A UK-based stem cell company, ReNeuron, has announced receipt of both European and US orphan drug designation for an experimental therapy to treat retinitis pigmentosa. The regulatory milestone is typically granted to treatments with the potential to provide major benefits for patients with rare diseases, diseases defined in the EU as having a prevalence of less than 5 per 10,000 people or, in the US, as a disease affecting fewer than 200,000 people per annum. Potential advantages of receiving orphan drug designation include market exclusivity for 10 years, in addition to a number of R&D tax credits.