Patients And Carriers Of Tay Sachs Disease example essay topic

Tay Sachs disease (TSD) What is TSD? TSD is a rare hereditary disease caused by a genetic mutation that leaves the body unable to produce an enzyme (hex A) 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. Tay-Sachs Disease is a fatal disorder of infancy. The most common form of the disease affects babies. Affected babies appear healthy at birth and seem to develop normally for the first few months of life.

After this time, development slows and symptoms begin. Symptoms of classical Tay-Sachs disease first appear at 4 to 6 months of age when an apparently healthy baby gradually stops smiling, crawling or turning over, loses its ability to grasp or reach out and, eventually, becomes blind, paralyzed and unaware of its surroundings. Death occurs by age 5. Are there other forms or types of diseases as TSD? A much rarer form of the disorder which occurs in patients in their twenties and early thirties is characterized by unsteadiness of gait and progressive neurological deterioration.

Patients with Tay-Sachs have a "cherry-red" spot in the back of their eyes. The condition is caused by insufficient activity of an enzyme hex A. TSD snd the allied diseases are genetic conditions classified as storage diseases. They are caused by the abnormal accumulation, or storage, of certain waste products in the cells or tissues of affected individuals. As these products build up, cells become damaged and gradually lose their ability to function properly, causing disease symptoms. Who Is at Risk of Tay-Sachs Disease?

Tay-Sachs disease occurs most frequently in descendants of Central and Eastern European (Ashkenazi) Jews. About one out of every 30 American Jews carries the Tay-Sachs gene. Some non-Jewish individuals of French-Canadian ancestry (from the East St. Lawrence River Valley of Quebec), and members of the Cajun population in Louisiana, are at similarly increased risk. These groups have about 100 times the rate of occurrence of other ethnic groups. The juvenile form of Tay-Sachs, however, may not be increased in these groups.

What is caused by? Tay-Sachs disease and related diseases result from storage of a certain lipid, GM 2 ganglioside, in lysosomes. These lysosomes are tiny digestive sacks inside nerve cells and other kinds of cells, too. These lysosomes have dozens of digestive enzymes that the cell uses to break down all kinds of compounds, such as lipids (fats), sugars, proteins, nucleic acids and other materials.

If one of these digestive enzymes is missing or inactive (in the case of TSD it is the enzyme called hex A), because of a genetic deficiency for example, then everything else gets digested except the "stuff" that the missing enzyme was supposed to digest. This "stuff", GM 2 ganglioside (fatty substance) in the case of Tay-Sachs disease, then accumulates in the lysosomes which puff up and get bigger and bigger until they stop the cell's function. The cell is not breaking ganglioside down, that is not digesting it fast enough. Ganglioside are made and biodegraded rapidly in early life as the brain develops. Patients and carriers of Tay-Sachs disease can be identified by a simple blood test that measures hex A activity.

How Is the Disease Transmitted? Only through heredity. A Tay-Sachs carrier has one normal gene for hex A and one Tay-Sachs gene. The carrier does not have the illness and leads a normal, healthy and full life. However, when two carriers become parents: There is a one-in-four chance that any child they have will inherit a Tay-Sachs gene from each parent and have the disease.

There is a one-in-four chance that the child will inherit the normal gene from each parent and be completely free of the disease and the Tay-Sachs gene. There is a two-in-four chance that the child will inherit one of each kind of gene and be a carrier like the parents and free of disease. If only one parent is a carrier, none of their children can have the disease, but each child has a 50-50 chance of inheriting the Tay-Sachs gene and being a carrier. Can Tay-Sachs Disease Be Diagnosed Before Birth? Yes. Prenatal tests called amniocentesis and chorionic villus sampling (CVS) can diagnose Tay-Sachs before birth.

In amniocentesis, which usually is done between the 15th and 18th week of pregnancy, a needle is inserted into the mother's abdomen to take a sample of fluid that surrounds the fetus. The fluid contains fetal cells that can be examined for the presence of hex A. In CVS, the doctor retrieves a sample of cells either through a thin tube inserted through the vagina and cervix to the placenta or by inserting a needle through the mother's abdomen. The placenta contains cells that are genetically identical to those of the fetus, and these cells are examined for the presence of hex A. CVS usually is done between the 10th and 12th week of pregnancy. If prenatal testing shows that hex A is present, the baby will not have Tay-Sachs. If it is missing, he or she will be affected. In unusual cases, DNA-based genetic testing can determine whether the fetus has infantile Tay-Sachs or another hex A deficiency and, possibly, how severely affected the baby will be.

Other approaches using in vitro fertilization (with genetic testing of the embryos, so that only healthy ones are implanted in the mother) are under investigation, but the safety and accuracy of these methods are as yet uncertain. How Can People Find out if They Are Carriers? You can take a test that measures the amount of the hex A enzyme in your blood. Tay-Sachs carriers have about half as much of the enzyme as non carriers, but this is plenty for the carrier's own needs. A blood sample also can be used to perform DNA-based genetic testing. These are tests that look for known mutations (changes) in the hex A gene that cause the four forms of Tay-Sachs.

This kind of testing may be recommended if the results of the usual carrier screening test discussed above are uncertain. DNA tests also can be used to diagnose late onset forms of hex A deficiency. Is There Any Treatment for Tay-Sachs? Tragically, there is no cure, and no treatment that will prevent the disease from running its course. Affected children can only be made as comfortable as possible.

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