A treatment which corrects errors in a person's genetic code has been approved for commercial use in Europe for the first time.
The European Commission has given Glybera marketing authorisation, meaning it can be sold throughout the EU.
It is a gene therapy for a rare disease which leaves people unable to properly digest fats.
The manufacturers say it will be available next year.
Gene therapy has a simple premise. If there is a problem with part of a patient's genetic code then change the code.
However, the field has been plagued with problems. Patients have developed leukaemia and in one trial in the US a teenager died.
In Europe and the US, the therapies are used only in research labs.
Glybera is used to treat lipoprotein lipase deficiency. One in a million people have damaged copies of a gene which is essential for breaking down fats.
It means fat builds up in the blood leading to abdominal pain and life-threatening inflammation of the pancreas (pancreatitis).
The only way to manage the condition is by having a very low-fat diet.
The therapy, developed by UniQure, uses a virus to infect muscle cells with a working copy of the gene.
The European Medicines Agency recommended the therapy was made available for the most severely ill patients earlier in 2012.
UniQure chief executive officer Jorn Aldag said: "The final approval of Glybera from the European Commission marks a major step forward in making gene therapies available not only for lipoprotein lipase deficiency, but also for a large number of rare diseases with a very high unmet medical need."
The company said it would apply for regulatory approval in the US and Canada.
China was the first country to officially sanction a gene therapy.