Skeletal abnormalities in mice with Dnmt3a missense mutations.

Overgrowth and intellectual disability disorders in humans are typified by length/height and/or head circumference ≥ 2 standard deviations above the mean as well as intellectual disability and behavioral comorbidities, including autism and anxiety. Tatton-Brown-Rahman Syndrome is one type of overgrowth and intellectual disability disorder caused by heterozygous missense mutations in the DNA methyltransferase 3A (DNMT3A) gene. Numerous DNMT3A mutations have been identified in Tatton-Brown-Rahman Syndrome patients and may be associated with varying phenotype severities of clinical presentation. Two such mutations are the R882H and P904L mutations which result in severe and mild phenotypes, respectively. Mice with paralogous mutations (Dnmt3aP900L/+ and Dnmt3aR878H/+) exhibit overgrowth in their long bones (e.g., femur, humerus), but the mechanisms responsible for their skeletal overgrowth remain unknown. The goal of this study is to characterize skeletal phenotypes in mouse models of Tatton-Brown-Rahman Syndrome and identify potential cellular mechanisms involved in the skeletal overgrowth phenotype. We report that mature mice with the Dnmt3aP900L/+ or Dnmt3aR878H/+ mutation exhibit tibial overgrowth, cortical bone thinning, and weakened bone mechanical properties. Dnmt3aR878H/+ mutants also contain larger bone marrow adipocytes while Dnmt3aP900L/+ mutants show no adipocyte phenotype compared to control animals. To understand the potential cellular mechanisms regulating these phenotypes, growth plate chondrocytes, osteoblasts, and osteoclasts were assessed in juvenile mutant mice using quantitative static histomorphometry and dynamic histomorphometry. Tibial growth plates appeared thicker in mutant juvenile mice, but no changes were observed in osteoblast activity or osteoclast number in the femoral mid-diaphysis. These studies reveal new skeletal phenotypes associated with Tatton-Brown-Rahman Syndrome in mice and provide a rationale to extend clinical assessments of patients with this condition to include bone density and quality testing. These findings may be also informative for skeletal characterization of other mouse models presenting with overgrowth and intellectual disability phenotypes.

Non-CG DNA methylation and MeCP2 stabilize repeated tuning of long genes that distinguish closely related neuron types.

The extraordinary diversity of neuron types in the mammalian brain is delineated at the highest resolution by subtle gene expression differences that may require specialized molecular mechanisms to be maintained. Neurons uniquely express the longest genes in the genome and utilize neuron-enriched non-CG DNA methylation (mCA) together with the Rett syndrome protein, MeCP2, to control gene expression, but the function of these unique gene structures and machinery in regulating finely resolved neuron type-specific gene programs has not been explored. Here, we employ epigenomic and spatial transcriptomic analyses to discover a major role for mCA and MeCP2 in maintaining neuron type-specific gene programs at the finest scale of cellular resolution. We uncover differential susceptibility to MeCP2 loss in neuronal populations depending on global mCA levels and dissect methylation patterns and intragenic enhancer repression that drive overlapping and distinct gene regulation between neuron types. Strikingly, we show that mCA and MeCP2 regulate genes that are repeatedly tuned to differentiate neuron types at the highest cellular resolution, including spatially resolved, vision-dependent gene programs in the visual cortex. These repeatedly tuned genes display genomic characteristics, including long length, numerous intragenic enhancers, and enrichment for mCA, that predispose them to regulation by MeCP2. Thus, long gene regulation by the MeCP2 pathway maintains differential gene expression between closely-related neurons to facilitate the exceptional cellular diversity in the complex mammalian brain.

Distinct disease mutations in DNMT3A result in a spectrum of behavioral, epigenetic, and transcriptional deficits.

Phenotypic heterogeneity is a common feature of monogenic neurodevelopmental disorders that can arise from differential severity of missense variants underlying disease, but how distinct alleles impact molecular mechanisms to drive variable disease presentation is not well understood. Here, we investigate missense mutations in the DNA methyltransferase DNMT3A associated with variable overgrowth, intellectual disability, and autism, to uncover molecular correlates of phenotypic heterogeneity in neurodevelopmental disease. We generate a DNMT3A P900L/+ mouse model mimicking a disease mutation with mild-to-moderate severity and compare phenotypic and epigenomic effects with a severe R878H mutation. We show that the P900L mutation leads to disease-relevant overgrowth, obesity, and social deficits shared across DNMT3A disorder models, while the R878H mutation causes more extensive epigenomic disruption leading to differential dysregulation of enhancers elements. We identify distinct gene sets disrupted in each mutant which may contribute to mild or severe disease, and detect shared transcriptomic disruption that likely drives common phenotypes across affected individuals. Finally, we demonstrate that core gene dysregulation detected in DNMT3A mutant mice overlaps effects in other developmental disorder models, highlighting the importance of DNMT3A-deposited methylation in neurodevelopment. Together, these findings define central drivers of DNMT3A disorders and illustrate how variable disruption of transcriptional mechanisms can drive the spectrum of phenotypes in neurodevelopmental disease.

Distinct disease mutations in DNMT3A result in a spectrum of behavioral, epigenetic, and transcriptional deficits.

Phenotypic heterogeneity in monogenic neurodevelopmental disorders can arise from differential severity of variants underlying disease, but how distinct alleles drive variable disease presentation is not well understood. Here, we investigate missense mutations in DNA methyltransferase 3A (DNMT3A), a DNA methyltransferase associated with overgrowth, intellectual disability, and autism, to uncover molecular correlates of phenotypic heterogeneity. We generate a Dnmt3aP900L/+ mouse mimicking a mutation with mild to moderate severity and compare phenotypic and epigenomic effects with a severe R878H mutation. P900L mutants exhibit core growth and behavioral phenotypes shared across models but show subtle epigenomic changes, while R878H mutants display extensive disruptions. We identify mutation-specific dysregulated genes that may contribute to variable disease severity. Shared transcriptomic disruption identified across mutations overlaps dysregulation observed in other developmental disorder models and likely drives common phenotypes. Together, our findings define central drivers of DNMT3A disorders and illustrate how variable epigenomic disruption contributes to phenotypic heterogeneity in neurodevelopmental disease.

Implications of full compliance with the computed tomography scanning recommendations of the National Institute for Clinical Excellence and Scottish Intercollegiate Guidelines Network guidelines for the management of head injury.

A prospective study was conducted to examine clinical practices in the management of head-injured patients preinception and postinception of the Scottish Intercollegiate Guidelines Network guidelines. Comparison was made between the Scottish Intercollegiate Guidelines Network and National Institute for Clinical Excellence guidelines on their indications for computed tomography scanning. Information was available on 2827 adult patients. Two hundred and thirty-two patients satisfied one or more Scottish Intercollegiate Guidelines Network criteria for computed tomography scanning. Four hundred and seventy-eight patients fulfilled one or more National Institute for Clinical Excellence criteria for scanning. No patient with Scottish Intercollegiate Guidelines Network or National Institute for Clinical Excellence indications for computed tomography scanning and who was not scanned, subsequently required neurosurgical treatment for a complication related to their injury. Full compliance with the scanning recommendations in the Scottish Intercollegiate Guidelines Network and National Institute for Clinical Excellence guidelines will require a significant increase in scanning resource and is unlikely to lead to the identification of a significant additional number of patients with intracranial lesions requiring neurosurgical intervention.

Laryngoscopic views during rapid sequence intubation in the emergency department.

OBJECTIVES: Our objective was to document and compare the views obtained at laryngoscopy during emergency department (ED) rapid sequence intubation (RSI) by anesthetists and emergency physicians of varying seniority and experience. METHODS: Data were prospectively collected on every intubation attempt in 7 urban Scottish EDs for 2 calendar years, commencing Jan. 11, 1999. Data included patient's age, gender, grade and specialty of intubator, laryngoscopic grade, and number of intubation attempts. Quality of laryngoscopic visualization was graded using the Cormack-Lehane scale, with grades I and II considered good visualization. A descriptive analysis was performed, and key statistical comparisons made. RESULTS: During the study period, 735 patients underwent RSI, and grade of intubation was documented in 672 cases (91%). In total, 68.2%, 23.4%, 6.1% and 2.4% of the intubations were classified as Cormack-Lehane grade I, II, III and IV respectively. Overall, anesthetists and anesthesia trainees achieved good laryngoscopic visualization in 94.0% of cases (95% confidence interval [CI], 90.8%-96.4%) and emergency physicians and emergency medicine trainees did so in 89.2% of cases (95% CI, 85.5%-92.3%; p = 0.027). Specialist registrars and senior house officers in anesthesia were more likely to obtain good visualization than their emergency medicine counterparts (p = 0.034 and 0.035 respectively). Consultants in emergency medicine were more likely to obtain good views than their anesthesia counterparts, but this difference was not statistically significant. CONCLUSIONS: Anesthetic trainees obtain better laryngoscopic views than emergency medicine trainees, but these differences disappear with increasing emergency physician seniority, suggesting a training and experience effect. Emergency medicine trainees may benefit from additional focus on laryngoscopic visualization techniques early in their training period.

Eleven years of liver trauma: the Scottish experience.

The aim of this population based study was to assess the incidence, mechanisms, management, and outcome of patients who sustained hepatic trauma in Scotland (population 5 million) over the period 1992-2002. The Scottish Trauma Audit Group database was searched for details of any patient with liver trauma. Data on identified patients were analyzed for demographic information, mechanisms of injury, associated injuries, hemodynamic stability on presentation, management, and outcome. A total of 783 patients were identified as having sustained liver trauma. The male-to-female ratio was 3:1 with a median age of 31 years. Blunt trauma (especially road traffic accidents) accounted for 69% of injuries. Liver trauma was associated with injuries to the chest, head, and abdominal injuries other than liver injury; most commonly spleen and kidneys. In all, 166 patients died in the emergency department, and a further 164 died in hospital. The mortality rate was higher in patients with increasing age (p < 0.001), hemodynamic instability (p < 0.001), blunt trauma (p < 0.001), and increasing severity of liver injury (p < 0.001). The incidence of liver trauma in Scotland is low, but it accounts for significant mortality. Associated injuries were common. Outcome was worse in patients with advanced age, blunt trauma, multiple injuries and those requiring an immediate laparotomy.

Scottish urban versus rural trauma outcome study.

BACKGROUND: Outcome following trauma and health care access are important components of health care planning. Resources are limited and quality information is required. We set the objective of comparing the outcomes for patients suffering significant trauma in urban and rural environments in Scotland. METHOD: The study was designed as a 2 year prospective observational study set in the west of Scotland, which has a population of 2.58 million persons. Primary outcome measures were defined as the total number of inpatient days, total number of intensive care unit days, and mortality. The participants were patients suffering moderate (ISS 9-15) and major (ISS>15) trauma within the region. The statistical analysis consisted of chi square test for categorical data and Mann Whitney U test for comparison of medians. RESULTS: There were 3,962 urban (85%) and 674 rural patients (15%). Urban patients were older (50 versus 46 years, p = 0.02), were largely male (62% versus 57%, p = 0.02), and suffered more penetrating traumas (9.9% versus 1.9%, p < 0.001). All prehospital times are significantly longer for rural patients (p < 0.001), include more air ambulance transfers (p < 0.001), and are characterized by greater paramedic presence (p < 0.001). Excluding neurosurgical and spinal injuries transfers, there was a higher proportion of transfers in the rural major trauma group (p = 0.002). There were more serious head injuries in the urban group (p = 0.04), and also a higher proportion of urban patients with head injuries transferred to the regional neurosurgical unit (p = 0.037). There were no differences in length of total inpatient stay (median 8 days, p = 0.7), total length of stay in the intensive care unit (median two days, p = 0.4), or mortality (324 deaths, moderate trauma, p = 0.13; major trauma, p = 0.8). CONCLUSION: Long prehospital times in the rural environment were not associated with differences in mortality or length of stay in moderately and severely injured patients in the west of Scotland. This may lend support to a policy of rationalization of trauma services in Scotland.

Patients with a head injury who "talk and die" in the 1990s.

BACKGROUND: Patients who "talk and die" after head injury may represent a group who suffer delayed and therefore potentially preventable complications after injury. We have compared the clinical and pathologic features of patients who talk and die with those who "talk and live" after head injury. METHODS: Data collected prospectively by the Scottish Trauma Audit Group were used to identify patients with a head injury and classify them according to verbal response at admission to hospital. All "talking" patients in the catchment area of a regional neurosurgical center were selected and those who died were compared with those who survived. RESULTS: Seven hundred eighty-nine talking patients were identified. Seven hundred twenty-seven patients survived and 62 died. Patients who talked and died were older, had more severe extracranial injuries, had lower consciousness levels, and reached theater more quickly than those who talked and lived. Thirty-one of the patients that died had extra-axial hematomas. CONCLUSION: Even with increased availability of computed tomographic scanning, some patients still talk and die after head injury.

Rapid sequence intubation of trauma patients in Scotland.

BACKGROUND: Endotracheal intubation remains the gold standard for trauma airway management. Rapid sequence intubation (RSI) has traditionally been performed by anesthesiologists but increasingly, emergency physicians are also undertaking RSI. We aimed to compare success and complication rates for trauma intubations for the two specialties. METHODS: Two year, prospective multi-center descriptive study of trauma RSI in seven Scottish urban emergency departments. RESULTS: 439 trauma patients were identified, including 233 RSIs. Patients intubated by emergency physicians had a higher median ISS (p < 0.001) and lower median RTS (p < 0.001) compared with anesthesiologists. For RSI, anesthesiologists had more grade I & II views at laryngoscopy (p = 0.051) and more successful first attempt intubations (p = 0.034) but there was no difference in the number of patients suffering complications (emergency physicians 10.0%, anesthesiologists 10.6%). CONCLUSION: There is no significant difference in complication rates for trauma RSI between emergency physicians and anesthesiologists in Scottish urban centers. A collaborative approach to the critical trauma airway is vital. Emergency physicians should consult with senior anesthesiologists before RSI when intubation is predicted to be difficult.