Tay Sachs Disease
What Is It?
Tay Sachs disease is a genetic disorder that primarily affects the brain and presents in early childhood. It is due to a mutation of a single gene on chromosome 15 that produces a protein called hexosaminidase A
. Normally, this protein is an enzyme that breaks down compounds found in nerve cells called gangliosides. In a Tay-Sachs patient, the lack of this enzyme leads to a build up of these compounds in nerve cells in the brain. In particular, a ganglioside called ganglioside GM2
builds up to toxic levels. These excess amounts start to cause damage the nerve cells and thus the brain, leading to deterioration of brain function.
Tay Sachs disease is a recessive genetic disease. This means that an individual must have 2 copies of the abnormal gene in order to have the disease. If they only have one copy, they are a carrier and can pass this gene on to children, but they will not exhibit symptoms of the disease. Therefore, to get 2 copies, both parents must have been carriers who had a copy of the defective gene. In these cases, each offspring of 2 parent carriers have a 25% chance of inheriting the disease.
Although the defective gene can be found in anyone, by far the most common population to carry the gene are Ashkenazi Jews with close to 4% of all Ashkenazi Jews being a carrier.
By far, the most common form of the disease is known as infantile, meaning that it presents very early in life. In fact, the nerve cell injury is already beginning while the fetus is still in the womb and symptoms can start to be obvious by 3 to 6 months of life. More rarely, there are later onset forms of the disease that present in later juvenile periods or adulthood. These are relatively very rare compared to the infantile form.
What Types of Symptoms Are Typical?
In the most common infantile form, symptoms of Tay-Sachs first start to become evident around 3 to 6 months of age. It can eventually impact almost all functions of the nervous system but some common symptoms include deafness, blindness (often first presenting with decreased eye contact with parents and others), weakness, delayed or deteriorating mental and social skills, irritability, delayed or loss of motor skills, seizures and slowed growth.
Symptoms are progressive, meaning that they steadily get worse over time. Unfortunately, because it is incurable, the affected individuals usually die by the time they are 4 to 5 years old.
How Is The Diagnosis Typically Made?
First of all, adults can be tested by a simple genetic blood test to determine if they are a carrier of the defective gene. This can be used to aid genetic counseling of parents. In particular, if prospective parents are in an at risk population, particular the Ashkenazi Jewish population, they can find out before having children if they are a carrier. If both parents are carriers, each child will have a 25% chance of getting 2 copies and having the disease.
Additionally, during pregnancy, amniotic fluid testing can identify the abnormal genes and make the diagnosis of Tay Sachs disease in the womb.
In a child with suspected Tay Sachs disease, after a thorough examination and history, genetic testing can identify the disease. Other testing, such as analysis of blood or body tissues for hexosaminidase levels or eye examination to identify a characteristic cherry-red spot on the retina, may be performed as well.
What Are Some Common Treatments?
Unfortunately, there is no cure or treatment for Tay Sachs disease. After the diagnosis is made, education of the parents on what to expect is critical. Additionally, steps to ensure the patient is as comfortable as can be are often taken. However, none of these help prolong the life-expectancy and the disease will continue to progress until the patient dies.
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This site is not intended to offer medical advice. Every patient is different, and only your personal physician can help to counsel you about what is best for your situation. What we offer is general reference information about various disorders and treatments for your education.