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DNA

International collaboration discovers new cause for dwarfism

DNA

An international collaboration resulted in the identification of a new cause of dwarfism: mutations in a gene known as DNMT3A.

Beyond diabetes, short stature is the most common reason for children in the U.S. to visit an endocrinologist. For the vast majority of children with short stature, the cause remains unknown – even though many of these conditions stem from an as-yet unidentified genetic cause, says Andrew Dauber, M.D., M.M.Sc., division chief of Endocrinology at Children’s National Health System.

“Parents are concerned about why their child isn’t growing and if there are other complications or health problems they’ll need to watch out for,” he says. “Without a diagnosis, it’s very hard to answer those questions.”

Dauber’s research focuses on using cutting-edge genetic techniques to unravel the minute differences in DNA that limit growth. This research recently led him and his colleagues to identify a new cause of dwarfism: mutations in a gene known as DNMT3A. The discovery, which the team published in the January 2019 Nature Genetics, didn’t happen in isolation – it required a rich collaboration of labs spread across the world in Scotland, Spain, France and New Zealand, in addition to Dauber’s lab in the U.S.

The journey that brought Dauber into this group effort got its start with a young patient in Spain. The boy, then four years old, was at less than 0.1 percentile on the growth curve for height with a very small head circumference and severe developmental delays. This condition, known as microcephalic dwarfism, is incredibly rare and could stem from one of several different genetic causes. But his doctors didn’t know the reason for this child’s specific syndrome.

To better understand this condition, Dauber used a technique known as whole exome sequencing, a method that sequences all the protein-coding regions in an individual’s entire genome. He found a mutation in DNMT3A – a change known as a de novo missense mutation, meaning that the mutation happened in a single letter of the boy’s genetic code in a way that hadn’t been inherited from his parents. But although this mutation was clear, its meaning wasn’t. The only clue that Dauber had as to DNMT3A’s function was that he’d read about overgrowth syndromes in which the function of this gene is lost, leading to large individuals with large heads, the exact opposite of this patient’s condition.

To gather more information, Dauber reached out to Andrew Jackson, Ph.D., a researcher who studies human genes for growth at the University of Edinburgh in Scotland. Coincidentally, Jackson had already started studying this gene after two patients with a shared mutation in a neighboring letter in the genetic code – who also had short stature and other related problems – were referred to him.

Dauber and his colleagues sent the results from their genetic analysis back across the Atlantic to Jackson’s Edinburgh lab, and the doctors from Spain sent more information to Jackson’s lab, including the patient’s clinical information, blood samples and skin biopsy samples. Then the whole team of collaborators from around the globe set to work to discover the processes influencing short stature in each of these three patients.

Their results showed that these mutations appear to cause a gain of function in DNMT3A. This gene codes for a type of enzyme known as a methyltransferse, which places methyl groups on other genes and on the protein spools called histones that DNA wraps around. Each of these functions changes how cells read the instructions encoded in DNA. While the mutations that cause the overgrowth syndromes appear to allow stem cells to keep dividing long past when they should taper off and differentiate into different cell types – both normal processes in development – the gain of function that appears to be happening in these three patients prompts the opposite situation: Stem cells that should be dividing for a long time during development stop dividing and differentiate earlier, leading to smaller individuals with far fewer cells overall.

The researchers confirmed their findings by inserting one of the gain-of-function human DNMT3A mutations into a mouse, leading to short animals with small heads.

Eventually, says Dauber, these findings could help lead to new treatments for this and other types of dwarfism that act on these genetic pathways and steer them toward normal growth. These and other scientific discoveries hinge on the type of international collaboration that he and his colleagues engaged in here, he adds – particularly for the types of rare genetic syndromes that affect the patients that he and his colleagues study. With only a handful of individuals carrying mutations in certain genes, it’s increasingly necessary to combine the power of many labs to better understand the effects of these differences and how doctors might eventually intervene.

“The expertise for all aspects of any single research project is rarely centered in one institution, one city, or even one country,” Dauber says. “Often, you really need to reach out to people with different areas of expertise around the world to make these types of new discoveries that can have pivotal impacts on human health.”

zika virus

Will the Zika epidemic re-emerge in 2017?

Anthony Fauci

Anthony S. Fauci, M.D., director of the National Institute of Allergy and Infectious Diseases at the National Institutes of Health, discussed the possibility of a reemergence of Zika virus at Children’s National Research and Education Week.

Temperatures are rising, swelling the population of Aedes mosquitoes that transmit the Zika virus and prompting an anxious question: Will the Zika epidemic re-emerge in 2017?

Anthony S. Fauci, M.D., director of the National Institute of Allergy and Infectious Diseases at the National Institutes of Health (NIH), sketched out contrasting scenarios. Last year in Puerto Rico, at least 13 percent of residents were infected with Zika, “a huge percentage of the population to get infected in any one outbreak,” Dr. Fauci says. But he quickly adds: “That means that 87 percent of the population” did not get infected. When the chikungunya virus swept through the Caribbean during an earlier outbreak, it did so in multiple waves. “We are bracing for a return of Zika, but we shall see what happens.” Dr. Fauci says.

When it comes to the continental United States, however, previous dengue and chikungunya outbreaks were limited to southern Florida and Texas towns straddling the Mexican border. Domestic Zika transmission last year behaved in much the same fashion.

“Do we think we’re going to get an outbreak [of Zika] that is disseminated throughout the country? The answer is no,” Dr. Fauci adds. “We’re not going to see a major Puerto Rico-type outbreak in the continental United States.”

Dr. Fauci’s remarks were delivered April 24 to a standing-room-only auditorium as part of Research and Education Week, an annual celebration of the cutting-edge research and innovation happening every day at Children’s National. He offered a sweeping, fact-filled summary of Zika’s march across the globe: The virus was first isolated from a primate placed in a treehouse within Uganda’s Zika forest to intentionally become infected; Zika lurked under the radar for the first few decades, causing non-descript febrile illness; it bounced from country to country, causing isolated outbreaks; then, it transformed into an infectious disease of international concern when congenital Zika infection was linked to severe neural consequences for babies born in Brazil.

zika virus

Zika virus lurked under the radar for several decades, causing non-descript febrile illness; it bounced from country to country, resulting in isolated outbreaks; then, it transformed into an infectious disease of international concern.

“I refer to Brazil and Zika as the perfect storm,” Dr. Fauci told attendees. “You have a country that is a large country with a lot of people, some pockets of poverty and economic depression –  such as in the northeastern states –  without good health care there, plenty of Aedes aegypti mosquitoes and, importantly, a totally immunologically naive population. They had never seen Zika before. The right mosquitoes. The right climate. The right people. The right immunological status. And then, you have the explosion in Brazil.”

In Brazil, 139 to 175 babies were born each year with microcephaly – a condition characterized by a smaller than normal skull – from 2010 to 2014. From 2015 through 2016, that sobering statistic soared to 5,549 microcephaly cases, 2,366 of them lab-confirmed as caused by Zika.

Microcephaly “was the showstopper that changed everything,” says Dr. Fauci. “All of a sudden, [Zika] went from a relatively trivial disease to a disease that had dire consequences if a mother was infected, particularly during the first trimester.”

As Zika infections soared, ultimately affecting more than 60 countries, the virus surprised researchers and clinicians a number of times, by:

  • Being spread via sex
  • Being transmitted via blood transfusion, a finding from Brazil that prompted the Food and Drug Administration to recommend testing for all U.S. donated blood and blood products
  • Decimating developing babies’ neural stem cells and causing a constellation of congenital abnormalities, including vision problems and contractions to surviving infants’ arms and legs
  • Causing Guillain-Barré syndrome
  • Triggering transient hearing loss
  • Causing myocarditis, heart failure and arrhythmias

When it comes to the U.S. national response, Dr. Fauci says one of the most crucial variables is how quickly a vaccine becomes available to respond to the emerging outbreak. For Zika, the research community was able to sequence the virus and launch a Phase I trial in about three months, “the quickest time frame from identification to trial in the history of all vaccinology,” he adds.

Zika is a single-stranded, enveloped RNA virus that is closely related to dengue, West Nile, Japanese encephalitis and Yellow fever viruses, which gives the NIH and others racing to produce a Zika vaccine a leg up. The Yellow fever vaccine, at 99 percent effectiveness, is one of the world’s most effective vaccines.

“I think we will wind up with an effective vaccine. I don’t want to be over confident,” Dr. Fauci  says. “The reason I say I believe that we will is because [Zika is] a flavivirus, and we have been able to develop effective flavivirus vaccines. Remember, Yellow fever is not too different from Zika.”

Sarah Mulkey Columbia Zika Study

Damage may lurk in “normal” Zika-exposed brains

Sarah Mulkey Columbia Zika Study

An international study that includes Sarah B. Mulkey, M.D., Ph.D., aims to answer one of the most vexing questions about Zika: If babies’ brains appear “normal” at birth, have they survived Zika exposure in the womb with few neurological repercussions? Dr. Mulkey presented preliminary findings at PAS2017.

It has been well established by researchers, including scientists at Children’s National Health System, that the Zika virus is responsible for a slew of birth defects – such as microcephaly, other brain malformations and retinal damage – in babies of infected mothers. But how the virus causes these often devastating effects, and who exactly is affected, has not been explained fully.

Also unknown is whether exposed babies that appear normal at birth are truly unaffected by the virus or have hidden problems that might surface later. The majority of babies born to Zika-infected mothers in the United States appear to have no evidence of Zika-caused birth defects, but that’s no guarantee that the virus has not caused lingering damage.

Recently, Sarah B. Mulkey, M.D., Ph.D., made a trip to Colombia, where Children’s National researchers are collaborating on a clinical study. There, she tested Zika-affected babies’ motor skills as they sat, stood and lay facing upward and downward. The international study aims to answer one of the most vexing questions about Zika: If babies’ brains appear “normal” at birth, have they survived Zika exposure in the womb with few neurological repercussions?

“We don’t know the long-term neurological consequences of having Zika if your brain looks normal,” says Dr. Mulkey, a fetal-neonatal neurologist who is a member of Children’s Congenital Zika Virus Program. “That is what’s so scary, the uncertainty about long-term outcomes.”

According to the Centers for Disease Control and Prevention (CDC), one in 10 pregnancies across the United States with laboratory-confirmed Zika virus infection results in birth defects in the fetus or infant. For the lion’s share of Zika-affected pregnancies, then, babies’ long-term prospects remain a mystery.

“This is a huge number of children to be impacted and the impact, as we understand, has the potential to be pretty significant,” Dr. Mulkey adds.

Dr. Mulkey, the lead author, presented the research group’s preliminary findings during the 2017 annual meeting of the Pediatric Academic Societies (PAS). The presentation was one of several that focused on the Zika virus. Roberta L. DeBiasi, M.D., M.S., chief of the Division of Pediatric Infectious Diseases at Children’s National, organized two invited symposia devoted to the topic of Zika: Clinical perspectives and knowledge gaps; and the science of Zika, including experimental models of disease and vaccines. Dr. DeBiasi’s presentation included an overview of the 68 Zika-exposed or infected women and infants seen thus far by Children’s multidisciplinary Congenital Zika Virus Program.

“As the world’s largest pediatric research meeting, PAS2017 is an ideal setting for panelists to provide comprehensive epidemiologic and clinical updates about the emergence of Congenital Zika Syndrome and to review the pathogenesis of infection as it relates to the fetal brain,” Dr. DeBiasi says. “With temperatures already rising to levels that support spread of the Aedes mosquito, it is imperative for pediatricians around the world to share the latest research findings to identify the most effective interventions.”

As one example, Dr. Mulkey’s research sought to evaluate the utility of using magnetic resonance imaging (MRI) to evaluate fetal brain abnormalities in 48 babies whose mothers had confirmed Zika infection during pregnancy. Forty-six of the women/infant pairs enrolled in the prospective study are Colombian, and two are Washington, D.C. women who were exposed during travel to a Zika hot zone.

The women were infected with Zika during all three trimesters and experienced symptoms at a mean gestational age of 8.4 weeks. The first fetal MRIs were performed as early as 18 weeks’ gestation. Depending upon the gestational age when they were enrolled in the study, the participants had at least one fetal MRI as well as serial ultrasounds. Thirty-six fetuses had a second fetal MRI at about 31.1 gestational weeks. An experienced pediatric neuroradiologist evaluated the images.

Among the 48 study participants, 45 had “normal” fetal MRIs.

Three fetuses exposed to Zika in the first or second trimester had abnormal fetal MRIs:

  • One had heterotopia and an early, abnormal fold on the surface of the brain, indications that neurons did not migrate to their anticipated destination during brain development. This pregnancy was terminated at 23.9 gestational weeks.
  • One had parietal encephalocele, a rare birth defect that results in a sac-like protrusion of the brain through an opening in the skull. According to the CDC, this defect affects one in 12,200 births, or 340 babies, per year. It is not known if this rare finding is related to Zika infection.
  • One had a thin corpus callosum, dysplastic brainstem, heterotopias, significant ventriculomegaly and generalized cerebral/cerebellar atrophy.

“Fetal brain MRI detected early structural brain changes in fetuses exposed to the Zika virus in the first and second trimester,” Dr. Mulkey says. “The vast majority of fetuses exposed to Zika in our study had normal fetal MRI, however. Our ongoing study, underwritten by the Thrasher Research Fund, will evaluate their long-term neurodevelopment.”

Adré J. du Plessis, MB.Ch.B., M.P.H., director of the Fetal Medicine Institute and senior author of the paper, notes that this group “is a very important cohort to follow as long as Dr. Mulkey’s funding permits. We know that microcephaly is among the more devastating side effects caused by Zika exposure in utero. Unanswered questions remain about Zika’s impact on hearing, vision and cognition for a larger group of infants. Definitive answers only will come with long-term follow-up.”

Many of the Colombian families live in Sabanalarga, a relatively rural, impoverished area with frequent rain, leaving pockets of fresh water puddles that the mosquito that spreads Zika prefers, Dr. Mulkey adds. Families rode buses for hours for access to fetal MRI technology, which is not common in Colombia.

“The mothers are worried about their babies. They want to know if their babies are doing OK,” she says.