Tay-Sachs disease


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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

 [ta saks]
the infantile form of neuronal ceroid-lipofuscinosis, inherited as an autosomal recessive trait and affecting chiefly Ashkenazic Jews. With each pregnancy couples who are carriers have a one in four chance of having a child with the condition, a one in two chance of having a carrier like themselves, and a one in four chance of having a child who neither has the disease nor is a carrier. It is a progressive disorder marked by degeneration of brain tissue and the maculas (with formation of a cherry red spot on both retinas) and by dementia, blindness, and death. Tay-Sachs disease is a sphingolipidosis in which the inborn error of metabolism is a deficiency of the enzyme hexosaminidase A, resulting in accumulation of GM2 ganglioside in the brain.



It is possible to test for this disease in the unborn fetus at 14 weeks of pregnancy. An absence of hexosaminidase A indicates conclusively that the fetus has Tay-Sachs disease. Carriers of the trait have lowered levels of the enzyme in their blood, thus permitting screening of populations most susceptible to transmission of the trait to their offspring and genetic counseling of known carriers. No therapy is currently available. Most children with Tay-Sachs disease die of bronchopneumonia at 3 to 4 years of age.

The National Tay-Sachs and Allied Diseases Association (NTSAD) is dedicated to the treatment and prevention of Tay-Sachs, canavan, and related diseases. It provides information and support services to individuals and families affected by the diseases, as well as to the public at large. Their address is National Tay-Sachs and Allied Diseases Association, 2001 Beacon Street, Suite 204, Boston MA 02135. The telephone number is 800-906-8723.

Tay-Sachs dis·ease

(tā saks),
a lysosomal storage disease, resulting from hexosaminidase A deficiency. The monosialoganglioside is stored in central and peripheral neuronal cells. Infants present with hyperacusis and irritability, hypotonia, and failure to develop motor skills. Blindness with macular cherry red spots and seizures are evident in the first year. Death occurs within a few years. Autosomal-recessive transmission; found primarily in Jewish people.

Tay-Sachs disease

(tā′săks′)
n.
A hereditary disease that affects young children almost exclusively of eastern European Jewish descent, in which an enzyme deficiency leads to the accumulation of gangliosides in the brain and nerve tissue, resulting in intellectual disability, convulsions, blindness, and, ultimately, death.

Tay-Sachs disease

[tā′saks′]
Etymology: Warren Tay, English ophthalmologist, 1843-1927; Bernard Sachs, American neurologist, 1858-1944
an inherited, neurodegenerative disorder of lipid metabolism caused by a deficiency of the enzyme hexosaminidase A, which results in the accumulation of sphingolipids in the brain. The condition, which is transmitted as an autosomal-recessive trait, occurs predominantly in families of Eastern European Jewish origin, specifically the Ashkenazic Jews. It is characterized by progressive mental and physical retardation and early death. Symptoms first appear by 6 months of age, after which no new skills are learned and there is progressive loss of those skills already acquired. Convulsions and atrophy of the optic nerve head occur after 1 year, followed by blindness, with a cherry-red spot on each retina; spasticity; dementia; and paralysis. Most children die between 2 and 4 years of age. There is no specific therapy for the condition, and intervention is purely symptomatic and supportive. The disease can be diagnosed in utero through amniocentesis. Also called amaurotic familial idiocy, gangliosidosis type I, infantile cerebral sphingolipidosis, Sachs' disease. See also Sandhoff's disease.
enlarge picture
Cherry red spot in Tay-Sachs disease

Tay-Sachs disease

GM2-gangliosidosis Pediatric neurology A rare AR lipid storage disease, most common in Ashkenazi Jews–carrier frequency 1:30, due to hexosaminidase A deficiency, resulting in accumulation of gangliosides in neurons, cerebellum, axons Clinical Onset at 4-6 months with arrest and decline of psychomotor activities, irritability, hyperacusis, convulsions, chorioathetosis, spasticity, decerebrate rigidity, death by age 3. See Gangliosidosis.

Tay-Sachs dis·ease

(tā saks di-zēz')
A lysosomal storage disease resulting from hexosaminidase-A deficiency. The monosialoganglioside is stored in central and peripheral neuronal cells. Infants present with hyperacusis and irritability, hypotonia, and failure to develop motor skills. Blindness with macular cherry-red spots and seizures are evident in the first year.

Tay-Sachs disease

A recessive genetic disorder, affecting mainly Ashkenazi Jews, in which the absence of an enzyme necessary for the breakdown of ganglioside in the nervous system leads to damaging accumulation of this material. The condition appears soon after birth and features blindness, deafness, progressive dementia, seizures, paralysis and death, usually before the age of 3. There is no effective treatment but the diagnosis can be made before birth by CHORIONIC VILLUS SAMPLING and termination of pregnancy considered. (Warren Tay, 1843–1927, British ophthalmologist; and Bernard Sachs, 1858–1944, American neurologist).

Tay-Sachs disease

a lethal human condition in which children who are apparently normal at birth show signs within six months of marked deterioration of brain and spinal cord. By the age of one year the child can only lie helplessly, becoming mentally retarded, increasingly blind and paralysed. Death occurs between three and four years, with no known survivors and no cure. The condition is controlled by the recessive alleles of a gene located on chromosome 15, double recessives producing a deficient amount of the enzyme hexosaminidase A which leads to the accumulation of complex fatty substances in the CENTRAL NERVOUS SYSTEM.

Sachs,

Bernard, U.S. neurologist, 1858-1944.
Tay-Sachs disease - see under Tay

Tay,

Warren, English physician, 1843-1927.
Tay cherry-red spot - the ophthalmoscopic appearance of the normal choroid beneath the fovea centralis. Synonym(s): cherry-red spot
Tay-Sachs disease - cerebral sphingolipidosis, infantile type. Synonym(s): infantile GM2 gangliosidosis

Tay-Sachs dis·ease

(tā saks di-zēz')
A lysosomal storage disease resulting from hexosaminidase-A deficiency.

Tay-Sachs disease (tā-saks),

n.pr an inherited, neurodegenerative disorder of lipid metabolism caused by a deficiency of the enzyme hexosaminidase A, which results in the accumulation of sphingolipids in the brain. The condition, which is transmitted as an autosomal recessive trait, occurs predominantly in families of Eastern European Jewish origin, specifically the Ashkenazic Jews.

Tay-Sachs disease

a sphingolipidosis of humans in which the inborn error of metabolism is a deficiency of the enzyme hexosaminidase A that results in accumulation of GM2 ganglioside in the brain. Similar to GM2gangliosidosis in German shorthaired pointer dogs.
References in periodicals archive ?
Genetic premarital screening is encouraged in Judaism for the purpose of discouraging at-risk marriages for a fatal illness such as Tay-Sachs disease.
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Most serious genetic disorders, such as cystic fibrosis, sickle cell disease, and Tay-Sachs disease, are caused by a single pair of abnormal recessive genes (see illustration at right).
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