In a decision with broad implications for patent applicants, the USPTO Patent Trial and Appeal Board has reversed an examiner’s rejection of claims involving Markush groupings.
The case, *Ex parte Chowdhury*, Appeal 2025-002261, was decided on February 5, 2026, and has since been designated as “informative” by the USPTO.
The Board held 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.”
The decision is particularly relevant for applicants pursuing claims where structurally diverse species are capable of performing the same function within an invention.
Markush claims, as defined by the USPTO in MPEP ยง 2117(I), recite “a list of alternatively useable members” and are most frequently used in chemistry, pharmacology, biology, and related fields.
The patent claims at issue in *Chowdhury* were directed to methods of treating radiation-induced damage in a human subject, with Dana-Farber Cancer Institute, Inc. and Albert Einstein College of Medicine, Inc. identified as the real parties-in-interest.
More specifically, the claims related to the isolation and detection of microRNA, known as miRNA, to determine a patient’s risk of radiation exposure.
The Board credited 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.”
Reasoning from that premise, the Board concluded 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.”
The Board further found that “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.”
Because the examiner had not disputed that shared commonality, the PTAB determined the Markush claim language was not improper and reversed the rejection accordingly.
The informative designation is notable for its alignment with recent Federal Circuit case law encouraging flexibility in Markush grouping analyses, drawing on predecessor court rulings.
The PTAB’s approach in *Chowdhury* follows the direction set by the Federal Circuit’s 2020 decision in *Amgen v. Amneal Pharmaceuticals*, which found a recited Markush group was not closed to unrecited members due to the presence of “comprising” transitional language.
In announcing the informative designation, the USPTO acknowledged the case was nominated by an agency stakeholder, as the Office permits anonymous nominations for precedential or informative designation.
Beyond radiation exposure cases, the ruling may offer significant benefits in other biomarker contexts where structurally diverse proteins or nucleic acids correlate with the same physiological state, even when their biological functions differ.