KidsHealth.org Mon May 16, 8:00 PM ET
A healthy baby is able to develop vision, movement, hearing, and other vital functions, in part, because enzymes clear out fatty protein and other unwanted material that can interfere with growth.
But a baby with Tay-Sachs disease is born without one of those important enzymes, called Hexosaminidase A (Hex A). So, as those fatty proteins build up in the brain, they hurt the baby’s sight, hearing, movement, and mental development.
A child can only get Tay-Sachs by inheriting it. The genetic trait is relatively common among certain ethnic groups, such as Ashkenazi Jews. Because the disease can be detected before a child is born, couples in those ethnic groups who are thinking of having children may want to get a blood test to find out whether their child would be likely to have the disease.
Who Is at Risk for Tay-Sachs?
Each year, about 16 cases of Tay-Sachs are diagnosed in the United States. Although Ashkenazi Jews (Jews of central and eastern European descent) are at the highest risk for the disease, it is now also prevalent in non-Jewish populations, including Cajuns in Louisiana and French Canadians who live near the St. Lawrence River.
Some people carry the genetic mutation that causes Tay-Sachs, but do not develop the full-blown disease. Among Ashkenazi Jews, one in 27 people are carriers. In the general population, one in 250 people are carriers.
A child can only have Tay-Sachs 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
Screening for Tay-Sachs Disease
Couples who are considering having children – or are already expecting – can get screened for the Tay-Sachs gene with a simple blood test. If both the mother and father carry the Tay-Sachs gene, an obstetrician/gynecologist may refer the couple to a genetic counselor for more information.
Prenatal Diagnosis of Tay-Sachs Disease
Pregnant mothers can have their unborn babies screened for the Hex A deficit that causes Tay-Sachs disease. (If the tests do not detect Hex A, the infant will have Tay-Sachs disease. If the tests do detect Hex A, the infant won’t have it.)
Between the 10th and 12th weeks of pregnancy, an expectant mother can get a chorionic villus sampling, or CVS, in which a small sample of the placenta is drawn into a needle or a small tube for analysis.
Between the 15th and 18th weeks of pregnancy, the mother can also have an amniocentesis to screen for the Tay-Sachs gene. In this test, a needle is inserted into the mother’s belly to draw a sample of the amniotic fluid that surrounds the fetus.
What Are the Signs and Symptoms of Tay-Sachs?
A child is usually tested for Tay-Sachs after he or she starts having hearing, sight, and movement problems. A doctor can identify the disease with a physical exam and blood tests.
A baby born with Tay-Sachs develops normally in the first 3 to 6 months of life. During the next months – or even years – the baby will progressively lose the ability to see, hear, and move. A red spot will develop in the back of the child’s eyes. The child will stop smiling, crawling, turning over, and reaching out for things. By the age of 2, the child may have seizures and become completely disabled. Death usually occurs by the time the child is 5 years old.
In rare forms of the disease, a child may have the Hex A enzyme, but not enough of it to prevent developmental problems. In one of these forms, called Juvenile Hex A Deficiency, those problems may not appear until the child is 2 to 5 years old. The disease progresses more slowly, but death usually occurs by the time the child is 15 years old. In another, milder form of Tay-Sachs, the disease causes muscle weakness and slurred speech, but sight, hearing, and mental capabilities remain intact.