A couple returns for genetic counseling to discuss their genetic test results for cystic fibrosis (CF). Their daughter had an abnormal sweat test and CFTR sequencing that identified one known mutation and one variant of unknown significance (VUS). Parental testing revealed that both the mutation and VUS were maternally inherited. Which of the following should the genetic counselor do next?
A. Tell the family their daughter is a carrier and no further testing is warranted.
B. Tell the family that more research is needed to determine the significance of the VUS.
C. Recommend paternal uniparental disomy testing.
D. Recommend CFTR deletion/duplication testing.