Some Genetic Disorders, Such as Tay-Sachs Disease, Are Always Fatal

Some genetic disorders, such as Tay-Sachs disease, are always fatal, and yet these diseases occur in the offspring of two parents without the disorders themselves.How is this possible?

A) They are due to chromosomal abnormalities that occur as a result of aging of the ova or from exposure to environmental hazards.
B) They are spontaneous mutations that occur in response to stressors in the environment.
C) They are recessive disorders that occur when both parents are heterozygous carriers of the recessive gene.
D) They are the result of damage to the fetus during pregnancy and not inherited directly from the parents.