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In (decided Feb. 5, 2026), the USPTO Patent Trial and Appeal Board reversed an Examiner’s rejection of claims the Examiner found contained “improper” Markush groupings. The USPTO has designated this decision as “informative” for its holding that “a Markush grouping is proper if it recites members of a subgenus and the specification describes those recited members as performing similar functions in the context of the invention.” This decision could be helpful to applicants pursuing claims where structurally diverse species can perform the same function.

Markush Claims

As defined by the USPTO in MPEP § 2117(I), “Markush claims” recite “a list of alternatively useable members.” As noted in the MPEP, “Inventions in metallurgy, refractories, ceramics, chemistry, pharmacology and biology are most frequently claimed under the Markush formula, but purely mechanical features or process steps may also be claimed by using the Markush style of claiming.”

Under MPEP § 2117(II), a Markush claim may be rejected for containing an “improper grouping” if either:

(1) the members of the Markush group do not share a “single structural similarity” or

(2) the members do not share a common use. 

The rejection at issue in this case was based on reason (1).

The Markush Language at Issue

The application at issue (US Patent Application No. 17/005,548), describes methods of using miRNA biomarkers to determine the efficacy of a treatment for reducing radiation-induced damage. The application identifies a number of miRNAs whose serum levels are said to change in a dose-dependent manner following total body irradiation.

The claims on appeal recited methods of treating radiation-induced damage in a human subject comprising, among other steps, determining serum levels of certain miRNAs before and after administering a treatment for reducing radiation induced damage. The Markush language at issue stated:

The Examiner rejected the claims for containing “improper Markush groupings” because the listed miRNAs “do not share a single structural similarity” because each has a different nucleotide sequence, with the “only structural similarity present” being that all comprise nucleotides. The Examiner also reasoned that the miRNAs did not belong to a recognized class because “there is no expectation from the knowledge in the prior art that the miRNAs behave in the same manner and can be substituted for one another.” The Examiner agreed that the miRNAs “are all disclosed in the specification to be correlated with the radiation exposure” and “are transcribed and processed the same way,” but maintained that “they do not share a substantial structural similarity essential to this activity.”

In its appeal of the Examiner’s rejection, the applicant argued that “when the Markush group occurs in a claim reciting a process or a combination (not a single compound), it is sufficient if the members of the group are disclosed in the specification to possess at least one property in common which is mainly responsible for their function in the claimed relationship.”  The applicant also argued that “[t]he miRNAs recited in the claim[s] are markers, i.e., whose presence or relative amount( s) trigger (or not) the steps of the claimed method of treatment.” As markers, “the miRNAs of the claims are substitutable for one another and they are structurally similar enough to be classified as a unified class in the context of the claimed methods.”

The Board’s Analysis

The Board found the applicant’s arguments “persuasive” and reversed the rejection.

The Board reviewed relevant case law and explained the touchstone for proper Markush groupings as follows:

The Board explained that the Examiner’s focus on how each of the listed miRNAs functions was misplaced because “[i]ndividual miRNA functionality is not contemplated in the context of the claimed invention.”  

Crediting statements in the application that “the claimed miRNA species …. can be observed to either increase or decrease in quantity as a patient’s reaction to such exposure,” the Board reasoned that “[t]he listed miRNA species need not function as miRNAs, in the same way, to the same end, or at all, for the invention to work.” That is, “what matters in the context of the invention is whether the claimed miRNAs are produced in response to radiation exposure, and at what level they are produced.” Since the Examiner had not disputed that commonality, the Markush claim language was not improper.

Key Takeaways

This USPTO decision could be helpful to applicants pursuing claims where structurally diverse species can perform the same function, including in other “biomarker” cases where structurally diverse proteins or nucleic acids may be correlated with the same physiological state, even if they have distinct biological functions. Under Ex parte Chowdhury, as long as the patent application discloses that the listed members of a Markush grouping can play the same role in the claimed invention, the Markish grouping should be proper, even if the listed members play different roles in other contexts. While Ex parte Chowdhury has been designated as “informative” rather than “precedential,” it provides a clear roadmap for challenging improper Markush grouping rejections.

Applicants facing similar rejections should consider citing this decision and, where rejections are maintained, pursuing an appeal. �鶹ֱ��’s patent counseling practitioners have extensive experience navigating patent prosecution, including representing clients in ex parte appeals of examiner rejections. Contact the authors or your �鶹ֱ�� attorney for more information.