Tag Archive for: Corbin

Histological section of a brain.

Study finds new genetic cause of neurodevelopmental disorders

Histological section of a brain.

Nissel staining of pre-clinical model brain.

A cross-disciplinary team of researchers and physicians from Children’s National Hospital and Washington University School of Medicine in St. Louis, in collaboration with physicians from around the world, identified a new genetic cause of neurodevelopmental disorders (NDDs). In a new study published in the American Journal of Human Genetics, researchers found 14 unrelated patients with 15 different sequence variants in HECTD1 – 10 missense, 3 frameshift, 1 nonsense and 1 splicing variant – with NDDs, including autism, attention-deficit/hyperactivity disorder (ADHD) and epilepsy.

Moving the field forward

Many patients suspected of having a genetic disorder remain undiagnosed. In about 10% of these cases, the genetic change is in a gene unknown to cause the disorder.

“Describing a new genetic cause of neurodevelopmental disorders will allow for the characterization of the gene’s role in brain development, the genetic syndrome and the mechanisms of disease,” says Irene Zohn, PhD, principal investigator in the Center for Genetic Medicine Research at Children’s National and co-lead of the study. “This information will lead to developing treatments to improve the lives of patients.”

The patient benefit

“Our study represents the first report of HECTD1 in NDDs,” says Dr. Zohn. “Now that this gene is linked to the disorder, clinicians with patients with sequence variation in this gene can enroll in studies to understand this new HECTD1 syndrome.”

Proper genetic diagnosis is important so that comorbidities and the natural history of the disorder can be described, which will lead to improvements in patient care.

What we hope to discover

Now that a new genetic syndrome has been defined, researchers hope to establish how prevalent the syndrome is and describe its features. Using pre-clinical models, they’ll continue to study the developmental basis of the disorder and the molecular mechanisms to develop therapies.

Children’s National leads the way

The HECTD1 gene was discovered in Dr. Zohn’s laboratory, and her research team connected with Christina Gurnett, MD, PhD, co-lead of the study from Washington University School of Medicine, to link this gene to human disease.

Additional authors from Children’s National include – Elias Oxman, Keito Ishibashi, Sonia Sebaoui, Kathryn Luedtke, Bryce Winrow, Seth Berger, MD, PhD, Christina L. Grant, MD, PhD, and Joshua Corbin, PhD.

You can read the full study Sequence Variants in HECTD1 Result in a Variable Neurodevelopmental Disorder in the American Journal of Human Genetics.

The cover of Trends in Neurosciences

Review: New insights into brain development and behavior

The cover of Trends in Neurosciences

A recent review by researchers at Children’s National, published in Trends in Neurosciences, offers a new and in-depth understanding of how the amygdala is formed during fetal developmental.

The medial amygdala (MeA) is a central structure of the brain for regulation of social and emotional behaviors. Amygdala dysfunction is associated with a host of developmental conditions including autism spectrum disorders (ASD), post-traumatic stress disorder (PTSD) and the consequences of early life stress. To date, there has been a lack of comprehensive understanding of how the amygdala forms developmentally.

A recent review by researchers at Children’s National Hospital, published in Trends in Neurosciences, offers a new and in-depth understanding of how this complex structure is formed during fetal developmental and the role it plays in social behavior.

“This extensive review conveys the latest findings on how the amygdala is formed from development across preclinical models and humans,” says Joshua Corbin, PhD, interim director of the Center for Neuroscience Research at Children’s National and lead author of the review. “Past and present work in our lab has contributed critical knowledge of how this important structure forms from development and implications for human conditions.”

Moving the field forward

Malformation of the amygdala is a hallmark feature of disorders of social cognition such as ASD. Additionally, amygdala development is highly susceptible to early life stress and influences altered fear and anxiety responses in individuals who have been faced with early life stress.

“Despite our growing understanding of MeA development and its role in behavior, many critical questions remain. However, with cutting-edge tools like transcriptomic profiling, subcircuit-level circuit mapping, CRISPR mutagenesis and targeted gene delivery, we’re on the brink of uncovering different neurons in the amygdala form and shape social behaviors,” says Dr. Corbin.

Children’s National leads the way

Dr. Corbin’s team is among only a handful of groups in the world focused on understanding amygdala development. Investigators within the Center for Neuroscience Research at Children’s National have a shared goal of understanding the biological underpinnings of neurodevelopmental disorders.

You can read the full review published in Trends in Neurosciences. 

Hands holding letters that spell autism

Gene associated with autism affects social interactions differently in males and females

Hands holding letters that spell autism

The loss function of a gene associated with autism spectrum disorder (ASD), Foxp2, impacts brain circuits that control olfactory processing, social interaction, mating, aggressive and parental behaviors in a pre-clinical model. Sex differences were most notable in females with low social interaction and higher aggression behavior compared to males, suggesting ASD-like behavior in females, according to the study published in Frontiers in Behavioral Neuroscience.

ASD affects social communication and behavior in approximately 1 in 68 people, many of the symptoms appear in the first two years of life, and the disorder is mostly seen in males. Recent studies suggest that FOXP2 mutations have been implicated in a subset of individuals with ASD.

“Our work provides insights into how this gene may function mechanistically to control social interactions in both males and females,” said Joshua Corbin, Ph.D., principal investigator at Children’s National Hospital and senior author. “Foxp2 is an autism susceptibility gene, thus potentially revealing insights into the neurobiological underpinnings of deficits in social communication in neurodevelopmental disorders.”

Dopamine (DA) also plays a role in motivation and reward-seeking behavior. Herrero et al. further found that patterns of Foxp2+ cell activation in the amygdala, a structure involved in social motivation, differed in females and males in response to DA, with greater activation in females. Although how this ties together with the function of Foxp2 in social behavior remains to be elucidated, this finding suggests an intriguing link between this important neuropeptide and Foxp2 function.

FOXP2 mutations in humans are associated with disorders affecting speech and language. The scientific community has extensively studied the Foxp2 gene in other brain regions, most notably those involved in language production, such as the cerebral cortex and basal ganglia (striatum). Still, little is known regarding the function of Foxp2 in male or female social behavior, which has a large amygdala component.

“Rational interventions for human disorders and diseases relies on an understanding of the underlying biology of these conditions,” said Corbin. “Our work presents an important step toward elucidating the genetic pathways required for neurotypical social behavior.”

To better understand the role that Foxp2 plays in the amygdala-linked social behaviors, the researchers used a comprehensive panel of behavioral tests in male and female subjects. The research team relied on visual observation and video recordings to collect and score the behavioral data, work that was conducted as part of Children’s National NIH funded DC-IDDRC.

The set of behavioral tests included a “social interaction assay” that utilized a 3-chamber device, an “olfactory habituation and discrimination assay,” which pooled several odors with a cotton swab and a “maternal aggression assay” that measured aggressive encounters of a lactating female to a male intruder.

The researchers also compared the ex vivo tissue samples of female and male subjects to assess protein changes in the amygdala that might affect the activation of DA pathways.

illustration of the amygdaloid body

Research reveals physiological sex differences in medial amygdala neurons

illustration of the amygdaloid body

The medial amygdala (MeA) is a region of the brain that modulates innate social and non-social behaviors in several mammals, including humans.

The medial amygdala (MeA) is a region of the brain that modulates innate social and non-social behaviors in several mammals, including humans. Notedly sexually dimorphic, MeA neurons exhibit well-documented sex differences in anatomy, morphology and molecular characteristics. Recently, a pioneer study published in eNeuro from the Children’s National Hospital Center for Neuroscience Research has unveiled new information regarding physiological sex differences in MeA neurons, which, until now, has remained a missing piece in understanding how the MeA codes differently in males and females.

Previous research from Children’s National has shown that two subpopulations of MeA inhibitory output neurons descended from Dbx1 and Foxp2 transcription factors display different responses to innate olfactory cues and in a sex-specific manner. The newest study examines whether these transcription factor defined neurons also possess sex-specific biophysical signatures. The scientists posit that understanding how sex and lineage impact upstream differences at the neuronal level can help illuminate how the MeA processes information and codes for sex-specific behavioral differences.

Using whole-cell patch clamp recording and stepwise current injection, the researchers were able to analyze the intrinsic electrophysiological profiles of the two subclasses of MeA neurons in males and females in a pre-clinical model. Data revealed that the spike frequency of Dbx1-lineage and Foxp2-lineage neurons differed by lineage, sex and stimulus strength. Dbx1-lineage neurons in females discharged more spikes than those in males during high-amplitude current injection, while Foxp2-lineage neurons in females discharged more spikes than those in males during low-amplitude current injection. Across lineage, researchers observed that Dbx1-lineage neurons discharged more spikes than Foxp2-lineage neurons in females, but only at the highest amplitude stimulus, while Dbx1-lineage neurons spiked more than Foxp2-lineage neurons in males during low rather than high-amplitude current injection.

Different spiking patterns are generally indicative of different intrinsic cell properties. However, this study found that the intrinsic properties of the cell – such as membrane potential, resistance, and rheobase – were the same at rest across sex and lineage. The only significant difference was found in capacitance, an electrical measurement that roughly corresponds with cell size. Additionally, the study found that spike frequency adaptation correlated with neuronal lineage and sex, with males having a higher adaptation factor than females and Foxp2-lineage neurons displaying a higher adaptation factor than Dbx1-lineage neurons. In tandem, these results indicated that changes in the intrinsic properties were taking place during stimulation.

The researchers then used waveform phase-plots to visualize phases of the different action potentials and contrived an innovative new method of analyzing these quantitatively instead of solely qualitatively. This allowed them to know that broadly, ion channels that work with repolarization are likely different, and prompted them to focus on the family of ion channels that are known to modify the repolarization phase. From 62 candidate ion channels, the researchers chose 10 to investigate. Experiments ultimately revealed that only one ion channel was found to exhibit statistically significant sex differences in the Foxp2 population. This result indicated that molecular expression of these ion channels are likely driving differences in the physiology of the cells which may be the basis of behavioral expression. Future research topics include how and when sex hormones shape MeA neuronal firing properties and how this relates to network function.

“This is a small piece of contribution to the overall understanding of how the brain as a biological machine codes for different outputs,” says first author Heidi Y. Matos, Ph.D.

By showing sex differences in neural function, this research represents progress in understanding the biological underpinnings of a host of developmental disorders, particularly those diagnosed in different proportions between males and females. Autism spectrum disorders, for example, often have symptoms that manifest through social interaction, and understanding these disorders requires a better understanding of normal MeA physiology.

“In order to get to the why, we have to get to the how of that circuit,” says Dr. Matos.

Just as the brain harnesses the collective power of a diverse range of neurons, the Center for Neuroscience harnesses the aggregate talent of a diverse group of neuroscientists to produce innovative work. This study in particular champions diversity in the sciences, with more than half of the authors coming from underrepresented minorities, including Dr. Matos.

“I think this work is a shining example of the tremendous contributions that are made by neuroscientists from all backgrounds,” says principal investigator Joshua G. Corbin, Ph.D.

“Sex Differences in Biophysical Signatures across Molecularly Defined Medial Amygdala Neuronal Subpopulations” was published in eNeuro. Additional authors include David Hernandez-Pineda, Claire M. Charpentier, Allison Rusk and Kevin S. Jones, Ph.D.

DNA moleucle

PAC1R mutation may be linked to severity of social deficits in autism

DNA moleucle

A mutation of the gene PAC1R may be linked to the severity of social deficits experienced by kids with autism spectrum disorder (ASD), finds a study from a multi-institutional research team led by Children’s National faculty. If the pilot findings are corroborated in larger, multi-center studies, the research published online Dec. 17, 2018, in Autism Research represents the first step toward identifying a potential novel biomarker to guide interventions and better predict outcomes for children with autism.

As many as 1 in 40 children are affected by ASD. Symptoms of the disorder – such as not making eye contact, not responding to one’s name when called, an inability to follow a conversation of more than one speaker or incessantly repeating certain words or phrases – usually crop up by the time a child turns 3.

The developmental disorder is believed to be linked, in part, to disrupted circuitry within the amygdala, a brain structure integral for processing social-emotional information. This study reveals that PAC1R is expressed during key periods of brain development when the amygdala – an almond-shaped cluster of neurons – develops and matures. A properly functioning amygdala, along with brain structures like the prefrontal cortex and cerebellum, are crucial to neurotypical social-emotional processing.

“Our study suggests that an individual with autism who is carrying a mutation in PAC1R may have a greater chance of more severe social problems and disrupted functional brain connectivity with the amygdala,” says Joshua G. Corbin, Ph.D., interim director of the Center for Neuroscience Research at Children’s National Health System and the study’s co-senior author. “Our study is one important step along the pathway to developing new biomarkers for autism spectrum disorder and, hopefully, predicting patients’ outcomes.”

The research team’s insights came through investigating multiple lines of evidence:

  • They looked at gene expression in the brains of an experimental model at days 13.5 and 18.5 of fetal development and day 7 of life, dates that correspond with early, mid and late amygdala development. They confirmed that Pac1r is expressed in the experimental model at a critical time frame for brain development that coincides with the timing for altered brain trajectories with ASD.
  • They looked at gene expression in the human brain by mining publicly available genome-wide transcriptome data, plotting median PAC1R expression values for key brain regions. They found high levels of PAC1R expression at multiple ages with higher PAC1R expression in male brains during the fetal period and higher PAC1R expression in female brains during childhood and early adulthood.
  • One hundred twenty-nine patients with ASD aged 6 to 14 were recruited for behavioral assessment. Of the 48 patients who also participated in neuroimaging, 20 were able to stay awake for five minutes without too much movement as the resting state functional magnetic resonance images were captured. Children who were carriers of the high-risk genotype had higher resting-state connectivity between the amygdala and right posterior temporal gyrus. Connectivity alterations in a region of the brain involved in processing visual motion may influence how kids with ASD perceive socially meaningful information, the authors write.
  • Each child also submitted a saliva sample for DNA genotyping. Previously published research finds that a G to C single nucleotide polymorphism, a single swap in the nucleotides that make up DNA, in PAC1R is associated with higher risk for post traumatic stress disorder in girls. In this behavioral assessment, the research team found children with autism who carried the homozygous CC genotype had higher scores as measured through a validated tool, meaning they had greater social deficits than kids with the heterozygous genotype.

All told, the project is the fruit of six years of painstaking research and data collection, say the researchers. That includes banking patients’ saliva samples collected during clinical visits for future retrospective analyses to determine which genetic mutations were correlated with behavioral and functional brain deficits, Corbin adds.

“Lauren Kenworthy, who directs our Center for Autism Spectrum Disorders, and I have been talking over the years about how we could bring our programs together. We homed in on this project to look at about a dozen genes to assess correlations and brought in experts from genetics and genomics at Children’s National to sequence genes of interest,” he adds. “Linking the bench to bedside is especially difficult in neuroscience. It takes a huge amount of effort and dozens of discussions, and it’s very rare. It’s an exemplar of what we strive for.”

In addition to Corbin, study co-authors include Lead Author Meredith Goodrich and Maria Jesus Herrero, post-doctoral fellow, Children’s Center for Neuroscience Research; Anna Chelsea Armour and co-Senior Author Lauren Kenworthy, Ph.D., Children’s Center for Autism Spectrum Disorders; Karuna Panchapakesan, Joseph Devaney and Susan Knoblach, Ph.D., Children’s Center for Genetic Medicine Research; Xiaozhen You and Chandan J. Vaidya, Georgetown University; and Catherine A.W. Sullivan and Abha R. Gupta, Yale School of Medicine.

Financial support for the research described in this report was provided by DC-IDDRC under awards HD040677-07 and 1U54HD090257, the Clinical and Translational Science Institute at Children’s National, The Isidore and Bertha Gudelsky Family Foundation and the National Institutes of Health under awards MH083053-01A2 and MH084961.