Summary
On August 25, 2026, the Patent Trial and Appeal Board (PTAB) designated its decision in Ex parte Chowdhury (Appeal 2025-002261) as informative. The decision reverses an examiner's rejection of diagnostic and treatment claims for improper Markush grouping, holding that listed members need not share rigid chemical structural similarity if they perform a shared functional role described in the specification. This ruling offers patent applicants a clear defense against restriction and improper Markush rejections in biotech and diagnostic prosecution.
The Event
In Ex parte Chowdhury, the PTAB reviewed the final rejection of claim 60 and related claims directed to methods for treating radiation-induced damage in a human subject. The claims required determining levels of one or more microRNAs (miRNAs) selected from a defined Markush group of 15 specific miRNAs (such as miR-130a-3p, miR-150-5p, and miR-142-5p) before and after administering a therapeutic countermeasure.
The patent examiner rejected the claims on the ground that the recited list constituted an improper Markush group under M.P.E.P. guidelines. The examiner asserted that the miRNAs did not share sufficient physical or chemical structural similarity beyond comprising nucleotides, did not belong to a recognized chemical class, and lacked prior-art expectation of interchangeability.
The PTAB reversed the rejection. Drawing on CCPA precedent in In re Harnisch and In re Jones, as well as the Federal Circuit's ruling in Multilayer Stretch Cling Film Holdings, Inc. v. Berry Plastics Corp., the Board held that a Markush grouping is proper when members are alternatively usable for the purpose of the invention. In combination and process claims, possessing a common property responsible for their function in the claimed relationship establishes unity and constitutes a proper grouping.
Context
Under USPTO practice, examiners frequently challenge Markush groupings under M.P.E.P. § 2117 if the recited members do not share a recognized chemical structure or belonging to an art-recognized class. While this test is strictly applied to single-molecule composition-of-matter claims, applicants have long contended that process, method, and combination claims operate under broader functional criteria.
In biomarker panels, individual nucleic acid or protein targets often lack overall sequence or structural homology. Instead, their relatedness arises entirely from their shared biological behavior, such as expression changes following radiation or disease exposure. The examiner's narrow structural requirement threatened to force applicants into filing dozens of divisional applications for single-marker method claims.
Implications
The designation of Ex parte Chowdhury as informative gives patent practitioners persuasive administrative authority to overcome improper Markush rejections in functional, diagnostic, and biomarker-guided treatment claims. By confirming that a shared functional relationship described in the specification supports a Markush group, the PTAB reduces the risk of artificial claim splitting during pre-grant prosecution.
For corporate IP teams and patent prosecutors, the ruling requires a concrete drafting practice: ensure the original specification explicitly defines the shared functional mechanism or signature tying the panel members together. Stating clearly in the specification that each biomarker functions as an indicator of the specific condition provides the necessary evidentiary foundation to defeat structural-similarity rejections.
For Korean and Asian filers prosecuting US applications, this standard provides relief when claiming multi-marker diagnostic panels before the USPTO. In contrast, when prosecuting parallel applications before KIPO, applicants should note that Korean practice evaluates unity of invention under Article 45 of the Korean Patent Act, where shared technical effect must be rooted in a common technical feature. While KIPO tends to scrutinize whether different markers share a unified inventive concept, establishing clear functional equivalence in the original disclosure assists prosecution across both jurisdictions.
Outlook
Because the decision is designated as informative rather than precedential, it does not strictly bind all PTAB panels or examiners, but it serves as official agency guidance reflecting best practices. Practitioners facing pending improper Markush rejections on functional lists should cite Ex parte Chowdhury directly in their Office Action responses.
While the USPTO continues to refine its guidance on claim groupings, prosecution teams should maintain dual claim sets: broad Markush groupings supported by express functional definitions in the specification, paired with dependent claims or sub-panels to preserve fallback positions during both pre-grant examination and post-grant clearance reviews.