Hand it over: satisfying the written description requirement in patent filings

A recent ruling by the US Court of Appeals for the Federal Circuit is a timely reminder to assess an often-overlooked requirement that must be heeded when drafting a patent specification. The written description requirement of 35 USC Section 112, and recent litigation focusing on it, highlights the delicate balance that patent applicants strive to strike between obtaining patent protection on an invention and simultaneously preserving the so-called ‘secret sauce’ that underlies its implementation. In order to obtain an enforceable patent, the Federal Circuit reminds us that the applicant must hand it all over – down to the very last detail.

US courts and the USPTO review the written description requirement in the same way: by assessing the scope of the claims and then determining whether the remainder of the disclosure as a whole adequately demonstrates that that subject matter was within the possession of the inventor and part of their invention at the time of filing. With regard to patent prosecution before the USPTO, the scope of the claims of any given patent application frequently (and sometimes substantially) varies between filing and the close of prosecution. In each case where the scope of the claim set changes, it is imperative to confirm that the scope of each claim in the revised claim set is commensurate with that described in the remainder of the application, as filed.

Claim amendments are often made in response to prior art unearthed during prosecution, or in response to publications made by competitors during prosecution, to cover a potentially contentious subject matter. With regard to the former, a prior art search is best practice to enable the drafting of a specification and claim set, which both avoid the prior art and adequately disclose alternative embodiments that are less likely to be covered by the prior art.

Quake v Lo, decided last month by the Federal Circuit, highlights the potential pitfalls with making claim amendments. The patent at issue was directed to a method for determining the presence of a chromosomal abnormality using massively parallel sequencing (MPS). In one instance, MPS can be accomplished randomly by amplifying and sequencing all DNA in a sample. In another instance, MPS can be targeted to specific DNA sequences. The owner of the patent at issue initially described a targeted MPS method, but pivoted during prosecution, shortly after a competitor published on the random MPS method, by deleting all pending claims in favour of claims directed to random MPS. The Federal Circuit agreed that the claims at issue in Quake, directed to random MPS, were unpatentable. The Federal Circuit found that the patent's specification focused primarily on targeted MPS, and while a limited number of vague references to non-targeted DNA sequences were made in the disclosure, there was no embodiment describing the specific statistical analysis needed to determine the presence of a chromosomal abnormality from data generated by random MPS.

The written description, which requires sufficient disclosure of the claimed invention so as to place that invention into the public domain (upon expiration of the patent term), is distinct from the enablement requirement, which requires disclosure sufficient to enable a skilled artisan to practice the claimed invention. That is, a generic disclosure of a genus of chemical compounds, which presumably enables the synthesis of each and every member of the genus, may nonetheless not satisfy the written description requirement for certain specific compounds in the genus, if they are not specifically described, such that it is clear that the inventor was in possession of those inventive compound(s) and any claimed methods related to the manufacture or use of same.

The sufficiency of the disclosure necessary to satisfy the written description requirement is analogous to marking trails by making blaze marks on trees to find one's way through the woods of a specification such that a skilled artisan would be able to follow that trail and understand what the inventors had invented. Therefore, before filing an application it is best practice to thoroughly consider each potential embodiment, ideally in light of the known prior art after a thorough search and specific disclosure of each element or method step of each such embodiment. This will give the applicant the widest latitude to amend claims during prosecution as necessary to produce an allowance and to save the applicant from being lost in the woods.