Tay-Sachs is a genetic disease. It happens when Chromosome 15 has a genetic problem. The problem is caused by a defective HEXA gene. It is recessive, which means both parents must give the baby the defective gene for the baby to have Tay-Sachs. One in every twenty seven Jewish American has one defective gene and can give Tay-Sachs the defective gene to their child. The disease is very rare. It is most common in Jewish families. There is a blood test to see if a person has the Tay Sachs gene. This blood test has helped reduce the number of babies born with Tay-Sachs. In 1800’s, there were 60 new cases and in the 21st century there were 5.