Consensus core clinical data elements for meningiomas (v2021.1).

BACKGROUND: With increasing molecular analyses of meningiomas, there is a need to harmonize language used to capture clinical data across centers to ensure that molecular alterations are appropriately linked to clinical variables of interest. Here the International Consortium on Meningiomas presents a set of core and supplemental meningioma-specific common data elements (CDEs) to facilitate comparative and pooled analyses. METHODS: The generation of CDEs followed the 4-phase process similar to other National Institute of Neurological Disorders and Stroke (NINDS) CDE projects: discovery, internal validation, external validation, and distribution. RESULTS: The CDEs were organized into patient- and tumor-level modules. In total, 17 core CDEs (10 patient level and 7 tumor level) as well as 14 supplemental CDEs (7 patient level and 7 tumor level) were defined and described. These CDEs are now made publicly available for dissemination and adoption. CONCLUSIONS: CDEs provide a framework for discussion in the neuro-oncology community that will facilitate data-sharing for collaborative research projects and aid in developing a common language for comparative and pooled analyses. The meningioma-specific CDEs presented here are intended to be dynamic parameters that evolve with time and The Consortium welcomes international feedback for further refinement and implementation of these CDEs.

Esophageal Adenocarcinoma Metastasizing to a Solitary Fibrous Tumor: An Unprecedented Case of Tumor-to-tumor Metastasis.

BACKGROUND: Tumor-to-tumor (TMT) metastasis is a rare phenomenon in which a primary malignancy undergoes metastasis to an additional synchronous or metachronous primary tumor. CASE REPORT: This is a case report of a tumor-to-tumor metastasis from a poorly differentiated adenocarcinoma of the esophagus to a solitary fibrous tumor (SFT) of the right posterior neck, in a 70-year-old-male with a solitary right vertebral artery. After appropriate work-up and involvement of the necessary specialties, the patient underwent a complex surgical resection with negative margins. CONCLUSION: We present the unique case of a patient with TMT from esophageal adenocarcinoma to an SFT in the posterior neck, not previously reported in the literature. This rare condition with unique oncologic implications highlights the need for a multidisciplinary approach, in this case involving thoracic surgery, head-and-neck surgery, medical oncology, radiation oncology, pathology, and neurosurgical sub-specialty services.

Clinical Uncertainty and Equipoise in the Management of Recurrent Glioblastoma.

BACKGROUND: A significant proportion of glioblastoma (GBM) patients are considered for repeat resection, but evidence regarding best management remains elusive. Our aim was to measure the degree of clinical uncertainty regarding reoperation for patients with recurrent GBM. METHODS: We first performed a systematic review of agreement studies examining the question of repeat resection for recurrent GBM. An electronic portfolio of 37 pathologically confirmed recurrent GBM patients including pertinent magnetic resonance images and clinical information was assembled. To measure clinical uncertainty, 26 neurosurgeons from various countries, training backgrounds, and years' experience were asked to select best management (repeat surgery, other nonsurgical management, or conservative), confidence in recommended management, and whether they would include the patient in a randomized trial comparing surgery with nonsurgical options. Agreement was evaluated using κ statistics. RESULTS: The literature review did not reveal previous agreement studies examining the question. In our study, agreement regarding best management of recurrent GBM was slight, even when management options were dichotomized (repeat surgery vs. other options; κ=0.198 [95% confidence interval: 0.133-0.276]). Country of practice, years' experience, and training background did not change results. Disagreement and clinical uncertainty were more pronounced within clinicians with (κ=0.167 [0.055-0.314]) than clinicians without neuro-oncology fellowship training (κ=0.601 [0.556-0.646]). A majority (51%) of responders were willing to include the patient in a randomized trial comparing repeat surgery with nonsurgical alternatives in 26/37 (69%) of cases. CONCLUSION: There is sufficient uncertainty and equipoise regarding the question of reoperation for patients with recurrent glioblastoma to support the need for a randomized controlled trial.

How to live with a meningioma: experiences, symptoms, and challenges reported by patients.

BACKGROUND: We aimed to explore gaps in the care of meningioma patients that could improve quality of care by better understanding symptoms experienced by patients at various stages of treatment, and afterwards. METHODS: A novel 19-item self-administered questionnaire was provided for patients with meningiomas to complete by the American Brain Tumor Association (ABTA) over a 3-month period. RESULTS: A total of 1852 unique respondents were included. Nearly one-third of all respondents felt they received insufficient information about meningiomas at initial diagnosis (N = 607, 32.9%) and 28.8% (N = 530) believed they received insufficient information about treatment options. In fact, 34.5% of respondents received the majority of their information from the internet and nonhealthcare professionals. The most common concerns after initial diagnosis were risks associated with surgery and/or treatment (36.5%) followed by how the tumor would impact daily life (25%) and the risk of tumor recurrence (12.4%). Respondents indicated that a list of resources available for patients with meningiomas (N = 597, 32.3%) would have been most beneficial in regards to their disease experience after their initial diagnosis. Moreover, we found that a substantial proportion of patients continued to report symptoms long after treatment, with fatigue being the most common compared to before treatment (38.2% vs. 57.7%, χ 2 = 128, P < .001). CONCLUSIONS: Patients with meningiomas exhibit symptoms that continue well after treatment with fatigue and cognitive impairments as the most bothersome. Moreover, patients report key communication gaps that can be addressed to improve their disease experience and care.

Multiple recurrences of spindle cell oncocytoma: A case report and literature review.

Spindle cell oncocytoma (SCO) is a rare tumor originating from pituicytes of the neurohypophysis. It typically occurs in the adult population between 50 and 60 years of age and is often misdiagnosed preoperatively as pituitary adenoma because of similar clinical presentation and neuroimaging features. Diffuse nuclear immunoreactivity for TTF-1 (also known as NK2 homeobox 1 factor) is characteristic of SCO and other tumors of the posterior pituitary. We report a case of SCO in a patient who underwent multiple surgical resections for recurrence. The aim of this case report and literature review is to provide an overview of what is currently known about SCO as well as raise the awareness of this entity to endocrinologists, neurologists, neurosurgeons, and neuropathologists. Our case is also unusual in that the tumor displayed immunoreactivity for neuronal markers, which is a very rare occurrence.

Intraoperative acquisition of DTI in cranial neurosurgery: readout-segmented DTI versus standard single-shot DTI.

OBJECTIVE: Diffusion tensor imaging (DTI) tractography is commonly used in neurosurgical practice but is largely limited to the preoperative setting. This is due primarily to image degradation caused by susceptibility artifact when conventional single-shot (SS) echo-planar imaging (EPI) DTI (SS-DTI) is acquired for open cranial, surgical position intraoperative DTI (iDTI). Readout-segmented (RS) EPI DTI (RS-DTI) has been reported to reduce such artifact but has not yet been evaluated in the intraoperative MRI (iMRI) environment. The authors evaluated the performance of RS versus SS EPI for DTI of the human brain in the iMRI setting. METHODS: Pre- and intraoperative 3-T 3D T1-weighted and 2D multislice RS-iDTI (called RESOLVE [readout segmentation of long variable echo-trains] on the Siemens platform) and SS-iDTI images were acquired in 22 adult patients undergoing intraaxial iMRI resections for suspected low-grade glioma (14; 64%), high-grade glioma (7; 32%), or focal cortical dysplasia. Regional susceptibility artifact, anatomical deviation relative to T1-weighted imaging, and tractographic output for surgically relevant tracts were compared between iDTI sequences as well as the intraoperative tract shifts from preoperative DTI. RESULTS: RS-iDTI resulted in qualitatively less regional susceptibility artifact (resection cavity, orbitofrontal and anterior temporal cortices) and mean anatomical deviation in regions most prone to susceptibility artifact (RS-iDTI 2.7 ± 0.2 vs SS-iDTI 7.5 ± 0.4 mm) compared to SS-iDTI. Although tract reconstruction success did not significantly differ by DTI method, susceptibility artifact-related tractography failure (of at least 1 surgically relevant tract) occurred for SS-iDTI in 8/22 (36%) patients, and in 5 of these 8 patients RS-iDTI permitted successful reconstruction. Among cases with successful tractography for both sequences, maximal intersequence differences were substantial (mean 9.5 ± 5.7 mm, range -27.1 to 18.7 mm). CONCLUSIONS: RS EPI enables higher quality and more accurate DTI for surgically relevant tractography of major white matter tracts in intraoperative, open cranium neurosurgical applications at 3 T.

Life after surgical resection of a meningioma: a prospective cross-sectional study evaluating health-related quality of life.

Background: Few studies have evaluated the health-related quality of life (HRQoL) of patients with meningiomas. Here, we report the largest prospective, longitudinal cross-sectional cohort study of HRQoL in meningiomas to date, in order to identify possible actionable determinants of global HRQoL. Methods: Adults who had undergone resection of a grade I intracranial meningioma and were in routine follow-up at a single large tertiary center underwent HRQoL assessment using the QLQ-C30 questionnaire administered opportunistically at follow-up visits. Averaged transformed QLQ-C30 scores at 12-month intervals were compared with scores from a normative reference population, with reference to known minimal clinically meaningful difference (CMD) in scores. To evaluate for possible determinants of changes in global HRQoL, global HRQoL scores were correlated (Spearman's Rho) with subdomain and symptom scores and with interval time from surgical resection. Results: A total of 291 postoperative patients with histologically confirmed and surgically treated grade I meningiomas consented to participation and a total of 455 questionnaires were included for analysis. Patients with meningiomas reported reduced global HRQoL at nearly every 12-month interval with clinically and statistically significant impairments at 12, 48, 108, and 120 months postoperative compared with the normative population (P < 0.05). Meningioma patients at the 12-month interval also reported a reduction of each subdomain of HRQoL assessment (P < 0.05); however, a CMD was only seen in cognitive functioning. Physical, emotional, cognitive, and social subdomains, as well as fatigue and sleep/insomnia, were significantly associated with global HRQoL at the first 12-month interval. Overall, there was no significant correlation between time from surgery and global HRQoL or the subdomain functional or symptom sections of the QLQ-C30. Conclusions: Meningioma patients report considerable limitations in HRQoL for more than 120 months after surgery, particularly in cognitive, emotional, and social function, as well as suffering significant fatigue and sleep impairment compared with a normative reference population. The majority of these reported functional impairments and symptoms are strongly associated with global HRQoL and thus can be considered determinants of global HRQoL that if treated, have the potential to improve HRQoL for our meningioma patients. This hypothesis requires future study of targeted interventions to determine their efficacy.

Endoscopic management of Esthesioneuroblastoma: Our experience and review of the literature.

During the last two decades evolution of the endoscopic endonasal approaches (EEA) has offered the option of minimally invasive techniques in the management of esthesioneuroblastomas (ENB), either as endoscope assisted cranial resection or as pure endoscopic procedures. This study presents the use of pure EEA in the management of ENB in our center, along with a literature review. We retrospectively reviewed the clinical, radiology and pathology records of patients with ENB treated during the period July 2006 to January 2016. During the above period, ten patients with ENB were treated using pure EEA. The mean age was 47.5 years. The gender distribution was: eight males, two females. The most common presenting symptoms were nasal obstruction and discharge or epistaxis (8/10). The mean duration of symptoms was 1.5 years. All patients had preoperative confirmation of ENB by biopsy. Five patients received neoadjuvant radiation and four underwent postoperative radiation. One patient did not receive any radiotherapy and no patient received chemotherapy. Gross total resection was achieved in all patients and intraoperative microscopically negative surgical margins achieved in 9/10 (90%). No major intraoperative complications occurred. The most common postoperative complication was nasal infection. Cerebrospinal fluid leak was noted in one patient. During the follow-up period of 6-120 months (mean 74.8) two cases of neck lymph node recurrence were observed. No deaths due to the disease occurred during the follow-up period. Pure EEA offer excellent results in the management of ENB. Neoadjuvant radiation treatment is promising although more studies need to establish its role.

Therapeutic radiation for childhood cancer drives structural aberrations of NF2 in meningiomas.

Cranial radiotherapy improves survival of the most common childhood cancers, including brain tumors and leukemia. Unfortunately, long-term survivors are faced with consequences of secondary neoplasia, including radiation-induced meningiomas (RIMs). We characterized 31 RIMs with exome/NF2 intronic sequencing, RNA sequencing and methylation profiling, and found NF2 gene rearrangements in 12/31 of RIMs, an observation previously unreported in sporadic meningioma (SM). Additionally, known recurrent mutations characteristic of SM, including AKT1, KLF4, TRAF7 and SMO, were not observed in RIMs. Combined losses of chromosomes 1p and 22q were common in RIMs (16/18 cases) and overall, chromosomal aberrations were more complex than that observed in SM. Patterns of DNA methylation profiling supported similar cell of origin between RIMs and SMs. The findings indicate that the mutational landscape of RIMs is distinct from SMs, and have significant therapeutic implications for survivors of childhood cranial radiation and the elucidation of the molecular pathogenesis of meningiomas.Radiation-induced meningiomas are often more aggressive than sporadic ones. In this study, the authors perform an exome, methylation and RNA-seq analysis of 31 cases of radiation-induced meningioma and show NF2 rearrangement, an observation previously unreported in the sporadic tumors.

Radiosurgery for brainstem metastases with and without whole brain radiotherapy: clinical series and literature review.

OBJECTIVE: The objective of this study was to investigate outcomes for patients with brainstem metastases treated with stereotactic radiosurgery (SRS). METHODS: Patients with brainstem metastases treated with SRS between April 2006 and June 2012 were identified from a prospective database. Patient and treatment-related factors were recorded. Kaplan-Meier analysis was used to calculate survival and freedom from local and distant brain progression. Univariate and multivariate Cox regression was used to identify factors important for overall survival. RESULTS: In total, 44 patients received SRS for 48 brainstem metastases of whom 33 (75 %) also received whole brain radiotherapy (WBRT): 23 patients (52 %) WBRT prior to SRS, 6 (13.6 %) WBRT concurrently with SRS and 4 (9.0 %) WBRT after SRS. Eight patients received a second course of WBRT at further progression. Median target volume was 1.33 cc (range 0.04-12.17) and median prescribed marginal dose was 15 Gy (range 10-22). There were four cases of local failure, and 6-month and 1-year freedom from local failure was 84.6 and 76.9 %, respectively. Median overall survival (OS) was 5.4 months. There were four cases of radionecrosis, 2 (4.8 %) of which were symptomatic. The absence of external beam brain radiotherapy (predominantly WBRT) showed a trend towards improved OS on univariate analysis. Neither local nor distant brain failure significantly impacted OS. CONCLUSION: This retrospective series of patients treated with SRS for brainstem metastases, largely in combination with at least one course of WBRT, demonstrates that this approach is safe and results in good local control. In this cohort, no variables significantly impacted OS, including intracranial control.

Neurofibromatosis Clinic: A Report on Patient Demographics and Evaluation of the Clinic.

BACKGROUND: Neurofibromatosis type 1 (NF1) is a common single-gene disorder. A multidisciplinary approach to the management of NF1 patients is necessitated by the heterogeneity of clinical manifestations. Although multidisciplinary paediatric clinics have been well established, there is a dearth of such resources for adults with NF1. Herein we report our one-year institutional experience with a multidisciplinary adult NF1 clinic. METHODS: A multidisciplinary team was assembled, and an NF Patient Registry Initiative questionnaire was adapted to collect patient-reported data during clinics. Multiple databases were searched to identify publications pertaining to the experience of other multidisciplinary NF1 clinics focusing on adult patients. Data on patient epidemiology and clinical staff were compared to our data. RESULTS: A total of 77 patients were scheduled, and 68 attended the clinic, of whom 66 completed the intake questionnaire. The demographic and clinical data from this Canadian population are mostly consistent with previous reports, with some exceptions. Clinical data related to immune system involvement such as asthma, airway/breathing-related difficulties or allergies were striking in our NF1 population. Six relevant published reports of other NF1 clinics were identified. Reports from these studies pertained to periods ranging from 10 to 38 months, and the number of adults assessed ranged from 19 to 177 patients. CONCLUSIONS: The structure of our clinic and the patient volume are comparable to those of other established centres found in the literature. Our data offer valuable cross-sectional prevalence statistics in the Canadian population. The patient-reported data concerning involvement of the immune system contribute to an emerging recognized medical concern within the NF1 population and warrant further clinical and basic investigation.

TFE3-Expressing Perivascular Epithelioid Cell Neoplasm (PEComa) of the Sella Turcica.

We report a primary central nervous system (CNS) perivascular epithelioid cell tumor (PEComa) in a middle-aged female patient. The tumor occurred in suprasellar location with secondary extension into the sella turcica. The patient presented with intracranial hemorrhage and an altered level of consciousness. The tumor had morphologic features matching those of other previously described TFE3-translocated PEComas, including epithelioid morphology, diffuse and strong nuclear immunoreactivity for TFE3, and minimal staining with myoid markers. The TFE3 break-apart FISH testing showed a slight splitting of one of the TFE3 signals in 49.5 % of nuclei. This case illustrates that PEComas should be added to the growing list of mesenchymal tumors that can be encountered in the CNS and specifically in the vicinity of the pituitary gland. The recognition of this entity is of significance given their underlying pathogenesis and possible management implications.

Same-day discharge after craniotomy for supratentorial tumour surgery: a retrospective observational single-centre study.

PURPOSE: Enhanced Recovery After Surgery is a multimodal perioperative care pathway designed to achieve early discharge in patients undergoing major surgery. Recent advances in neurosurgery allow for shorter duration of anesthesia and surgery, faster recovery, and earlier discharge from hospital. The purpose of this retrospective observational study was to assess the incidence of early discharge from hospital in patients undergoing craniotomy for supratentorial brain tumours as well as to explore the associated perioperative factors, anesthesia techniques, and complications. METHODS: The medical records of all patients who underwent craniotomy (less than four-hour duration) for supratentorial tumour over a five-year period were retrospectively reviewed. The data analyzed included the postoperative discharge destination, type of anesthesia-i.e., general anesthesia (GA) vs awake craniotomy (AC), and the incidence of adverse events. RESULTS: Data from 329 patients [mean (SD) age 48 (12) yr; 164 male, 165 female] were analyzed, including 198 (AC, n = 157; GA, n = 41) patients who were preoperatively scheduled for same-day discharge. Successful same-day discharge occurred in 175/198 (88.4%) of these patients (AC, n = 139; GA, n = 36). Five (2.9%) of the 175 patients (4 AC, 1 GA) with same-day discharge required readmission to hospital within the first 12 hr after discharge. Six (1.8%) of the 329 total patients had a documented postoperative intracranial bleed, but none occurred after initial discharge from hospital. CONCLUSION: Same-day discharge from hospital is possible in carefully selected patients after both GA and AC for supratentorial tumour surgery.

The Influence of Corticosteroids on Diagnostic Accuracy of Biopsy for Primary Central Nervous System Lymphoma.

Classical neurosurgical teaching suggests that corticosteroid administration reduces the diagnostic yield of stereotactic brain biopsy for primary central nervous system lymphoma (PCNSL). In a single-center series spanning 6 years, we reviewed 155 consecutive biopsy patients, 135 treated with prebiopsy corticosteroids. PCNSL was correctly diagnosed on initial biopsy in 15 of 16 steroid-treated patients; in the single nondiagnostic specimen, polymerase chain reaction reanalysis by an outside institution showed evidence of lymphoproliferative disease consistent with PCNSL. Our data challenge the notion that it is necessary to withhold corticosteroid therapy for cerebral edema in patients awaiting stereotactic biopsy for suspected PCNSL.

Outpatient brain tumor craniotomy under general anesthesia.

OBJECTIVE Outpatient craniotomy has many advantages to the psychological and physical well-being of patients, as well as benefits to the health care system. Its efficacy and safety have been well demonstrated, but barriers to its widespread adoption remain. Among the challenges is a perception that its application is limited to cases performed under conscious sedation, which is not always feasible given certain patient or surgeon factors. The object of this study was to characterize the rate of patient discharge from the day surgery unit (DSU) following craniotomy for tumor resection in a patient under general anesthesia. The authors identify postoperative complications and discuss appropriate patient selection for day surgery craniotomy. METHODS Patients undergoing elective craniotomy for supratentorial tumors between January 2010 and June 2014 were prospectively considered for outpatient management. Authors of the present study performed a retrospective chart review of these patients, analyzing cases by intention to treat. RESULTS Of 318 craniotomies undertaken in the study period, 141 were performed with the patient under general anesthesia. The day surgery protocol was initiated in 44 cases and completed in 38 (86%). Five patients required admission from the DSU, and 1 was discharged but admitted within the 1st postoperative day. In-hospital medical complications were fewer in the outpatient group, and no patients experienced an adverse outcome due to early discharge. CONCLUSIONS Close clinical and imaging surveillance in the early postoperative period allows for safe discharge of patients following craniotomy for tumor resection performed under general anesthesia. Therefore, general anesthesia does not preclude the application of outpatient craniotomy.

A preclinical study demonstrating the efficacy of nilotinib in inhibiting the growth of pediatric high-grade glioma.

Solid tumors arising from malignant transformation of glial cells are one of the leading causes of central nervous system tumor-related death in children. Recurrence in spite of rigorous surgical and chemoradiation therapies remains a major hurdle in management of these tumors. Here, we investigate the efficacy of the second-generation receptor tyrosine kinase inhibitor nilotinib as a therapeutic option for the management of pediatric gliomas. We have utilized two independent pediatric high-grade glioma cell lines with either high platelet-derived growth factor receptor alpha (PDGFRα) or high PDGFRß expression in in vitro assays to investigate the specific downstream effects of nilotinib treatment. Using in vitro cell-based assays we show that nilotinib inhibits PDGF-BB-dependent activation of PDGFRα. We further show that nilotinib is able to decrease cell proliferation and anchorage-independent growth via suppression of AKT and ERK1/2 signaling pathways. Our results suggest that nilotinib may be effective for management of a PDGFRα-dependent group of pediatric gliomas.

Investigation of the in vitro therapeutic efficacy of nilotinib in immortalized human NF2-null vestibular schwannoma cells.

Vestibular schwannomas (VS) are a common posterior fossa brain tumor, and though benign can cause significant morbidity, particularly loss of hearing, tinnitus, vertigo and facial paralysis. The current treatment options for VS include microsurgical resection, stereotactic radiosurgery or close surveillance monitoring, with each treatment option carrying associated complications and morbidities. Most importantly, none of these options can definitively reverse hearing loss or tinnitus. Identification of a novel medical therapy, through the use of targeted molecular inhibition, is therefore a highly desirable treatment strategy that may minimize complications arising from both tumor and treatment and more importantly be suitable for patients whose options are limited with respect to surgical or radiosurgical interventions. In this study we chose to examine the effect of Nilotinib on VS. Nilotinib (Tasigna®) is a second-generation receptor tyrosine kinase (RTK) inhibitor with a target profile similar to that of imatinib (Gleevec®), but increased potency, decreased toxicity and greater cellular and tissue penetration. Nilotinib targets not only the BCR-ABL oncoprotein, but also platelet-derived growth factor (PDGF) receptor signalling. In this preclinical study, the human NF2-null schwannoma cell line HEI-193 subjected to nilotinib inhibition demonstrated decreased viability, proliferation and anchorage-independent growth, and increased apoptosis. A daily dose of nilotinib for 5 days inhibited HEI-I93 proliferation at a clinically-relevant concentration in a dose-dependent manner (IC(50) 3-5 µmol/L) in PDGF-stimulated cells. These anti-tumorigenic effects of nilotinib were correlated to inhibited activation of PDGFR-α and PDGFR-ß and major downstream signalling pathways. These experiments support a therapeutic potential for Nilotinib in VS.

The molecular structure of Rv2074, a probable pyridoxine 5'-phosphate oxidase from Mycobacterium tuberculosis, at 1.6 angstroms resolution.

The crystal structure of a conserved hypothetical protein corresponding to open reading frame Rv2074 from Mycobacterium tuberculosis (Mtb) has been solved by the two-wavelength anomalous dispersion method. Refinement of the molecular structure at 1.6 angstroms resolution resulted in an R(work) of 0.178 and an R(free) of 0.204. The crystal asymmetric unit contains an Rv2074 monomer; however, the crystallographic twofold symmetry operation of space group P4(3)2(1)2 generates dimeric Rv2074. Each monomer folds into a six-stranded antiparallel beta-barrel flanked by two alpha-helices. The three-dimensional structure of Rv2074 is very similar to that of Mtb Rv1155, a probable pyridoxine 5'-phosphate oxidase (PNPOx), which corroborates well with the relatively high sequence similarity (52%) between the two. A structural comparison between Rv2074 and Rv1155 revealed that the core structure (a six-stranded beta-barrel) is also well conserved; the major differences between the two lie in the N- and C-termini and in the small helical domain. Two citric acid molecules were observed in the active site of Rv2074, the crystals of which were grown in 0.2 M sodium citrate buffer pH 5.0. The citric acid molecules are bound to Rv2074 by hydrogen-bonding interactions with Thr55, Gln60 and Lys61. One of the two citric acid molecules occupies the same spatial position that corresponds to the position of the phosphate and ribose sugar moieties of the flavin mononucleotide (FMN) in the Mtb Rv1155-FMN, Escherichia coli PNPOx-FMN and human PNPOx-FMN complex structures. Owing to its extensive structural similarity with Mtb Rv1155 and to the E. coli and human PNPOx enzymes, Rv2074 may be involved in the final step in the biosynthesis of pyridoxal 5'-phosphate (PLP; a vitamin B6).