The true prevalence of TS is unknown, but its prevalence has recently been estimated to be 1 in 10,000 in the general population to 1 in 6,000 live births. There are 25,000 to 40,000 individuals in the U.S. and more than 1,000,000 worldwide. TS occurs in both sexes and in all races and ethnic groups.

TS is a genetic disease, so it is not contagious. However, parents may pass TS on to their children. TS has autosomal dominant inheritance, meaning that if one parent has TS, every child born to that parent has a 50% chance of inheriting the TS gene in one of 22 pairs of chromosomes. A parent provides only one of each pair of his or her chromosomes to the child. Thus, there is a fifty -fifty chance of passing the chromosome with the abnormal gene to the offspring.

In at least 50% to 60% of families, no symptoms or signs of TS are found in either parent. It appears that a normal gene mutates to the abnormal form sometime before conception. We still do not know how mutation occurs, but seemingly unaffected parents of normal children may conceive a child with TS. It is also possible that one of the parents has TS, but does not show any of the signs of symptoms, and thus totally unaware of having the disease. The tests presently available do not allow us to rule out the possibility that a parent has TS when he or she does not show any signs of it. Only when a genetic test for TS is developed will it be possible to make a definitive diagnosis.