Effort To Map Down Syndrome Brain Raises Prospect Of Treatment
MADISON, Wis. — In a lab near UW Hospital, Megan Jandy grows stem cells from people with Down syndrome — 10 batches of cells, most in three-dimensional clusters, each batch featuring one group with the extra chromosome that causes the disorder and one group without it.
Under a microscope, the graduate student examines clusters 33 days after they were created. The clumps, coaxed to become brain cells, look like tiny potatoes, marked with dots that suggest sprouts, or eyes. Each dot could become a ventricle, which in a fully developed brain contains cerebral spinal fluid.
“It gives the cells signals of what they need to become,” she said.
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Jandy and other UW-Madison scientists are creating an atlas of the prenatal brain in Down syndrome. The multi-layered catalog will show how cell types, gene expression and functions like synapse-firing differ at various stages of fetal development between people who have the condition and those who don’t.
Like the stem cell research field upon which their project is based, the goal is to better understand biology, but the implications raise ethical questions: Could Down syndrome be treated or even cured? Should it be?
“We know that individuals with Down syndrome have smaller brains, and there are fewer neurons in parts of the brain,” said Anita Bhattacharyya, a UW-Madison associate professor of cell and regenerative biology who leads the group. “We don’t know how those differences lead to the intellectual disability … Maybe there are opportunities for changing brain development or outcomes in a way that might benefit people with Down syndrome.”
Twenty-five years after UW-Madison researcher James Thomson ushered in the field of stem cell research by isolating and growing human embryonic stem cells, clinical trials are testing therapies for conditions such as macular degeneration, Parkinson’s disease, cancer and stroke as research continues on many other disorders. Thompson’s research, published in the journal Science on Nov. 6, 1998, set off an ethical debate about destroying embryos to produce stem cells.
In 2007, Thomson and Japanese researcher Shinya Yamanaka developed induced pluripotent stem cells, or iPS cells, skin or blood cells reprogrammed to their embryonic state. The ability to generate the pliable cells that can give rise to all parts of the body, without using embryos, eased critics’ concerns.
The legacy of Thomson, who retired from UW-Madison last year, carries on through stem cell studies around the world, including by some 100 faculty members at the university whose labs span about 50 departments across campus.
Mapping the brain
The brain atlas project, involving four faculty and 15 lab researchers, is part of a federal program started five years ago to boost research funding for Down syndrome, the most common genetic cause of intellectual disability. Much of the effort involves investigating medical conditions common in people with the disorder, such as heart disease and Alzheimer’s disease.
With an $11 million “transformative research” grant from the National Institutes of Health, Bhattacharyya and her colleagues at UW-Madison’s Waisman Center are setting out to do what hasn’t been done before: chart the many ways in which having three copies of chromosome 21, instead of two, in Down syndrome disrupts molecular pathways and alters the brain before birth.
They’re relying in part on fetal tissue from elective abortions, obtained from tissue banks under federal regulations. The tissue can show exactly what’s different in Down syndrome compared to normal tissue. But it can be hard to obtain. It’s available only from about 10 weeks’ gestation to about 20 weeks’ gestation, with each sample fixed in time. It comes frozen, so it’s partially inactive.
To analyze how prenatal cells interact with each other differently in Down syndrome, such as when they exchange electrical or chemical signals through synapses, the researchers are turning to iPS cells made from people with the condition. The cells come from a small group of people with mosaic Down syndrome, in which some cells have the extra chromosome and some don’t. This allows researchers to grow and compare cells thought to be otherwise identical.
“We can generate living nerve cells that are hopefully equivalent to the different types of cells in the brain,” said Su-Chun Zhang, a professor of neuroscience and neurology on the research team. “When they connect to each other, when they talk to each other, we can measure them.”
The long-term goal is to rely on iPS cells, instead of fetal tissue, to study Down syndrome, Bhattacharyya said. The atlas will help the team grow the cells in ways that best capture the many differences they identify.
“What can we model in our iPS cells that is reminiscent of what happens in the tissue?” she said. “We can see a lot of things, but whether they’re relevant, we need that atlas.”
Search for treatments
The atlas, to be published online, will provide information that could speed up efforts to find drugs to treat Down syndrome by improving cognition, which could allow people with the disorder to live more independently. Researchers have even found a way to turn off the extra chromosome 21 in stem cells, which some say points to a possible “cure.”
Clinical trials have tested at least 15 drugs or devices to improve learning difficulties in Down syndrome, including the Alzheimer’s drug memantine and basmisanil, a drug developed by the Swiss company Roche that was tested in some patients at the Waisman Center. Many of the experimental therapies showed promise in mice, but most have failed to have an effect in people.
One of the latest leading candidates is a protein called gonadotropin-releasing hormone, or GnRH, used in fertility treatments and tied to brain development. In a pilot study of seven men with Down syndrome who received GnRH through pumps on their arms, their cognitive scores improved by 10% to 30% after six months, French and Swiss scientists reported last year. The researchers are now studying 32 adults with the condition, comparing those who get the drug with those who receive a fake treatment.
Scientists in Massachusetts silenced the extra chromosome 21 in Down syndrome stem cells a decade ago. They did this by inserting a gene called XIST, which resides on the X chromosome and shuts off one of the two X chromosomes in females. In 2020, the researchers used XIST to turn off the extra chromosome 21 in stem cells that had evolved to become brain cells, bolstering the potential of the technique.
But shutting down the chromosome in every cell of a human fetus would be challenging, and chromosome or drug treatments could have medical complications such as an increased risk of cancer, researchers say.
Then there are moral considerations: Would removing the extra chromosome or improving intellectual capacity through drugs fundamentally change who people with Down syndrome are? In a survey of more than 500 parents of people with Down syndrome, 68% said they would use a hypothetical pill to enhance their child’s memory and attention, but some worried it could make their children less affectionate and more self-conscious.
Some 51% of the parents said they would choose prenatal chromosome silencing, while others feared a possible increased risk of miscarriage and unknown impacts on fetal development.
“I would rather have a child with (Down syndrome) than lose that child because I wanted to fix her,” one parent said, the bioethicists who conducted the survey, from Mayo Clinic, in Rochester, Minn., reported in 2020.
A cherished girl
In the front yard of her home in Monona, Olivia Witte’s sisters pushed her on a swing on a recent afternoon as her “brothers,” miniature Irish doodles, chased her. Daniela Witte, 14, and Gabriela Witte, 13, like to play basketball, go swimming and color with Olivia, 11, who has Down syndrome.
Having a sister with Down syndrome “has brought a lot of joy,” said Daniela, in ninth grade at Monona Grove High School.
“She can do things everyone else can,” said Gabriela, an eighth-grader at Glacial Drumlin Middle School.
Dave Witte, who has been a middle school principal in McFarland and an administrator at the Madison School District, and Dr. Cristina Delgadillo, a UW Health pediatrician, also consider Olivia, their daughter, a blessing. “We have always tried to treat her just like our other daughters,” Witte said.
But Olivia’s condition has come with complications. She needed open heart surgery a week after birth and again at eight months old, to correct heart defects common in children with Down syndrome. Shortly before she turned 3, she had brain surgery following a stroke that stemmed from a rare blood vessel disorder seen more often in people with Down syndrome. At age 8, she fell off a swing and lost the use of her legs for more than a week, an accident unrelated to her disorder that required intensive physical therapy to walk again.
The ordeals, along with helping Olivia fit in at Winnequah Elementary School, where she is in fifth grade, have been challenging, Witte said.
But he loves seeing his daughter at bat in Miracle League baseball and said she is extraordinarily kind to people. “It’s innate,” he said.
After Delgadillo’s father died in July, she said Olivia seemed to sense when she was most feeling the loss, and would give her a kiss. “She’s my shadow,” Delgadillo said. “She has our freckles.”
Both parents said they’re conflicted about the possibility of treatments for Down syndrome, even as they favor research like the brain atlas project. Delgadillo said she “certainly disagrees” with chromosome silencing and is worried drugs like GnRH might cause cancer, given that Olivia and others with Down syndrome are already at increased risk for leukemia.
“It’s just too new to feel comfortable with it,” Delgadillo said.
Witte said he wishes Olivia could have avoided her complex surgeries, but having Down syndrome is a big part of the child he loves.
“I don’t want to limit Olivia, but I also don’t want to lose my Olivia,” he said.
A family deliberates
David Egan, 46, who has Down syndrome, has contributed skin cells for iPS cell research at the Waisman Center, as has his father, John Egan.
David was born in Madison, when his parents were graduate students at UW-Madison. In 1979, he was in the first class of preschoolers in the Waisman Early Childhood Program, which today reserves a third of its enrollment for children with developmental disabilities. When David was 8, the family moved to Virginia, where they still live.
John Egan, whose degree was in physics, said silencing of the extra chromosome 21 should “of course” be pursued. “If you did it, I’m not sure it would be magical, but I think a lot of the problems that Down syndrome people have could be corrected,” he said.
Kathleen Egan, David’s mother, said the focus should be on improving education and the childhood environment for people with Down syndrome. Trained in psychology and education, she said the condition “is not an obstacle for a happy and productive life.”
In 2020, David published a book, “More Alike than Different: My Life with Down Syndrome,” with assistance from his mother. He has testified before Congress and worked at a nonprofit. Despite struggling with lingering complications of COVID-19 the past year, David spoke in Madison Oct. 12 at an event celebrating the Waisman Center’s 50th anniversary.
In an interview, he said he is not sure what to think about drugs that might reduce intellectual disability in Down syndrome. “There’s no proven way of knowing what to expect,” he said. “It can be very complicated.”
In monthly lab meetings for the brain atlas project, potential treatments for Down syndrome seem far off. In a sixth-floor conference room at the Waisman Center, which overlooks campus soccer and lacrosse fields next to the UW Hospital complex on Madison’s West Side, the scientists talk about tools and techniques to study their tissue and cells.
How can they coax their stem cells to produce more outer radial glia, cells that give rise to upper layers of the cerebral cortex, thought to be affected in Down syndrome? How do they analyze terabytes of data from gene sequencing of different kinds of brain cells in their tissue samples? How do they find the time to train graduate students to do patch-sequencing, a new way of recording the electrical activity of individual cells? It requires delicate handling of a pipette.
“It’s probably the hardest technique in biology to learn,” said André Sousa, an assistant professor of neuroscience on the team. “You need to have very good hands.”
Daifeng Wang, an associate professor of biostatics and medical informatics, is the fourth faculty member involved. He has worked on Psych Encode, a federal database of genetic influences on psychiatric conditions such as autism, bipolar disorder and schizophrenia. The database, culled from samples from adults, is similar to what the Madison team is trying to assemble prenatally for Down syndrome.
“I do all the data magic,” Wang said of his role in the brain atlas.
Bhattacharyya said she was drawn to Down syndrome research because of the biological puzzle it presents. People with the disorder have a third more of the 350 or more genes on chromosome 21, an extra load that has a cascade effect on the body, accounting for features from almond-shaped eyes and short stature to poor muscle tone and a higher risk of hearing loss.
But, unlike with some neurological conditions, people with Down syndrome can communicate, hold jobs, have relationships and live well into their 60s or 70s.
Despite the extra genes, “so much goes right,” Bhattacharyya said. “If someone had asked me, ‘If you put a whole extra chromosome into a cell, how would that person develop?’ I wouldn’t have expected someone to be as functional as people with Down syndrome are.”
The brain atlas will focus on the prefrontal cortex, the area behind the forehead and eyes that controls planning and decision making. The project may eventually include areas in the core of the brain, such as the striatum, involved in voluntary movement.
Bhattacharyya acknowledges the therapeutic potential of the information the atlas will provide. But she said she’s cautious about how it’s used.
For now, “we don’t have enough knowledge to know how to treat,” she said. “I’m not a proponent of, ‘Let’s find a drug to do something in Down syndrome’ until we know what the target is.”
© 2023 The Wisconsin State Journal
Distributed by Tribune Content Agency, LLC
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