RAD51 Inhibitor and Radiation Toxicity in Vestibular Schwannoma.

OBJECTIVE: To describe the RAD51 response (DNA repair) to radiation-induced DNA damage in patient-derived vestibular schwannoma (VS) cells and investigate the utility of RAD51 inhibitor (RI-1) in enhancing radiation toxicity. STUDY DESIGN: Basic and translational science. SETTING: Tertiary academic facility. METHODS: VS tumors (n = 10) were cultured on 96-well plates and 16-well slides, exposed to radiation (0, 6, 12, or 18 Gy), and treated with RI-1 (0, 5, or 10 µM). Immunofluorescence was performed at 6 hours for γ-H2AX (DNA damage marker), RAD51 (DNA repair protein), and p21 (cell cycle arrest protein). Viability assays were performed at 96 hours, and capillary Western blotting was utilized to determine RAD51 expression in naïve VS tumors (n = 5). RESULTS: VS tumors expressed RAD51. In cultured VS cells, radiation initiated dose-dependent increases in γ-H2AX and p21 expression. VS cells upregulated RAD51 to repair DNA damage following radiation. Addition of RI-1 reduced RAD51 expression in a dose-dependent manner and was associated with increased γ-H2AX levels and decreased viability in a majority of cultured VS tumors. CONCLUSION: VS may evade radiation injury by entering cell cycle arrest and upregulating RAD51-dependent repair of radiation-induced double-stranded breaks in DNA. Although there was variability in responses among individual primary VS cells, RAD51 inhibition with RI-1 reduced RAD51-dependent DNA repair to enhance radiation toxicity in VS cells. Further investigations are warranted to understand the mechanisms of radiation resistance in VS and determine whether RI-1 is an effective radiosensitizer in patients with VS.

Haller's Ansa: An Unrecognized Route of Facial Movement After Skull Base Surgery.

A direct communication between the glossopharyngeal and facial nerves known as Haller's ansa exists in a minority of patients. Clinical manifestations of this anastomosis are not commonly observed. We describe post-operative facial movement with swallowing after facial nerve sacrifice in two patients who underwent surgery for skull base tumors. Patient 1, a 49-year-old male, received a transcochlear approach for resection of endolymphatic sac tumor and intratemporal facial nerve sacrifice without nerve reconstruction. Patient 2, a 23-year-old female, underwent surgery for left jugular paraganglioma, requiring facial nerve sacrifice and cable graft. Both patients had preoperative facial weakness and intraoperative preservation of the glossopharyngeal nerve. A literature review related to Haller's ansa was performed using PubMed, EMBASE, and Scopus from 1920-2021. Post-operatively, both patients demonstrated oral commissure movement with swallowing, suggesting a communication between the glossopharyngeal nerve and the facial nerve (Haller's ansa). Although anatomical references to Haller's ansa exist, there are no reported clinical manifestations of this neural anastomosis. Glossopharyngeal-facial nerve communications may contribute to facial tone and movement. Pre- and post-operative assessment of facial nerve movement with swallowing may help assess for the presence of Haller's ansa. Better understanding of this neural anastomosis may have implications for facial reanimation surgery. Laryngoscope, 132:1750-1752, 2022.

Review of Genotype-Phenotype Correlations in Usher Syndrome.

Usher syndrome (USH) encompasses a group of clinically and genetically heterogenous disorders defined by the triad of sensorineural hearing loss (SNHL), vestibular dysfunction, and vision loss. USH is the most common cause of deaf blindness. USH is divided clinically into three subtypes-USH1, USH2, and USH3-based on symptom severity, progression, and age of onset. The underlying genetics of these USH forms are, however, significantly more complex, with over a dozen genes linked to the three primary clinical subtypes and other atypical USH phenotypes. Several of these genes are associated with other deaf-blindness syndromes that share significant clinical overlap with USH, pointing to the limits of a clinically based classification system. The genotype-phenotype relationships among USH forms also may vary significantly based on the location and type of mutation in the gene of interest. Understanding these genotype-phenotype relationships and associated natural disease histories is necessary for the successful development and application of gene-based therapies and precision medicine approaches to USH. Currently, the state of knowledge varies widely depending on the gene of interest. Recent studies utilizing next-generation sequencing technology have expanded the list of known pathogenic mutations in USH genes, identified new genes associated with USH-like phenotypes, and proposed algorithms to predict the phenotypic effects of specific categories of allelic variants. Further work is required to validate USH gene causality, and better define USH genotype-phenotype relationships and disease natural histories-particularly for rare mutations-to lay the groundwork for the future of USH treatment.

Bilateral vocal cord paralysis caused by accidental button battery ingestion in children: A case report and literature review.

Button battery ingestion in pediatric populations is a common occurrence with severe sequelae. Multiple case reports have established the occurrence of death, fistula formation, mucosal erosion, esophageal perforation, and bleeding post-ingestion of button batteries. However, there is a gap in the literature on the occurrence of bilateral vocal cord paralysis post-lithium battery ingestion. We present a case in which a 12-month-old male developed bilateral vocal cord paralysis following ingestion of a button battery. We compare our case to eleven other reports that exist in the literature based on age, sex, time until removal, clinical presentation, day upon which vocal cord paralysis developed, anatomic location, and post-operative course. We conclude that bilateral vocal cord paralysis is a time-sensitive complication which requires prompt diagnosis. Any child with stridor following button battery ingestion should undergo consultation with pediatric otolaryngology immediately. In addition, long-term follow-up is necessary to evaluate return of normal vocal cord function.

Understanding the Radiobiology of Vestibular Schwannomas to Overcome Radiation Resistance.

Vestibular schwannomas (VS) are benign tumors arising from cranial nerve VIII that account for 8-10% of all intracranial tumors and are the most common tumors of the cerebellopontine angle. These tumors are typically managed with observation, radiation therapy, or microsurgical resection. Of the VS that are irradiated, there is a subset of tumors that are radioresistant and continue to grow; the mechanisms behind this phenomenon are not fully understood. In this review, the authors summarize how radiation causes cellular and DNA injury that can activate (1) checkpoints in the cell cycle to initiate cell cycle arrest and DNA repair and (2) key events that lead to cell death. In addition, we discuss the current knowledge of VS radiobiology and how it may contribute to clinical outcomes. A better understanding of VS radiobiology can help optimize existing treatment protocols and lead to new therapies to overcome radioresistance.

Primary Vestibular Schwannoma Cells Activate p21 and RAD51-Associated DNA Repair Following Radiation-Induced DNA Damage.

HYPOTHESIS: Vestibular Schwannoma (VS) can avoid cell death following radiation injury by entering cell cycle arrest and activating RAD51-related DNA repair. BACKGROUND: Although the radiobiology of various cancers is well-studied, the radiobiological effects in VS are poorly understood. In this study, we describe how VS cells enter cell cycle arrest (through p21 expression), activate DNA repair (through RAD51 upregulation), and avoid cell death after radiation-induced double-stranded breaks (DSB) in DNA (as measured by γ-H2AX). METHODS: Primary human VS cells were cultured on 96-well plates and 16-well culture slides at 10,000 cells/well and exposed to either 0 or 18 Gray of radiation. Viability assays were performed at 96 h in vitro. Immunofluorescence for γ-H2AX, RAD51, and p21 was performed at 6 h. RESULTS: Radiation (18 Gy) induced the expression of γ-H2AX, p21, and RAD51 in six cultured VS, suggesting that irradiated VS acquire DSBs, enter cell cycle arrest, and initiate RAD51 DNA repair to evade cell death. However, viability studies demonstrate variable responses in individual VS cells with 3 of 6 VS showing radiation resistance to 18 Gy. On further analyses, radiation-resistant VS cells expressed significantly more p21 than radiation-responsive tumors. CONCLUSIONS: In response to radiation-induced DNA damage, primary VS cells can enter cell cycle arrest and express RAD51 DNA repair mechanisms to avoid cell death. Radioresistant VS cells may mount a more robust p21 response to ensure sufficient time for DNA repair. Further investigation into DNA repair proteins and cell cycle checkpoints may provide important insight on the radiobiology of VS and mechanisms for resistance.

Medical Students' Reflections on the Recent Changes to the USMLE Step Exams.

The United States Medical Licensing Examination (USMLE) consists of Step 1, Step 2 Clinical Knowledge, Step 2 Clinical Skills, and Step 3. To be licensed to practice medicine in the United States, medical students must pass all parts of the USMLE. However, in addition to that pass/fail grade, students are currently given a numerical score for Step 1, Step 2 Clinical Knowledge, and Step 3. Residency program directors have come to use the Step 1 score to efficiently screen a growing number of residency applicants. As a result, a deleterious environment in undergraduate medical education has been created, given the importance of Step 1 to medical students matching to their preferred residency program. It was announced in February 2020 that the score-reporting protocol for Step 1 would be changed from a 3-digit numerical score to pass/fail only, beginning no earlier than January 1, 2022. This decision will undoubtedly impact medical students, medical schools, and residency program directors. Here, the authors discuss the impact that the change to Step 1 scoring will have on these key stakeholder groups, from their perspective as students at MD-granting medical schools in the United States. They also call attention to outstanding issues with the USMLE that must be addressed to improve undergraduate medical education for all stakeholders, and they offer advice for further improvements to the residency application process.

Transcatheter aortic valve replacement in low risk patients: a review of PARTNER 3 and Evolut low risk trials.

Transcatheter aortic valve replacement (TAVR) has become a mainstay in treatment for patients with severe aortic stenosis who are considered high-risk surgical candidates. The use of TAVR in low-risk patients with severe aortic stenosis is being explored as an alternative to surgical aortic valve replacement (SAVR). Recent results from the Medtronic Evolut Low Risk trial and the Placement of Aortic Transcatheter Valves (PARTNER) 3 trial shed light on the use of TAVR in low-risk surgical candidates. The Evolut Low Risk trial compared TAVR with a self-expanding supra-annular bioprosthesis to SAVR in 1468 patients with severe aortic stenosis who were low surgical risk. Patients with a mean age of 74 and a mean Society of Thoracic Surgeons (STS) risk score of 1.9% were randomized to either TAVR or SAVR groups. Using the composite end point of death or disabling stroke at 24 months, the study found an incidence of 5.3% in the TAVR arm and 6.7% in the surgical arm. The Evolut Low Risk trial thus concluded that TAVR was statistically noninferior but not superior to SAVR (difference, -1.4 percentage points; 95% Bayesian credible interval for the difference, -4.9 to 2.1; posterior probability of noninferiority, >0.999). The PARTNER 3 trial assigned 1,000 patients with severe aortic stenosis and low surgical risk to either TAVR with transfemoral placement of balloon expandable valve or SAVR. Patients with a mean age of 73 and a mean STS score of 1.9% were randomized to either TAVR or SAVR groups. With respect to the primary endpoint of composite death from any cause, stroke, or rehospitalization, the study found an occurrence of 8.5% in TAVR and 15.1% in SAVR, confirming both noninferiority and superiority in the TAVR group [absolute difference, -6.6 percentage points; 95% confidence interval (CI), -10.8 to -2.5; P<0.001 for noninferiority; hazard ratio, 0.54; 95% CI, 0.37 to 0.79; P=0.001 for superiority]. Both the Evolut low risk trial and the PARTNER 3 trial provide evidence that the use of TAVR extends beyond the scope of high and intermediate risk surgical patients and is at the very least equivalent to SAVR in the treatment low-risk surgical candidates when using a transfemoral approach in patients without bicuspid aortic valves. In this article we provide an extensive review on the Evolute low risk and PARTNER 3 trials, including a discussion on clinically relevant outcomes.

Unisexual reproduction promotes competition for mating partners in the global human fungal pathogen Cryptococcus deneoformans.

Courtship is pivotal for successful mating. However, courtship is challenging for the Cryptococcus neoformans species complex, comprised of opportunistic fungal pathogens, as the majority of isolates are α mating type. In the absence of mating partners of the opposite mating type, C. deneoformans can undergo unisexual reproduction, during which a yeast-to-hyphal morphological transition occurs. Hyphal growth during unisexual reproduction is a quantitative trait, which reflects a strain's ability to undergo unisexual reproduction. In this study, we determined whether unisexual reproduction confers an ecological benefit by promoting foraging for mating partners. Through competitive mating assays using strains with different abilities to produce hyphae, we showed that unisexual reproduction potential did not enhance competition for mating partners of the same mating type, but when cells of the opposite mating type were present, cells with enhanced hyphal growth were more competitive for mating partners of either the same or opposite mating type. Enhanced mating competition was also observed in a strain with increased hyphal production that lacks the mating repressor gene GPA3, which contributes to the pheromone response. Hyphal growth in unisexual strains also enables contact between adjacent colonies and enhances mating efficiency during mating confrontation assays. The pheromone response pathway activation positively correlated with unisexual reproduction hyphal growth during bisexual mating and exogenous pheromone promoted bisexual cell fusion. Despite the benefit in competing for mating partners, unisexual reproduction conferred a fitness cost. Taken together, these findings suggest C. deneoformans employs hyphal growth to facilitate contact between colonies at long distances and utilizes pheromone sensing to enhance mating competition.

To revascularize or not before transcatheter aortic valve implantation?

Concomitant coronary artery disease (CAD) and aortic stenosis occur in approximately 60-75% of patients referred for surgical or transcatheter aortic valve replacement (TAVR). Current guidelines support simultaneous surgical aortic valve replacement and bypass surgery with a class IIa recommendation, based on observational, non-randomized data. With the inception of TAVR, this strategy has been challenged, as observational studies have not shown significant outcome differences in patients with and without CAD treated with TAVR. Performing percutaneous coronary intervention (PCI) in patients with aortic stenosis is safe, but the indication and timing remain controversial. Complete revascularization before TAVR with low residual Syntax score (<8) may be considered in selected cases with extensive, proximal, and severe CAD to improve outcomes. PCI before TAVR may require less contrast and reduce the risk of acute kidney injury, but uninterrupted dual antiplatelet therapy may increase the risk of bleeding during TAVR. Combined PCI and TAVR can be considered for unstable patients with simple lesions or ostial lesions, with risk of coronary occlusion after deployment of the transcatheter heart valve. PCI after TAVR may be considered in patients who remain symptomatic with significant residual ischemia despite optimal medical therapy. In the near future, it is expected that randomized clinical trials will further clarify the indications and role of revascularization in patients undergoing TAVR. In this article we provide an extensive review on the management of CAD in TAVR candidates, including additional considerations on technical aspects, device selection, and adjunctive pharmacological therapies.