Mutations that revert a DNA sequence back in-frame can be among the following: (A) sites of truncating nonsense mutations where additional base substitutions result in non-truncating changes, (B) sites of truncating nonsense mutations where additional encompassing nonframeshift deletions result in non-truncating changes, (C) sites of truncating frameshift mutations where additional nearby frameshift mutations result in non-truncating changes, or (D) sites of truncating frameshift mutations where encompassing nonframeshift deletions result in non-truncating changes.