Martine Rothblatt. Elijah Nouvelage/REUTERS Soon after Martine Rothblatt founded what would become Sirius XM, her daughter, Jenesis, was diagnosed with pulmonary arterial hypertension.

The disease is marked by too much pressure in the blood vessels leading from the heart to the lungs, causing them to narrow and not carry enough oxygen.

At the time, in the 1990s, this type of pulmonary hypertension was a fatal disease, Rothblatt said at Smithsonian's Future Is Here Festival on April 23, where she told the incredible story.

"The doctors said, 'There's no medicines approved for it; she's got maybe three months to live,'" she recalled. "I felt like my only purpose in life now was not to help move to the stars with satellites and stuff like that. It was to save Jenesis. So I just stopped everything I was doing."

Rothblatt dove into journals and biology textbooks, searching for a way to save her daughter. She found one specific molecule that might be able to help.

Pharmaceutical giant GlaxoSmithKline owned the molecule but didn't want to develop it — and the company wouldn't hand it over to a non-scientist like Rothblatt for ethical reasons. So she gathered a scientific team to convince Glaxo to let her buy the rights, founding the company now called United Therapeutics.

But once she had those rights, there was still no way of making that potentially helpful molecule in large quantities.

"To make that molecule, it took a 23-step chemical synthesis with two explosive stages that had to be avoided," Rothblatt said.

So she spent a year going to chemistry labs across the country until she found a scientist at the University of Illinois who said he could produce the molecule if she gave him $100,000. With that grant, he made just 1 gram. Amazingly, that was enough to keep scaling up the process step-by-step.

Today, Rothblatt said, United Therapeutics makes about 50 kg of that molecule per year. The US Food and Drug Administration approved the medicine as "Remodulin" in 2002.

See how much smaller the arteries in the lungs of a patient with hypertension are? CDC

The medicine has been a boon to people's health, but it's been an incredible business opportunity, too. Rothblatt said the drug, and several other the company has developed since, now make over $1 billion a year. And as United Therapeutic's chairman and CEO, Rothblatt made $31.6 million in 2014 — making her the second-highest paid female CEO that year.

"Now there's tens of thousands of people living a healthy, happy life with pulmonary hypertension," Rothblatt said. "Best of all — and I just owe enormous gratitude for this whole story to her, because she's my inspiration — my own daughter Jenesis is now 30 years old, works at United Therapeutics, and is a happy, healthy young lady."

In the time with Jenesis's diagnosis, other companies have developed a variety of drugs and treatments for pulmonary hypertension — some equally or more effective than Remodulin — so they have contributed to the increase in survival for patients, too. But there is still no cure for the rare disease.

If any patients can't pay for Remodulin, Rothblatt said, United Therapeutics gives it to them for free.

"It hasn't stopped us from being a successful pharmaceutical company," she said. "I think actually doing the right thing always helps you do the best thing."