Last month the European Court of Justice ruled that inventions derived from human embryonic stem cells are largely unpatentable. This ruling will shape the development of stem-cell technology. So, to prevent confusion, we wish to point out that the ruling contains crucial errors with respect to the underlying science.

At issue is the dividing line between what does and does not constitute an individual human. Under European law, individuals are not patentable. The new ruling misleadingly classifies pseudo-fertilized eggs, or parthenotes (lumping together those made with and without nuclear transfer), as requiring the protections of personhood. This classification was made on the grounds that these eggs are “capable of commencing the process of development of a human being just as an embryo created by fertilization of an ovum can”.

However, mammalian parthenogenetic embryos do not develop in the same way as normal embryos; nor are they developmentally viable if made without nuclear transplant. They are far down the sliding scale of developmental potential shared by all cells (including cells in the adult human body). It is therefore misguided for the ruling to put all parthenote-derived cells, which have technological potential (see A. A. Kiessling Nature 434, 145; 2005), at the same end of the scale as cells that can fully differentiate (totipotent cells).

The ruling sensibly prevents a second confusion: inventions derived from human embryonic stem cells that require prior destruction of embryos are, it says, unpatentable. Because the technology already exists to make human embryonic stem-cell lines that preserve the viability of the donor embryo (Y. Chung et al. Cell Stem Cell 2, 113–117; 2008), embryo destruction is unnecessary. The scope of the ruling may therefore be narrower than some might conclude.

Whether one is for or against biological patenting (and we have no settled view or financial interest at stake here), it will be unfortunate if the wording of the European Court's ruling should inadvertently inhibit a potentially useful, ethical technology using parthenotes just because of a lapse in scientific understanding.