Tay Sachs Disease
Tay-Sachs disease is a fatal genetic disorder that causes gradual deterioration of the central nervous system. Tay-Sachs disease is normally noticed in infants. Important enzymes such as Hexosaminidase A (Hex A) are responsible for removing the fatty substances in the brain to facilitate the growth in the baby. These enzymes also help the infants to develop vision, hearing, movement and such other important functions of the body. Absence of this vital enzyme leads to Tay-Sachs disease. High amount of a fatty substance called ganglioside builds up in tissues and nerve cells of the brain. Defects in a gene on chromosome 15 that facilitates production of the enzyme Hex-A.
This is a genetic disorder. Both parents must be carriers for the child to be affected. When both the parents are carriers there is a 1 in 4 chance that their child will inherit a Tay-Sachs gene. In few of the cases, children may just become carriers and not have the disease. There is also 25% chance that, when both the parents are carriers, the child will not be a carrier and not have the disease. Tay-Sachs disease normally occurs in infants. Very rarely the symptoms begin in later childhood or adolescence and adulthood. Most children with Tay-Sachs disease usually die before reaching the age of five.
This disease is normally found in the people of Ashkenazi (eastern and central European) Jews. It is also found in French-Canadian communities of Quebec, the Old Order Amish community in Pennsylvania, and the Cajun population of Louisiana.
Signs and Symptoms of Tay-Sachs
The signs and symptoms of the Tay-Sachs differ according to the onset of the disease. Infants with Tay-Sachs disease appear to develop normally for the first few months of their life. It is only after 5 or 6 months, that gradually baby loses the vision, ability to hear, and move. A red spot develops in the back of the child's eyes. The child experiences loss of motor skills like crawling, turning over, and reaching out for things. As the child ages, he/she may suffer from seizures, mental retardation, paralysis and become completely disabled. Death usually occurs by the time the child is 5 years old.
One more form of Tay-Sachs disease is adult-onset. It is rare to find this form of the disease. Symptoms of Tay-Sachs disease for late onset include muscle weakness, loss of muscle coordination, difficulty in movement, speech problems and even mental illness.
Apart from studying the symptoms, family history, a simple blood test is conducted to assess the level of Hex-A in a person's blood. Carriers have less Hex-A in their body fluid and cells than non-carriers.
Expectant mothers can go for prenatal testing for Tay-Sachs around the 11th week of pregnancy through chorionic villi sampling (CVS). Between the 15th and 18th weeks of pregnancy, fetus can be tested with amniocentesis for the Tay-Sachs gene.
Treatment for Tay-Sachs
Presently, there is no cure or effective treatment for Tay-Sachs. Few anticonvulsant medicines are prescribed to control seizures. Patients with Tay-Sachs tend to get dehydrated easily, hence sufficient amount of fluids is recommended along with proper nutrition. Special care also needs to be taken to keep the airways open.
Chorionic Villus Sampling
The diagnostic procedure of taking out a sample tissue (Choroinic Villi) from the placenta to detect congenital abnormalities in a fetus is known as Chorionic Villus Sampling (CVS). With the guidance of ultrasound, the position of placenta is first determined. There are two methods - trans-cervical and trans-abdominal to perform this test. The position of the placenta helps the physician choose a suitable method. For trans-cervical CVS, parameters like the position of the uterus, the size of the gestational sac and the position of the placenta inside the uterus are first determined using abdominal ultrasound. Using a good antiseptic, the vulva, vagina and the cervix are cleansed. The abdomen is also cleansed for trans-abdominal procedure.
Trans cervical procedure: A thin plastic tube is inserted through the vagina and cervix for the trans-cervical procedure to reach the placenta. A tiny sample of chorionic villus tissue is taken out after locating the exact position of the placenta.
Trans-abdominal procedure: This procedure is similar to the earlier one, but a needle is inserted through the abdomen in this test to reach the uterus and then to the placenta. The chorionic villus sample tissue is drawn into the syringe, while the needle is guided by ultrasound.
This sample is then taken to the laboratory for evaluation. This procedure can be conducted even earlier than amniocentesis to detect any congenital defects present in the fetus. It is done at around 10 to 12 weeks after the last menstruation. Study of the DNA, chromosomes and enzymes of the fetus can be conducted using the sample taken out during the test. Results are available within a week or two. If there are any abnormalities found in the fetus, it is easy to conduct a therapeutic abortion, in case it is necessary. Pregnant women over the age of 35 who are at risk for giving birth to a baby with Downs Syndrome or those who have had birth defects in an earlier pregnancy are advised this test. For detecting neural tube defects and the Rh-incompatibility, amniocentesis is a better option. Hemoglobinopathies and Tay-Sachs disease can be detected through Chorionic Villus Sampling.
The risk involved in using CVS is slightly higher when compared to amniocentesis. Some complications like rupture of the amniotic membrane, miscarriage, infection, bleeding, Rh-incompatibility in the mother if she is Rh-negative and contamination of the sample with maternal cells can occur. When CVS is performed after 10 weeks of gestational period, there is a risk for limb defects in the fetus. If the mother's blood is Rh-negative, she has to receive Rho GAM to avoid Rh incompatibility. After the CVS, it is advised to have an ultrasound done after about two or four days to ensure the fetus is fine.
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Bibliography / Reference
Collection of Pages - Last revised Date: February 18, 2020