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Lindsay Karlin, courtesy of the Karlin family
ScienceOnly Human

A New Gene Therapy, an Old Hard Truth

Medicine is so often about playing the odds. Give a 60-year-old a new hip and she might enjoy 20 more years of tennis, but give one to a frail 85-year-old and he’ll die on the operating table. A cabinet full of inhalers helps open the lungs of someone with emphysema, at the cost of swollen feet and bruised, shaky hands. If a two-year-old isn’t talking, her parents could start expensive behavioral intervention, or wait six months and see if she comes around.

This is the calculus that doctors do, ideally aided by their own experience, their patient’s preferences, and the collective wisdom of the scientific literature.

But what if there are no studies to turn to, no doctor’s intuition, no odds on which to base a rational decision? That’s the dilemma faced by some 350 million people who have a rare disease.

Helene and Roger Karlin unwittingly joined that community 18 years ago when their infant daughter, Lindsay, was diagnosed with Canavan disease. She was born with a genetic fluke that would gradually damage the bundles of white matter in her brain.

Her doctors didn’t know much. They couldn’t know much, not with only a few hundred people across the world reported to have the disease. Lindsay would probably have seizures and vision loss, never walk or talk, and die young. Nothing could be done, they said.

The Karlins started making phone calls, asking questions, finding other Canavan families. They were not just parents but advocates, raising money to get scientists interested in a disease that will never have a colored ribbon or national research institute. After years of frustration, in 2001 a clinical trial began to test the safety of inserting a therapeutic gene into the brains of 13 children with Canavan disease, including Lindsay.

A decade has passed, and during that time the therapy has not caused any serious problems in the children, the researchers reported in a study last month. That kind of long-term safety data is incredibly important for the field of gene therapy, which is still reeling from causing a teenager’s death in 1999. Yet the new study also found that the trial, which cost more than $3 million, didn’t much improve Canavan’s devastating symptoms.

This isn’t a story of medical miracles. It’s about rare-disease trailblazers and the slow, deliberate pace of science.

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Paola Leone

When Lindsay was born, in July of 1994, she looked perfectly healthy. But her mother worried about her eyes. “She never seemed to really fixate on my face, she never really tracked,” says Helene Karlin. A child psychologist, Karlin knew that most babies begin smiling at their mother around 9 or 10 weeks of age. One day when Lindsay was 11 weeks old, Karlin caught her smiling at the wallpaper. “I was quite upset,” she says. “But nobody else could see what was wrong.”

In September, the Karlins took Lindsay to a neurologist at Yale University. A genetic test pointed to Canavan disease, caused by recessive mutations in a gene called ASPA. The gene makes an enzyme that’s crucial for cells throughout the brain and central nervous system. Children lacking ASPA have severe deficits in myelin, a fatty substance that insulates the nerve projections connecting one brain cell to another. By three months of age, Lindsay had low muscle tone and couldn’t lift her head. “It was like carrying around a rag doll,” Karlin says. “She almost looked like she was in a stupor, like she was drugged.”

Not long after getting the diagnosis, the Karlins showed up at Matthew During’s laboratory, also at Yale. His team had just published a high-profile study using a rat model of Parkinson’s disease. The scientists showed that the shell of a virus could deliver a single gene into the brain of the sick rats and improve some of their motor impairments. The Karlins wanted to talk to the scientists about using a similar approach in kids with Canavan.

Bench scientists don’t often cross paths with human patients. Meeting Lindsay that day had a profound effect on one of During’s postdoctoral fellows, Paola Leone. “I didn’t know how to approach it, but I just thought, god, I would love to help this child,” Leone says.

Leone soon convinced During to work on gene therapy approaches for Lindsay and one other young girl with Canavan. Because During had another academic appointment at the University of Auckland, they set up their first clinical trial in New Zealand, thinking it would be easier to get regulatory approval there. It wasn’t. “There’s a tremendous amount of regulation that you have to go through in order to get one of these trials approved,” Karlin says. “We jumped through lots and lots of hoops.”

The trial was eventually approved, though, and Lindsay got her first surgery at 18 months old. “A couple of days after the surgery, it was the most striking thing, she turned to me and she smiled,” Karlin says. “It was heart-breakingly sweet.”

The Karlins noticed other improvements in Lindsay’s motor function and attention, but they were short lived. After about a year her brain cells stopped expressing the gene. The failure resulted from the particular type of gene therapy, which used fat molecules to deliver the ASPA gene into cells.

The newly published trial, in contrast, used a viral delivery method, which is much more targeted and efficient. But Lindsay didn’t get the new surgery until she was nearly 7. Regulatory red tape, this time in the United States, was again responsible for the delay. It was even more onerous than previous attempts because a tragedy had just happened during another American trial.

In 1999, 18-year-old Jesse Gelsinger died a few days after getting an experimental gene therapy for a metabolic disease. The delivery virus triggered a deadly reaction by Gelsinger’s immune system. The Canavan trial would be using a different kind of virus but it didn’t matter. “The regulatory agencies were under tremendous scrutiny,” Karlin says. “For us, it was a horrible, horrible rollercoaster ride.”

The Canavan trial began in the summer of 2001 and would include 13 surgeries over the next four years. Into six holes in each patient’s brain the surgeons injected the gene therapy: a virus called AAV2 carrying a healthy ASPA gene.

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A boy with Canavan disease gets prepped for gene therapy surgery

Two of the children had surgical complications (unrelated to the gene therapy) that cleared up within a few months. The AAV2-ASPA combo didn’t cause cancer or serious immune reactions. But did it work?

All of the children are still alive today, which the researchers attribute to the gene therapy. Brain scans showed that after treatment participants had lower levels of a molecule called NAA that is normally degraded by ASPA — suggesting that the new gene had started doing at least one of its important jobs. “We turned a fatal disease into a treatable disease,” says Leone, now the director of the Cell and Gene Therapy Center at the University of Medicine and Dentistry of New Jersey.

Others aren’t so sure. The three oldest children, including Lindsay, are just as disabled as they were before the procedure. The rest showed some minor improvements in basic motor functions and alertness, and fewer seizures. But because the disease is so rare and so variable, it’s hard to know whether the gains were due to gene therapy, better medical care and seizure medications, or chance.

“I think this is a first step, but clearly there’s a long way to go before we can say that we can really treat kids with this disorder so that they can have a high quality of life,” says Mark Kay, a gene therapy expert at Stanford University.

The reason it didn’t work is likely because of the AAV2 virus, which only invades neurons. It can’t get into oligodendrycytes, the cells that make up myelin. It also can’t affect cells far away from the injection site, such as neurons in the brain stem that help control movement. “For a disease like Canavan’s, where you have to have widespread delivery throughout the entire brain, spinal cord, and brain stem, [AAV2] becomes somewhat problematic,” says Brian Kaspar, an investigator at Nationwide Children’s Hospital in Columbus, Ohio.*

When the trial began, AAV2 was state of the art. Researchers have since discovered better delivery methods. Both Kay and Kaspar cite other viruses in the AAV family that can target a variety of brain cells. Kaspar says that a virus called AAV9 can also cross the blood-brain barrier, the sheet of cells that protects the brain from the blood supply. If a gene therapy could penetrate this wall, then it could be injected into blood and brain surgery wouldn’t be necessary. “It’s changed the way we think about getting into the brain,” Kaspar says.

These new approaches may one day help young children with Canavan and similar conditions. And if that happens, it will be partly thanks to the efforts of the Karlins and the other trailblazing families. But Lindsay is still very sick, confined to a wheelchair and nearly blind. She communicates “yes” and “no” by blinking and moving her lips. She tries to sing with her sisters sometimes, but can’t get the words out.

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The Karlin family

The Karlins have shifted their focus to another experimental treatment that could, theoretically, help Lindsay: stem cell transplants to replace oligodendrocytes. In preliminary experiments, Leone’s lab has tested the approach in a mouse model of Canavan disease. The Karlins’ non-profit, Canavan Research Foundation, and another family’s organization, Jacob’s Cure, are supporting the work, just as they did for the gene therapy.

In this story is a hard truth of medical research: It’s slow. And it’s to some extent meant to be that way, to avoid serious mistakes and ensure that treatments offered to the masses are sound. The system gives doctors and patients the solid data they need — the odds ratios — to make good decisions.

This contribution to future generations motivates and comforts Samantha Karlin, Lindsay’s 26-year-old sister, who’s recently taken the reins of her family’s foundation. “Sometimes I wonder, if we hadn’t had Lindsay, where would science be today?” she says. “All these things happened because of this little girl.”

*Kaspar has an academic position at Ohio State University, which is now also the home of Matthew During’s lab. The two have never collaborated, however.