Defining Amino Acid and Nucleic Acid Sequences in European Patent Applications

Welcome guidance on the interpretation of claims to amino acids and nucleic acids defined by their sequences is provided by updated Guidelines for Examination at the European Patent Office now in force.

New section F-IV-4.24 sets out that both amino acid sequences and nucleic acid sequences can be defined by "percentage identity". The percentage identity determines the number of identical residues over a defined length in a given alignment.Unless otherwise specified, the broadest interpretation will be applied using any reasonable algorithm or calculation method known at the relevant filing date.

Amino acid sequences may also be defined by "percentage similarity", which encompasses substitution of amino acid residues that are physicochemically similar. A similarity scoring matrix should be defined to enable determination of percentage similarity.If not, any reasonable similarity scoring matrix available at the relevant filing date will be used.

For amino acid sequences, an objection of lack of clarity/support may arise where percentage homology is used as the sole feature to distinguish from the prior art if the method of determining the percentage homology is not clearly defined in the application as filed.