In another diagnostic method dispute, the Federal Circuit found the asserted patent claims ineligible under 35 U.S.C. Section 101. In Athena Diagnostics v. Mayo Collaborative Services, Athena is the exclusive licensee of the '820 patent, covering methods of diagnosing neurological disorders such as myasthenia gravis (MG) by detecting antibodies to a protein referred to as MuSK. The '820 inventors discovered a relationship between MuSK antibody production and the autoimmune disorder MG. Athena also sells a test called FMUSK that evaluates the antibodies. After Mayo introduced competing tests that allegedly practice the claims of the '820 patent, Athena sued Mayo for infringement in the District of Massachusetts. Mayo moved to dismiss under Rule 12(b)(6), arguing that the asserted claims are invalid under 35 U.S.C. Section 101. The district court granted Mayo's motion, concluding that the '820 patent claims are directed to ineligible subject matter. 

The claims at issue on appeal recite a method for diagnosing disorders related to MuSK by mixing a patient's bodily fluid with a labeled antigen to the MuSK antibodies; immunoprecipitating any antibody/MuSK complexes from the fluid; and then monitoring for the label on any of the complexes in the precipitate, indicating the patient is suffering from a neurological disorder such as MG.

On appeal, Athena argued that the claims are not directed to a natural law because they recite innovative, specific, and concrete steps that do not preempt a natural law. In addition, Athena asserted that the claims are directed to a new laboratory technique that makes use of man-made molecules. Mayo, on the other hand, argued that the correlation between naturally-occurring MuSK antibodies and MuSK-related neurological diseases like MG is a natural law. Mayo further argued that the remaining steps apart from the natural law are standard immunoassay techniques that still leave the claims directed to a natural law. 

In an opinion written by Judge Lourie, the Federal Circuit agreed with the district court and Mayo that the claims at issue are directed to a law of nature; specifically, "the correlation between the presence of naturally-occurring MuSK autoantibodies in bodily fluid and MuSK-related neurological diseases like MG." According to the Court, this correlation exists in nature, even if only recently discovered by humans, and "there can thus be no dispute that it is an ineligible natural law." And although the Court acknowledged that the claims at issue include "certain concrete steps," it still determined that, as a whole, the claims are directed to an abstract idea because the "claimed advance was only in the discovery of a natural law" and "the additional recited steps only apply conventional techniques to detect that natural law." Supporting its determination, the Court cited portions of the '820 patent specification explaining that the "actual steps" are "known per se in the art" and are "standard techniques in the art." With respect to the creation and use of a man-made molecule, the Court held that "the use of a man-made molecule is not decisive if it amounts to only a routine step in a conventional method for observing a natural law."

In its decision, the Federal Circuit noted that it is important to recognize the difference between the claims in the '820 patent "which recite a natural law and conventional means for detecting it, and applications of natural laws, which are patent eligible." The Court explained that claiming a natural cause of a disorder and well-known means of observing it "is not eligible for patent because such a claim in effect only encompasses the natural law itself." However, in distinguishing the 2018 Vanda opinion, the Court noted that "claiming a new treatment for an ailment, albeit using natural law, is not claiming the natural law."

Judge Stoll joined Judge Lourie in the majority opinion and Judge Newman dissented, stating that "this court's decisions on the patent-ineligibility of diagnostic methods are not consistent" and the decision on the claims of the '820 patent "enlarge[d] the inconsistencies and exacerbate[d] the judge-made disincentives to development of new diagnostic methods, with no public benefit." Judge Newman explained that the claims at issue are for a "multi-step method of diagnosis, not a law of nature" because the inventors applied their discovery of the relationship between MuSK antibody production and MG to "create a new method of diagnosis, for a previously undiagnosable neurological condition." The dissent cautioned that Section 101 does not turn on whether any claim steps are "standard techniques," as the appropriate analysis of the "role of conventional process steps in claims to a new method is under Sections 102 and 103, not Section 101." And Judge Newman indicated "strong concerns for the consequences for biomedical diagnostics" based on the majority's analysis of the '820 patent claims and the inconsistent body of law with respect to Section 101. Addressing the dissent in a footnote, the majority opinion agreed that "the public interest is poorly served by adding disincentive to the development of new diagnostic methods," but added that "our precedent leaves no room for a different outcome here."    

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