The main finding of the paper is that the closer we reposition Pen to Pitx1, the more forelimb cells will start expressing Pitx1, and the more severe the phenotypic outcome will be.

Pitx1 is normally confined to hindlimbs for leg development. In 2018 we showed that Pitx1's ectopic activation in the forelimb, via access to its Pen enhancer, triggers Liebenberg Syndrome, leading to arm malformations. www.nature.com/articles/s41...