The US Court of Appeals for the Federal Circuit has revived an Elan lawsuit that the company filed against the Mayo Foundation for Medical Education and Research over Elan's genetically engineered mouse model for Alzheimer's disease research. In the third chapter of this ongoing saga, the case returned to a Federal Circuit three-person panel after the original decision was vacated by the en banc court — that is, the matter was referred to all the circuit judges in regular active service.

The crux of this case had centred around the doctrine of inherency, the understanding that information inherent in a patent belongs in the public domain, even if it was not known directly at the time of filing. Elan argued that their transgenic mice were not inherent in an earlier-filed patent by the inventor Mullan and the Mayo Foundation. Elan's US patent 5,455,169 concerns rodents transgenic for the 'Swedish mutation', a mutation found in humans that has been associated with Alzheimer's disease. Elan's claims further require that the transgenic rodent could produce sufficient levels of activating transcription factor–amyloid precursor protein (ATF–APP) to be detectable in a brain homogenate.

Previously, the District Court had decided that the patent by Mullan had discussed the possibility of creating transgenic animals based on the Swedish mutation of APP, and therefore reasoned that the remaining characteristics of Elan's claimed transgenic mouse would have been inherently recognized in the Mullan disclosure patent by those skilled in the art at the time that the Mullan patent was filed. In its appeal, Elan argued that Mullan's disclosure was not sufficient to anticipate Elan's invention either explicitly or inherently, because ATF–APP had not been disclosed in humans until after the Mullan patent was filed, and so would not have been recognized as inherent within Mullan's disclosure at that time.

However, the Federal Circuit concluded that the language and factual basis of Elan's argument encompassed the question of enablement, rather than inherency arguments — that is, there was enough knowledge in the public domain for enablement of Elan's transgenic mice by the filing date of the Elan patent. The District Court had not directly addressed the question of enablement, therefore, the Federal Circuit remanded the case back to the lower court for determination of whether the Mullan patent enabled persons of ordinary skill in the field of the invention to make the desired mutated mouse without undue experimentation.