This present invention relates to transgenic animals useful to study human diseases. Specifically, the invention relates to transgenic animals expressing at least two human proteins (optionally in replacement of the counterpart proteins in the animal) whereas a first human protein interacts with a second human protein. The transgenic animals can then be used for evaluating drugs or building disease models that are related to the expressed human proteins in the animals. The animals and methods disclosed herein reduce the possibility identifying a false-positive compound—the compound that show an effect in a naturally-occurring, non-transgenic animal but may not necessarily work or be therapeutic in human, since the compound may only interrupt the interaction between two animal proteins not necessarily two related human proteins. Also, the animals and methods disclosed herein reduce the possibility of identifying a false-negative compound—a compound that does not work or have any effect in a naturally-occurring, non-transgenic animal but may have therapeutic effect in human, since the compound may only interrupt the interaction between at least two relevant human proteins not necessarily two related animal proteins.