NEW YORK — After more than two decades of dashed expectations, the field of gene therapy appears close to reaching a milestone: a regulatory approval.

The European Medicines Agency has recommended approval of a gene therapy to treat a rare genetic disease, according to the agency’s website.

If the European Commission follows the advice, as it usually does, this would be the first regulatory approval of a gene therapy drug in the Western world. That could give a boost to the field, which at times has struggled for credibility and financing.

Gene therapy involves providing the body with genes it needs, such as correct copies of defective genes that cause genetic disorders. Its use in the West so far has been confined to clinical trials.

The therapy recommended for approval in Europe, called Glybera, was developed by uniQure, a Dutch company. It treats lipoprotein lipase deficiency, a disease that affects only several hundred people in the European Union and a similar number in North America.

People with the disease have a genetic mutation that prevents them from producing an enzyme needed to break down certain fat-carrying particles that circulate in the bloodstream after meals. Without the enzyme, so much fat can accumulate that the blood looks white rather than red.

People with the disease are prone to severe bouts of inflammation of the pancreas. There is no good treatment except an extremely low-fat diet.

Glybera provides correct copies of the lipoprotein lipase gene, which allows patients to make some of the needed enzyme. A single treatment, consisting of injections into multiple spots on the leg muscles on the same day, is expected to last for several years, if not longer, said Jorn Aldag, chief executive of uniQure.