How Rare Bone Disease Progresses (IMAGE) University of Pennsylvania School of Medicine Caption While normal human ACVR1 can rescue the altered developmental pattern of a zebrafish embryo lacking the zebrafish ACVR1 gene, the mutated FOP version of ACVR1 over-compensates for the lack of the zebrafish gene and causes excess formation of tail (ventral) structures at the expense of head (dorsal) structures. Credit Mary Mullins, PhD; Shawn Little, University of Pennsylvania School of Medicine Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.