with the disease.

Tay-Sachs disease is particularly common among Jewish people of Eastern European and Russian (Ashkenazi) origin. About one out of every 3,600 babies born to Ashkenazi Jewish couples will have the disease. Tay-Sachs is also more common among certain French-Canadian and Cajun French families.

Causes and symptoms

Tay-Sachs is caused by a defective gene. Genes are located on chromosomes, and serve to direct specific development/processes within the body. The genetic defect in Tay-Sachs disease results in the lack of an enzyme called hexosaminidase A. Without this enzyme, gangliosides cannot be degraded. They build up within the brain, interfering with nerve functioning. Because Tay-Sachs is a recessive disorder, only people who receive two defective genes (one from the mother and one from the father) will actually have the disease. People who have only one defective gene and one normal gene are called carriers. They carry the defective gene and thus the possibility of passing the gene and/or the disease onto their offspring.

When a carrier and a non-carrier have children, none of their children will actually have Tay-Sachs. It is likely that 50% of their children will be carriers themselves. When two carriers have children, their children have a 25% chance of having normal genes, a 50% chance of being carriers of the defective gene, and a 25% chance of having two defective genes. The two defective genes cause the disease itself.

Classic Tay-Sachs disease strikes infants around the age of six months. Up until this age, the baby will appear to be developing normally. When Tay-Sachs begins to show itself, the baby will stop interacting with other people and develop a staring gaze. Normal levels of noise will startle the baby to an abnormal degree. By about one year of age, the baby will have very weak, floppy muscles, and may be completely blind. The head will be quite large. Patients also present with loss of peripheral (side) vision, inability to breath and swallow, and paralysis as the disorder progresses. Seizures become a problem between ages one and two, and the baby usually dies by about age four.

A few variations from this classical progression of Tay-Sachs disease are possible:

• Juvenile hexosaminidase A deficiency. Symptoms appear between ages two and five; the disease progresses more slowly, with death by about 15 years.
• Chronic hexosaminidase A deficiency. Symptoms may begin around age five, or may not occur until age 20-30. The disease is milder. Speech becomes slurred. The individual may have difficulty walking due to weakness, muscle cramps, and decreased coordination of movements. Some individuals develop mental illness. Many have changes in intellect, hearing, or vision.

Diagnosis

Examination of the eyes of a child with Tay-Sachs disease will reveal a characteristic cherry-red spot at the back of the eye (in an area called the retina). Tests to determine the presence and quantity of hexosaminidase A can be performed on the blood, specially treated skin cells, or white blood cells. A carrier will have about half of the normal level of hexosaminidase A present, while a patient with the disease will have none.

Treatment

There is no treatment for Tay-Sachs disease.

Prognosis

Sadly, the prognosis for a child with classic Tay-Sachs disease is certain death. Because the chronic form of Tay-Sachs has been discovered recently, prognosis for this type of the disease is not completely known.

Prevention

Prevention involves identifying carriers of the disease and providing them with appropriate information concerning the chance of their offspring having Tay-Sachs disease. When the levels of hexosaminidase A are half the normal level, a person is a carrier of the defective gene. Blood tests of carriers reveals reduction of hexosaminidase A.

KEY TERMS

Ganglioside— A fatty (lipid) substance found within the brain and nerve cells.

When a woman is already pregnant, tests can be performed on either the cells of the baby (aminocentesis) or the placenta (chorionic villus sampling ) to determine whether the baby will have Tay-Sachs disease.

Resources

ORGANIZATIONS

Late Onset Tay-Sachs Foundation. 1303 Paper Mill Road, Erdenheim, PA 19038. (800)672-2022.

March of Dimes Birth Defects Foundation. 1275 Mamaroneck Avenue, White Plains, NY 10605. (888) 663-4637. resourcecenter@modimes.org. 〈http://www.modimes.org〉.

Tay-Sachs disease , rare hereditary disease caused by a genetic mutation that leaves the body unable to produce an enzyme necessary for fat metabolism in nerve cells, producing central nervous system degeneration. The disease is named for a British ophthalmologist, Warren Tay, who first described the disease, in 1881, and a New York neurologist, Bernard Sachs, who first described the cellular changes and the genetic nature of the disease, in 1887. In infants, it is characterized by progressive mental deterioration, blindness, paralysis, epileptic seizures, and death, usually between ages three and five. Late-onset Tay-Sachs occurs in persons who have a genetic mutation that is similar but allows some production of the missing enzyme. There is no treatment for Tay-Sachs.

Course of the Disease

The enzyme involved in Tay-Sachs is called hexosaminidase A. Its absence allows a lipid called GM ₂ ganglioside to build up in the brain, destroying the nerve cells. The process starts in the fetus; the disease is clinically apparent in the first few months of life. Initial symptoms vary, but usually include a general slowing of development and loss of peripheral vision. By the age of one, most children are experiencing convulsions. The damage to the nervous system progresses inexorably, bringing with it an inability to swallow, difficulty in breathing, blindness, mental retardation, and paralysis.

In late-onset Tay-Sachs, which is often misdiagnosed, the symptoms (ataxia, dysarthria, and muscle weakness) usually become apparent late in childhood or early in adulthood. About 40% of the patients display symptoms of bipolar disorder . Life expectancy does not appear to be affected.

Genetic Basis and Screening

Tay-Sachs disease occurs primarily among Jews of Eastern European descent but is also found in French Canadians whose roots are in the St. Lawrence region, certain Cajuns in Louisiana, and some Amish communities. Tay-Sachs is an autosomal recessive disorder; a person must have two defective genes (one from each parent) in order for the disease to occur. Carriers, people with only one gene for the disorder, are physically unaffected. When both parents are carriers, each child has a 25% chance of getting the disease. If only one parent is a carrier, there is no chance that the child will get the disease, but there is a 50% chance that the child will be a carrier. The gene may be carried by many generations without a manifestation. For this reason, plus the historical lack of accurate diagnosis and routinely high infant mortality of past generations, there is often no known family history of the disease.

Genetic screening for the disease has been possible since the early 1970s and is encouraged in high-risk populations. Blood tests of carriers reveal a reduced amount of the hexosaminidase A. If a couple elects to go forward with a pregnancy, fetal status (again utilizing hexosaminidase A levels) can be ascertained via chorionic villus sampling or amniocentesis . Genetic screening and counseling has greatly reduced the incidence of the disease.

Bibliography

See M. M. Kaback, ed., Tay-Sachs Disease: Screening and Prevention (1977); W. Stockton, Altered Destinies (1979).

TAY-SACHS DISEASE

DEFINITION

Tay-Sachs disease (pronounced tay-SACKS) is a genetic disorder that can lead to paralysis, blindness, convulsions, mental retardation (see mental retardation entry) and death. A genetic disorder is a medical problem passed down from one generation to the next. The disorder occurs because of a faulty gene. Genes are the chemical units in all cells that tell cells what functions they should perform. When those genes are absent or faulty, cells do not function properly and a medical disorder results.

DESCRIPTION

Gangliosides (pronounced GANG-glee-uh-SIDES) are fatty substances needed for the proper development of the brain and nerve cells. Under normal conditions, gangliosides are continuously broken down so that the correct amount of gangliosides is always present.

The chemical required to break down gangliosides is an enzyme. Enzymes are chemical compounds present in all cells. These compounds make possible thousands of different reactions needed to keep cells operating normally. In a person with Tay-Sachs disease, the enzyme needed to break down gangliosides is missing. As a result, gangliosides continue to build up in the brain. When the brain becomes clogged with this fatty material it is no longer able to function normally.

Tay-Sachs is especially common among Jewish people of eastern European and Russian origin, sometimes referred to as Ashkenazic Jews. About 1 in every 3,600 babies born to Ashkenazic Jewish couples will have Tay-Sachs disease. The disease is also relatively common among certain French-Canadian and Cajun French families. Tay-Sachs disease is quite rare in families of other ethnic backgrounds.

CAUSES

Every child receives two sets of genes, one from its mother and one from its father. These genes may be either dominant or recessive. A dominant gene is "stronger" than a recessive gene and controls the way a cell is going to function.

If a recessive gene is paired with a dominant gene, the recessive gene has no effect on the way a cell functions. The dominant gene overcomes the recessive gene. The only way a recessive gene has any effect on a cell if it is paired with another recessive gene. In such cases, the two recessive genes work together to direct a cell's operation.

Tay-Sachs is caused by a recessive gene. A child with one recessive gene shows no effect as a result of having the gene. The child is a carrier for the disease. A carrier is a person who has one recessive gene for a characteristic. The carrier can pass the gene on to his or her children even though the carrier does not have the disease.

A child with a pair of these recessive genes, however, will show the symptoms of Tay-Sachs disease because the child will lack a normal gene to makes the enzyme needed to break down gangliosides.

SYMPTOMS

Tay-Sachs disease normally shows up at about the age of six months. Prior to that time, the baby acts normally. Once the symptoms of Tay-Sachs begin to appear the baby stops interacting with other people. It may develop a staring gaze. Normal levels of noise tend to startle the baby to an abnormal degree.

Tay-Sachs Disease: Words to Know

Dominant gene:

A form of a gene that predominates over a second form of the same gene.

Enzymes:

Chemicals present in all cells that make possible the chemical reactions needed to keep a cell alive.

Ganglioside:

A fatty substance found in brain and nerve cells.

Gene:

A chemical unit that carries instructions as to the functions a cell should perform.

Genetic disorder:

A medical problem caused by one or more defective genes.

Recessive gene:

A form of a gene that does not operate in the presence of a dominant form of the same gene.

By the time the baby is one year old, it has weak, floppy muscles. The baby may be completely blind, and will usually have a large head. Seizures become a problem between the ages of one and two years and the baby usually dies by the age of four.

DIAGNOSIS

A preliminary diagnosis for Tay-Sachs disease can usually be made by looking into the baby's eyes. If a baby has Tay-Sachs a characteristic cherryred spot can be seen at the back of the eye.

In order to confirm this diagnosis, blood tests are performed that measure the amount of enzyme needed to break down gangliosides. If the level is very low, the baby has Tay-Sachs disease.

TREATMENT

There is currently no treatment for Tay-Sachs disease. Scientists hope to develop some type of treatment eventually. The treatment would involve providing babies with Tay-Sachs disease new genes. These genes would take

over the job of making the enzyme the babies currently lack. While this technology is now being investigated, no technique has yet been shown to work satisfactorily.

PROGNOSIS

At the present time, the prognosis for a baby born with Tay-Sachs disease is certain death. Nothing can be done to keep the baby alive.

PREVENTION

Once a baby receives recessive genes from both parents, it is destined to develop Tay-Sachs disease. The only way to prevent this condition from happening, then, is to make sure no baby receives two recessive genes.

Parents from ethnic groups at risk for Tay-Sachs have the option of being tested for recessive genes. If only one parent has a recessive gene, the baby will not develop Tay-Sachs disease. If both parents have the recessive gene, the child will develop the disorder. Couples can use this kind of information to decide whether or not to have children.

Prenatal testing can also provide information about Tay-Sachs disease. A pregnant woman can be tested to see if her child has Tay-Sachs disease. She and her partner can then decide whether or not to continue with the pregnancy.

FOR MORE INFORMATION

Organizations

Late Onset Tay-Sachs Foundation. 1303 Paper Mill Rd., Erdenheim, PA 19038. (800) 672–2022.

March of Dimes Birth Defects Foundation. National Office. 1275 Mamaroneck Ave., White Plains, NY 10605. http://www.modimes.org.

National Tay-Sachs and Allied Diseases Association, Inc. 2001 Beacon St., Suite 204, Brookline, MA 02146. (800) 672–2022.

Web sites

"Ask NOAH About: Neurological Problems." NOAH: New York Online Access to Health. [Online] http://www.noah.cuny.edu/neuro/neuropg.html#TAYSACHS (accessed on October 31, 1999).

Tay-Sachs Disease

What Is Tay-Sachs Disease?

How Does Tay-Sachs Disease Affect the Body?

How Do People Get Tay-Sachs Disease?

Is There α Cure for Tay-Sachs Disease?

Resources

Tay-Sachs disease is a rare inherited disorder that results in slow destruction of the central nervous system (brain and spinal cord).

KEYWORDS

for searching the Internet and other reference sources

Hexosaminidase A (Hex-A)

Neurology

What Is Tay-Sachs Disease?

Tay-Sachs disease is a rare metabolic disorder with severe neurologic (nervous system) symptoms. “Metabolic” refers to the body’s chemical processes that produce protein and other substances, and break down nutrients to release energy. Tay-Sachs disease is a metabolic disorder because it is caused by the absence of the enzyme (a type of protein) hexosaminidase A (Hex-A). Hex-A is necessary for breaking down fatty substances called lipids. Without Hex-A, these lipids build up in, and eventually destroy, the nerve cells in the brain. Ultimately, the nervous system stops functioning properly.

How Does Tay-Sachs Disease Affect the Body?

Classical Tay-Sachs

The most common form of Tay-Sachs disease (classical Tay-Sachs) affects children and usually is fatal. It is caused by a complete lack of Hex-A. Destruction of nerve cells begins before birth, but an affected baby does not begin to lose nerve function until he or she is about six months old. By age two, the child may have seizures* and begins to lose skills such as crawling, sitting, turning over, and reaching for things. Eventually, the child will be blind, paralyzed, and mentally retarded. Children with this form of Tay-Sachs disease do not live past age five.

* seizures

are sudden attacks of disease, often referring to some type of violent spasms.

A variation of this scenario is when children develop symptoms between the ages of two and five rather than as an infant. The same symptoms emerge, but the disease progresses more slowly. Children with this form usually die by age 15.

Late onset Tay-Sachs (LOTS)

Late onset Tay-Sachs disease (LOTS) is less common than the infantile form. It affects teenagers and adults in their twenties and thirties by causing a gradual loss of nerve function. People with LOTS have low levels of Hex-A rather than a complete lack of it. As LOTS develops, people affected by it may grow clumsy, uncoordinated, and moody. They may experience muscle weakness, twitching, slurred speech, and intellectual impairment. The symptoms vary in type and severity from person to person. Because this form develops so gradually, life expectancy of affected people seems to be similar to that of unaffected people.

How Do People Get Tay-Sachs Disease?

Tay-Sachs disease is caused by a mutation (abnormal change) in the gene that codes for Hex-A, and it is a recessive trait. This means that people will have the disease if they have two copies of the defective gene, but they will not have the disease if they have at least one unaffected copy. People with one normal copy and one defective copy are called carriers, because they can pass the disease on to their children.

Just about anyone can be a carrier of the gene for Tay-Sachs disease. In the general population, about 1 in 250 people carries the gene.

What’s in a Name?

Tay-Sachs disease was named for two scientists working on opposite sides of the Atlantic Ocean.

Warren Tay (1843-1927) was a British eye doctor. In 1881, he described a patient with a cherry red spot on the retina of eye (the structure inside the eye that receives light). This spot is characteristic of the classical form of the disease.

An American neurologist (nerve and brain specialist) named Bernard Sachs (1858-1944) described the changes in cells caused by the disease. He also recognized that it was an inherited condition that ran in families and that most babies with the disease were of eastern European Jewish descent.

However, some populations of people include more carriers than others. For example, 1 in 27 people of eastern European Jewish (Ashkenazi) descent in the United States is a carrier. People of French-Canadian ancestry from one part of Quebec and the Cajun population in Louisiana also have a higher than usual risk of carrying the Tay-Sachs gene.

Is There α Cure for Tay-Sachs Disease?

Although researchers are actively looking for a way to prevent or treat Tay-Sachs disease, currently no treatment or cure exists. However, tests have been developed that allow people to find out if they carry the defective gene. Blood tests can determine the level of Hex-A in people’s blood (carriers have about half as much as noncarriers) and DNA tests may find evidence of mutations in the Hex-A gene. Testing is particularly useful for people who have had relatives with Tay-Sachs disease and for people in high-risk populations. Finding out about risk before having a baby can prevent the anguish of watching a child develop and then die from Tay-Sachs disease.

Prenatal tests also exist for women who already are pregnant. The amniotic fluid (the fluid in which the fetus develops) or the chorionic villus (structures inside the mother’s uterus) both contain fluid from the developing baby that can be sampled and tested for the presence of Hex-A. If Hex-A is present, that means that the fetus does not have Tay-Sachs disease.

See also

Genetic Diseases

Resources

National Tay-Sachs and Allied Diseases Association, Inc., 2001 Beacon Street, Suite 204, Brookline, MA 02146. Telephone 800-906-8723 http://www.ntsad.org/

Late Onset Tay-Sachs Foundation, 1303 Paper Mill Road, Erdenheim, PA 19038. Telephone 800-672-2022

March of Dimes Foundation, 1275 Mamaroneck Avenue, White Plains, NY 10605. Telephone 888-663-4637 http://www.modimes.org/

Tay-Sachs disease (amaurotic familial idiocy) (tay-saks) n. an inherited disorder of lipid metabolism (see lipidosis) in which abnormal accumulation of lipid in the brain leads to blindness, mental retardation, and death in infancy. [ W. Tay (1843–1927), British physician; B. Sachs (1858–1944), US neurologist]