Tay-Sachs disease is caused by a genetic mutation on the 15th chromosome that results in a lack of a critical enzyme, Hexosaminidase A, needed for fatty acid metabolism. In people with this condition, fatty compounds build up in the body and cause neurological problems like blindness, seizures, and developmental disabilities. Tay-Sachs causes have been a subject of extensive study, and this was one of the first genetic diseases to be studied, with the goal of learning more about it and developing programs for treatment and prevention.
There are two forms of the disease, one that appears early in childhood and another late-onset form. People with Tay-Sachs disease must inherit two copies of the defective gene, one from each parent, and the presentation of the disease can vary depending on the precise nature of the mutation. Tay-Sachs causes can include a family history of the disease and inheritance of the mutation, or a spontaneous mutation that creates a new carrier.
Three populations have an increased risk of this disease, and study of these groups has provided more information about Tay-Sachs causes. Ashkenazi Jews and Lousiana Cajuns are both more likely to have copies of the mutation, and French Canadians have a slightly different mutation. Historically, some researchers theorized that contact with the Jewish community was the cause of mutations in the Cajun and French Canadian community, but genetic analysis disproves this and suggests that Tay-Sachs causes are more likely the result of a handful of independent “founder couples” who developed the mutation.
Tay-Sachs disease and other recessive genetic conditions are more likely to appear in close-knit populations. Members of the community may not marry outside, and deleterious genes become concentrated in the population. A single couple with carrier genes can transmit the condition to their descendants, who take them with them when they intermarry, creating an increased risk as the genes pass through multiple generations. In the Jewish community, testing programs to help people determine if they are carriers before marriage have been an important part of prevention. Individual couples can have tests to see if they are carriers, and fetal diagnosis is available as well.
With awareness of the genetic nature of Tay-Sachs causes, researchers can focus on limiting the risks of having a child with the condition, and developing treatments to address the enzyme deficiency in people with this mutation. The original reason for the proliferation of the genes may not be known, although researchers have put forward theories. It is possible that the mutation was attached to a beneficial mutation, as is the case with sickle-cell anemia, or that parents with children who died of Tay-Sachs disease had more children to replace them, thus ensuring that the genes remained in the population.