2020 Collaborative Research Network Conference

In November, The TBRS Community hosted its first Collaborative Research Network meeting. Around 60 doctors and researchers attended this two-day virtual event, which featured a dozen presentations by leading scientists. The topics included clinical profiles of individuals with TBRS, mouse models of DNMT3A variants, the neurobiology of overeating, cancer risks due to DNMT3A mutations, the epigenetics of overgrowth disorders, and more.

The conference was a huge success in bringing together experts from different fields whose work has relevance to TBRS. There were live Q&A and discussion sessions held through Zoom, which gave attendees a chance to connect. The conference was invitation-only to encourage researchers to present unpublished data and to foster collaboration with one another.

In addition to facilitating conversations among researchers, the conference was also a way to introduce scientists and doctors to TBRS and to The TBRS Community. Many families contributed footage that went into videos aired during the conference featuring our amazing community members. Dr. Vicken Totten, a TBRS parent, also presented the results of a survey of families’ priorities that was conducted over the summer.

We were pleased to hear from researchers after the event that they learned a great deal about TBRS and efforts to better understand it. It is clear our rare syndrome is now on the radar of many more scientists and clinicians. The TBRS Community plans to keep the momentum going this year through several more Collaborative Research Network events, including brief virtual presentations and discussions in the spring and summer and the larger annual conference in the fall.

You can view the list of speakers here, watch some of the talks on our YouTube channel, and read summaries of several of the presentations below:

Dr. Amanda Smith, Washington University School of Medicine: “Characterizing the epigenome of TBRS”

Overgrowth syndromes are a heterogeneous group of rare disorders that are characterized by global or localized tissue hypertrophy; the genetic causes of these syndromes are emerging as more patients’ genomes are analyzed. The first report of DNMT3A Overgrowth Syndrome (DOS, also called Tatton-Brown Rahman Syndrome; TBRS; MIM 615879) described a syndrome of increased growth, defined as height and/or head circumference at least two standard deviations above the mean, associated with facial dysmorphism and intellectual disability occurring in patients with de novo heterozygous germline mutations in DNMT3A. Somatic mutations in DNMT3A are one of the most common initiating mutations in acute myeloid leukemia (AML) patients. Although mutations occur throughout the DNMT3A gene in AML patients, more than half occur at amino acid R882, which is also emerging as the most commonly mutated amino acid in TBRS patients.

DNMT3A is a DNA methyltransferase and modifies DNA by adding the functional methyl group to specific cytosine residues within the genome. The functional changes that result from this modification have are not well understood despite decades of study; current hypotheses suggest that DNA methylation impacts the structure of DNA and the binding of transcription factor proteins to sites in the genome that alter the expression of specific genes. Importantly, our group and others have shown that DNMT3A-R882 mutations result in a reduction in the methyltransferase activity of DNMT3A, leading to a focal loss of DNA methylation at very specific regions in the genomes in hematopoietic (blood and bone marrow) cells. In this study, we showed that “non-R882” mutations also reduce the methylation of blood cell genomes, although the methylation loss is not as severe. We have also developed a mouse model of TBRS with the R882 mutation inherited from the parents, to help us better understand the consequences of the R882 mutation in the whole organism. These mice have many features of the human syndrome, including overgrowth (longer femurs and skull alterations), obesity, and reduced movement in the absence of any obvious metabolic conditions such as diabetes. Finally, the R882 mice spontaneously develop B-cell and myeloid leukemias after a long latent period, suggesting that TBRS patients should be prospectively monitored for the development of hematologic malignancies.

Dr. Ana Oliveira, University of Heidelberg: “DNMT3A role in cognitive abilities”

It is well established that the formation of memories is initiated when we learn new information. During learning signals are sent to the nucleus of neurons that initiate the synthesis of certain proteins. These proteins are responsible for modifying the strength of the connection between neurons which is an essential step in the formation of memory. The work from my group aims to understand how the nucleus of neurons decodes the signals that arrive from the synapse and convert them into the synthesis of new proteins.

We have found that the two enzymes (Dnmt3a1 and Dnmt3a2) that are coded by the Dnmt3a gene – the one mutated in TBRS – are required for the formation of memories. These findings were supported by experiments in which we observed that reducing the levels of Dnmt3a1 or Dnmt3a2 in the mouse brain impaired their ability to form memories. Our experiments further point in the direction that Dnmt3a1 and Dnmt3a2 coordinate the response of the nucleus of neurons to the signals that arrive from the synapse. Therefore, impairments in cognitive abilities, as found in TBRS, may be a result of improper activity of Dnmt3a1 or Dnmt3a2 during memory formation.

Dr. Harrison Gabel, Washington University: “Defining the impact of DNMT3A mutation on the neuronal epigenome”

Watch Dr. Gabel’s full presentation on our YouTube channel.

Harrison Gabel, an assistant professor in the Department of Neuroscience at Washington University in St. Louis, reported on the efforts of his research group to understand how mutation of the DNMT3A gene in TBRS affects the brain. His studies are focused on understanding what the DNMT3A gene does in our brain cells and how the mutation of DNMT3A in TBRS alters the functions of the gene in these cells. He presented initial studies from his lab showing the different ways that DNMT3A gene mutations in different individuals with TBRS disrupt the function of DNMT3A. By studying different DNMT3A mutant genes in cells cultured in a dish, he showed that even though there are many ways in which the DNMT3A gene can be altered by different mutations, all of these mutations lead to common effects on the chemical modification of DNA known as DNA methylation.

To follow up these findings, Dr. Gabel’s group established a mouse that carries a mutation in its DNMT3A that is similar to one type of mutation in individuals with TBRS. Their research showed that this mouse exhibits changes in growth and behavior that mimic aspects of TBRS in humans. This indicates that it will be a good model for understanding the disease.

Finally, Dr. Gabel described how his group has used this mouse to study the cellular and molecular changes that occur in the brain during TBRS. This analysis uncovered evidence that some of the changes that occur in brain cells in individuals with TBRS are likely to be similar to changes that occur in a prominent neurodevelopmental disorder, Rett Syndrome. This is significant because researchers have studied Rett syndrome extensively and insights from the Rett syndrome field may help us better understand TBRS.

Together, Dr. Gabel’s work in cells and mice is defining the cellular events that occur in the brain of individuals TBRS and exploring how these changes share some features with other disorders. This work can help researchers begin to that targeted the root causes of intellectual challenges that occur in TBRS and related disorders.

Dr. Chao Lu, Columbia University: “Interplay between DNA and histone methylation in developmental overgrowth syndromes”

Watch Dr. Lu’s full presentation on our YouTube channel.

Tatton Brown Rahman Syndrome (TBRS) belongs to a group of childhood overgrowth and intellectual disability (OGID) syndromes. TBRS is defined by mutations in DNMT3A, which encodes for an enzyme that mediates addition of methylation to DNA. DNA methylation is critical for controlling gene expression. In addition to DNA methylation, methylation in proteins known as histones are also important for regulation of gene expression. Interestingly, several other OGID syndromes, including Sotos syndrome and Weaver syndrome, are defined by mutations in enzymes catalyzing histone methylation such as the NSD1 gene. We reason that because patients with OGID syndromes such as TBRS and Sotos share overlapping features, NSD1 and DNMT3A may work together to ensure precise gene regulation. Indeed, we found that NSD1 is important for the accurate recruitment of DNMT3A to our genome. Cells deficient for NSD1 or DNMT3A have similar decreases in DNA methylation, particularly affecting regions known as enhancers that are critical for gene expression.

Our ongoing work aims to further understand the interplay between NSD1 and DNMT3A, and to test if any of the recently developed drugs targeting DNA and histone methylation could attenuate the abnormal patterns of DNA methylation and gene expression. We hope that these efforts will ultimately lead to a better understanding of the etiology of TBRS and novel treatment for the disease.

Dr. Jikui Song, University of California, Riverside: “DNMT3A-mediated DNA methylation in health and disease: a structural perspective”

Watch Dr. Song’s full presentation on our YouTube channel.

Our study focuses on understanding of how DNMT3A R882H, a frequent mutation in Acute Myeloid Leukemia and Tatton Brown Rahman Syndrome, affects the structure and function of DNMT3A. Through solving the atomic structures of DNMT3A, both wild-type and R882H-mutated, in complex with functional regulator DNMT3L and DNA substrates, combined with biochemical assays, our study reveals that the R882H mutation disrupts an intramolecular interaction of DNMT3A required for its specific substrate recognition, leading to reduced enzymatic activity and substrate specificity. In summary, our work provides a framework for mechanistic understanding of DNMT3A mutations in diseases.

Dr. Qingchun Tong, University of Texas Health Science Center: “A novel neurocircuit for emotional feeding”

Watch Dr. Tong’s full presentation on our YouTube channel.

Our feeding behaviors are not only controlled by the homeostatic energy needs, but also greatly influenced by emotion. The latter can be appreciated by eating disorders frequently comorbid with psychiatric diseases. It remains largely unknown what is wrong in the brain causing this condition. The presentation illustrates a study that identified a group of brain neurons that function as a switch to turn on or off feeding behavior associated with signs of emotional changes, i.e. “good” feeling with feeding turned on and “bad” feeling with turned off. More studies are required to ascertain whether this group of brain neurons are involved in eating disorders.

Funded projects in partnership with RDMM

The TBRS Community and the Rare Diseases Models & Mechanisms Network (RDMM) are funding two research projects on Tatton Brown Rahman Syndrome:

Dr. Serge McGraw, University of Montreal: “Modeling TBRS in discovery research”

At this time, we still lack mechanistic understanding on how altered DNMT3A function leads to the neurodevelopmental and other associated disorders observed in patients with TBRS. The enzyme DNMT3A is particularly crucial during development prior to birth. Discerning the underlying neuropathological dysfunctions associated with altered DNMT3A function and identifying therapeutic strategies to treat TBRS individuals has proven challenging due to the inherent lack of appropriate TBRS patient sample availability and animal models not accurately recapitulating specific disease phenotypes. Support from the TBRS Community will allow us to generate a unique patient-derived TBRS mouse model and allow us to identify the initial disrupted molecular pathways occurring in the various cell types of the body during prenatal development and identify how these perturbations can lead to future specific TBRS associated phenotypes. Since TBRS patients have overlapping congenital defects, this novel TBRS-derived research model will provide much needed information on disease pathogenesis, and provide a potential avenue to test therapeutic interventions.

Dr. William Gibson, BC Children’s Hospital Research Institute: “Mechanisms of obesity in mouse models of TBRS”

The overgrowth in TBRS is known to affect height and head circumference, though
many patients also develop obesity. Dr. Gibson’s lab at BC Children’s Hospital in Vancouver has been awarded funding from the TBRS Society to investigate mechanisms of obesity in mouse models of TBRS. His lab has a state-of-the-art system of metabolic cages that measure food intake, water intake, oxygen consumption and carbon dioxide production, so they can calculate total energy expenditure paired to food intake, and adjust appropriately for muscle mass and fat mass (which is not as easy as it sounds). These detailed metabolic studies are difficult to do in human patients, though work by other researchers has shown that some patients with rare obesity disorders have reduced metabolic rates, which contribute to their obesity over time. Dr. Gibson’s team hopes to translate the metabolic findings from mouse models of TBRS into humans, and also has the infrastructure to measure resting energy expenditure and body composition (fat mass, lean mass and bone mass) in children and adults with rare genetic variants.