Key Takeaway: A Markush group of structurally dissimilar biomolecules is proper if the specification describes its members as performing the same function within the claimed invention.
On August 25, 2026, the USPTO designated Ex parte Chowdhury, Appeal 2025-00226, as an “informative” decision. The Board reversed an examiner’s improper Markush grouping rejection and articulated a rule that should interest patent practitioners prosecuting biomarker, diagnostic, or other biomolecule claims.
The designation of the decision as “informative” means that while the decision is not binding on other panels or on examiners as it would be if designated as “precedential”, it does illustrate the Board’s norms and provide guidance on recurring issues. The fact that this designation arrived through the Office’s stakeholder nomination process signals that practitioners saw the decision as worth elevating.
The Application and the Claim
Chowdhury’s application is directed to methods of treating radiation-induced damage in a human subject. The specification teaches that serum levels of particular miRNAs shift in a radiation dose-dependent manner and correlate with the risk of developing radiation sickness and related tissue damage.
Representative claim 60 recites a four-step method for treating radiation-induced damage. Step (a) requires determining, at a first time point, a first level of one or more miRNAs in a first serum sample, the miRNAs selected from a Markush group of fifteen different miRNA species.
The Rejection
The examiner found the Markush grouping improper. The fifteen recited miRNAs, in the examiner’s view, shared no structural similarity beyond being composed of nucleotides as each miRNA had a distinct sequence. The examiner further reasoned that the species did not belong to a recognized chemical class whose members would have been expected to behave similarly or to be interchangeable in achieving the same result, and that nothing in the prior art supplied that expectation.
Notably, the examiner appears to have accepted that the recited miRNAs all exhibited dose-dependent changes following irradiation, while maintaining that they lacked the “substantial structural similarity” essential to this activity.”
The Board’s Decision
The Board’s holding is stated thus: “…if a recited Markush group lists a set of things that the inventor describes as a subgenus, and those things are described in the specification as useful for the function of the invention because of their similarities, then their inclusion in a Markush group is not improper.” (emphasis in original).
The Board’s central move was to relocate the inquiry from whether each molecule’s individual biological function is the same to whether their role within the claimed invention is the same. What matters is whether the alternatives are interchangeable for the purposes of the claimed invention, not whether they perform the same biological function generally. Because the specification described each recited miRNA as one whose serum level could be quantified and used as an indicator of radiation exposure and consequent damage, the species “all reportedly function as quantitatively representative of patient radiation exposure” and were therefore substitutable members of an art-recognized class.
What Actually Changed — and What Did Not
It is tempting to read Chowdhury as abolishing the structural prong of MPEP § 2117 for biomolecules. That reading overstates the holding.
The Board did not hold that structural similarity is irrelevant. It held that the structural similarity prong can be established by the specification’s description of common function in the context of the claim, rather than by a shared common function disclosed in the prior art. The structural prong survives; what changed is the evidence that will satisfy whether that structural feature results in a shared common function, and — importantly — where that evidence can come from.
That last point deserves emphasis. The examiner relied on the prior art for an expectation of similar function. In contrast, the Board was willing to look to the applicant’s own specification. For a genuinely novel biomarker panel, the prior art will rarely supply an art-recognized class, because the panel is the invention.
Practice Takeaways
- Draft the common-function statement into the specification, expressly. It may be advisable to expressly state the common function expressly, rather than leaving the shared function of a group of species to inference. State plainly that the recited members are disclosed as alternatives because each performs the same role in the invention — each serves as a quantifiable indicator, each catalyzes the same conversion, each binds the same target. Chowdhury turned on what the specification said.
- Frame the grouping at the level of the claim, not the molecule. When responding to an improper Markush rejection, if it is not possible to argue structural similarity or homology of the members of the Markush group based on a preexisting classification in the prior art, argue instead based on their interchangeability for the purposes of the claimed invention.
- Cite the decision but know the limits of “informative.” As an informative decision, Chowdhury is a legitimate and useful citation in prosecution, and examiners in the biotech art units can be expected to be aware of it. However, informative decisions are not binding on other panels or on examiners the way precedential decisions are; they illustrate the Board’s norms and provide guidance on recurring issues. An examiner is not obliged to follow Chowdhury, but a well-framed argument tracking its reasoning is considerably harder to brush aside than one without it.
Looking Ahead
Chowdhury lands alongside a broader trend of the Office revisiting how rigidly it polices claim formats in the life sciences. Whether the reasoning holds up under a precedential designation or Federal Circuit review remains to be seen. In the meantime, the decision may prove to be a useful tool in overcoming improper Markush rejections.
Editor: Brenden S. Gingrich, Ph.D.
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