Multiple choice

A sequence-based molecular diagnostic test reveals that an affected child has a missense mutation in a gene known to be associated with a dominantly-inherited disorder. The child is the first member of the family to be affected, and the disorder is associated with complete penetrance. The mutation has never been seen before, either in affected individuals or in controls. Which of the following would be the most powerful evidence that the mutation is pathogenic?

  1. Test both parents to see if the mutation is found only in the child.

  2. Determine whether the mutation affects an amino acid that is conserved in evolution.

  3. Examine the structure of the protein to see if the mutation has a major effect on protein function.

  4. Review the literature to see if the mutation has been reported to be pathogenic.
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A Correct answer
Explanation

The child is expected to have a new mutation, given that the disorder displays complete penetrance and both parents are unaffected. One would therefore predict that the mutation would not be found in either parent (although germline mosaicism would be possible).

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