Vanishing white matter: Eukaryotic initiation factor 2B model and the impact of missense mutations

In vivo base editing of a pathogenic Eif2b5 variant improves vanishing white matter phenotypes in mice

Vanishing white matter (VWM) is a fatal leukodystrophy caused by recessive mutations in subunits of the eukaryotic translation initiation factor 2B. Currently, there are no effective therapies for VWM. Here, we assessed the potential of adenine base editing to correct human pathogenic VWM variants in mouse models. Using adeno-associated viral vectors, we delivered intein-split adenine base editors into the cerebral ventricles of newborn VWM mice, resulting in 45.9% ± 5.9% correction of the Eif2b5R191H variant in the cortex. Treatment slightly increased mature astrocyte populations and partially recovered the integrated stress response (ISR) in female VWM animals. This led to notable improvements in bodyweight and grip strength in females; however, locomotor disabilities were not rescued. Further molecular analyses suggest that more precise editing (i.e., lower rates of bystander editing) as well as more efficient delivery of the base editors to deep brain regions and oligodendrocytes would have been required for a broader phenotypic rescue. Our study emphasizes the potential, but also identifies limitations, of current in vivo base-editing approaches for the treatment of VWM or other leukodystrophies.

Screening of premature ovarian insufficiency associated genes in Hungarian patients with next generation sequencing

BACKGROUND

Premature ovarian insuffiency (POI) is one of the main cause behind infertility. The genetic analysis of POI should be part of the clinical diagnostics, as several genes have been implicated in the genetic background of it. The aim of our study was to analyse the genetic background of POI in a Hungarian cohort.

METHODS

The age of onset was between 15 and 39 years. All patients had the 46,XX karyotype and they were prescreened for the most frequent POI associated FMR1 premutation. To identify genetic alterations next-generation sequencing (NGS) of 31 genes which were previously associated to POI were carried out in 48 unrelated patients from Hungary.

RESULTS

Monogenic defect was identified in 16.7% (8 of 48) and a potential genetic risk factor was found in 29.2% (14 of 48) and susceptible oligogenic effect was described in 12.5% (6 of 48) of women with POI using the customized targeted panel sequencing. The genetic analysis identified 8 heterozygous damaging and 4 potentially damaging variants in POI-associated genes. Further 10 potential genetic risk factors were detected in seven genes, from which EIF2B and GALT were the most frequent. These variants were related to 15 genes: AIRE, ATM, DACH2, DAZL, EIF2B2, EIF2B4, FMR1, GALT, GDF9, HS6ST2, LHCGR, NOBOX, POLG, USP9X and XPNPEP2. In six cases, two or three coexisting damaging mutations and risk variants were identified.

CONCLUSIONS

POI is characterized by heterogenous phenotypic features with complex genetic background that contains increasing number of genes. Deleterious variants, which were detected in our cohort, related to gonadal development (oogenesis and folliculogenesis), meiosis and DNA repair, hormonal signaling, immune function, and metabolism which were previously associated with the POI phenotype. This is the first genetic epidemiology study targeting POI associated genes in Hungary. The frequency of variants in different POI associated genes were similar to the literature, except EIF2B and GALT. Both of these genes potential risk factor were detected which could influence the phenotype, although it is unlikely that they can be responsible for the development of the disease by themselves. Advances of sequencing technologies make it possible to aid diagnostics of POI Since individual patients show high phenotypic variance because of the complex network controlling human folliculogenesis. Comprehensive NGS screening by widening the scope to genes which were previously linked to infertility may facilitate more accurate, quicker and cheaper genetic diagnoses for POI. The investigation of patient's genotype could support clinical decision-making process and pave the way for future clinical trials and therapies.

GDF15 is a dynamic biomarker of the integrated stress response in the central nervous system

AIM

Characterize Growth Differentiation Factor 15 (GDF15) as a secreted biomarker of the integrated stress response (ISR) within the central nervous system (CNS).

METHODS

We determined GDF15 levels utilizing in vitro and in vivo neuronal systems wherein the ISR was activated. Primarily, we used the murine model of vanishing white matter disease (VWMD), a neurological disease driven by persistent ISR in the CNS, to establish a link between levels of GDF15 in the cerebrospinal fluid (CSF) and ISR gene expression signature in the CNS. GDF15 was also determined in the CSF of VWM patients.

RESULTS

GDF15 expression was increased concomitant to ISR activation in stress-induced primary astrocytes as well as in retinal ganglion cells following optic nerve crush, while treatment with 2Bact, a specific eIF2B activator, suppressed both the ISR and GDF15. In the VWMD model, CSF GDF15 levels corresponded with the magnitude of the ISR and were reduced by 2BAct. In VWM patients, mean CSF GDF15 was elevated >20-fold as compared to healthy controls, whereas plasma GDF15 was undifferentiated.

CONCLUSIONS

These data suggest that CSF GDF15 is a dynamic marker of ISR activation in the CNS and may serve as a pharmacodynamic biomarker for ISR-modulating therapies.

Core protocol development for phase 2/3 clinical trials in the leukodystrophy vanishing white matter: a consensus statement by the VWM consortium and patient advocates

BACKGROUND

The leukodystrophy "Vanishing White Matter" (VWM) is an orphan disease with neurological decline and high mortality. Currently, VWM has no approved treatments, but advances in understanding pathophysiology have led to identification of promising therapies. Several investigational medicinal products are either in or about to enter clinical trial phase. Clinical trials in VWM pose serious challenges, as VWM has an episodic disease course; disease phenotype is highly heterogeneous and predictable only for early onset; and study power is limited by the small patient numbers. To address these challenges and accelerate therapy delivery, the VWM Consortium, a group of academic clinicians with expertise in VWM, decided to develop a core protocol to function as a template for trials, to improve trial design and facilitate sharing of control data, while permitting flexibility regarding other trial details. Overall aims of the core protocol are to collect safety, tolerability, and efficacy data for treatment assessment and marketing authorization.

METHODS

To develop the core protocol, the VWM Consortium designated a committee, including clinician members of the VWM Consortium, family and patient group advocates, and experts in statistics, clinical trial design and alliancing with industries. We drafted three age-specific protocols, to stratify into more homogeneous patient groups, of ages ≥ 18 years, ≥ 6 to < 18 years and < 6 years. We chose double-blind, randomized, placebo-controlled design for patients aged ≥ 6 years; and open-label non-randomized natural-history-controlled design for patients < 6 years. The protocol describes study populations, age-specific endpoints, inclusion and exclusion criteria, study schedules, sample size determinations, and statistical considerations.

DISCUSSION

The core protocol provides a shared uniformity across trials, enables a pool of shared controls, and reduces the total number of patients necessary per trial, limiting the number of patients on placebo. All VWM clinical trials are suggested to adhere to the core protocol. Other trial components such as choice of primary outcome, pharmacokinetics, pharmacodynamics, and biomarkers are flexible and unconstrained by the core protocol. Each sponsor is responsible for their trial execution, while the control data are handled by a shared research organization. This core protocol benefits the efficiency of parallel and consecutive trials in VWM, and we hope accelerates time to availability of treatments for VWM.

TRIAL REGISTRATION

NA. From a scientific and ethical perspective, it is strongly recommended that all interventional trials using this core protocol are registered in a clinical trial register.

Vector enabled CRISPR gene editing - A revolutionary strategy for targeting the diversity of brain pathologies

Brain pathologies are considered one of the greatest contributors of death and disability worldwide. Neurodegenerative Alzheimer's disease is the second leading cause of death in adults, whilst brain cancers including glioblastoma multiforme in adults, and pediatric-type high-grade gliomas in children remain largely untreatable. A further compounding issue for patients with brain pathologies is that of long-term neuropsychiatric sequela - as a symptom or arising from high dose therapeutic intervention. The major challenge to effective, low dose treatment is finding therapeutics that successfully cross the blood-brain barrier and target aberrant cellular processes, while having minimum effect on essential cellular processes, and healthy bystander cells. Following over 30 years of research, CRISPR technology has emerged as a biomedical tour de force with the potential to revolutionise the treatment of both neurological and cancer related brain pathologies. The aim of this review is to take stock of the progress made in CRISPR technology in relation to treating brain pathologies. Specifically, we will describe studies which look beyond design, synthesis, and theoretical application; and focus instead on in vivo studies with translation potential. Along with discussing the latest breakthrough techniques being applied within the CRISPR field, we aim to provide a prospective on the knowledge gaps that exist and challenges that still lay ahead for CRISPR technology prior to successful application in the brain disease treatment field.

The Coexistence of Two Genetic Astrocytopathies-Megalencephalic Leukoencephalopathy and Vanishing White Matter Disease-in an Indian Child

A 9-month-old male child, born of second-degree consanguinity, presented with a progressively enlarging head since early infancy. The child had normal early development, but further acquisition of milestones after 6 months was delayed. He had afebrile seizures at 9 months, followed by the appearance of appendicular spasticity. First magnetic resonance imaging (MRI) showed nonenhancing, diffuse, bilaterally symmetrical T1/fluid-attenuated inversion recovery (FLAIR) hypointensity and T2 hyperintensity of the cerebral white matter and anterior temporal cysts. Subsequently, the periventricular and deep white matter developed microcystic changes with a pattern of radial stripes. Next-generation sequencing revealed homozygous autosomal recessive variations in the MLC1 gene [c.188T > G, (p.Leu63Arg)] on exon 3 and also in the EIF2B3 gene [c.674G > A, (p.Arg225Gln)] on exon 7, the parents being heterozygous carriers for both variations. This article highlights the rare occurrence of two leukodystrophies of diverse pathogenesis in a child from a nonpredisposed community.

Guanabenz ameliorates disease in vanishing white matter mice in contrast to sephin1

OBJECTIVE

Vanishing white matter (VWM) is a leukodystrophy, characterized by stress-sensitive neurological deterioration and premature death. It is currently without curative treatment. It is caused by bi-allelic pathogenic variants in the genes encoding eukaryotic initiation factor 2B (eIF2B). eIF2B is essential for the regulation of the integrated stress response (ISR), a physiological response to cellular stress. Preclinical studies on VWM mouse models revealed that deregulated ISR is key in the pathophysiology of VWM and an effective treatment target. Guanabenz, an α2-adrenergic agonist, attenuates the ISR and has beneficial effects on VWM neuropathology. The current study aimed at elucidating guanabenz's disease-modifying potential and mechanism of action in VWM mice. Sephin1, an ISR-modulating guanabenz analog without α2-adrenergic agonistic properties, was included to separate effects on the ISR from α2-adrenergic effects.

METHODS

Wild-type and VWM mice were subjected to placebo, guanabenz or sephin1 treatments. Effects on clinical signs, neuropathology, and ISR deregulation were determined. Guanabenz's and sephin1's ISR-modifying effects were tested in cultured cells that expressed or lacked the α2-adrenergic receptor.

RESULTS

Guanabenz improved clinical signs, neuropathological hallmarks, and ISR regulation in VWM mice, but sephin1 did not. Guanabenz's effects on the ISR in VWM mice were not replicated in cell cultures and the contribution of α2-adrenergic effects on the deregulated ISR could therefore not be assessed.

INTERPRETATION

Guanabenz proved itself as a viable treatment option for VWM. The exact mechanism through which guanabenz exerts its ameliorating impact on VWM requires further studies. Sephin1 is not simply a guanabenz replacement without α2-adrenergic effects.

Association Between Late-Onset Leukoencephalopathy With Vanishing White Matter and Compound Heterozygous EIF2B5 Gene Mutations: A Case Report and Review of the Literature

Leukoencephalopathy with vanishing white matter (LVWM) is an autosomal recessive disease. Ovarioleukodystrophy is defined as LVWM in females showing signs or symptoms of gradual ovarian failure. We present a 38-year-old female with ovarioleukodystrophy who showed status epilepticus, gait instability, slurred speech, abdominal tendon hyperreflexia, and ovarian failure. Abnormal EEG, characteristic magnetic resonance, and unreported EIF2B5 compound heterozygous mutations [c.1016G>A (p.R339Q) and c.1157G>A (p.G386D)] were found. Furthermore, the present report summarizes 20 female patients with adult-onset ovarioleukodystrophy and EIF2B5 gene mutations. In conclusion, a new genetic locus for LVWM was discovered. Compared with previous cases, mutations at different EIF2B5 sites might have different clinical manifestations and obvious clinical heterogeneity.

The role of eIF2 phosphorylation in cell and organismal physiology: new roles for well-known actors

Control of protein synthesis (mRNA translation) plays key roles in shaping the proteome and in many physiological, including homeostatic, responses. One long-known translational control mechanism involves phosphorylation of initiation factor, eIF2, which is catalysed by any one of four protein kinases, which are generally activated in response to stresses. They form a key arm of the integrated stress response (ISR). Phosphorylated eIF2 inhibits eIF2B (the protein that promotes exchange of eIF2-bound GDP for GTP) and thus impairs general protein synthesis. However, this mechanism actually promotes translation of certain mRNAs by virtue of specific features they possess. Recent work has uncovered many previously unknown features of this regulatory system. Several studies have yielded crucial insights into the structure and control of eIF2, including that eIF2B is regulated by several metabolites. Recent studies also reveal that control of eIF2 and the ISR helps determine organismal lifespan and surprising roles in sensing mitochondrial stresses and in controlling the mammalian target of rapamycin (mTOR). The latter effect involves an unexpected role for one of the eIF2 kinases, HRI. Phosphoproteomic analysis identified new substrates for another eIF2 kinase, Gcn2, which senses the availability of amino acids. Several genetic disorders arise from mutations in genes for eIF2α kinases or eIF2B (i.e. vanishing white matter disease, VWM and microcephaly, epileptic seizures, microcephaly, hypogenitalism, diabetes and obesity, MEHMO). Furthermore, the eIF2-mediated ISR plays roles in cognitive decline associated with Alzheimer's disease. New findings suggest potential therapeutic value in interfering with the ISR in certain settings, including VWM, for example by using compounds that promote eIF2B activity.

Therapy Trial Design in Vanishing White Matter: An Expert Consortium Opinion

Vanishing white matter (VWM) is a leukodystrophy caused by recessive variants in the genes EIF2B1-EIF2B5. It is characterized by chronic neurologic deterioration with superimposed stress-provoked episodes of rapid decline. Disease onset spans from the antenatal period through senescence. Age at onset predicts disease evolution for patients with early onset, whereas disease evolution is unpredictable for later onset; patients with infantile and early childhood onset consistently have severe disease with rapid neurologic decline and often early death, whereas patients with later onset have highly variable disease. VWM is rare, but likely underdiagnosed, particularly in adults. Apart from measures to prevent stressors that could provoke acute deteriorations, only symptomatic care is currently offered. With increased insight into VWM disease mechanisms, opportunities for treatment have emerged. EIF2B1-EIF2B5 encode the 5-subunit eukaryotic initiation factor 2B complex, which is essential for translation of mRNAs into proteins and is a principal regulator of the integrated stress response (ISR). ISR deregulation is central to VWM pathology. Targeting components of the ISR has proven beneficial in mutant VWM mouse models, and several drugs are now in clinical development. However, clinical trials in VWM pose considerable challenges: low numbers of known patients with VWM, unpredictable disease course for patients with onset after early childhood, absence of intermediate biomarkers, and novel first-in-human molecular targets. Given these challenges and considering the critical need to offer therapies, we have formulated recommendations for enhanced diagnosis, drug trial setup, and patient selection, based on our expert evaluation of molecular, laboratory, and clinical data.

Correlation Between Genotype and Age of Onset in Leukoencephalopathy With Vanishing White Matter

Purpose: Leukoencephalopathy with vanishing white matter (VWM) is an autosomal recessive leukoencephalopathy caused by mutations in any of the five genes encoding the subunits of eukaryotic translation initiation factor 2B (eIF2B). The severity of the disease varies considerably, and its genotypic-phenotypic correlation is still unclear. Age of onset is the only independent clinical predictor for VWM severity. In this study, the correlation between genotype and age at onset of patients was investigated.

Methods: Data were collected from patients with VWM in the available literature reports and from those diagnosed in Peking University First Hospital. The age of onset was divided into early-onset (≤4 years) and late-onset type (>4 years) for the analysis of the correlation between genotype and age of onset in patients with VWM.

Results: A total of 341 patients were included, 281 were reported in 87 available articles and 60 were diagnosed in our center. A total of 180 different mutations were found, among which 86.1% were missense. The gene (EIF2B1-5) in which the mutation located, and the number of null alleles were not associated with age of onset in these patients. Certain mutations such as eIF2Bε[Arg195His] and eIF2Bε[Arg269Gln] that were predicted to have a serious influence on eIF2B structure were related to earlier age of onset. EIF2Bγ[Ala87Val] which was predicted to have a minimal influence on eIF2B structure, was related to later age of onset. Whereas eIF2Bβ[Glu213Gly], eIF2Bβ[Gly200Val] and eIF2Bε[Thr91Ala], also predicted having a small effect on the structure of eIF2B, did not show correlation with the age of onset. The onset age of patients with one or biallelic missense mutations located in the catalytic domain or other homologous domains in catalytic subunits (eIF2Bγ, ε) was earlier than that of patients with biallelic mutations located in the NT domain.

Conclusion: The onset age of patients with different genotypes varied greatly. The degree of influence in protein structure of some missense mutations was correlated with phenotypic severity, but the results were not completely consistent. The combined effect of biallelic mutations, the role of regulatory genes, environmental stress and other potential factors on phenotypes need to be further explored.

A (dis)integrated stress response: Genetic diseases of eIF2α regulators

The integrated stress response (ISR) is a conserved mechanism by which eukaryotic cells remodel gene expression to adapt to intrinsic and extrinsic stressors rapidly and reversibly. The ISR is initiated when stress-activated protein kinases phosphorylate the major translation initiation factor eukaryotic translation initiation factor 2ɑ (eIF2ɑ), which globally suppresses translation initiation activity and permits the selective translation of stress-induced genes including important transcription factors such as activating transcription factor 4 (ATF4). Translationally repressed messenger RNAs (mRNAs) and noncoding RNAs assemble into cytoplasmic RNA-protein granules and polyadenylated RNAs are concomitantly stabilized. Thus, regulated changes in mRNA translation, stability, and localization to RNA-protein granules contribute to the reprogramming of gene expression that defines the ISR. We discuss fundamental mechanisms of RNA regulation during the ISR and provide an overview of a growing class of genetic disorders associated with mutant alleles of key translation factors in the ISR pathway. This article is categorized under: RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications RNA in Disease and Development > RNA in Disease Translation > Translation Regulation RNA in Disease and Development > RNA in Development.

MRI Natural History of the Leukodystrophy Vanishing White Matter

Background In vanishing white matter (VWM), a form of leukodystrophy, earlier onset is associated with faster clinical progression. MRI typically shows rarefaction and cystic destruction of the cerebral white matter. Information on the evolution of VWM according to age at onset is lacking. Purpose To determine whether nature and progression of cerebral white matter abnormalities in VWM differ according to age at onset. Materials and Methods Patients with genetically confirmed VWM were stratified into six groups according to age at onset: younger than 1 year, 1 year to younger than 2 years, 2 years to younger than 4 years, 4 years to younger than 8 years, 8 years to younger than 18 years, and 18 years or older. With institutional review board approval, all available MRI scans obtained between 1985 and 2019 were retrospectively analyzed with three methods: (a) ratio of the width of the lateral ventricles over the skull (ventricle-to-skull ratio [VSR]) was measured to estimate brain atrophy; (b) cerebral white matter was visually scored as percentage normal, hyperintense, rarefied, or cystic on fluid-attenuated inversion recovery (FLAIR) images and converted into a white matter decay score; and (c) the intracranial volume was segmented into normal-appearing white and gray matter, abnormal but structurally present (FLAIR-hyperintense) and rarefied or cystic (FLAIR-hypointense) white matter, and ventricular and extracerebral cerebrospinal fluid (CSF). Multilevel regression analyses with patient as a clustering variable were performed to account for the nested data structure. Results A total of 461 examinations in 270 patients (median age, 7 years [interquartile range, 3-18 years]; 144 female patients) were evaluated; 112 patients had undergone serial imaging. Patients with later onset had higher VSR [F(5) = 8.42; P < .001] and CSF volume [F(5) = 21.7; P < .001] and lower white matter decay score [F(5) = 4.68; P < .001] and rarefied or cystic white matter volume [F(5) = 13.3; P < .001]. Rate of progression of white matter decay scores [b = -1.6, t(109) = -3.9; P < .001] and VSRs [b = -0.05, t (109) = -3.7; P < .001] were lower with later onset. Conclusion A radiologic spectrum based on age at onset exists in vanishing white matter. The earlier the onset, the faster and more cystic the white matter decay, whereas with later onset, white matter atrophy and gliosis predominate. © RSNA, 2021.