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 Web site.

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.

An approval “is really potentially going to change the way the field is looked at,” said Jeffrey Ostrove, chief executive of Ceregene, a gene therapy company in San Diego. Some pharmaceutical companies have been reluctant to invest in the field, he said, because “there are no approved products in the major markets they sell in.”