Correlating quantitative MR imaging with histopathology in X-linked adrenoleukodystrophy

The pathology of X-linked adrenoleukodystrophy: tissue specific changes as a clue to pathophysiology

Although the pathology of X-linked adrenoleukodystrophy (ALD) is well described, it represents the end-stage of neurodegeneration. It is still unclear what cell types are initially involved and what their role is in the disease process. Revisiting the seminal post-mortem studies from the 1970s can generate new hypotheses on pathophysiology. This review describes (histo)pathological changes of the brain and spinal cord in ALD. It aims at integrating older works with current insights and at providing an overarching theory on the pathophysiology of ALD. The data point to an important role for axons and glia in the pathology of both the myelopathy and leukodystrophy of ALD. In-depth pathological analyses with new techniques could help further unravel the sequence of events behind the pathology of ALD.

Leukodystrophy Imaging: Insights for Diagnostic Dilemmas

Leukodystrophies, a group of rare demyelinating disorders, mainly affect the CNS. Clinical presentation of different types of leukodystrophies can be nonspecific, and thus, imaging techniques like MRI can be used for a more definitive diagnosis. These diseases are characterized as cerebral lesions with characteristic demyelinating patterns which can be used as differentiating tools. In this review, we talk about these MRI study findings for each leukodystrophy, associated genetics, blood work that can help in differentiation, emerging diagnostics, and a follow-up imaging strategy. The leukodystrophies discussed in this paper include X-linked adrenoleukodystrophy, metachromatic leukodystrophy, Krabbe's disease, Pelizaeus-Merzbacher disease, Alexander's disease, Canavan disease, and Aicardi-Goutières Syndrome.

Initial frontal lobe involvement in adult cerebral X-linked adrenoleukodystrophy

OBJECTIVE

Adult cerebral X-linked adrenoleukodystrophy (ACALD) with initial frontal lobe involvement is a rare genetic disease that is easily misdiagnosed and underdiagnosed. We sought to improve the early identification of such diseases.

METHODS

We present three cases of adult X-linked adrenoleukodystrophy (ALD) with initial frontal lobe involvement and identify an additional 13 cases from the database. The clinical and imaging characteristics of the overall sixteen cases were analyzed.

RESULTS

The average age of onset was 37 years, with 15 male and 1 female patient. A total of 12 patients (75%) developed a decline in cerebral executive and cognitive functions. Brain trauma is the possible trigger for the onset of ALD in five patients (31%). An elevated level of very-long-chain fatty acids (VLCFA) was observed in all 15 patients on whom a plasma VLCFA was performed.10 patients with gene tests showed different mutation sites in the ABCD1 gene. Brain MRI of six patients (46%) were characterized by frontal lobe "butterfly wings"-like lesions with peripheral rim enhancement. Four patients underwent brain biopsies (patients 1, 3, 15, and 13), and five patients (31%) were initially misdiagnosed (patients 1, 2, 3, 11, and 15). Nine of the patients with follow-up records experienced poor prognoses, and five of them, unfortunately, died (56%).

CONCLUSION

ACALD patients with anterior patterns tend to be misdiagnosed. The early clinical manifestation is a decline in cerebral executive and cognitive function. Brain trauma may be a trigger for this pattern. Brain MRI findings are characterized by frontal lobe "butterfly wing"-like lesions with peripheral rim enhancement. The determination of the VLCFA levels and the genetic detection of the causative mutations are required to confirm the diagnosis.

Efficacy of HDAC Inhibitors in Driving Peroxisomal β-Oxidation and Immune Responses in Human Macrophages: Implications for Neuroinflammatory Disorders

Elevated levels of saturated very long-chain fatty acids (VLCFAs) in cell membranes and secreted lipoparticles have been associated with neurotoxicity and, therefore, require tight regulation. Excessive VLCFAs are imported into peroxisomes for degradation by β-oxidation. Impaired VLCFA catabolism due to primary or secondary peroxisomal alterations is featured in neurodegenerative and neuroinflammatory disorders such as X-linked adrenoleukodystrophy and multiple sclerosis (MS). Here, we identified that healthy human macrophages upregulate the peroxisomal genes involved in β-oxidation during myelin phagocytosis and pro-inflammatory activation, and that this response is impaired in peripheral macrophages and phagocytes in brain white matter lesions in MS patients. The pharmacological targeting of VLCFA metabolism and peroxisomes in innate immune cells could be favorable in the context of neuroinflammation and neurodegeneration. We previously identified the epigenetic histone deacetylase (HDAC) inhibitors entinostat and vorinostat to enhance VLCFA degradation and pro-regenerative macrophage polarization. However, adverse side effects currently limit their use in chronic neuroinflammation. Here, we focused on tefinostat, a monocyte/macrophage-selective HDAC inhibitor that has shown reduced toxicity in clinical trials. By using a gene expression analysis, peroxisomal β-oxidation assay, and live imaging of primary human macrophages, we assessed the efficacy of tefinostat in modulating VLCFA metabolism, phagocytosis, chemotaxis, and immune function. Our results revealed the significant stimulation of VLCFA degradation with the upregulation of genes involved in peroxisomal β-oxidation and interference with immune cell recruitment; however, tefinostat was less potent than the class I HDAC-selective inhibitor entinostat in promoting a regenerative macrophage phenotype. Further research is needed to fully explore the potential of class I HDAC inhibition and downstream targets in the context of neuroinflammation.

Ryu J, Akassoglou K, Talebian S, Chu P, Pisani L, Musolino P, Steinman L, Doyle K, Robinson WH, Sharpe O, Cayrol R, Orchard P, Lund T, Vogel H, Lenail M, Han MH, Bonkowsky JL, Van Haren KP. A novel mouse model of cerebral adrenoleukodystrophy highlights NLRP3 activity in lesion pathogenesis

Objective

We sought to create and characterize a mouse model of the inflammatory, cerebral demyelinating phenotype of X-linked adrenoleukodystrophy (ALD) that would facilitate the study of disease pathogenesis and therapy development. We also sought to cross-validate potential therapeutic targets such as fibrin, oxidative stress, and the NLRP3 inflammasome, in post-mortem human and murine brain tissues.

Background

ALD is caused by mutations in the gene ABCD1 encoding a peroxisomal transporter. More than half of males with an ABCD1 mutation develop the cerebral phenotype (cALD). Incomplete penetrance and absence of a genotype-phenotype correlation imply a role for environmental triggers. Mechanistic studies have been limited by the absence of a cALD phenotype in the Abcd1-null mouse.

Methods

We generated a cALD phenotype in 8-week-old, male Abcd1-null mice by deploying a two-hit method that combines cuprizone (CPZ) and experimental autoimmune encephalomyelitis (EAE) models. We employed in vivo MRI and post-mortem immunohistochemistry to evaluate myelin loss, astrogliosis, blood-brain barrier (BBB) disruption, immune cell infiltration, fibrin deposition, oxidative stress, and Nlrp3 inflammasome activation in mice. We used bead-based immunoassay and immunohistochemistry to evaluate IL-18 in CSF and post-mortem human cALD brain tissue.

Results

MRI studies revealed T2 hyperintensities and post-gadolinium enhancement in the medial corpus callosum of cALD mice, similar to human cALD lesions. Both human and mouse cALD lesions shared common histologic features of myelin phagocytosis, myelin loss, abundant microglial activation, T and B-cell infiltration, and astrogliosis. Compared to wild-type controls, Abcd1-null mice had more severe cerebral inflammation, demyelination, fibrin deposition, oxidative stress, and IL-18 activation. IL-18 immunoreactivity co-localized with macrophages/microglia in the perivascular region of both human and mouse brain tissue.

Interpretation

This novel mouse model of cALD suggests loss of Abcd1 function predisposes to more severe cerebral inflammation, oxidative stress, fibrin deposition, and Nlrp3 pathway activation, which parallels the findings seen in humans with cALD. We expect this model to enable long-sought investigations into cALD mechanisms and accelerate development of candidate therapies for lesion prevention, cessation, and remyelination.

Quantitative MRI in leukodystrophies

Leukodystrophies constitute a large and heterogeneous group of genetic diseases primarily affecting the white matter of the central nervous system. Different disorders target different white matter structural components. Leukodystrophies are most often progressive and fatal. In recent years, novel therapies are emerging and for an increasing number of leukodystrophies trials are being developed. Objective and quantitative metrics are needed to serve as outcome measures in trials. Quantitative MRI yields information on microstructural properties, such as myelin or axonal content and condition, and on the chemical composition of white matter, in a noninvasive fashion. By providing information on white matter microstructural involvement, quantitative MRI may contribute to the evaluation and monitoring of leukodystrophies. Many distinct MR techniques are available at different stages of development. While some are already clinically applicable, others are less far developed and have only or mainly been applied in healthy subjects. In this review, we explore the background, current status, potential and challenges of available quantitative MR techniques in the context of leukodystrophies.

Novel mutations in the ABCD1 gene caused adrenomyeloneuropathy in the Chinese population

Background

As a rare genetic disease, adrenomyeloneuropathy (AMN) is the most common adult phenotype of X-linked adrenoleukodystrophy (X-ALD). Mutations in the ABCD1 gene have been identified to cause AMN.

Methods

We applied clinical evaluation, laboratory tests, and neuroimaging on three patients with progressive spastic paraparesis. In genetic analysis, we investigated ABCD1 gene mutations by whole-exome sequencing and Sanger sequencing. Bioinformatics tools were used to predict the effects of identified ABCD1 mutations on the protein.

Results

All three patients were men with adult-onset disease, mainly characterized by progressive spastic paraparesis. Among them, two patients had peripheral neuropathy and one patient had signs of adrenal insufficiency. All three patients showed cerebral involvement on brain MRI, while two patients were found with diffuse cord atrophy on spinal MRI. High-VLCFA levels in plasma, as well as C24:0/C22:0 and C26:0/C22:0 ratios, were found in all three patients. In addition, three different ABCD1 mutations were identified in three unrelated Chinese families, including one known mutation (c.1415_1416delAG) and two novel mutations (c.217C>T and c.160_170delACGCAGGAGGC). Based on the clinical assessment, radiographic, biochemical, and genetic testing, the final diagnosis was AMN in these patients with spastic paraparesis.

Conclusion

This study reported three patients with AMN and identified two novel mutations in the ABCD1 in the Chinese population. Our finding emphasized that X-ALD is an important cause of adult-onset spastic paraplegia. Thus, neuroimaging, VLCFA testing, and especially the detection of the ABCD1 gene have important implications for the etiological diagnosis of adult patients with spastic paraplegia.

Imaging in X-Linked Adrenoleukodystrophy

Magnetic resonance imaging (MRI) is the gold standard for the detection of cerebral lesions in X-linked adrenoleukodystrophy (ALD). ALD is one of the most common peroxisomal disorders and is characterized by a defect in degradation of very long chain fatty acids (VLCFA), resulting in accumulation of VLCFA in plasma and tissues. The clinical spectrum of ALD is wide and includes adrenocortical insufficiency, a slowly progressive myelopathy in adulthood, and cerebral demyelination in a subset of male patients. Cerebral demyelination (cerebral ALD) can be treated with hematopoietic cell transplantation (HCT) but only in an early (pre- or early symptomatic) stage and therefore active MRI surveillance is recommended for male patients, both pediatric and adult. Although structural MRI of the brain can detect the presence and extent of cerebral lesions, it does not predict if and when cerebral demyelination will occur. There is a great need for imaging techniques that predict onset of cerebral ALD before lesions appear. Also, imaging markers for severity of myelopathy as surrogate outcome measure in clinical trials would facilitate drug development. New quantitative MRI techniques are promising in that respect. This review focuses on structural and quantitative imaging techniques-including magnetic resonance spectroscopy, diffusion tensor imaging, MR perfusion imaging, magnetization transfer (MT) imaging, neurite orientation dispersion and density imaging (NODDI), and myelin water fraction imaging-used in ALD and their role in clinical practice and research opportunities for the future.

Pathology of the neurovascular unit in leukodystrophies

The blood-brain barrier is a dynamic endothelial cell barrier in the brain microvasculature that separates the blood from the brain parenchyma. Specialized brain endothelial cells, astrocytes, neurons, microglia and pericytes together compose the neurovascular unit and interact to maintain blood-brain barrier function. A disturbed brain barrier function is reported in most common neurological disorders and may play a role in disease pathogenesis. However, a comprehensive overview of how the neurovascular unit is affected in a wide range of rare disorders is lacking. Our aim was to provide further insights into the neuropathology of the neurovascular unit in leukodystrophies to unravel its potential pathogenic role in these diseases. Leukodystrophies are monogenic disorders of the white matter due to defects in any of its structural components. Single leukodystrophies are exceedingly rare, and availability of human tissue is unique. Expression of selective neurovascular unit markers such as claudin-5, zona occludens 1, laminin, PDGFRβ, aquaporin-4 and α-dystroglycan was investigated in eight different leukodystrophies using immunohistochemistry. We observed tight junction rearrangements, indicative of endothelial dysfunction, in five out of eight assessed leukodystrophies of different origin and an altered aquaporin-4 distribution in all. Aquaporin-4 redistribution indicates a general astrocytic dysfunction in leukodystrophies, even in those not directly related to astrocytic pathology or without prominent reactive astrogliosis. These findings provide further evidence for dysfunction in the orchestration of the neurovascular unit in leukodystrophies and contribute to a better understanding of the underlying disease mechanism.

Can MRI measure myelin? Systematic review, qualitative assessment, and meta-analysis of studies validating microstructural imaging with myelin histology

Recent years have seen an increased understanding of the importance of myelination in healthy brain function and neuropsychiatric diseases. Non-invasive microstructural magnetic resonance imaging (MRI) holds the potential to expand and translate these insights to basic and clinical human research, but the sensitivity and specificity of different MR markers to myelination is a subject of debate. To consolidate current knowledge on the topic, we perform a systematic review and meta-analysis of studies that validate microstructural imaging by combining it with myelin histology. We find meta-analytic evidence for correlations between various myelin histology metrics and markers from different MRI modalities, including fractional anisotropy, radial diffusivity, macromolecular pool, magnetization transfer ratio, susceptibility and longitudinal relaxation rate, but not mean diffusivity. Meta-analytic correlation effect sizes range widely, between R2 = 0.26 and R2 = 0.82. However, formal comparisons between MRI-based myelin markers are limited by methodological variability, inconsistent reporting and potential for publication bias, thus preventing the establishment of a single most sensitive strategy to measure myelin with MRI. To facilitate further progress, we provide a detailed characterisation of the evaluated studies as an online resource. We also share a set of 12 recommendations for future studies validating putative MR-based myelin markers and deploying them in vivo in humans.

Dentate Nucleus Signal Intensity Changes in Children with Adrenoleukodystrophy in Comparison to Primary Brain Tumor with and without Radiotherapy after Gadobutrol Administration

BACKGROUND AND PURPOSE

To determine whether cerebral adrenoleukodystrophy (cALD) or brain irradiation in patients with primary brain tumor affects T1-weighted imaging (T1WI) signal intensity (SI) of the dentate nucleus (DN) in a pediatric cohort who had received consecutive macrocyclic gadolinium-based contrast agent (mcGBCA) gadobutrol.

METHODS

This study included 97 pediatric patients who underwent mcGBCA-enhanced MRI from 2010 to 2020 (29 children with primary brain tumors without brain radiation therapy [mcGBCA group-1], 33 children with primary brain tumors and radiation treatment [mcGBCA group-2], 35 children with cALD [mcGBCA group-3], and 97 sex-/age-matched control subjects [subgroups matched to each of the three subject groups] without GBCA administration). The DN-to-middle cerebellar peduncle (MCP) SI ratios on T1WI were then determined. A paired t-test was performed to compare SI ratios between children exposed to mcGBCA in each group and control subjects. The relationships between SI ratios and confounding variables were analyzed utilizing the Pearson correlation analysis.

RESULTS

The DN-to-MCP SI ratio was significantly higher of mcGBCA group-2 (1.046±.071) or mcGBCA group-3 (.972±.038) than in the control group-2 (.983±.041, P<.001) and control group-3 (.937±.051, P = .002), respectively, but no significant difference of the SI ratio was noted between mcGBCA group-1 (.984±.032) and control-group-1 (.982±.035, P = .860). No significant correlation was noted between SI ratio values and the cumulative dose or number of mcGBCA administrations, age, or the elapsed time between the MRI examinations (all P>.05).

CONCLUSIONS

Hyperintense T1WI signal in the DN may be seen in children with brain tumors undergoing brain irradiation, as well as in children with cALD.

Endocrine dysfunction in adrenoleukodystrophy

X-linked adrenoleukodystrophy (ALD) is a peroxisomal disorder caused by mutations in the ABCD1 gene and characterized by impaired very long-chain fatty acid beta-oxidation. Clinically, male patients develop adrenal failure and a progressive myelopathy in adulthood, although age of onset and rate of progression are highly variable. Additionally, 40% of male patients develop a leukodystrophy (cerebral ALD) before the age of 18 years. Women with ALD also develop a myelopathy but generally at a later age than men and with slower progression. Adrenal failure and leukodystrophy are exceedingly rare in women. Allogeneic hematopoietic cell transplantation (HCT), or more recently autologous HCT with ex vivo lentivirally transfected bone marrow, halts the leukodystrophy. Unfortunately, there is no curative treatment for the myelopathy. In the following chapter, the biochemistry, pathology, and clinical spectrum of ALD are discussed in detail.

Myelin quantification with MRI: A systematic review of accuracy and reproducibility

OBJECTIVES

Currently, multiple sclerosis is treated with anti-inflammatory therapies, but these treatments lack efficacy in progressive disease. New treatment strategies aim to repair myelin damage and efficacy evaluation of such new therapies would benefit from validated myelin imaging techniques. Several MRI methods for quantification of myelin density are available now. This systematic review aims to analyse the performance of these MRI methods.

METHODS

Studies comparing myelin quantification by MRI with histology, the current gold standard, or assessing reproducibility were retrieved from PubMed/MEDLINE and Embase (until December 2019). Included studies assessed both myelin histology and MRI quantitatively. Correlation or variance measurements were extracted from the studies. Non-parametric tests were used to analyse differences in study methodologies.

RESULTS

The search yielded 1348 unique articles. Twenty-two animal studies and 13 human studies correlated myelin MRI with histology. Eighteen clinical studies analysed the reproducibility. Overall bias risk was low or unclear. All MRI methods performed comparably, with a mean correlation between MRI and histology of R²=0.54 (SD=0.30) for animal studies, and R²=0.54 (SD=0.18) for human studies. Reproducibility for the MRI methods was good (ICC=0.75-0.93, R²=0.90-0.98, COV=1.3-27%), except for MTR (ICC=0.05-0.51).

CONCLUSIONS

Overall, MRI-based myelin imaging methods show a fairly good correlation with histology and a good reproducibility. However, the amount of validation data is too limited and the variability in performance between studies is too large to select the optimal MRI method for myelin quantification yet.

Multi-Omic Approach to Identify Phenotypic Modifiers Underlying Cerebral Demyelination in X-Linked Adrenoleukodystrophy

X-linked adrenoleukodystrophy (ALD) is a peroxisomal metabolic disorder with a highly complex clinical presentation. ALD is caused by mutations in the ABCD1 gene, and is characterized by the accumulation of very long-chain fatty acids in plasma and tissues. Disease-causing mutations are 'loss of function' mutations, with no prognostic value with respect to the clinical outcome of an individual. All male patients with ALD develop spinal cord disease and a peripheral neuropathy in adulthood, although age of onset is highly variable. However, the lifetime prevalence to develop progressive white matter lesions, termed cerebral ALD (CALD), is only about 60%. Early identification of transition to CALD is critical since it can be halted by allogeneic hematopoietic stem cell therapy only in an early stage. The primary goal of this study is to identify molecular markers which may be prognostic of cerebral demyelination from a simple blood sample, with the hope that blood-based assays can replace the current protocols for diagnosis. We collected six well-characterized brother pairs affected by ALD and discordant for the presence of CALD and performed multi-omic profiling of blood samples including genome, epigenome, transcriptome, metabolome/lipidome, and proteome profiling. In our analysis we identify discordant genomic alleles present across all families as well as differentially abundant molecular features across the omics technologies. The analysis was focused on univariate modeling to discriminate the two phenotypic groups, but was unable to identify statistically significant candidate molecular markers. Our study highlights the issues caused by a large amount of inter-individual variation, and supports the emerging hypothesis that cerebral demyelination is a complex mix of environmental factors and/or heterogeneous genomic alleles. We confirm previous observations about the role of immune response, specifically auto-immunity and the potential role of PFN1 protein overabundance in CALD in a subset of the families. We envision our methodology as well as dataset has utility to the field for reproducing previous or enabling future modifier investigations.

SIRT1 activation alleviates brain microvascular endothelial dysfunction in peroxisomal disorders

Peroxisomal disorders are genetically heterogeneous metabolic disorders associated with a deficit of very long chain fatty acid β-oxidation that commonly manifest as early-onset neurodegeneration. Brain microvascular endothelial dysfunction with increased permeability to monocytes has been described in X-linked adrenoleukodystrophy, one of the most common peroxisomal disorders caused by mutations of the ATP binding cassette subfamily D member 1 (ABCD1) gene. The present study demonstrated that dysregulation of sirtuin 1 (SIRT1) in human brain microvascular endothelial cells (HBMECs) mediates changes in adhesion molecules and tight-junction protein expression, as well as increased adhesion to monocytes associated with peroxisomal dysfunction due to ABCD1 or hydroxysteroid 17-β dehydrogenase 4 silencing. Furthermore, enhancement of the function of SIRT1 by resve-ratrol attenuated this molecular and functional dysregulation of HBMECs via modulation of the nuclear factor-κB and Krüppel-like factor 4 signaling pathways.

MRI brain lesions in asymptomatic boys with X-linked adrenoleukodystrophy

OBJECTIVE

To describe the brain MRI findings in asymptomatic patients with childhood cerebral adrenoleukodystrophy (CCALD).

METHODS

We retrospectively reviewed a series of biochemically or genetically confirmed cases of adrenoleukodystrophy followed at our institution between 2001 and 2015. We identified and analyzed 219 brain MRIs from 47 asymptomatic boys (median age 6.0 years). Patient age, MRI scan, and brain lesion characteristics (e.g., contrast enhancement, volume, and Loes score) were recorded. The rate of lesion growth was estimated using a linear mixed effect model.

RESULTS

Sixty percent of patients (28/47) showed brain lesions (median Loes score of 3.0 points; range 0.5-11). Seventy-nine percent of patients with CCALD (22/28) had contrast enhancement on first lesional or subsequent MRI. Lesion progression (Loes increase of ≥0.5 point) was seen in 50% of patients (14/28). The rate of lesion growth (mL/mo) was faster in younger patients (r = -0.745; p < 0.0001). Older patients (median age 14.4 y/o) tended to undergo spontaneous arrest of disease. Early lesions grew 46× faster when still limited to the splenium, genu of the corpus callosum, or the brainstem (p = 0.001).

CONCLUSION

We provide a description of CCALD lesion development in a cohort of asymptomatic boys. Understanding the early stages of CCALD is crucial to optimize treatments for children diagnosed by newborn screening.

ABCD1 dysfunction alters white matter microvascular perfusion

Cerebral X-linked adrenoleukodystrophy is a devastating neurodegenerative disorder caused by mutations in the ABCD1 gene, which lead to a rapidly progressive cerebral inflammatory demyelination in up to 60% of affected males. Selective brain endothelial dysfunction and increased permeability of the blood–brain barrier suggest that white matter microvascular dysfunction contributes to the conversion to cerebral disease. Applying a vascular model to conventional dynamic susceptibility contrast magnetic resonance perfusion imaging, we demonstrate that lack of ABCD1 function causes increased capillary flow heterogeneity in asymptomatic hemizygotes predominantly in the white matter regions and developmental stages with the highest probability for conversion to cerebral disease. In subjects with ongoing inflammatory demyelination we observed a sequence of increased capillary flow heterogeneity followed by blood–brain barrier permeability changes in the perilesional white matter, which predicts lesion progression. These white matter microvascular alterations normalize within 1 year after treatment with haematopoietic stem cell transplantation. For the first time in vivo, our studies unveil a model to assess how ABCD1 alters white matter microvascular function and explores its potential as an earlier biomarker for monitoring disease progression and response to treatment.

X-linked adrenoleukodystrophy in a chimpanzee due to an ABCD1 mutation reported in multiple unrelated humans

BACKGROUND

X-linked adrenoleukodystrophy (X-ALD) is a genetic disorder leading to the accumulation of very long chain fatty acids (VLCFA) due to a mutation in the ABCD1 gene. ABCD1 mutations lead to a variety of phenotypes, including cerebral X-ALD and adrenomyeloneuropathy (AMN) in affected males and 80% of carrier females. There is no definite genotype-phenotype correlation with intrafamilial variability. Cerebral X-ALD typically presents in childhood, but can also present in juveniles and adults. The most affected tissues are the white matter of the brain and adrenal cortex. MRI demonstrates a characteristic imaging appearance in cerebral X-ALD that is used as a diagnostic tool.

OBJECTIVES

We aim to correlate a mutation in the ABCD1 gene in a chimpanzee to the human disease X-ALD based on MRI features, neurologic symptoms, and plasma levels of VLCFA.

METHODS

Diagnosis of X-ALD made using MRI, blood lipid profiling, and DNA sequencing.

RESULTS

An 11-year-old chimpanzee showed remarkably similar features to juvenile onset cerebral X-ALD in humans including demyelination of frontal lobes and corpus callosum on MRI, elevated plasma levels of C24:0 and C26:0, and identification of the c.1661G>A ABCD1 variant.

CONCLUSIONS

This case study presents the first reported case of a leukodystrophy in a great ape, and underscores the fidelity of MRI pattern recognition in this disorder across species.

Overview of Inflammation in Neurometabolic Diseases

Neuroinflammation is an intrinsic component of the neurodegeneration of inborn errors of neurometabolic diseases. Diseases resulting in lysosomal, peroxisomal, and autophagocytic disruption lead to neuroinflammation by different mechanisms relating to accumulated substrates and/or downstream deficiencies that cause presymptomatic microglial activation, axonal instabilities and/or direct hyperactivation of intrinsic inflammatory mechanisms. Only in selected diseases is the blood-brain barrier (BBB) breached, thereby permitting peripheral adaptive immune mechanisms to amplify intrinsic immune reactions in the central nervous system. These result in evoking several different programmed cell death pathways, including apoptosis, necroptosis, and pyroptosis, with the subsequent neuronal death of specific types and in selected regions of the brain or spinal cord. In addition to correction of the primary genetic or metabolic defects, successful therapeutic interventions require greater molecular understanding of the specific neuroinflammatory components of neurometabolic diseases to permit identification of significant targets for intervention.

Quantitative MRI in hypomyelinating disorders

Objective:

To assess the correlation of tissue parameters estimated by quantitative magnetic resonance (MR) techniques and motor handicap in patients with hypomyelination.

Methods:

Twenty-eight patients with different causes of hypomyelination (12 males, 16 females; mean age 10 years) and 61 controls (33 males, 28 females; mean age 8 years) were prospectively investigated. We quantified T2 relaxation time, magnetization transfer ratio, fractional anisotropy, mean, axial, and radial diffusivities, and brain metabolites. We performed measurements in the splenium, parietal deep white matter, and corticospinal tracts in the centrum semiovale. We further analyzed diffusion measures using tract-based spatial statistics. We estimated severity of motor handicap by the gross motor function classification system. We evaluated correlation of handicap with MR measures by linear regression analyses.

Results:

Fractional anisotropy, magnetization transfer ratio, choline, and N-acetylaspartate/creatine ratio were lower and diffusivities, T2 values, and inositol were higher in patients than in controls. Tract-based spatial statistics showed that these changes were widespread for fractional anisotropy (96% of the white matter skeleton), radial (93%) and mean (84%) diffusivity, and less so for axial diffusivity (20%). Correlation with handicap yielded radial diffusivity and N-acetylaspartate/creatine ratio as strongest independent explanatory variables.

Conclusions:

Gross motor function classification system grades are in part explained by MR measures. They indicate that mainly lack of myelin and, to a lesser degree, loss of axonal integrity codetermine the degree of motor handicap in patients with hypomyelinating disorders. These MR measures can be used to evaluate strategies that are aimed at promotion of myelination.

Brain endothelial dysfunction in cerebral adrenoleukodystrophy

See Aubourg (doi:10.1093/awv271) for a scientific commentary on this article.X-linked adrenoleukodystrophy is caused by mutations in the ABCD1 gene leading to accumulation of very long chain fatty acids. Its most severe neurological manifestation is cerebral adrenoleukodystrophy. Here we demonstrate that progressive inflammatory demyelination in cerebral adrenoleukodystrophy coincides with blood-brain barrier dysfunction, increased MMP9 expression, and changes in endothelial tight junction proteins as well as adhesion molecules. ABCD1, but not its closest homologue ABCD2, is highly expressed in human brain microvascular endothelial cells, far exceeding its expression in the systemic vasculature. Silencing of ABCD1 in human brain microvascular endothelial cells causes accumulation of very long chain fatty acids, but much later than the immediate upregulation of adhesion molecules and decrease in tight junction proteins. This results in greater adhesion and transmigration of monocytes across the endothelium. PCR-array screening of human brain microvascular endothelial cells after ABCD1 silencing revealed downregulation of both mRNA and protein levels of the transcription factor c-MYC (encoded by MYC). Interestingly, MYC silencing mimicked the effects of ABCD1 silencing on CLDN5 and ICAM1 without decreasing the levels of ABCD1 protein itself. Together, these data demonstrate that ABCD1 deficiency induces significant alterations in brain endothelium via c-MYC and may thereby contribute to the increased trafficking of leucocytes across the blood-brain barrier as seen in cerebral adrenouleukodystrophy.

The Role of MR Imaging in the Assessment of Clinical Outcomes in Children with X-Linked Adrenoleukodystrophy after Allogeneic Haematopoietic Stem Cell Transplantation

Background

The aim of the study was to analyse MR images of the brain, including advanced MR techniques, such as single voxel spectroscopy (MRS) and diffusion tensor imaging (DTI), in children with X-linked adrenoleukodystrophy (X-ALD) before and after haematopoietic stem cell transplantation (HSCT) and to establish the imaging criteria which may be helpful in the assessment of disease staging, qualification to HSCT and follow-up.

Material/Methods

Seven boys, aged 5–10 years, (mean 8.14 years) with biochemically proved X-ALD, underwent plain MR imaging with a 1.5 T unit before and after HSCT. Structural images were analyzed using an MRI severity scale (Loes scale). In one patient the follow-up examinations included MRS with the assessment of metabolite ratios (NAA/Cr, Cho/Cr, mI/Cr), as well as DTI with evaluation of fractional anisotropy (FA) and apparent diffusion coefficient (ADC) in several white matter tracts.

Results

Two boys had an MRI severity score before HSCT equal to <8 points, and after HSCT they showed no clinical or radiological progression. In 5 patients with a higher severity score (from 8 to 16 points, mean 10.9) before HSCT, clinical and radiological progression was observed (MRI severity score from 17 to 25 points, mean 20.9). Follow-up advanced MRI techniques in one boy showed metabolic alterations, as well as decreased FA and ADC values in all evaluated areas.

Conclusions

Children at an early stage of X-ALD (below 8 points in MRI severity scale) are more likely to benefit from HSCT. DTI and MRS seem to be more useful imaging methods to assess the progression of X-ALD.

X-linked adrenoleukodystrophy: correlation between Loes score and diffusion tensor imaging parameters

OBJECTIVE

The present study was aimed at evaluating the correlation between diffusion tensor imaging parameters and Loes score as well as whether those parameters could indicate early structural alterations.

MATERIALS AND METHODS

Diffusion tensor imaging measurements were obtained in 30 studies of 14 patients with X-linked adrenoleukodystrophy and were correlated with Loes scores. A control group including 28 male patients was created to establish agematched diffusion tensor imaging measurements. Inter- and intraobserver statistical analyses were undertaken.

RESULTS

Diffusion tensor imaging measurements presented strong Pearson correlation coefficients (r) of -0.86, 0.89, 0.89 and 0.84 for fractional anisotropy and mean, radial and axial diffusivities (p < 0.01). Analysis of changes in diffusion tensor measurements at early stage of the disease indicates that mean and radial diffusivities might be useful to predict the disease progression.

CONCLUSION

Measurements of diffusion tensor parameters can be used as an adjunct to the Loes score, aiding in the monitoring of the disease and alerting for possible Loes score progression in the range of interest for therapeutic decisions.

Adult cerebral adrenoleukodystrophy and Addison's disease in a female carrier

We described a 38-year-old woman of rapidly progressive dementia with white matter encephalopathy and death. She had Addison's disease but the adrenal glands were hyperplastic. Brain magnetic resonance imaging revealed diffuse white matter lesion predominantly in the frontal lobe with band-like contrast enhancement. l-Methyl-11C-methionine positron emission tomography revealed accumulation of tracer in bilateral frontal lobes. Stereotactic biopsy demonstrated demyelination changes. A number of urinary organic acids were elevated. Adrenoleukodystrophy was diagnosed by elevated plasma very long chain fatty acid and ABCD1 gene mutation (C1544C/T). Adrenoleukodystrophy should be considered as a differential diagnosis in women with rapidly progressive white matter encephalopathy.

Childhood cerebral X-linked adrenoleukodystrophy: diffusion tensor imaging measurements for prediction of clinical outcome after hematopoietic stem cell transplantation

BACKGROUND AND PURPOSE

DTI in cerebral X-linked adrenoleukodystrophy may demonstrate abnormalities in both affected and nonaffected WM; these values have not been studied serially after hematopoietic stem cell transplantation. The purpose of this study was to study pretransplant and posttransplant DTI parameters serially and ultimately to determine the ability of pretransplant DTI parameters to predict clinical outcome after HSCT in children with ALD.

MATERIALS AND METHODS

Eight patients with posterior-pattern cerebral ALD underwent DTI at 3T before HSCT (T0), at 30-60 days (T1), 90-120 days (T2), 180 days (T3), and 1 year (T4) after HSCT. FA and MD were serially measured in 19 regions, and these measurements were compared with those in control patients. MR imaging severity (Loes) scores were recorded. Correlations were performed between DTI parameters and Loes scores, neurologic function scores, and several neuropsychologic scores.

RESULTS

Both FA and MD in subjects differed significantly from that in controls at nearly every time point within cerebellar WM, callosal splenium, and parieto-occipital WM; FA alone was significantly different at each time point within the optic radiations, lateral geniculate, and the Meyer loop (P < .05). Loes scores at T0 correlated strongly with each clinical score at T4 (r = 0.771-0.986, P < .05). The only significant DTI correlation at T0 with a clinical score at T4 was callosal body FA with adaptive function (r = 0.976, P < .001). Correlating the change in DTI values with change in NFS (change between T0 and T4) showed that only ΔMD within the optic radiations correlated strongly with ΔNFS (r = 0.903, P < .05).

CONCLUSIONS

DTI values at T0 were generally poor predictors of outcome at 1 year, whereas Loes scores were generally good predictors. ΔMD within the optic radiations strongly correlates with ΔNFS over that year. In addition, certain normal-appearing regions, such as cerebellar WM, may have DTI abnormalities before HSCT that persist after HSCT.

Hypoperfusion predicts lesion progression in cerebral X-linked adrenoleukodystrophy

Magnetic resonance imaging sequences such as diffusion and spectroscopy have been well studied in X-linked adrenoleukodystrophy, but no data exist on magnetic resonance perfusion imaging. Since inflammation is known to modulate the microcirculation, we investigated the hypothesis that changes in the local perfusion might be one of the earliest signs of lesion development. Twenty patients with different phenotypes of adrenoleukodystrophy and seven age-matched controls were evaluated between 2006 and 2011. Fluid attenuated inversion recovery, post-contrast T(1)-weighted and normalized dynamic susceptibility contrast magnetic resonance perfusion cerebral blood volume maps were co-registered, segmented when cerebral lesion was present, and normalized cerebral blood volume values were analysed using a Food and Drug Association approved magnetic resonance perfusion software (NordicICE). Clinical and imaging data were reviewed to determine phenotype and status of progression. All eight patients with cerebral adrenoleukodystrophy had an average 80% decrease in normalized cerebral blood volume at the core of the lesion (P < 0.0001). Beyond the leading edge of contrast enhancement cerebral perfusion varied, patients with progressive lesions showed an average 60% decrease in normalized cerebral blood volume (adults P < 0.05; children P < 0.001), while one child with arrested progression normalized cerebral blood volume in this region. In six of seven patients with cerebral adrenoleukodystrophy lesions and follow-up imaging (2-24 month interval period), we found progression of contrast enhancement into the formerly hypoperfused perilesional zone. Asymptomatic, adrenomyeloneuropathy and female heterozygote patients had no significant changes in cerebral perfusion. Our data indicate that decreased brain magnetic resonance perfusion precedes leakage of the blood-brain barrier as demonstrated by contrast enhancement in cerebral adrenoleukodystrophy and is an early sign of lesion progression.

Metabolic disorders of the brain: part I

Due to nonspecific clinical presentation, diagnosis of metabolic disorders affecting the brain is very challenging for physicians. It is always the constellation of the clinical examination, biochemical assay and imaging that helps in reaching the diagnosis of metabolic disorders. Diagnosis of these disorders or even limiting the differential diagnosis on imaging may pose a formidable challenge to the radiologist. In these two articles (Metabolic Disorders of the Brain: Parts I and II) we have tried to highlight the important clinical and imaging pearls of the major and more commonly encountered metabolic disorders. In the first article we discuss metabolic disorders related to dysfunction of the cellular organelle namely lysosomal, peroxisomal, and mitochondrial. We have also discussed the relevant genetic abnormalities, biochemical findings and application of newer imaging techniques which may aid in diagnosis of these various disorders.