Tay-Sachs disease is a fatal disorder of the nervous system. It is a genetic disorder, meaning it is inherited by a child from the parents, that leads to the progressive destruction of the brain, spinal cord, and nerves.
In a fetus that has inherited the genes for Tay-Sachs disease, the destruction of the nervous system begins during early pregnancy, but the signs and symptoms of the disease aren’t often noticeable until a baby is about 6 months old. By 2 years old, a child with Tay-Sachs will have seizures and decreased mental function. The child’s motor and cognitive skills will regress and the child will eventually be unable to walk, crawl, turn over, sit up, or even reach for things. The child will likely become blind, paralyzed, and non-responsive. A distinct feature of Tay-Sachs is the appearance of cherry red spots in the eyes, which occurs because of the degeneration of certain tissues in the eyes. By the age of 3 or 4 years, the destruction of the nervous system is widespread and death usually occurs by the time a child is 5.
A small portion of people affected by Tay-Sachs disease experience later-onset forms. Juvenile onset appears between 2 and 10 years of age. Its first signs and symptoms include clumsiness and problems with coordination. Like infantile-onset Tay-Sachs, this form results in regression of cognitive and motor skills and children will usually die by the age of 15.
Late-onset Tay-Sachs varies in appearance and severity. Its signs and symptoms, including intellectual and neurological impairment, appear in adulthood—anywhere from the 20s to the 60s or even 70s. Late-onset forms of the disease may also be accompanied by psychiatric issues such as paranoia, hallucinations, bipolar episodes, and depression. Unfortunately, there is currently no cure for any form of Tay-Sachs: treatment involves trying to manage the symptoms.
Since Tay-Sachs is an inherited disease, you may be wondering if your baby can inherit the disease. Read on to find out about risk factors for the disease and who is most likely to be affected.
Genes and Tay-Sachs
Genes carry the information that tells your cells and your body how to grow, function, and reproduce. Genes are connected in long strands of DNA and DNA is wound into tiny packages called chromosomes that are carried by every cell in your body. Everyone has two copies of every gene, one inherited from each parent.
Tay-Sachs disease is the result of a defect in a gene that provides instructions your body needs to make a certain type of enzyme. The enzyme, hexosaminidase A, normally breaks down fats. Without the enzyme, these fats build up in the brain and nerve cells, which prevents the nervous system from functioning normally.
If a person has two healthy, normal copies of the gene for hexosaminidase A, they produce plenty of the enzyme and do not have Tay-Sachs disease. If a person has 1 normal copy and 1 abnormal copy of the gene, they, also, are healthy and do not have Tay-Sachs. However, they may pass the abnormal gene to a child. People with 1 normal and 1 abnormal gene are known as “carriers”—people who do not have the disease but are at risk for passing it on. A person must have two abnormal copies of the gene to have the disease.
If both parents have two healthy genes, they have no chance of passing on a defective gene to their child. If both parents are carriers of Tay-Sachs, they have a 25% chance of having a child with active Tay-Sachs disease and a 50% chance of having a child who is a carrier of the defective gene. There is a 25% chance that the child will not have the disease and will not be a carrier.
Who is at risk?
In the general population, about 1 in 250 people are carriers of the defective gene that causes Tay-Sachs. The disease is more common among certain ethnic groups: it occurs most often in people of Eastern and Central European (also known as Ashkenazi) Jewish decent: 1 in 27 people in this group is a carrier of the Tay-Sachs gene. It also occurs more frequently among non-Jewish French Canadians living near the St. Lawrence River and in Cajun communities of Louisiana, as well as some Amish communities in Pennsylvania.
How do I know if my baby is at risk?
A blood test can tell you if you are a carrier of the Tay-Sachs gene. These tests, as well as education within communities at highest risk of Tay-Sachs, have significantly decreased the occurrence of the disease. Every year, only about 16 cases of Tay-Sachs are diagnosed in the United States, so, for most people, the chance of having a baby with the disease is very small.
If you or your partner is a carrier of the Tay-Sachs gene, you may choose to speak with a genetic counselor to understand the risks of conceiving. If you are already pregnant, you can have the unborn baby tested for the disease.