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A Dallas Startup Aims to Build a Big Business—and Transform Lives—by Curing Rare Diseases

Babies born with spinal muscular atrophy often live brief, heartbreaking lives. They miss key developmental milestones. They cry weakly. They can’t roll over. They never sit up on their own or feed themselves.

The disease occurs when the body is starved of a protein so vital for movement that it’s literally called the “survival of motor neuron” protein, or SMN. You inherit two copies of the primary gene that codes for that protein, one from each of your parents. If one is flawed, the good one will cover for it, and you may never know you carry a mutation. But about one in every 10,000 kids gets two bad copies.

For decades, scientists have dreamed of curing diseases such as spinal muscular atrophy—diseases born of a single genetic glitch—by replacing the flawed gene with a working one. Progress toward this goal has proven excruciatingly slow. Only in recent years have several gene therapies been approved by the FDA. Among those is Zolgensma, a treatment for spinal muscular atrophy from Chicago-area start-up Avexis.

RA Session was an executive at Avexis, commuting to Chicago four days a week from his native Dallas, as the company developed Zolgensma. A veteran of both multinational pharmaceutical conglomerates and small biotech, Session told me recently about a boy named Matteo, who visited the Avexis office in 2017. Matteo had been diagnosed in utero with spinal muscular atrophy and treated with an experimental infusion of Zolgensma shortly after birth. “He’s throwing blocks against the wall,” Session recalled. “He’s running. He was like, you know, a crazy two-year-old. And with that disease, he should have never been able to do anything.”

That day, Session knew he would never again work in any field but gene therapy, which represents the best, and possibly only, hope for children like Matteo. “You see something like that, you can’t go back to conventional therapeutics,” he said. “I want people to have the best opportunity to have what I have, which is a healthy, happy, beautiful child.”  

The idea behind gene therapy sounds as straightforward as changing a tire. The reality is exceedingly complex. “If you take a typical drug from your medicine cabinet, it’s a very small molecule that will travel throughout your whole body,” said Dr. Ed Neilan, the chief medical and scientific officer of the National Organization for Rare Disorders. It’s like a drop of water seeping across a paper towel. “A gene won’t spread like that.”

A therapeutic gene must reach the exact cells where a given protein is needed—in the case of Zolgensma, primarily motor neurons in the brain and spinal cord—and those cells must produce the right amount of the protein. The most common way to deliver a gene is by packaging it inside a harmless virus. Viruses make their living by slipping inside cells; the gene simply hitches a ride.

Conceived of in the seventies, the first gene therapy of this sort wasn’t approved by the FDA until 2017—a treatment for a form of inherited blindness. Gene therapies using somewhat different mechanisms to treat types of leukemia and lymphoma have also hit the market, and Zolgensma was approved in 2019. 

Complicating the drug-development process is the financial math, which doesn’t favor gene repair. Pharmaceutical companies seek the biggest consumer pools possible; create a drug for high blood pressure, and you’ve got 100 million potential customers in the U.S. The roughly seven thousand known rare diseases—defined by the FDA as those that affect fewer than 200,000 Americans—are an iffier financial proposition, which could be why only about five hundred of those conditions have any approved treatment. Funding for clinical trials for treatments of rare conditions often falls to the families of patients, who turn to lemonade stands, golf tournaments, and crowdfunding platforms to raise millions of dollars. 

The roughly seven thousand known rare diseases are an iffier financial proposition, which could be why only about five hundred of those conditions have any approved treatment.

Zolgensma’s success may have helped change the industry’s calculations. It showed that a treatment for a rare disease could pay off financially. Session helped broker the Swiss pharmaceutical giant Novartis’s $8.7 billion purchase of Avexis in 2018, just before the company submitted Zolgensma for FDA approval. Venture capitalists took note. One biotech CEO told MIT Technology Review, “In my mind, the Avexis deal—there is a before and there is an after.”

Now Session, who left Avexis following the Novartis acquisition, is leading the Dallas-based venture Taysha Gene Therapies, a partnership with the University of Texas Southwestern Medical Center. The company launched from Session’s kitchen table during the COVID-19 pandemic lockdown in April 2020, with $30 million in seed money. Today it’s valued at more than $700 million and has a handful of clinical trials underway. With Taysha, Session hopes to demonstrate on an even bigger scale that gene therapy for rare diseases can pay off—in profits for shareholders, and in lifesaving treatments for kids.


Appropriately for a company devoted to helping children, Session’s nine-year-old daughter came up with the name. “Taysha” is a word from the Caddo Nation of Native American tribes, whose territory once included much of what is now Northeast Texas. It means friend, or ally. According to some historical accounts, when Spanish explorers first encountered the word “taysha,” they heard it as “tejas”—which eventually became “Texas.”

Less than two years after its founding, Taysha has grown from just a handful of employees to more than 150, with three clinical trials ongoing and two more on deck. Session, 42, has helped run companies from New Jersey to Chicago, but is happy to be home. Sitting in his office on the fourteenth floor of a shiny new tower off Interstate 35E, near UT Southwestern, he enjoys a view of the downtown skyline and the Trinity River floodway. Fit and affable, he speaks in excited, rapid-fire crescendos. He points out the window and across the river to where he was born, Methodist Dallas Medical Center, its rooftop cross barely visible through the summer haze. His parents still live in the sixties-era ranch-style house in Oak Cliff where he was raised. His mother worked at the post office. His father, a welder at General Motors, grew up working in East Texas cotton fields half the year. “I’m one generation removed from a sharecropper, really,” Session said.

His father taught him how fine clothes are the uniform of confidence—“Superman has his cape”—and instilled in him a fascination with the churn of money through corporations and Wall Street. In 2002 Session earned a degree in finance from the University of North Carolina at Charlotte, which he attended on a soccer scholarship. After getting his MBA from Texas A&M–Commerce in 2004, he was courted by a who’s who of banks, but he took the one offer he got from a company that made something tangible: Johnson & Johnson. He went to work in 2005 in its pharmaceutical division. “The first week I got there, I went into a couple of meetings. I had no idea what anyone was saying,” he said. He began carting a medical dictionary around. “I didn’t want to seem like the guy that didn’t know what they were talking about.”

Session grew to love biomedicine, along with the business model that transformed laboratory discoveries into commercial drugs. After a stint at J&J, he worked for another international firm, AstraZeneca. Yet he soon realized that Big Pharma wasn’t his passion. He wanted to be closer to patients and to work on drugs that could save lives. So he entered the turbulent world of small biotech—taking a job with a New Jersey company that was developing a treatment for Duchenne muscular dystrophy. He left when it looked like the drug might not work—a frequent reality in the industry—and returned to Dallas to join another biotech company. Eventually, he landed at Avexis and got hooked on gene therapy.

Session left Avexis before the FDA green-lighted Zolgensma. (The agency stood by its approval even after the company admitted that data in its application had been improperly manipulated. Session said he had no knowledge of the manipulation.) In Dallas, looking for a new opportunity on the heels of his Avexis success, Session learned that UT Southwestern had recruited one of the country’s gene therapy pioneers, molecular biologist Steven Gray, to launch a new gene therapy program just a few months earlier. At the University of North Carolina at Chapel Hill, Gray had worked on a promising treatment for a rare condition called giant axonal neuropathy. “Everybody wanted this guy,” Session told me.

The two men met in June 2018, at UT Southwestern. “He basically puts up a slide that says, ‘These are all the diseases that we’re working on.’ And it was like thirty diseases,” Session said. “I’m just looking at this, and I’m like, ‘Steve, what are you doing with this? How are you funding it?’  ” Gray was piecing together the research money himself—through government grants and the money raised by patients’ parents—but drug companies were also interested in investing. Session remembers telling him, “If you partner any one of these out to a Big Pharma company, you’re not going to be able to work on anything else because they’re going to suck up all your time. You’re going to lose control.” He advised Gray and his team to form their own company to commercialize the treatments.

Gray had no interest in leaving UT Southwestern, but he liked Session’s drive. “Very high energy,” he said of Session. “He’s very good at figuring out how to get things done.” They formed a partnership with the university to share scientific expertise and potential profit. Session took the helm of what would become Taysha. As the world was shutting down amid the pandemic early last year, he gathered an executive team and laid the groundwork for an IPO. “We raised three hundred million from my kitchen table, which is crazy,” he said. “I took a company public from my kitchen table, on Zoom.”


Avexis helped prove that there can be significant money in rare diseases. The price tag for a Zolgensma infusion is $2.1 million. It’s the world’s most expensive drug. (The gene therapy treating inherited blindness costs $425,000 per eye; the lymphoma treatment costs up to $475,000.) Session argues that most patients don’t pay that sum because the drug is typically covered by insurance, and that if the onetime treatment cures the disease, it could actually save families money in the long run compared to the costs of ongoing conventional therapies. The nonprofit Institute for Clinical and Economic Review concurs, at least in cases where the condition is identified in prenatal screening and treated early. 

Session also points to the economic benefits of children growing into adulthood rather than dying young. “Potentially allowing a patient to be a productive member of society, hold a job, get an education, pay taxes,” he said. “All that value back to society is significantly meaningful.”

Even so, Neilan, of the National Organization for Rare Disorders, said that if many more gene therapy drugs reach the market with a Zolgensma-size sticker shock, the health-care system could face a reckoning. “There will be more and more companies asking for very high prices to make up for the cost of developing a drug for a small group,” Neilan said. “I think it needs to eventually be a rebalancing that both allows the companies to make enough money that the innovations continue, but balances that with not overburdening the health-care system.” Some experts have said that the U.S. health-care system needs to rethink its fee-for-service model, which wasn’t designed for revolutionary, but breathtakingly expensive, one-off therapies.

First, though, more gene therapies need to cross the finish line, and start-ups such as Taysha could take the burden of funding those efforts off the backs of families. That includes Kasey Woleben and her husband, Doug, who have raised more than $1 million in pursuit of a cure for their son Will. After his birth in 2011, Will seemed like any other baby boy—babbling, smiling, crawling, and eventually walking around their home in McKinney, about thirty miles north of Dallas. But at two years old, Will started to stumble often. Doctors weren’t initially concerned, but Kasey’s gut told her something was wrong.

Then, one day in 2014, Will fell on the living room floor and couldn’t stand back up. Doctors took an MRI and found that his basal ganglia—the brain’s command center for motor functions—was deteriorating. He was diagnosed with Leigh syndrome, a condition only a few thousand children worldwide are born with each year. “It was like a nightmare,” Kasey said, “and I wanted to wake up.”

Will has a mutation in a gene necessary for the normal functioning of mitochondria, the power plants inside cells. The Wolebens asked doctors about gene therapy, but, Kasey told me, “They said, ‘No, that’s twenty years out. Don’t waste your time or energy. Just don’t even bother.’ And of course, my husband and I said, ‘No, that is not an option for us. We are going to fight until the end.’ ” They set out to raise enough money to fund a trial of a gene therapy drug. Their efforts got a boost in 2018, when their story was featured on the front page of the Dallas Morning News and caught the attention of some Dallas billionaires, who opened their wallets. But even that wasn’t enough.

When Taysha formed last year, Kasey said, “there was a sense of relief because we didn’t have to raise millions and millions and millions of dollars. We can focus on our rare-disease child.” Yet Taysha’s help comes with a trade-off: ceding significant control to the company. A clinical trial for a drug that could help Will, who now uses a wheelchair and a feeding tube, will come on Taysha’s schedule. It’s unknown when that might happen. “If I were in charge, this would have been done months and months ago,” Kasey said, adding that she understands that the company isn’t answering just to parents, but to its shareholders as well.

There is another uncertainty. Even once Taysha launches a gene therapy trial for Leigh syndrome, Will might not be included if he doesn’t meet the study’s criteria for inclusion—for instance, if his condition is seen as too far along for him to benefit from the treatment. Meanwhile, the Wolebens stand by eagerly and anxiously, like so many other parents of children with rare conditions. “It’s painful, just heartbreaking as a mom,” Kasey said. “All you want is your child to be treated. I want him to have a long, long life—a healthy, happy life.”

Steven Gray understands the frustration of families like the Wolebens. “I think everybody feels the sense of urgency,” he said. “But the science has to dictate the pace of progress.”


Laura Beil, a former Dallas Morning News medical reporter, has also written for Men’s Health, the New York Times, and Cosmopolitan.

This article originally appeared in the November 2021 issue of Texas Monthly with the headline “Investing in Rare Diseases.” Subscribe today.

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