Figure 4.

Summary of potential sources of genomic instability associated with PM and FM alleles. Transcription of long CGG-repeat tracts promotes a form of MMR-dependent DSBR that leads to expansion (i). As the repeat number increases, the incidence of replication fork stalling increases. Repair of the stalled fork can lead to contractions or deletions (ii). Aneuploidy can result when stalled forks are not repaired (iii), while chromosome fragility results when repair of the stalled forks by MiDAS is incomplete (iv).