The Muller F element (4.2 Mb, ~80 protein-coding genes) is an unusual autosome of Drosophila melanogaster; it is mostly heterochromatic with a low recombination rate. To investigate how these properties impact the evolution of repeats and genes, we manually improved the sequence and annotated the genes on the D. erecta, D. mojavensis, and D. grimshawi F elements and euchromatic domains from the Muller D element. We find that F elements have greater transposon density (25–50%) than euchromatic reference regions (3–11%). Among the F elements, D. grimshawi has the lowest transposon density (particularly DINE-1: 2% vs. 11–27%). F element genes have larger coding spans, more coding exons, larger introns, and lower codon bias. Comparison of the Effective Number of Codons with the Codon Adaptation Index shows that, in contrast to the other species, codon bias in D. grimshawi F element genes can be attributed primarily to selection instead of mutational biases, suggesting that density and types of transposons affect the degree of local heterochromatin formation. F element genes have lower estimated DNA melting temperatures than D element genes, potentially facilitating transcription through heterochromatin. Most F element genes (~90%) have remained on that element, but the F element has smaller syntenic blocks than genome averages (3.4–3.6 vs. 8.4–8.8 genes per block), indicating greater rates of inversion despite lower rates of recombination. Overall, the F element has maintained characteristics that are distinct from other autosomes in the Drosophila lineage, illuminating the constraints imposed by a heterochromatic milieu.

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INTRODUCTION Clostridium difficile infection (CDI) is the most common infectious cause of nosocomial diarrhea, comprising 10-20% of all cases. CDI is a significant complication for IBD patients. Not only can CDI induce IBD flare, IBD patients also experience significantly higher CDI recurrence when compared to the general population. New monoclonal antibody (mAB) therapies, such as bezlotoxumab, have improved management of recurrent CDI (rCDI). The MODIFY I/II trial included 44 patients with known IBD, 28 of which received bezlotoxumab. Among these 28 patients, there was a 27.2% absolute reduction in the incidence of rCDI. Encouraged by these results, we recently prescribed bezlotoxumab in a UC patient with rCDI and herein report our experience. CASE REPORT A 21-year-old female with a history of ulcerative colitis (UC) diagnosed in 2017 presented for treatment of rCDI. Her first episode of CDI occurred in 2019 during an active UC flare treated with steroids and infliximab induction. CDI was successfully treated with a four-week course of 125mg oral vancomycin twice daily followed by once daily for an additional four weeks. She had a recurrent episode of CDI one year after her initial infection while on vedolizumab for UC treatment. She was treated with 125mg oral vancomycin, four times daily, and tapered down by one dose over a four-month period. Two years after her initial CDI, she developed worsening non-bloody diarrhea, nausea, and anorexia with weight loss. She again tested positive for C. difficile via glutamate dehydrogenase antigen and PCR for toxin B. Fecal calprotectin was 2190 mg/g. She was treated with 14-day course fidaxomicin 200mg BID and a single infusion of bezlotoxumab 10mg/kg. Treatment for UC was not adjusted. At follow up one month later, her symptoms had resolved and fecal calprotectin normalized (17 mg/g). Six months later, she remains asymptomatic. DISCUSSION Recurrent CDI is a frequent culprit for inducing IBD flares, and is difficult to manage. Fecal transplant (FMT) is an option for rCDI, but often entails logistical challenges and risks cross-contamination of endoscopic facilities. Bezlotoxumab is an appealing option for rCDI as a single dose medication with few reported side effects in the MODIFY clinical trials. While the number of IBD patients in the MODIFY trial was small, results were promising. In our patient, bezlotoxumab quickly resolved her rCDI and IBD flare without need for alteration or escalation of her biologic therapy, and she has remained asymptomatic for six months. This case corroborates the prospect that bezlotoxumab positively affects the clinical outcomes of UC patients with rCDI compared to those on repetitive antimicrobial therapy and/or FMT without mAB therapy. Further investigation into the long-term efficacy of this therapy is merited for the IBD patient population in the real-world setting.

Syphilis hepatitis is a rare cause of acute liver injury. Primary biliary cholangitis (PBC) is a progressive autoimmune disease characterized by the typical presentation of a cholestatic liver injury and the presence of antimitochondrial antibodies (AMAs). We present a case of syphilis hepatitis that presented as a mimic to PBC with positive AMA. The eradication of syphilis led to the resolution of the liver injury and down trending of the antibody level. We recommend excluding syphilis in patients with high-risk behaviors presenting with a cholestatic liver injury and positive AMA before the diagnosis of PBC.

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