The natural history of Pelizaeus-Merzbacher disease caused by PLP1 duplication: A multiyear case series.

This study aimed to characterize the clinical features, developmental milestones, and the natural history of Pelizaeus-Merzbacher disease (PMD) associated with PLP1 gene duplications. The study examined 16 PMD Patients ranging in age from 7 to 48 years, who had a documented PLP1 gene duplication. The study examined and analyzed the medical and developmental histories of the subjects utilizing a combination of resources that included medical history questionnaires, medical record reviews, and a 31-point functional disability scale that had been previously validated. The data extracted from the medical records and questionnaires for analysis included information related to medical and developmental histories, level of ambulation and cognition, and degree of functional disability. The summation of findings among the study population demonstrated that the presenting symptoms, developmental milestones achieved, and progression of symptoms reported are consistent with many previous studies of patients with PLP1 duplications. All patients exhibited onset within the first year of life, with nystagmus predominating as the first symptom noticed. All patients exhibited delays in both motor and language development; however, many individuals were able to meet several developmental milestones. They exhibited some degree of continued motor impairment with none having the ability to walk independently. All patients were able to complete at least some of the cognition achievements and although not all were verbal, a number were able to use communication devices to complete these tasks. A critical tool of the study was the functional disability scale which provided a major advantage in helping quantify the clinical course of PMD, and for several, we were able to gather this information at more than one point in time. These reported findings in our cohort contribute important insight into the clinical heterogeneity and potential underlying mechanisms that define the molecular pathogenesis of the disease. This is one of only a small number of natural history studies examining the clinical course of a cohort of patients with PLP1 duplications within the context of a validated functional disability scoring system. This study is unique in that it is limited to subjects with PLP1 gene duplications. This study demonstrated many commonalities to other studies that have characterized the features of PMD and other PLP1-related disorders but also provide significant new insights into the evolving story that marks the natural history.

USMLE step 1 and step 2 CK as indicators of resident performance.

BACKGROUND: The purpose of this systematic review was to (1) determine the scope of literature measuring USMLE Step 1 and Step 2 CK as predictors or indicators of quality resident performance across all medical specialties and (2) summarize the ability of Step 1 and Step 2 CK to predict quality resident performance, stratified by ACGME specialties, based on available literature. METHODS: This systematic review was designed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) [16]. The original search strategy surveyed MEDLINE and was adapted to survey Cochrane Library and Embase. A study was deemed eligible if it provided all three of the following relevant information: (a) Step 1 or Step 2 CK as indicators for (b) resident outcomes in (c) any ACGME accredited specialty training program. RESULTS: A total of 1803 articles were screened from three separate databases. The 92 included studies were stratified by specialty, with Surgery (21.7% [20/92]), Emergency Medicine (13.0% [12/92]), Internal Medicine (10.9% [10/92]), and Orthopedic Surgery (8.7% [8/92]) being the most common. Common resident performance measures included ITE scores, board certification, ACGME milestone ratings, and program director evaluations. CONCLUSIONS: Further studies are imperative to discern the utility of Step 1 and Step 2 CK as predictors of resident performance and as tools for resident recruitment and selection. The results of this systematic review suggest that a scored Step 1 dated prior to January 2022 can be useful as a tool in a holistic review of future resident performance, and that Step 2 CK score performance may be an effective tool in the holistic review process. Given its inherent complexity, multiple tools across many assessment modalities are necessary to assess resident performance comprehensively and effectively.

Development of an assessment technique for basic science retention using the NBME subject exam data.

INTRODUCTION: One of the challenges in medical education is effectively assessing basic science knowledge retention. National Board of Medical Examiners (NBME) clerkship subject exam performance is reflective of the basic science knowledge accrued during preclinical education. The aim of this study was to determine if students' retention of basic science knowledge during the clerkship years can be analyzed using a cognitive diagnostic assessment (CDA) of the NBME subject exam data. METHODS: We acquired a customized NBME item analysis report of our institution's pediatric clerkship subject exams for the period of 2017-2020 and developed a question-by-content Q-matrix by identifying skills necessary to master content. As a pilot study, students' content mastery in 12 major basic science content areas was analyzed using a CDA model called DINA (deterministic input, noisy "and" gate). RESULTS: The results allowed us to identify strong and weak basic science content areas for students in the pediatric clerkship. For example: "Reproductive systems" and "Skin and subcutaneous tissue" showed a student mastery of 83.8 ± 2.2% and 60.7 ± 3.2%, respectively. CONCLUSIONS: Our pilot study demonstrates how this new technique can be applicable in quantitatively measuring students' basic science knowledge retention during any clerkship. Combined data from all the clerkships will allow comparisons of specific content areas and identification of individual variations between different clerkships. In addition, the same technique can be used to analyze internal assessments thereby creating an opportunity for the longitudinal tracking of student performances. Detailed analyses like this can guide specific curricular changes and drive continuous quality improvement in the undergraduate medical school curriculum.

Altered high-energy phosphate and membrane metabolism in Pelizaeus-Merzbacher disease using phosphorus magnetic resonance spectroscopy.

Pelizaeus-Merzbacher disease is an X-linked recessive leucodystrophy of the central nervous system caused by mutations affecting the major myelin protein, proteolipid protein 1. The extent of the altered in vivo neurochemistry of protein, proteolipid protein 1 duplications, the most common form of Pelizaeus-Merzbacher disease, is, however, poorly understood. Phosphorus magnetic resonance spectroscopy is the only in vivo technique that can assess the biochemistry associated with high-energy phosphate and membrane phospholipid metabolism across different cortical, subcortical and white matter areas. In this cross-sectional study, whole-brain, multi-voxel phosphorus magnetic resonance spectroscopy was acquired at 3 T on 14 patients with Pelizaeus-Merzbacher disease with protein, proteolipid protein 1 duplications and 23 healthy controls (all males). Anabolic and catabolic levels of membrane phospholipids (phosphocholine and phosphoethanolamine, and glycerophosphoethanolamine and glycerophosphocholine, respectively), as well as phosphocreatine, inorganic orthophosphate and adenosine triphosphate levels relative to the total phosphorus magnetic resonance spectroscopy signal from 12 different cortical and subcortical areas were compared between the two groups. Independent of brain area, phosphocholine, glycerophosphoethanolamine and inorganic orthophosphate levels were significantly lower (P = 0.0025, P < 0.0001 and P = 0.0002) and phosphocreatine levels were significantly higher (P < 0.0001) in Pelizaeus-Merzbacher disease patients compared with controls. Additionally, there was a significant group-by-brain area interaction for phosphocreatine with post-hoc analyses demonstrating significantly higher phosphocreatine levels in patients with Pelizaeus-Merzbacher disease compared with controls across multiple brain areas (anterior and posterior white matter, superior parietal lobe, posterior cingulate cortex, hippocampus, occipital cortex, striatum and thalamus; all P ≤ 0.0042). Phosphoethanolamine, glycerophosphoethanolamine and adenosine triphosphate levels were not significantly different between groups. For the first-time, widespread alterations in phosphorus magnetic resonance spectroscopy metabolite levels of Pelizaeus-Merzbacher disease patients are being reported. Specifically, increased high-energy phosphate storage levels of phosphocreatine concomitant with decreased inorganic orthophosphate across multiple areas suggest a widespread reduction in the high-energy phosphate utilization in Pelizaeus-Merzbacher disease, and the membrane phospholipid metabolite deficits suggest a widespread degradation in the neuropil content/maintenance of patients with Pelizaeus-Merzbacher disease which includes axons, dendrites and astrocytes within cortex and the myelin microstructure and oligodendrocytes within white matter. These results provide greater insight into the neuropathology of Pelizaeus-Merzbacher disease both in terms of energy expenditure and membrane phospholipid metabolites. Future longitudinal studies are warranted to investigate the utility of phosphorus magnetic resonance spectroscopy as surrogate biomarkers in monitoring treatment intervention for Pelizaeus-Merzbacher disease.

Modeling the Mutational and Phenotypic Landscapes of Pelizaeus-Merzbacher Disease with Human iPSC-Derived Oligodendrocytes.

Pelizaeus-Merzbacher disease (PMD) is a pediatric disease of myelin in the central nervous system and manifests with a wide spectrum of clinical severities. Although PMD is a rare monogenic disease, hundreds of mutations in the X-linked myelin gene proteolipid protein 1 (PLP1) have been identified in humans. Attempts to identify a common pathogenic process underlying PMD have been complicated by an incomplete understanding of PLP1 dysfunction and limited access to primary human oligodendrocytes. To address this, we generated panels of human induced pluripotent stem cells (hiPSCs) and hiPSC-derived oligodendrocytes from 12 individuals with mutations spanning the genetic and clinical diversity of PMD-including point mutations and duplication, triplication, and deletion of PLP1-and developed an in vitro platform for molecular and cellular characterization of all 12 mutations simultaneously. We identified individual and shared defects in PLP1 mRNA expression and splicing, oligodendrocyte progenitor development, and oligodendrocyte morphology and capacity for myelination. These observations enabled classification of PMD subgroups by cell-intrinsic phenotypes and identified a subset of mutations for targeted testing of small-molecule modulators of the endoplasmic reticulum stress response, which improved both morphologic and myelination defects. Collectively, these data provide insights into the pathogeneses of a variety of PLP1 mutations and suggest that disparate etiologies of PMD could require specific treatment approaches for subsets of individuals. More broadly, this study demonstrates the versatility of a hiPSC-based panel spanning the mutational heterogeneity within a single disease and establishes a widely applicable platform for genotype-phenotype correlation and drug screening in any human myelin disorder.

Novel pathologic findings in patients with Pelizaeus-Merzbacher disease.

Pelizaeus-Merzbacher disease (PMD) is an X-linked inherited hypomyelinating disorder caused by mutations in the gene encoding proteolipid protein (PLP), the major structural protein in central nervous system (CNS) myelin. Prior to our study, whether hypomyelination in PMD was caused by demyelination, abnormally thin sheaths or failure to form myelin was unknown. In this study, we compared the microscopic pathology of myelin from brain tissue of 3 PMD patients with PLP1 duplications to that of a patient with a complete PLP1 deletion. Autopsy tissue procured from PMD patients was embedded in paraffin for immunocytochemistry and plastic for electron microscopy to obtain highresolution fiber pathology of cerebrum and corpus callosum. Through histological stains, immunocytochemistry and electron microscopy, our study illustrates unique pathologic findings between the two different types of mutations. Characteristic of the patient with a PLP1 deletion, myelin sheaths showed splitting and decompaction of myelin, confirming for the first time that myelin in PLP1 deletion patients is similar to that of rodent models with gene deletions. Myelin thickness and g-ratios of some fibers, in relation to axon diameter was abnormally thin, suggesting that oligodendrocytes remain metabolically functional and/or are attempting to make myelin. Many fibers showed swollen, progressive degenerative changes to axons in addition to the dissolution of myelin. All three duplication cases shared remarkable fiber pathology including swellings, constriction and/or transection and involution of myelin. Characteristic of PLP1 duplication patients, many axons showed segmental demyelination along their length. Still other axons had abnormally thick myelin sheaths, suggestive of continued myelination. Thus, each type of mutation exhibited unique pathology even though commonality to both mutations included involution of myelin, myelin balls and degeneration of axons. This pathology study describes findings unique to each mutation that suggests the mechanism causing fiber pathology is likewise heterogeneous.

Diffusion tensor imaging of patients with proteolipid protein 1 gene mutations.

Pelizaeus-Merzbacher disease (PMD) is an X-linked disorder of the central nervous system (CNS) caused by a wide variety of mutations affecting proteolipid protein 1 (PLP1). We assessed the effects of PLP1 mutations on water diffusion in CNS white matter by using diffusion tensor imaging. Twelve patients with different PLP1 point mutations encompassing a range of clinical phenotypes were analyzed, and the results were compared with a group of 12 age-matched controls. The parallel (λ// ), perpendicular (λ⊥ ), and apparent diffusion coefficients (ADC) and fractional anisotropy were measured in both limbs of the internal capsule, the genu and splenium of corpus callosum, the base of the pons, and the cerebral peduncles. The mean ADC and λ⊥ in the PMD patient group were both significantly increased in all selected structures, except for the base of the pons, compared with controls. PMD patients with the most severe disease, however, had a significant increase of both λ// and λ⊥ . In contrast, more mildly affected patients had much smaller changes in λ// and λ⊥ . These data suggest that myelin, the structure responsible in part for the λ⊥ barrier, is the major site of disease pathogenesis in this heterogeneous group of patients. Axons, in contrast, the structures mainly responsible for λ// , are much less affected, except within the subgroup of patients with the most severe disease. Clinical disability in patients with PLP1 point mutation is thus likely determined by the extent of pathological involvement of both myelin and axons, with alterations of both structures causing the most severe disease. © 2014 Wiley Periodicals, Inc.

Neuroradiologic correlates of clinical disability and progression in the X-linked leukodystrophy Pelizaeus-Merzbacher disease.

OBJECTIVE: To determine whether quantitative measure of magnetic resonance imaging data from patients with the inherited leukodystrophy, Pelizaeus-Merzbacher disease (PMD) correlates with clinical severity or progression. METHODS: In our current work we have analyzed the clinical phenotypes and MRI scans of 51 male patients with PMD and 10 female carriers for whom the PLP1 genotype had been determined. In addition, we developed a 32-point functional disability scoring (FDS) system for PMD, and validated it for inter-rater reliability. Using conventional T1- and T2-weighted MRI images of the whole brain, we measured white matter and total brain volume (WMV and TBV), inter-caudate ratio (ICR), and corpus callosum area. RESULTS: There was a significant positive correlation of FDS with white matter fraction (WMV/TBV) and corpus callosum area. Also, when applying a median split based on FDS, patients with lower FDS showed reduced white matter fraction and corpus callosum area, and increased ICR compared to patients with relatively higher FDS, regardless of age. CONCLUSION: Although this patient population is heterogeneous, with multiple genetic and molecular mechanisms causing PMD, these data imply that white matter atrophy is a major pathological determinant of the clinical disability in most patients. Development of reliable non-invasive quantitative biomarkers of disease activity would be useful not only for following the natural history of the disease, but also raising the potential for evaluating future therapies.

Inhibition of amiodarone-induced lung fibrosis but not alveolitis by angiotensin system antagonists.

Earlier work in this laboratory showed that amiodarone induces apoptosis in alveolar epithelial cells by a mechanism inhibitable by angiotensin system antagonists. A variety of recent studies suggests a critical role for alveolar epithelial cell apoptosis in the pathogenesis of lung fibrosis. On this basis we hypothesized that amiodarone-induced alveolar epithelial cell apoptosis and lung fibrosis in vivo might be inhibitable by the angiotensin converting enzyme inhibitor captopril or the angiotensin receptor antagonist losartan. Amiodarone-induced lung fibrosis was induced in male Wistar rats by oral administration over six months. Replicate groups of rats received captopril or losartan in addition to amiodarone. Apoptosis was detected by increased total lung activity of caspase 3 and in situ end labeling (ISEL) of fragmented DNA. Collagen was localized and quantitated by the picrosirius red technique. Alveolar epithelial cell apoptosis was detected in amiodarone-treated animals as early as three weeks after the start of amiodarone administration; by six months exposure, the incidence of alveolar epithelial cell apoptosis was significantly reduced by coadministration of captopril or losartan. Alveolar wall collagen accumulation also was significantly attenuated by captopril (100%) or losartan (74%), but neither agent blunted the accumulation of alveolar macrophages evoked by amiodarone (5.3-fold at 6 months). Lung neutrophil content was unchanged by amiodarone treatment for three weeks or six months. These results indicate that amiodarone induces alveolar epithelial cell apoptosis in vivo that is inhibitable by angiotensin antagonists. They also support the hypothesis that blockade of angiotensin formation or function attenuates amiodarone-induced lung fibrosis irrespective of the severity of alveolitis.

Apoptosis-dependent acute lung injury and repair after intratracheal instillation of noradrenaline in rats.

Earlier work in this laboratory showed that noradrenaline (NA) induces apoptosis in primary cultures of alveolar epithelial cells (AECs). Apoptosis of alveolar epithelial cells may promote the collapse of lung barrier function. On this basis we hypothesized that exogenous NA, administered by intratracheal (I.T.) instillation, might induce AEC apoptosis in vivo followed by acute lung injury. Delivery of NA (10 microM) I.T. into male Wistar rats increased labelling of both fragmented DNA, measured by in situ end labelling (ISEL), and the active form of caspase 3 (anti-Casp3) 6 and 20 h after administration (P < 0.05), but instillation of the vehicle alone (PBS) had no effect. Both ISEL and anti-Casp3 labelling were attenuated by concurrent I.T. delivery of the broad-spectrum caspase inhibitor ZVADfmk. After 6 h, most ISEL- and Casp3-positive cells were located in the surfaces of alveolar walls, but after 20 h more were found in alveolar spaces (P < 0.05). Instillation of NA also increased the bronchoalveolar lavage (BAL) content of fluorescent albumin (BODIPY-alb), which had previously been injected intravenously; the increase was reversed by concurrent ZVADfmk administration. These data suggest that NA-induced apoptosis of AECs in vivo is sufficient to invoke transient collapse of AEC barrier function that is rapidly repaired.