All individuals with Tay-Sachs disease have a mutation in both copies of their HEXA genes. Some individuals with late onset Tay-Sachs disease have one late onset mutation and one infantile onset mutation. Others have two late onset mutations. If you have one infantile onset mutation and your partner does too, there is a 25% chance with each pregnancy that your child will have infantile or juvenile Tay-Sachs. If you have two late onset mutations and your partner is a carrier for late onset Tay-Sachs disease, your children are at risk for LOTS, but not early onset disease.
See the About Inheritance page for more information about autosomal recessive inheritance.