GPT and anemia (phenotype): To deal with ALT elevations, at least three trials including the valoctocogene roxaparvovec and SPK‐8011 trials in haemophilia A and the FLT180a trial in haemophilia B have used prophylactic steroid treatment.18, 24, 27 Other treatment‐emergent adverse events associated with GT include lethargy/fatigue,18, 22 anaemia 21 and back pain (Table 3B).18 Long‐term safety is uncertain as the length of follow‐up in published studies is generally from 1 year up to a maximum of eight years.28, 29 There are, however, positive safety reports from longer‐term follow‐up in animals.30.