Insufficient disclosure of a dependent claim combined with late filing of requests deleting this claim leads to revocation at the EPO

The Board of Appeal’s decision T 878/23 is a stark reminder that it is important to make sure that the claims of a European patent are all in line, do not contradict each other, and cannot give rise to issues which could put in question that they can be technically carried out over their entire scope. It also emphasizes the necessity to file all potentially helpful auxiliary requests at the earliest possibility

In this case, HOFFMANN EITLE patent attorney Elisabeth Engelhard objected that dependent claim 4 was insufficient as it defined a composition having a total amino acid content as low as 3.5 wt% when independent claim 1 required at least 10 wt%. Patentee argued that the discrepancy was a simple clarity issue and could thus not be raised during opposition. Patentee argued that the issue was one of an unclear “forbidden area”, that typically arises not from a technical impossibility to perform the invention, but from an ambiguity in the claim language. According to the established case law of the Boards of Appeal, such ambiguity comes under the provisions of clarity, rather than sufficiency.

However, the Board of Appeal followed HOFFMANN EITLE’s arguments that the effect of the dependent claim was not just an unclear boundary. They considered both claim 1 and claim 4 perfectly clear. Instead, the problem was that the claims were also "mutually exclusive, i.e. incompatible, over a substantial part of their ranges". In view of this contradiction, the Board of Appeal found that "the skilled person cannot technically prepare the composition as defined in [the dependent claim] across substantially the whole breadth claimed ".

As all auxiliary requests admitted into the proceedings included the same problematic dependent claim, all auxiliary requests were considered insufficient (Art. 83 EPC). Patentee attempted to fix this by filing new requests deleting this dependent claim in the final stage of appeal proceedings. However, the Board of Appeal held that, as the objection against claim 4 had been raised already in the opposition statement and Patentee could therefore have filed a request addressing this objection at the latest in reply to the Grounds of Appeal, the new requests were not admitted into the proceedings and the patent was revoked.