Stories about: Division of Genetics and Genomics

Gene active before birth regulates brain folding, speech motor development

SCN3A, linked to polymicrogyria, regulates speech motor development
ILLUSTRATIONS: RICHARD SMITH/BOSTON CHILDREN’S HOSPITAL

A handful of families from around the world with a rare brain malformation called polymicrogyria have led scientists to discover a new gene that helps us speak and swallow.

The gene, SCN3A, is turned “on” primarily during fetal brain development. When it’s mutated, a language area of the brain known as the perisylvian cortex develops multiple abnormally small folds, appearing bumpy. People with polymicrogyria in this region often have impaired oral motor development, including difficulties with swallowing, tongue movement and articulating words — especially if the polymicrogyria affects both sides of the brain.

The new study, published today in Neuron, ties together human genetics, measurements of electrical currents generated by neurons, studies of ferrets and more to start to connect the dots between SCN3A, the brain malformation and the oral motor impairment.

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Gene mutation in children with microcephaly reveals an essential ingredient for brain development

This electron microscope image shows two multivesicular bodies in the dendrites of neighboring neurons in the cerebellum of a normal mouse. Each contains vesicles bearing sonic hedgehog. (Michael Coulter/Boston Children’s Hospital)

In 2012, researchers in the Boston Children’s Hospital lab of Christopher Walsh, MD, PhD, reported a study of three unrelated families that had children with microcephaly. All had smaller-than-normal brains — both the cerebrum and the cerebellum were reduced in size— and all had mutations that knocked out the function of a gene called CHMP1A.

It was clear that CHMP1A is needed for the brain to grow to its proper dimensions. But the study stopped there.

“Then I came along, and my goal was to figure out what this gene is doing in brain during development, and why, when you lose it, you have a small brain,” says Michael Coulter, MD, PhD, who joined the Walsh lab as a student in 2012.

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Phenylketonuria without the ‘phe’: Enzyme therapy offers chance at a better life

Kaylee Goodwin credits pegvaliase for changing her life — including her engagement.
Kaylee Goodwin credits pegvaliase for changing her life — including her engagement. “It’s to the point where I don’t even think I have PKU anymore,” she says.

Kaylee Goodwin, 29, has struggled her whole life to control her blood levels of “phe” — the amino acid known as phenylalanine. “I was told that if my levels were controlled, I would be able to think more clearly and feel better overall,” she says.

Goodwin was born with phenylketonuria (PKU), a genetic metabolic disorder affecting roughly 1 in 16,000 newborns. Her body can’t break down phe because of a genetic mutation disabling the necessary enzyme, phenylalanine hydroxylase (PAH).

If left untreated, phe accumulates in the brain, causing intellectual disability and seizures. But starting in the early 1960s, newborn screening programs have been able to test for PKU. Goodwin tested positive and was prescribed a special phe-free diet by Harvey Levy, MD, at Boston Children’s Hospital.

Through the diet, Goodwin has dodged serious brain damage and was able to attend college and start a career as a dancer and actress. But because phe is in nearly all naturally occurring proteins, she couldn’t eat meat, eggs, dairy products, legumes, most grains and many fruits and vegetables. Instead, she had to consume a foul-tasting amino acid formula.

“I spent my entire life carrying special foods and medical formula around with me, and weighing and measuring foods,” she says.

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Mutant ferrets and kids with microcephaly shed light on brain evolution

ASPM, ferrets, microcephaly and brain evolution
Fawn Gracey illustration

Mouse brains are tiny and smooth. Ferret brains are larger and convoluted. And ferrets, members of the weasel family, could provide the missing link in understanding how we humans acquired our big brains.

Children with microcephaly, whose brains are abnormally small, have a part in the story too. Microcephaly is notorious for its link to the Zika virus, but it can also be caused by mutations in various genes. Some of these genes have been shown to be essential for growth of the cerebral cortex, the part of our brain that handles higher-order thinking.

Reporting in Nature today, a team led by Christopher A. Walsh, MD, PhD, of Boston Children’s Hospital and Byoung-Il Bae, PhD, at Yale University, inactivated the most common recessive microcephaly gene, ASPM, in ferrets. This replicated microcephaly and allowed the team to study what regulates brain size.

“I’m trained as a neurologist, and study kids with developmental brain diseases,” said Walsh in a press release from the Howard Hughes Medical Institute, which gave him a boost to his usual budget to support this work. “I never thought I’d be peering into the evolutionary history of humankind.”

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Mutations accumulate in our brain cells as we age. Do they explain cognitive loss?

the aging brain - do DNA mutations in neurons account for cognitive loss?

Scientists have long wondered whether somatic, or non-inherited, mutations play a role in aging and brain degeneration. But until recently, there was no good technology to test this idea.

Enter whole-genome sequencing of individual neurons. This fairly new technique has shown that our brain cells have a great deal of DNA diversity, making neurons somewhat like snowflakes. In a study published online today in Science, the same single-neuron technique provides strong evidence that our brains acquire genetic mutations over time.

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“Omics” study takes a comprehensive look at premature birth

Seven layers of omics study
Seven layers of “omics” included in the PREM-MAP study

Every year, one in 10 new babies in the United States is born preterm, or before 37 weeks of gestation. With the last few weeks of pregnancy crucial to proper development of the lungs and brain, prematurely born infants can suffer lifelong problems.

Now scientists at Boston Children’s Hospital and Beth Israel Deaconess Medical Center have launched a comprehensive study to understand the reasons and risk factors for premature births. Earlier this year, Olaf Bodamer, MD, PhD was awarded a grant for this work from uBiome, a microbial genomics company.

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Late-breaking mutations may play an important role in autism

somatic mutations in autism may occur at different times in the embryo
Post-zygotic mutations, which arise spontaneously in an embryonic cell after sperm meets egg, are important players in autism spectrum disorder, a large study suggests.

Over the past decade, mutations to more than 60 different genes have been linked with autism spectrum disorder (ASD), including de novo mutations, which occur spontaneously and aren’t inherited. But much of autism still remains unexplained.

A new study of nearly 6,000 families implicates a hard-to-find category of de novo mutations: those that occur after conception, and therefore affect only a subset of cells. Findings were published today in Nature Neuroscience.

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What genetic changes gave us the human brain? A $10 million center aims to find out

genes and human brain evolution

How did our distinctive brains evolve? What genetic changes, coupled with natural selection, gave us language? What allowed modern humans to form complex societies, pursue science, create art?

While we have some understanding of the genes that differentiate us from other primates, that knowledge cannot fully explain human brain evolution. But with a $10 million grant to some of Boston’s most highly evolved minds in genetics, genomics, neuroscience and human evolution, some answers may emerge in the coming years.

The Seattle-based Paul G. Allen Frontiers Group today announced the creation of an Allen Discovery Center for Human Brain Evolution at Boston Children’s Hospital and Harvard Medical School. It will be led by Christopher A. Walsh, MD, PhD, chief of the Division of Genetics and Genomics at Boston Children’s and a Howard Hughes Medical Institute investigator.

“To understand when and how our modern brains evolved, we need to take a multi-pronged approach that will reflect how evolution works in nature, and identifies how experience and environment affect the genes that gave rise to modern human behavior,” Walsh says.

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Two resilient dogs point to new targets for Duchenne muscular dystrophy

Duchenne muscular dystrophy protective genes
Suflair, at right, is alive and well at 11 years despite having the DMD mutation (courtesy Natássia Vieira)

Two golden retrievers that had the genetic mutation for Duchenne muscular dystrophy (DMD), yet remained healthy, have offered up yet another lead for treating this muscle-wasting disorder.

For several years, Natássia Vieira, PhD, of the University of São Paolo, also a fellow in the Boston Children’s Hospital lab of Louis Kunkel, PhD, has been studying a Brazilian colony of golden retrievers. All have the classic DMD mutation and, as expected, most of these dogs are very weak and typically die by 2 years of age. That’s analogous to children with DMD, who typically lose the ability to walk by adolescence and die from cardiorespiratory failure by young adulthood.

But two dogs appeared unaffected. Both ran around normally. The elder dog, Ringo, lived a full lifespan, and his son Suflair is still alive and well at age 11.

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