Alexander Disease Research Articles

A systematic review and meta-analysis of GFAP gene variants in Alexander disease

Alexander disease (ALXDRD) is a rare neurodegenerative disorder of astrocytes resulting from pathogenic variants in the GFAP gene. The genotype-phenotype correlation remains elusive due to the variable expressivity of clinical manifestations. In an attempt to clarify the effects of GFAP variants in ALXDRD, numerous studies were collected and analyzed. In particular, we systematically searched for GFAP variants associated with ALXDRD and collected information on the location within the gene and protein, prediction of deleteriousness/pathogenicity, occurrence, sex and country of origin of patients, DNA source, genetic testing, and clinical signs. To identify possible associations, statistical analyses and meta-analyses were applied, thus revealing a higher than expected percentage of adult patients with ALXDRD. Furthermore, substitution of Arginine, the most frequently altered residue among the 550 predominantly missense causative GFAP variants collected, were mostly de novo and more prevalent in early-onset forms of ALXDRD. The effect of defective splicing in modifying the impact of GFAP variants on the age of onset of ALXDRD was also postulated after evaluating the distribution of the corresponding deleterious predictive values. In conclusion, not only previously unrecognized genotype-phenotype correlations were revealed in ALXDRD, but also subtle mechanisms could explain the variable manifestations of the ALXDRD clinical phenotype.

Tadpole Brainstem Atrophy in Adult-Onset Alexander Disease: A Case Report and Review of Literature.

Tadpole Brainstem Atrophy in Adult-Onset Alexander Disease: A Case Report and Review of Literature.

A retrospective observational cohort study of the anesthetic management and outcomes of pediatric patients with Alexander disease undergoing lumbar puncture or magnetic resonance imaging.

Alexander disease is a rare, progressive leukodystrophy, which predisposes patients to complications under general anesthesia due to clinical manifestations including developmental delay, seizures, dysphagia, vomiting, and sleep apnea. However, study of anesthetic outcomes is limited. Our aim was to describe patient characteristics, anesthetic techniques, and anesthesia-related complications for Alexander disease patients undergoing magnetic resonance imaging and/or lumbar puncture at a quaternary-care children's hospital. We performed a retrospective review of anesthetic outcomes in patients with Alexander disease enrolled in a prospective observational study. Included patients had diagnosed Alexander disease and underwent magnetic resonance imaging and/or lumbar puncture at our institution. We excluded anesthetics for other procedures or at outside institutions. Collected data included patient characteristics, anesthetic techniques, medications, and complications under anesthesia and in the subsequent 24 h. We performed descriptive statistics as appropriate. Forty patients undergoing 64 procedures met inclusion criteria. Fifty-six procedures (87.5%) required general anesthesia or monitored anesthesia care (MAC) and eight (12.5%) did not. The general anesthesia/MAC group tended to be younger than nonanesthetized patients (median age 6 years [IQR 3.8; 9] vs. 14.5 years [IQR 12.8; 17.5]). In both groups, dysphagia (78.6% vs. 87.5%, respectively), seizures (62.5% vs. 25%), and recurrent vomiting (17.9% vs. 25%) were frequently reported preprocedure symptoms. Inhalational induction was common (N = 48; 85.7%), and two (3.6%) underwent rapid sequence induction. Serious complications were rare, with no aspiration or seizures. Hypotension resolving with ephedrine occurred in eight cases (14.3%). One patient each (1.8%) experienced postprocedure emergence agitation or vomiting. Fifty-three (94.6%) were ambulatory procedures. No inpatients required escalation in acuity of care. In this single-center study, patients with Alexander disease did not experience frequent or irreversible complications while undergoing general anesthesia/MAC. Co-morbid symptoms were not increased postanesthesia. Some patients may not require anesthesia to complete short procedures.

Adult-Onset Alexander Disease With Late-Presenting Vestibulopathy: A Case Report.

Adult-Onset Alexander Disease With Late-Presenting Vestibulopathy: A Case Report.

Brainstem Chipmunk Sign: A Diagnostic Imaging Clue across All Subtypes of Alexander Disease.

While classic brain MR imaging features of Alexander disease have been well-documented, lesional patterns can overlap with other leukodystrophies, especially in the early stages of the disease or in milder phenotypes. We aimed to assess the utility of a new neuroimaging sign to help increase the diagnostic specificity of Alexander disease. A peculiar bilateral symmetric hyperintense signal on T2-weighted images affecting the medulla oblongata was identified in an index patient with type I Alexander disease. Subsequently, 5 observers performed a systematic MR imaging review for this pattern by examining 55 subjects with Alexander disease and 74 subjects with other leukodystrophies. Interobserver agreement was assessed by the κ index. Sensitivity, specificity, and receiver operating characteristic curves were determined. The identified pattern was present in 87% of subjects with Alexander disease and 14% of those without Alexander disease leukodystrophy (P < .001), 3 with vanishing white matter, 4 with adult polyglucosan body disease, and 3 others. It was found equally in both type I and type II Alexander disease (28/32, 88% versus 18/21, 86%; P = .851) and in subjects with unusual disease features (2/2). Sensitivity (87.3%; 95% CI, 76.0%-93.7%), specificity (86.5%; 95% CI, 76.9%-92.5%), and interobserver agreement (κ index = 0.82) were high. The identified pattern in the medulla oblongata, called the chipmunk sign due to its resemblance to the face of this rodent, is extremely common in subjects with Alexander disease and represents a diagnostic tool that can aid in early diagnosis, especially in subjects with otherwise atypical MR imaging findings and/or clinical features.

Construct Validity of the 10-meter Walk/Run Test to Assess Motor Impairment in Patients with Alexander Disease (P2-8.004)

Construct Validity of the 10-meter Walk/Run Test to Assess Motor Impairment in Patients with Alexander Disease (P2-8.004)

Plasma concentrations of glial fibrillary acidic protein, neurofilament light, and tau in Alexander disease

IntroductionAlexander disease (AxD) is a rare leukodystrophy caused by dominant gain-of-function mutations in the gene encoding the astrocyte intermediate filament, glial fibrillary acidic protein (GFAP). However, there is an urgent need for biomarkers to assist in monitoring not only the progression of disease but also the response to treatment. GFAP is the obvious candidate for such a biomarker, as it is measurable in body fluids that are readily accessible for biopsy, namely cerebrospinal fluid and blood. However, in the case of ASOs, the treatment that is furthest in development, GFAP is the target of therapy and presumably would go down independent of disease status. Hence, there is a critical need for biomarkers that are not directly affected by the treatment strategy.MethodsWe explored the potential utility of biomarkers currently being studied in other neurodegenerative diseases and injuries, specifically neurofilament light protein (NfL), phosphorylated forms of tau, and amyloid-β peptides (Aβ42/40).Results and ConclusionsHere, we report that GFAP is elevated in plasma of all age groups afflicted by AxD, including those with adult onset. NfL and p-tau are also elevated, but to a much lesser extent than GFAP. In contrast, the levels of Aß40 and Aß42 are not altered in AxD.

Induced pluripotent stem cell-based assays recapture multiple properties of human astrocytes.

The majority of the population of glial cells in the central nervous system consists of astrocytes, and impairment of astrocytes causes various disorders. It is useful to assess the multiple astrocytic properties in order to understand their complex roles in the pathophysiology. Although we can differentiate human astrocytes from induced pluripotent stem cells (iPSCs), it remains unknown how we can analyse and reveal the multiple properties of astrocytes in complexed human disease conditions. For this purpose, we tested astrocytic differentiation protocols from feeder-free iPSCs based on the previous method with some modifications. Then, we set up extra- and intracellular assessments of iPSC-derived astrocytes by testing cytokine release, calcium influx, autophagy induction and migration. The results led us to analytic methods with conditions in which iPSC-derived astrocytes behave as invivo. Finally, we applied these methods for modelling an astrocyte-related disease, Alexander disease. An analytic system using iPSC-derived astrocytes could be used to recapture complexities in human astrocyte diseases.

Large-scale gene expression changes in APP/PSEN1 and GFAP mutation models exhibit high congruence with Alzheimer's disease.

Alzheimer's disease (AD) is a complex neurodegenerative disorder with both genetic and non-genetic causes. Animal research models are available for a multitude of diseases and conditions affecting the central nervous system (CNS), and large-scale CNS gene expression data exist for many of these. Although there are several models specifically for AD, each recapitulates different aspects of the human disease. In this study we evaluate over 500 animal models to identify those with CNS gene expression patterns matching human AD datasets. Approaches included a hypergeometric based scoring system that rewards congruent gene expression patterns but penalizes discordant gene expression patterns. The top two models identified were APP/PS1 transgenic mice expressing mutant APP and PSEN1, and mice carrying a GFAP mutation that is causative of Alexander disease, a primary disorder of astrocytes in the CNS. The APP/PS1 and GFAP models both matched over 500 genes moving in the same direction as in human AD, and both had elevated GFAP expression and were highly congruent with one another. Also scoring highly were the 5XFAD model (with five mutations in APP and PSEN1) and mice carrying CK-p25, APP, and MAPT mutations. Animals with the APOE3 and 4 mutations combined with traumatic brain injury ranked highly. Bulbectomized rats scored high, suggesting anosmia could be causative of AD-like gene expression. Other matching models included the SOD1G93A strain and knockouts for SNORD116 (Prader-Willi mutation), GRID2, INSM1, XBP1, and CSTB. Many top models demonstrated increased expression of GFAP, and results were similar across multiple human AD datasets. Heatmap and Uniform Manifold Approximation Plot results were consistent with hypergeometric ranking. Finally, some gene manipulation models, including for TYROBP and ATG7, were identified with reversed AD patterns, suggesting possible neuroprotective effects. This study provides insight for the pathobiology of AD and the potential utility of available animal models.

Chapter 6 - Childhood-inherited white matter disorders with calcification

Intracranial calcification (ICC) occurs in many neurologic disorders both acquired and genetic. In some inherited white matter disorders, it is a common or even invariable feature where the presence and pattern of calcification provides an important pointer to the specific diagnosis. This is particularly the case for the Aicardi-Goutières syndrome (AGS) and for Coats plus (CP) and leukoencephalopathy with calcifications and cysts (LCC), which are discussed in detail in this chapter. AGS is a genetic disorder of type 1 interferon regulation, caused by mutations in any of the nine genes identified to date. In its classic form, AGS has very characteristic clinical and neuroimaging features which will be discussed here. LCC is a purely neurologic disorder caused by mutations in the SNORD118 gene, whereas CP is a multisystem disorder of telomere function that may result from mutations in the CTC1, POT1, or STN genes. In spite of the different pathogenetic basis for LCC and CP, they share remarkably similar neuroimaging and neuropathologic features. Cockayne syndrome, in which ICC is usually present, is discussed elsewhere in this volume. ICC may occur as an occasional feature of many other white matter diseases, including Alexander disease, Krabbe disease, X-ALD, and occulodentodigital dysplasia.

Alexander disease a case series

Alexander disease a case series

Alexander Disease: Scientific Advancement and Therapeutic Intervention in Rare Disease Research

Alexander Disease (AxD) is a rare, heritable white matter condition, or leukodystrophy, that helps to understand how collaborative, translational research can identify therapeutic options in a complex illness. AxD is a rare disease, first described in 1949, that affects approximately one in 2.7 million births. The disease hinders the function of the central nervous system (CNS) through the biotoxic overproduction of protein aggregates which cause the deterioration of the myelin sheath. Given the extreme rarity of AxD, disease-specific research is relatively limited, and there is no disease-modifying treatment currently available. At present, a clinical trial is underway to examine the safety and efficacy of Ionis Pharmaceuticals’ ION373, an Antisense Oligonucleotide (ASO), that has reported success in preventing the progression of AxD in mouse models. This paper reviews the key components of AxD, therapeutic designs for AxD, and ultimately suggests future directions to optimize the therapeutic approach. This review also aims to promote rare disease awareness, as scientific progress for conditions like Alexander Disease is achieved through advocacy and promotion.

Juvenile Alexander Disease and Cleidocranial Dysplasia: A Rare Combination of Genetic Abnormalities in a Pediatric Patient

Cleidocranial dysplasia (CCD) and Alexander disease (AxD) are rare, autosomal dominant disorders that are characterized by a mutation in the runt-related transcription factor 2 ( RUNX2) and the glial fibrillary acidic protein ( GFAP) genes, respectively. There is no known relationship between RUNX2 and GFAP which would cause co-morbidity. We report a rare case of a 13-year-old with CCD who came to the clinic complaining of a 2-year history of progressively worsening episodic exacerbations of bulbar, ataxia, nystagmus, kyphoscoliosis, and nausea, but was intact cognitively. Initial diagnosis was a difficult process because preliminary symptoms for Juvenile AxD overlapped with previously diagnosed CCD and the initial genetic test identified our patient’s GFAP gene as a variant of uncertain significance. Our experience emphasizes the importance of continuing to report pathogenic variants of GFAP for AxD to build on our existing compendium of variants for GFAP for quicker and more efficient diagnosis of AxD.

Authors' response to: "Alexander disease genetics: Beyond GFAP exon sequencing?"

Authors' response to: "Alexander disease genetics: Beyond GFAP exon sequencing?"

Alexander disease genetics: Beyond GFAP exon sequencing?

Alexander disease genetics: Beyond GFAP exon sequencing?

Microglia sense astrocyte dysfunction and prevent disease progression in an Alexander disease model.

Alexander disease (AxD) is an intractable neurodegenerative disorder caused by GFAP mutations. It is a primary astrocyte disease with a pathological hallmark of Rosenthal fibres within astrocytes. AxD astrocytes show several abnormal phenotypes. Our previous study showed that AxD astrocytes in model mice exhibit aberrant Ca2+ signals that induce AxD aetiology. Here, we show that microglia have unique phenotypes with morphological and functional alterations, which are related to the pathogenesis of AxD. Immunohistochemical studies of 60TM mice (AxD model) showed that AxD microglia exhibited highly ramified morphology. Functional changes in microglia were assessed by Ca2+ imaging using hippocampal brain slices from Iba1-GCaMP6-60TM mice and two-photon microscopy. We found that AxD microglia showed aberrant Ca2+ signals, with high frequency Ca2+ signals in both the processes and cell bodies. These microglial Ca2+ signals were inhibited by pharmacological blockade or genetic knockdown of P2Y12 receptors but not by tetrodotoxin, indicating that these signals are independent of neuronal activity but dependent on extracellular ATP from non-neuronal cells. Our single-cell RNA sequencing data showed that the expression level of Entpd2, an astrocyte-specific gene encoding the ATP-degrading enzyme NTPDase2, was lower in AxD astrocytes than in wild-type astrocytes. In situ ATP imaging using the adeno-associated virus vector GfaABC1D ATP1.0 showed that exogenously applied ATP was present longer in 60TM mice than in wild-type mice. Thus, the increased ATP level caused by the decrease in its metabolizing enzyme in astrocytes could be responsible for the enhancement of microglial Ca2+ signals. To determine whether these P2Y12 receptor-mediated Ca2+ signals in AxD microglia play a significant role in the pathological mechanism, a P2Y12 receptor antagonist, clopidogrel, was administered. Clopidogrel significantly exacerbated pathological markers in AxD model mice and attenuated the morphological features of microglia, suggesting that microglia play a protective role against AxD pathology via P2Y12 receptors. Taken together, we demonstrated that microglia sense AxD astrocyte dysfunction via P2Y12 receptors as an increase in extracellular ATP and alter their morphology and Ca2+ signalling, thereby protecting against AxD pathology. Although AxD is a primary astrocyte disease, our study may facilitate understanding of the role of microglia as a disease modifier, which may contribute to the clinical diversity of AxD.

Quantitative diffusion imaging and genotype-by-sex interactions in a rat model of Alexander disease.

The clinical diagnosis and classification of Alexander disease (AxD) relies in part on qualitative neuroimaging biomarkers; however, these biomarkers fail to distinguish and discriminate different subtypes of AxD, especially in the presence of overlap in clinical symptoms. To address this gap in knowledge, we applied neurite orientation dispersion and density imaging (NODDI) to an innovative CRISPR-Cas9 rat genetic model of AxD to gain quantitative insights into the neural substrates and brain microstructural changes seen in AxD and to potentially identify novel quantitative NODDI biomarkers of AxD. Multi-shell DWI of age- and sex-matched AxD and wild-type Sprague Dawley rats (n = 6 per sex per genotype) was performed and DTI and NODDI measures calculated. A 3 × 2 × 2 analysis of variance model was used to determine the effect of genotype, biological sex, and laterality on quantitative measures of DTI and NODDI across regions of interest implicated in AxD. There is a significant effect of genotype in the amygdala, hippocampus, neocortex, and thalamus in measures of both DTI and NODDI brain microstructure. A genotype by biological sex interaction was identified in DTI and NODDI measures in the corpus callosum, hippocampus, and neocortex. We present the first application of NODDI to the study of AxD using a rat genetic model of AxD. Our analysis identifies alterations in NODDI and DTI measures to large white matter tracts and subcortical gray nuclei. We further identified genotype by sex interactions, suggesting a possible role for biological sex in the neuropathogenesis of AxD.

Acquisition and Loss of Developmental Milestones and Time to Disease-Related Outcomes in Cerebral Alexander Disease.

Objective: To determine the ages at acquisition of developmental milestones, loss of motor function, and clinical symptoms in Alexander disease. Methods: Patients with confirmed cerebral Alexander disease were included. Data abstraction of developmental and disease-specific milestones was performed from medical records, physical exams, and questionnaires. Mixed effects logistic regression was used to determine if key clinical features were associated with milestone achievement, controlling for patient age. Results: 51 patients with cerebral/infantile Alexander disease were evaluated at a mean age of 10.96 years (range 2.29-31.08 years). Developmental milestones in Alexander disease were often achieved but delayed. Ambulation was achieved in 44 subjects (86%); 34 (67%) subjects walked independently (mean age 1.9 years, range 0.91-3.25 years) and an additional 10 (20%) subjects walked with assistance (mean age 3.9 years, range 1.8-8 years) but did not progress to independent ambulation. Developmental delay was the earliest and most prevalent symptom (N = 48 [94%], mean age 0.58 years), compared to an initial seizure (N = 41 [80%], mean age 2.80 years), and macrocephaly (N = 28 [55%], mean age 4.04 years), P < .0001 between these ages of onset. Loss of independent ambulation occurred in 11 of the 34 (32%) children who had acquired ambulation (range 3.41-15.10 years). Presence of seizures or macrocephaly did not predict the achievement or loss of ambulation. Conclusions: The clinical triad of developmental delay, seizures, and macrocephaly are not universally present in cerebral Alexander disease. Clinicians should have a high index of suspicion for Alexander disease in patients with mild delays and a first seizure.

Adult-onset Alexander disease among patients of Jewish Syrian descent.

Alexander disease (AxD) is a rare autosomal dominant leukodystrophy caused by heterozygous mutations in the glial fibrillary acid protein (GFAP) gene. The age of symptoms onset ranges from infancy to adulthood, with variable clinical and radiological manifestations. Adult-onset AxD manifests as a chronic and progressive condition, characterized by bulbar, motor, cerebellar, and other clinical signs and symptoms. Neuroradiological findings typically involve the brainstem and cervical spinal cord. Adult-onset AxD has been described in diverse populations but is rare in Israel. We present a series of patients diagnosed with adult-onset AxD from three families, all of Jewish Syrian descent. Five patients (4 females) were diagnosed with adult-onset AxD due to the heterozygous mutationc.219G > A, p.Met73Ile in GFAP. Age at symptoms onset ranged from 48 to 61 years. Clinical characteristics were typical and involved progressive bulbar and gait disturbance, followed by pyramidal and cerebellar impairment, dysautonomia, and cognitive decline. Imaging findings included medullary and cervical spinal atrophy and mostly infratentorial white matter hyperintensities. A newly recognized cluster of adult-onset AxD in Jews of Syrian origin is presented. This disorder should be considered in differential diagnosis in appropriate circumstances. Genetic counselling for family members is required in order to discuss options for future family planning.

A defined roadmap of radial glia and astrocyte differentiation from human pluripotent stem cells.

Human gliogenesis remains poorly understood, and derivation of astrocytes from human pluripotent stem cells (hPSCs) is inefficient and cumbersome. Here, we report controlled glial differentiation from hPSCs that bypasses neurogenesis, which otherwise precedes astrogliogenesis during brain development and invitro differentiation. hPSCs were first differentiated into radial glial cells (RGCs) resembling resident RGCs of the fetal telencephalon, and modulation of specific cell signaling pathways resulted in direct and stepwise induction of key astroglial markers (NFIA, NFIB, SOX9, CD44, S100B, glial fibrillary acidic protein [GFAP]). Transcriptomic and genome-wide epigenetic mapping and single-cell analysis confirmed RGC-to-astrocyte differentiation, obviating neurogenesis and the gliogenic switch. Detailed molecular and cellular characterization experiments uncovered new mechanisms and markers for human RGCs and astrocytes. In summary, establishment of a glia-exclusive neural lineage progression model serves as a unique serum-free platform of manufacturing large numbers of RGCs and astrocytes for neuroscience, disease modeling (e.g., Alexander disease), and regenerative medicine.