Tay-Sachs Diseases Causes, Symptoms, Diagnosis, Treatment, Prevention

Tay-Sachs Diseases Causes, Symptoms, Diagnosis, Treatment, Prevention


What is Tay-Sachs Disease?



Tay-Sachs Diseases Causes, Symptoms, Diagnosis, Treatment, Prevention

Tay-Sachs disease is a fatal genetic disorder in which harmful quantities of a fatty substance called ganglioside GM2 accumulate in the nerve cells in the brain. Infants with Tay-Sachs disease appear to develop normally for the first few months of life. Then, as nerve cells become distended with fatty material, a relentless deterioration of mental and physical abilities occurs. The child becomes blind, deaf, and unable to swallow. Muscles begin to atrophy and paralysis sets in. 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 Diseases have a "cherry-red" spot in the back of their eyes. The condition is caused by insufficient activity of an enzyme called hexosaminidase A that catalyzes the biodegradation of acidic fatty materials known as gangliosides. Gangliosides 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 hexosaminidase A activity. Both parents must be carriers in order to have an affected child. When both parents are found to carry a genetic mutation in hexosaminidase A, there is a 25 percent chance with each pregnancy that the child will be affected with Tay-Sachs disease. Prenatal monitoring of pregnancies is available if desired.

If you have a family history of Tay-Sachs disease or if you're a member of a high-risk group and plan to have children, Mayo Clinic doctors strongly recommend genetic testing and genetic counseling.

Who Is at Risk for Tay-Sachs Diseases?

Each year, about 16 cases of Tay-Sachs Diseases are diagnosed in the United States. Although Ashkenazi Jews (Jews of central and eastern European descent) are at the highest risk, it is now also prevalent in non-Jewish populations, including people of French-Canadian/Cajun heritage.

Some people carry the genetic mutation that causes Tay-Sachs Diseases, but do not develop the full-blown disease. Among Ashkenazi Jews, 1 in 27 people are carriers; in the general population, 1 in 250 people are.

A child can only have Tay-Sachs Diseases disease if both parents are carriers of the gene. When two carriers have a child together, there's a:

  • 50% chance that their child will be a carrier, but not have the disease
  • 25% chance that their child will not be a carrier and not have the disease
  • 25% chance that their child will have the disease

Tay-Sachs Diseases Causes, Symptoms, Diagnosis, Treatment, Prevention

What causes Tay-Sachs Diseases?


All people have two copies of the Tay-Sachs gene (HEXA). Tay-Sachs Diseases occurs when neither of a person’s HEXA genes is working properly because of a mutation (harmful change). If a person has one working copy of the HEXA gene and the other copy has a mutation in it, he/she is called a "carrier." Carriers don’t show symptoms but when two carriers have children together each child (boy or girl) will have a 25% (1/4) chance of developing Tay-Sachs Diseases. If only one parent passes on the defective gene to the child (50% chance in each pregnancy), the child will not develop the disease but will be a carrier and have the potential to pass the disease on to his or her children.

Although anyone can be a carrier of Tay-Sachs disease, the disease is much more common among people of Ashkenazi (Eastern European) Jewish descent. One in every 30 people of Ashkenazi Jewish descent is a carrier. Other populations with as many (or more) carriers include French Canadians, Cajuns (from Louisiana) and Old Order Amish in Pennsylvania. Around 1 in every 300 people who are not of these backgrounds is a carrier for Tay-Sachs Diseases.

What are the symptoms of Tay-Sachs Diseases?


Symptoms of Tay-Sachs Diseases usually develop around 3-6 months of age when the child starts to have muscle weakness, low muscle tone, an increased startle response and sudden contractions of large muscles when falling asleep (myoclonic jerks).

Between 6 and 10 months of age, a child will not meet motor milestones and may lose the ability to perform tasks (such as sitting) that he/she had previously learned. Decreased eye movement and contact as well as attentiveness are also seen along with a specific change in the eye seen during exam called a cherry-red spot.

After 8 to 10 months of age, a baby will move less and become less responsive. Vision will be lost and many will have seizures by a year of age. A person’s head size will start to grow around 18 months of age and when a child is 2 years old, they typically have trouble swallowing and progress into an unresponsive vegetative state. Age of death is usually between 2 and 4 years, often from pneumonia.

In addition to classic Tay-Sachs Diseases, there are other forms of Hexosaminidase A deficiency that are sometimes referred to as forms of Tay-Sachs Diseases.

Juvenile Hexosaminidase


A deficiency begins with trouble walking (ataxia) and incoordination in early childhood. Symptoms are similar to those of classic Tay-Sachs Diseases although the cherry-red spot is not as common. Age of death is usually in teenage years, usually from infections, although some will die much sooner.

Chronic Hexosaminidase


A deficiency usually develops before age 10 but people do not lose as many motor skills as those with Tay-Sachs Diseases. Cognitive and verbal skills are affected later in the course.

Adult-onset Hexosaminidase


A deficiency causes slow but progressive muscle weakness and wasting as well as trouble speaking clearly, cognitive problems and dementia. Up to 40% of people have psychiatric problems (without dementia) Severity even within a family is very variable. Life expectancy can vary widely and may not be shortened.

How Is Tay-Sachs Diseases Diagnosed?


Prenatal tests, such as chorionic villus sampling (CVS) and amniocentesis, can diagnose Tay-Sachs disease. Genetic testing is generally done when one or both members of a couple are carriers of the disease.

CVS is performed between 10 and 12 weeks of pregnancy and involves taking a sample of cells from the placenta via the vagina or abdomen. Amniocentesis is done between 15 and 20 weeks of pregnancy and involves extracting a sample of the fluid surrounding the fetus using a needle through the abdomen.

If a child is displaying symptoms of Tay-Sachs Diseases, a doctor can perform a physical examination and collect a family history. Enzyme analysis can be done on the child’s blood or tissue samples, and an eye exam may reveal a red spot on his or her macula.

How Is Tay-Sachs Diseases Treated?


There is no cure for Tay-Sachs Diseases. Treatment typically consists of keeping the patient comfortable. This is called “palliative care.” Palliative care may include medication for pain or to control seizures, physical therapy, feeding tubes, and respiratory care to reduce mucus buildup in the lungs.

Medication


To reduce your child's symptoms, a number of prescription medications are available, including seizure medications.

Respiratory care


Children who have Tay-Sachs disease are at high risk of lung infections that cause breathing problems and frequently accumulate mucus in their lungs. Respiratory therapists at Mayo Clinic have extensive experience in reducing the mucus using chest physiotherapy (CPT) and in training family members to provide CPT to your child at home.

Feeding tubes


Your child may develop respiratory problems by inhaling food or liquid into the lungs while eating. To prevent those problems, your doctor may recommend an assistive feeding device such as a nasogastric tube, which is inserted through your child's nose and goes to your child's stomach. Or, a doctor trained in stomach surgery may surgically insert an esophagogastrostomy tube.

Physical therapy


As the disease progresses, your child may benefit from physical therapy to help keep joints flexible and maintain as much ability to move (range of motion) as possible. Physical therapy can delay joint stiffness and reduce or delay the loss of function and pain that can result from shortened muscles.

Family support


Your child's Mayo Clinic treatment team can provide resources and information to help you and your family cope with your child's needs. Your team can help connect you to local support groups.

Follow-up care and coordination. Your Mayo Clinic doctor will provide treatment and follow-up care for your child and will coordinate the treatment and support plan with your child's primary care doctor or pediatrician.

Emotional support for the family is also important. Seeking out support groups can help you cope. Taking care of a sick child is emotionally challenging and talking with other families combating the same disease can be comforting.

Prevention of Tay–Sachs disease


For Preventing Tay–Sachs disease, three main approaches have been used to prevent or reduce the incidence of Tay–Sachs disease in those who are at high risk:

Prenatal diagnosis


If both parents are identified as carriers, prenatal genetic testing can determine whether the fetus has inherited a defective copy of the gene from both parents. Couples may be willing to terminate the pregnancy, although abortion may raise ethical issues. Chorionic villus sampling (CVS), which can be performed after the 10th week of gestation, is the most common form of prenatal diagnosis. Both CVS and amniocentesis present developmental risks to the fetus that have to be balanced with the possible benefits, especially in cases where the carrier status of only one parent is known.

Mate selection


In Orthodox Jewish circles, the organization Dor Yeshorim carries out an anonymous screening program so that couples who are likely to conceive a child with Tay–Sachs or another genetic disorder can avoid marriage. Nomi Stone of Dartmouth College describes this approach. "Orthodox Jewish high school students are given blood tests to determine if they have the Tay–Sachs gene. Instead of receiving direct results as to their carrier status, each person is given a six-digit identification number. Couples can call a hotline, if both are carriers, they will be deemed 'incompatible.' Individuals are not told they are carriers directly to avoid possibility of stigmatization or discrimination. If the information were released, carriers could potentially become unmarriageable within the community." Anonymous testing eliminates the stigma of carriership while decreasing the rate of homozygosity in this population. Stone notes that this approach, while effective within a confined population such as Hasidic or Orthodox Jews, may not be effective in the general population.

Preimplantation genetic diagnosis


By retrieving the mother's eggs for in vitro fertilization and conceiving a child outside the womb, it is possible to test the embryo prior to implantation. Only healthy embryos are selected for transfer into the mother's womb. In addition to Tay–Sachs disease, PGD has been used to prevent cystic fibrosis, sickle cell anemia, Huntington's disease, and other genetic disorders. However this method is expensive. It requires invasive medical technologies, and is beyond the financial means of most couples.