What is Tay-Sachs disease?
Tay-Sachs disease (the most severe form of Hexosaminidase A deficiency) is a progressive, fatal genetic condition that affects the nerve cells in the brain. People with Tay-Sachs lack a specific protein (enzyme) called hexosaminidase A. This enzyme deficiency causes a fatty substance, GM2 ganglioside, to build up in the brain. It is this accumulation that causes the symptoms of Tay-Sachs.
What causes Tay-Sachs?
All people have two copies of the Tay-Sachs gene (HEXA). Tay-Sachs 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. 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. Some studies state that people of Irish ancestry have a 1 in 50 chance of being a carrier. Around 1 in every 300 people who are not of these backgrounds is a carrier for Tay-Sachs.
What are the symptoms of Tay-Sachs?
Symptoms of Tay-Sachs 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 called a cherry-red spot which can be seen during an eye exam.
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, there are other forms of Hexosaminidase A deficiency that are sometimes referred to as forms of Tay-Sachs.
Juvenile Hexosaminidase A deficiency begins with trouble walking (ataxia) and incoordination in early childhood. Symptoms are similar to those of classic Tay-Sachs 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. 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 (which can be present without dementia). Severity, even within a family, is very variable. Life expectancy can vary widely and may not be shortened.
How is Tay-Sachs diagnosed?
A blood test can be taken to measure the body's level of hexoaminidase A (patients with Tay-Sachs lack most or all of this protein whereas levels are reduced in other forms of Hexosaminidase A deficiency). A doctor may also conduct an eye examination to see if the patient has the classic cherry-red spot in the center of the eye's macula (part of the retina). For parents and other relatives of affected children, as well as people who are concerned that they may be carriers of the disease because of their ethnicity), genetic testing is available. Prenatal diagnosis (e.g., chorionic villus sampling, amniotic fluid testing) and even preimplantation genetic diagnosis (PGD) is more complicated. It is usually possible, but genetic counseling and testing is strongly recommended prior to pregnancy.
How is Tay-Sachs treated?
Unfortunately, there is no cure for Tay-Sachs disease itself. Treatment targets controlling some of the symptoms—such as providing anticonvulsants to control seizures—and proper nutrition and hydration as well as other comfort measures. Research is ongoing.
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This information is provided by the Cleveland Clinic and is not intended to replace the medical advice of your doctor or health care provider. Please consult your health care provider for advice about a specific medical condition. This document was last reviewed on: 10/9/2014…#14348