Tay-Sachs disease (tā`-săks`), rare hereditary disease caused by a genetic mutation that leaves the body unable to produce an enzyme enzyme, biological catalyst . The term enzyme comes from zymosis, the Greek word for fermentation , a process accomplished by yeast cells and long known to the brewing industry, which occupied the attention of many 19th-century chemists.
..... Click the link for more information. necessary for fat metabolism in nerve cells, producing central nervous system nervous system, network of specialized tissue that controls actions and reactions of the body and its adjustment to the environment. Virtually all members of the animal kingdom have at least a rudimentary nervous system.
..... Click the link for more information. 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 GM₂ 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 bipolar disorder, formerly manic-depressive disorder or manic-depression, severe mental disorder involving manic episodes that are usually accompanied by episodes of depression .
..... Click the link for more information. . 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 genetic screening, testing for genetic disorders. Most commonly, prospective parents or an embryo or fetus is tested when a specific genetic disorder is suspected (e.g., Tay-Sachs or sickle cell disease ).
..... Click the link for more information. 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 chorionic villus sampling (CVS) or chorionic villus biopsy (CVB) (kōr'ē-ŏn`ĭk, kôr'–)
..... Click the link for more information. or amniocentesis amniocentesis (ăm'nēō'sĕntē`sĭs)
..... Click the link for more information. . 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

Recessive hereditary metabolic disorder, mostly in Ashkenazi Jews, causing progressive mental and neurologic deterioration and death by age five. A lipid, ganglioside GM₂, accumulates in the brain (because of inadequate activity of the enzyme that breaks it down), with devastating neurological effects. Infants appear normal at birth but soon become listless and inattentive, lose motor abilities, and develop seizures. Blindness and general paralysis usually precede death. Tests can detect the disease in fetuses and the Tay-Sachs gene in carriers. There is no treatment.