Unlike traditional drugs, gene therapies are intended to be given once, transform the inner workings of the body and last for a lifetime.

Fewer than 2 percent of heavy smokers in the U.S. get recommended lung cancer screenings,

The announcement "will set an important precedent in the ongoing drug pricing debate here in the U.S.," says one analyst.

A proposed national "Right to Try" law would make it easier for terminally ill patients to get access to experimental drugs, but physicians and medical ethicists, as well as the drug industry, oppose such legislation.

In a novel arrangement, the drugmaker will offer discounts based on whether or not the drug works initially and remains effective for the estimated 1,000 to 2,000 patients in the U.S. with a type of inherited retinal disease.

Doctors blame holdups in getting the treatment paid for by Medicare and Medicaid, the two giant U.S. government health programs, as well as some of the U.S.s largest insurers.