What happens if a prior-filed application lacks adequate written description for a claimed invention?

This page is an FAQ based on guidance from the Manual of Patent Examining Procedure. It is provided as guidance, with links to the ground truth sources. This is information only: it is not legal advice.

If a prior-filed application lacks adequate written description for a claimed invention, the following consequences may occur:

• The claim in the later-filed application will not be entitled to the benefit of the filing date of the prior-filed application for that invention.
• The effective filing date for the claimed invention will be the filing date of the later-filed application.
• This may impact the patent’s validity if intervening prior art exists between the filing dates of the prior-filed and later-filed applications.

As stated in MPEP 211.05:

To be entitled to the benefit of the filing date of an earlier-filed application, the later-filed application must be an application for a patent for an invention which is also disclosed in the prior application (the parent or earlier-filed nonprovisional application or provisional application for which benefit is claimed); the disclosure of the invention in the prior application and in the later-filed application must be sufficient to comply with the requirements of 35 U.S.C. 112(a) except for the best mode requirement.

This emphasizes the importance of ensuring that the prior-filed application contains a complete and detailed disclosure of the claimed invention.