Figure 4.
The consequences of an intron-expansion event for the coding sequence of two flanking exons. (Upper) Regardless of the intron phase, a 2-nucleotide (or 1-nucleotide) expansion will result in a frameshift in all downstream codons. (Lower) A 3-nucleotide expansion results in the loss of a codon if the intron is in phase 0, but a loss of a codon plus one altered codon sequence if the intron is in phase 1 or 2.