RAD21 and chronic intestinal pseudoobstruction: In in vivo experiments using a zebrafish model, we recapitulated the CIPO phenotype observed in patients with the homozygous RAD21 variant showing a severe impairment of motility and a marked reduction in the pan-neuronal marker HuC/D-immunoreactive enteric neurons, a finding reminiscent of an oligo-neuronal hypoganglionosis detected in CIPO patients [30].