Repeat instability is frequently correlated with replication progression problems. ??Previously published data by Follonier et al showed replication stalling at Friedreich's ataxia GAA repeats within plasmid replicating in mammalian 293T cells, while no stalling was detected in a similar system used by Chandok et al. ?One possible explanation is the T-antigen amount present. We compared replication progression with and without T-antigen transfection and did not detect any difference, so some alternative hypothesis should be tested.