As a matter of fact, the dumbo gene is considered to be a defect or deformity. The first dumbo rats began showing up in the pet trade, and the scientific community was completely unaware of these adorable animals. After receiving word of them, they began studies and ultimately found that there were two genes that had a role in this mutation: Msx1 and Dlx1 genes. While the animals do not truly suffer from their differences in appearance, they do have other physical traits that differ from standard eared fancy rats.