The Korean Supreme Court rendered a decision that, even if there is no explicit definition of certain terms in the specification, patent claims may still meet the claim description requirement as long as a person skilled in the art can clearly understand the claimed invention (Supreme Court Case No. 2019 Hu 10296 dated December 30, 2021).

▶ Background of the Case

The claimed invention of the subject patent relates to a mixture of DNA fragments separated from fish semen or eggs. Claim 3 of the subject patent, which is the center of dispute, reads as follows:

[Claim 3]

A mixture of DNA fragments obtained by the method of claim 1, having the following properties:

Average of Molecular Formula: C9.83H12.33N3.72O6.01PNa

Molecular Weight: 50 ~ 1500 kDa

Physical Form: white crystalline powder

Solubility: poorly soluble in water and alkali, poorly soluble in alcohol, insoluble in ether and acetone

Particle Size: 1mm or less.

During prosecution, the KIPO Examiner rejected claim 3 of the subject application for failure to satisfy the claim description requirement, due to the use of the phrases “practically insoluble” and “very slightly soluble,” and the expression “average of molecular formula” of the mixture of DNA fragments, making the claim unclear. In response, the applicant amended both phrases

related to solubility to “poorly soluble,” while arguing that the expression “average of molecular formula” was commonly used in the relevant art. The applicant’s amendment and argument were accepted and the subject application was registered on October 4, 2010, despite the specification of the subject patent not providing any explanation or definitions regarding the meaning of the expressions “poorly soluble” and “average of molecular formula.”

In 2017, a pharmaceutical company filed an invalidation trial against the subject patent, arguing that the subject patent was invalid for lack of novelty and inventiveness, and for failure to meet the description requirement. The Trial Board, however, held the subject patent valid and the decision was immediately appealed to the Patent Court.

▶ The Patent Court Decision

The Patent Court overturned the Trial Board’s decision and held that claim 3 of the subject patent was in violation of Article 42(4)(ii) of the Korean Patent Act, which requires claim(s) to be described clearly and concisely, while reasoning that the terms should be defined in the specification and used uniformly throughout the specification when referring to something surpassing the ordinary meaning.

Specifically, the Patent Court found that the expression “poorly soluble” was ambiguous since the definition of the term was not provided in the subject specification and a skilled person in the art would understand the phrases “practically insoluble” and “very slightly soluble” as meaning “insoluble” and “poorly soluble,” respectively. In addition, the Court determined that the expression “average of molecular formula” recited in the claim was also unclear since the expression seemed to be incorrectly used to mean “average of empirical formula,” in light of the formula and the size of the molecular weight recited in the claim, and there was no explicit explanation or definition regarding the meaning of the term “molecular formula” in the subject specification.

▶ The Supreme Court Decision

On appeal, the Supreme Court reversed the Patent Court’s decision, under the reasoning that, since the term “poorly soluble” was used by those skilled in the pharmaceutical field to refer to the property of a substance having low solubility in water or other solvents, the mixture of DNA fragments of the claimed invention could be clearly understood to be poorly soluble in water, alkali or alcohol. The Court also clarified that the applicant had amended both phrases “practically insoluble” and “very slightly soluble” to “poorly soluble” in order to overcome a claim description rejection, and this amendment did not render the amended claim unclear.

In addition, the Supreme Court held that a person skilled in the art could clearly understand that the expression “average of molecular formula,” limiting the property of the mixture of DNA fragments in claim 3 of the subject patent, meant the average of the molecular formula of deoxyribonucleotides, the basic unit constituting the mixture, and not the average of the molecular formula of the mixture in light of the common knowledge in the art that the average of the molecular formula of deoxyribonucleotides could be derived from the ratio of the four types of deoxyribonucleotides constituting the mixture.

Based on the above, the Supreme Court reversed the Patent Court’s decision and reiterated the standard for determining the claim drafting requirement under Article 42(4)(ii) of the Korean Patent Act, that even if certain terms are not defined in the specification, patent claims may still meet the description requirement as long as one skilled in the art of the relevant field could clearly understand the claimed invention based on the context of the claims and common knowledge in the relevant field.