More than 160 drugs to treat rare diseases were approved by the FDA from 1995-2005, according to a report issued recently by PhRMA, the National Organization for Rare Disorders and the Genetic Alliance.

In comparison, there were 108 approvals from 19841994 and fewer than 10 in the 1970s, the report said.

Orphan drugs treat diseases that affect fewer than 200,000 people in the United States. According to the NIH's Office of Rare Diseases, there are 6,000 to 7,000 rare diseases that collectively affect approximately 25 million -- or one in 10 -- Americans.

One major driver of the increase in approvals was the passage of the Orphan Drug Act in 1983, which helped boost investment in research and development, the report said. The act provided tax relief and some marketing exclusivity for companies that developed an orphan drug. Scientific advancements also helped by improving understanding of molecular and genetic causes of rare diseases, according to the report.