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 The decision is not precedential.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 [...]
