Huntington's Disease Genetic Testing
Testing of a fetus (prenatal testing) presents special challenges and risks. In fact, some centers do not perform genetic testing for Huntington's disease on fetuses. Because a positive test result using direct genetic testing means the at-risk parent is also a gene carrier, at-risk individuals who are considering pregnancy are advised to seek genetic counseling prior to conception.
Some at-risk parents may wish to know the risk to their fetus but not their own risk. In this situation, parents may opt for prenatal testing using linked DNA markers rather than direct gene testing. In this case, testing does not look for the Huntington disease gene itself, but instead indicates whether the fetus has inherited a chromosome 4 from the affected grandparent or from the unaffected grandparent on the side of the family with Huntington's disease.
If the test shows that the fetus has inherited a chromosome number 4 from the affected grandparent, the parents then learn that the fetus's risk is the same as the parent (50-50), but they learn nothing new about the parent's risk. If the test shows that the fetus has inherited a chromosome number 4 from the unaffected grandparent, the risk to the fetus is very low (less than 1 percent) in most cases.
Another option open to parents is in vitro fertilization with pre-implantation screening. In this procedure, embryos are screened to determine which ones carry the Huntington's disease mutation. Embryos determined not to have the HD gene mutation are then implanted in the woman's uterus.