More than 30 million Americans suffer from one of 7,000 rare diseases — incurable, often genetic conditions affecting fewer than 200,000 people. There is no treatment for 95 percent of these diseases, in part because pharmaceutical companies have been reluctant to invest in developing drugs for such small potential markets. That began to change after Congress in 1983 created tax incentives and exclusive marketing rights for companies that develop treatments for rare diseases. Since then, more than 700 drugs targeting such conditions have been approved, and about half of all new pharmaceuticals approved in 2018 were for rare diseases. While these treatments, including expensive new gene therapies, save lives and offer patients hope, they often come with high price tags: One drug, a one-time treatment, costs more than $2 million. Some experts and policymakers question whether taxpayers need to continue subsidizing the development of such drugs. Meanwhile, patient advocacy organizations are investing in drug research, participating in clinical trials, sharing data and lobbying for continued government support and investment in treatments for rare diseases.