When Is a Markush Group Proper? Lessons from Ex parte Chowdhury
Patent claims sometimes define alternatives with a formula such as “selected from the group consisting of.” This structure—commonly called a Markush group—can efficiently cover a set of chemical compounds, biological materials, or components. But an examiner may object when the alternatives appear unrelated or do not share a qualifying common use.
The Patent Trial and Appeal Board’s decision in Ex parte Chowdhury, Appeal 2025-002261, offers timely guidance. On August 25, 2026, the U.S. Patent and Trademark Office designated the decision informative following a stakeholder nomination.
The decision is not precedential. It is nevertheless a useful illustration of how claim context can establish a common function even when the listed members have different structures and different biological roles outside the claimed invention.
The application and the rejected claims
The application concerned microRNA biomarkers used to quantify a subject’s exposure to ionizing radiation. The claims listed groups of miRNAs that could be measured in a biological sample and correlated with radiation dose.
The examiner rejected multiple claims on the ground that their Markush groupings were improper. The concern was that the listed miRNAs lacked a single structural similarity and did not share a common use.
The Board reversed. It concluded that the examiner’s analysis gave too little weight to what the miRNAs did in the claimed method.
The governing framework
The USPTO’s Manual of Patent Examining Procedure explains that a Markush grouping may be improper when its members do not share either a single structural similarity or a common use. In a claim to a combination or process, alternatives can satisfy the common-use inquiry when they are disclosed as functionally equivalent for the claimed purpose and can be substituted for one another to achieve the same intended result.
This does not mean that any list of alternatives becomes proper because the specification assigns them a broad label. The asserted commonality must be grounded in the disclosure and in the claim’s actual operation.
Context was decisive
The Board viewed the listed miRNAs in the context of the invention. The specification identified them as a subgenus that could be quantified and correlated with radiation exposure. For the claimed process, each alternative performed the same relevant role: it served as a measurable biomarker used to estimate dose.
The examiner had focused on the different biological functions associated with individual miRNAs. The Board found those differences beside the point because the claims did not require the miRNAs to perform their native biological functions. They needed to be measurable in the claimed method.
That distinction is the central lesson of Chowdhury. “Common use” should be evaluated at the level of the claimed result—not by searching for identity in every scientific characteristic the alternatives possess.
Why the informative designation matters
An informative decision is not binding in the same way as a precedential decision. It reflects a decision the USPTO considers useful for illustrating norms, recurring issues, or sound reasoning.
Applicants should therefore treat Chowdhury as persuasive guidance, not a safe harbor. A different record, a sparse specification, or alternatives that do not genuinely substitute for one another may produce a different result.
Drafting lessons for patent applicants
Define the shared result
The specification should explain precisely what the alternatives accomplish in the claimed invention. “Useful for diagnosis” may be too general; describing how each member is measured and correlated with a defined outcome is stronger.
Support functional interchangeability
If each alternative can replace another in the claimed step, say so and provide examples or data where appropriate. The disclosure should make the substitution credible across the claimed scope.
Distinguish irrelevant differences
Alternatives may have different structures or roles in other settings. The application can explain why those differences do not affect the function the claim actually requires.
Build fallback positions
Dependent claims can organize alternatives into narrower subgroups based on structure, performance, or evidentiary support. That gives the applicant options if the broad grouping faces prior art, enablement, written-description, or unity concerns.
Preserve the record
When responding to an improper-Markush rejection, connect the claim language to specific passages, examples, or data in the specification. A conclusory statement that all members share a use is less persuasive than a documented functional analysis.
Markush form does not answer every patentability question
Reversing an improper-grouping rejection does not establish that the claim is novel, nonobvious, enabled, or adequately described. Broad alternatives may create separate issues under Sections 102, 103, and 112. Claim strategy should address those doctrines together rather than treating Markush form as an isolated drafting exercise.
Businesses developing biotech, pharmaceutical, and diagnostic inventions can benefit from reviewing the shared function and evidentiary support before filing. Tucker Law advises clients on patent prosecution and portfolio strategy and represents parties in PTAB trial and appeal matters.
The bottom line
Ex parte Chowdhury shows that structurally different alternatives may form a proper Markush group when the disclosure establishes that they perform the same relevant function in the claimed invention. The correct level of analysis is the claim’s intended result, supported by the specification.
Applicants should use that principle carefully. Strong drafting identifies the common function, explains substitutability, documents support, and preserves narrower options. To discuss a Markush rejection or a biotechnology claim strategy, contact Tucker Law.
