In a recently designated informative decision, the Patent Trial & Appeal Board reversed an examiner’s rejection of claims reciting structurally distinct microRNAs (miRNAs) as an improper Markush group. The Board found the claimed alternatives sufficiently related because they performed similar functions in the context of the invention. Ex parte Chowdhury, Appeal No. 2025-002261 (PTAB Feb. 5, 2026) (Flax, Katz, Hardman, A.P.JJ.) (designated informative Aug. 25, 2026).
The patent application at issue concerns methods for assessing and treating radiation-induced damage using levels of particular miRNAs in a patient’s serum. The claims recited groups of different miRNAs whose measured levels could be used to assess radiation damage and inform treatment decisions.
The examiner rejected the claims as containing improper Markush groupings. The examiner found that the recited miRNAs did not share substantial structural similarity because each had a different nucleotide sequence. Their only structural similarity was that each comprised nucleotides. The examiner also found that the miRNAs did not belong to a recognized chemical class that would have been expected to behave similarly or to be interchangeable for achieving the same result.
The Board reversed. It explained that a proper Markush group generally requires the listed alternatives to belong to a recognized physical or chemical class or to be sufficiently related by a common property or function. In assessing that requirement, however, the relevant inquiry is whether the alternatives are interchangeable for the purposes of the claimed invention.
The Board found that the claimed miRNAs satisfied that standard. Although the individual miRNAs were structurally different and did not necessarily perform the same biological function, the claims did not depend on those biological functions. Instead, each miRNA served the same claimed purpose: its serum level could be quantified and used as an indicator relevant to radiation-induced damage and treatment.
As the Board explained, the listed miRNAs did not need to function biologically in the same manner or produce the same biological result. They needed only to be quantifiable and interchangeable as markers for the purposes of the claimed method. Because the specification described the recited miRNAs as performing that common function, the Board found that they constituted a proper Markush grouping.
read more


Subscribe

