The present invention concerns a non-human transgenic animal comprising a modification in its genome which results in the animal exhibiting a level of Erf expression and/or ERF activity which is reduced compared to a wildtype animal, wherein said animal has a defect in ossification. Further provided is a non-human transgenic animal comprising an insertion of a promoter-marker gene cassette in one or both Erf alleles wherein the cassette is present in an intron of Erf and wherein said animal exhibits an expression level of Erf and/or ERF activity which is reduced compared to a wildtype animal. Uses of these animals and of a non-human transgenic animal comprising a modification in its genome which results in the animal exhibiting a level of expression of Erf and/or ERF activity which is reduced compared to a wildtype animal for producing animals with ossification defects, for identifying treatments and as disease models are encompassed.
