Clinical and genetic characterization of adult-onset leukoencephalopathy with axonal spheroids and pigmented glia associated with CSF1R mutation

Distinct patterns of white matter hyperintensity and cortical thickness of CSF1R-related leukoencephalopathy compared with subcortical ischemic vascular dementia

BACKGROUND

CSF1R-related leukoencephalopathy is a type of autosomal dominant leukodystrophy caused by mutations in the colony stimulating factor 1 receptor (CSF1R) gene. Subcortical ischemic vascular dementia (SIVaD), which is caused by cerebral small vessel disease, is similar to CSF1R-related leukoencephalopathy in that it mainly affects subcortical white matter. In this study, we compared the patterns of white matter hyperintensity (WMH) and cortical thickness in CSF1R-related leukoencephalopathy with those in SIVaD.

METHODS

Fourteen patients with CSF1R-related leukoencephalopathy and 129 with SIVaD were retrospectively recruited from three tertiary medical centers. We extracted and visualized WMH data using voxel-based morphometry to compare the WMH distributions between the two groups. Cortical thickness was measured using a surface-based method. Statistical maps of differences in cortical thickness between the two groups were generated using a surface model, with age, sex, education, and intracranial volume as covariates.

RESULTS

Predominant distribution of WMH in the CSF1R-related leukoencephalopathy group was in the bilateral frontal and parietal areas, whereas the SIVaD group showed diffuse WMH involvement in the bilateral frontal, parietal, and temporal areas. Compared with the SIVaD group, the CSF1R-related leukoencephalopathy group showed more severe corpus callosum atrophy (CCA) and widespread cortical thinning.

CONCLUSIONS

To our knowledge, this is the first study using the automated MR measurement to capture WMH, cortical thinning, and CCA with signal changes in CSF1R-related leukoencephalopathy. It provides new evidence regarding differences in the patterns of WMH distribution and cortical thinning between CSF1R-related leukoencephalopathy and SIVaD.

Novel variants in CSF1R associated with adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP)

The CSF1R gene, located on chromosome 5, encodes a 108 kDa protein and plays a critical role in regulating myeloid cell function. Mutations in CSF1R have been identified as a cause of a rare white matter disease called adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP, also known as CSF1R-related leukoencephalopathy), characterized by progressive neurological dysfunction. This study aimed to broaden the genetic basis of ALSP by identifying novel CSF1R variants in patients with characteristic clinical and imaging features of ALSP. Genetic analysis was performed through whole-exome sequencing or panel analysis for leukodystrophy genes. Variant annotation and classification were conducted using computational tools, and the identified variants were categorized following the recommendations of the American College of Medical Genetics and Genomics (ACMG). To assess the evolutionary conservation of the novel variants within the CSF1R protein, amino acid sequences were compared across different species. The study identified six previously unreported CSF1R variants (c.2384G>T, c.2133_2919del, c.1837G>A, c.2304C>A, c.2517G>T, c.2642C>T) in seven patients with ALSP, contributing to the expanding knowledge of the genetic diversity underlying this rare disease. The analysis revealed considerable genetic and clinical heterogeneity among these patients. The findings emphasize the need for a comprehensive understanding of the genetic basis of rare diseases like ALSP and underscored the importance of genetic testing, even in cases with no family history of the disease. The study's contribution to the growing spectrum of ALSP genetics and phenotypes enhances our knowledge of this condition, which can be crucial for both diagnosis and potential future treatments.

Deciphering glial contributions to CSF1R-related disorder via single-nuclear transcriptomic profiling: a case study

CSF1R-related disorder (CSF1R-RD) is a neurodegenerative condition that predominantly affects white matter due to genetic alterations in the CSF1R gene, which is expressed by microglia. We studied an elderly man with a hereditary, progressive dementing disorder of unclear etiology. Standard genetic testing for leukodystrophy and other neurodegenerative conditions was negative. Brain autopsy revealed classic features of adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP), including confluent white matter degeneration with axonal spheroids and pigmented glial cells in the affected white matter, consistent with CSF1R-RD. Subsequent long-read sequencing identified a novel deletion in CSF1R that was not detectable with short-read exome sequencing. To gain insight into potential mechanisms underlying white matter degeneration in CSF1R-RD, we studied multiple brain regions exhibiting varying degrees of white matter pathology. We found decreased CSF1R transcript and protein across brain regions, including intact white matter. Single nuclear RNA sequencing (snRNAseq) identified two disease-associated microglial cell states: lipid-laden microglia (expressing GPNMB, ATG7, LGALS1, LGALS3) and inflammatory microglia (expressing IL2RA, ATP2C1, FCGBP, VSIR, SESN3), along with a small population of CD44+ peripheral monocyte-derived macrophages exhibiting migratory and phagocytic signatures. GPNMB+ lipid-laden microglia with ameboid morphology represented the end-stage disease microglia state. Disease-associated oligodendrocytes exhibited cell stress signatures and dysregulated apoptosis-related genes. Disease-associated oligodendrocyte precursor cells (OPCs) displayed a failure in their differentiation into mature myelin-forming oligodendrocytes, as evidenced by upregulated LRP1, PDGFRA, SOX5, NFIA, and downregulated NKX2-2, NKX6.2, SOX4, SOX8, TCF7L2, YY1, ZNF488. Overall, our findings highlight microglia-oligodendroglia crosstalk in demyelination, with CSF1R dysfunction promoting phagocytic and inflammatory microglia states, an arrest in OPC differentiation, and oligodendrocyte depletion.

Therapeutic potential of human microglia transplantation in a chimeric model of CSF1R-related leukoencephalopathy

Microglia replacement strategies are increasingly being considered for the treatment of primary microgliopathies like adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP). However, available mouse models fail to recapitulate the diverse neuropathologies and reduced microglia numbers observed in patients. In this study, we generated a xenotolerant mouse model lacking the fms-intronic regulatory element (FIRE) enhancer within Csf1r, which develops nearly all the hallmark pathologies associated with ALSP. Remarkably, transplantation of human induced pluripotent stem cell (iPSC)-derived microglial (iMG) progenitors restores a homeostatic microglial signature and prevents the development of axonal spheroids, white matter abnormalities, reactive astrocytosis, and brain calcifications. Furthermore, transplantation of CRISPR-corrected ALSP-patient-derived iMG reverses pre-existing spheroids, astrogliosis, and calcification pathologies. Together with the accompanying study by Munro and colleagues, our results demonstrate the utility of FIRE mice to model ALSP and provide compelling evidence that iMG transplantation could offer a promising new therapeutic strategy for ALSP and perhaps other microglia-associated neurological disorders.

CSF1R-Related Disorder: Prevalence of CSF1R Variants and Their Clinical Significance in the UK Population

Background and Objectives

CSF1R-related disorder (CSF1R-RD) is a devastating neurodegenerative disorder caused by variants in the colony stimulating factor-1 receptor (CSF1R) gene. CSF1R-RD leads to a variable combination of cognitive impairment, movement disorders, upper motor neuron signs, and spasticity with associated imaging abnormalities in brain white matter. Although increasingly recognized, there is evidence that it is significantly underdiagnosed or misdiagnosed, and its true prevalence is unknown. We leveraged the large data set of the UK Biobank to determine the prevalence of CSF1R mutations in the UK population and identify clinical phenotypes associated with these variants.

Methods

Pathogenic and likely pathogenic CSF1R variants were identified in UK Biobank whole-exome sequencing data (N = 470,000). Medical history, including neurologic and psychiatric disease, were determined from self-reported and hospital collected codes, and the volume of MRI white matter hyperintensities were compared between variant carriers and controls.

Results

We identified 25 individuals carrying 18 unique pathogenic variants and 107 individuals carrying 44 unique likely pathogenic variants-combined prevalence 132 (∼1 in 3,500). Pathogenic CSF1R variant carriers had increased risk of psychiatric disease (OR: 5.15, p = 0.0079), depression (OR: 10.52, p = 0.0015), and Parkinson disease (OR: 19.80, p = 0.0038). Using algorithmically defined diagnosis data, pathogenic or likely pathogenic variants (the combined group) carriers were at higher risk for both dementia (OR: 2.50, p = 0.046) and vascular dementia (OR: 4.72, p = 0.032).

Discussion

Damaging variants in CSF1R are more common than expected in the general population and are associated with cognitive, psychiatric, and movement disorder diagnoses, which may reflect clinical manifestation of the disease. This study suggests that CSF1R-RD is either underreported, not diagnosed because of lack of genetic screening or that there is reduced penetrance.

Identification and characterization of a novel intronic splicing mutation in CSF1R-related leukoencephalopathy

AIMS

Colony stimulating factor 1 receptor (CSF1R)-related leukoencephalopathy is a rapidly progressing neurodegenerative disease caused by CSF1R gene mutations. This study aimed to identify and investigate the effect of a novel intronic mutation (c.1754-3C>G) of CSF1R on splicing.

METHODS

A novel intronic mutation was identified using whole-exome sequencing. To investigate the impact of this mutation, we employed various bioinformatics tools to analyze the transcription of the CSF1R gene and the three-dimensional structure of its encoded protein. Furthermore, reverse transcription polymerase chain reaction (RT-PCR) was performed to validate the findings.

RESULTS

A novel mutation (c.1754-3C>G) in CSF1R was identified, which results in exon 13 skipping due to the disruption of the 3' splice site consensus sequence NYAG/G. This exon skipping event was further validated in the peripheral blood of the mutation carrier through RT-PCR and Sanger sequencing. Protein structure prediction indicated a disruption in the tyrosine kinase domain, with the truncated protein showing significant structural alterations.

CONCLUSIONS

Our findings underscore the importance of intronic mis-splicing mutations in the diagnosis and management of CSF1R-related leukoencephalopathy.

The Phenotypic and Genotypic Spectrum of CSF1R-Related Disorder in China

BACKGROUND

Colony-stimulating factor 1 receptor (CSF1R)-related disorder (CRD) is a rare autosomal dominant disease. The clinical and genetic characteristics of Chinese patients have not been elucidated.

OBJECTIVE

The objective of the study is to clarify the core features and influence factors of CRD patients in China.

METHODS

Clinical and genetic-related data of CRD patients in China were collected. Mini-Mental State Examination (MMSE), Montreal Cognitive Assessment (MoCA), and Sundal MRI Severity Score were evaluated. Whole exome sequencing was used to analyze the CSF1R mutation status. Patients were compared between different sexes, mutation types, or mutation locations.

RESULTS

A total of 103 patients were included, with a male-to-female ratio of 1:1.51. The average age of onset was (40.75 ± 8.58). Cognitive impairment (85.1%, 86/101) and parkinsonism (76.2%, 77/101) were the main clinical symptoms. The most common imaging feature was bilateral asymmetric white matter changes (100.0%). A total of 66 CSF1R gene mutants (22 novel mutations) were found, and 15 of 92 probands carried c.2381 T > C/p.I794T (16.30%). The MMSE and MoCA scores (17.0 [9.0], 11.90 ± 7.16) of female patients were significantly lower than those of male patients (23.0 [10.0], 16.36 ± 7.89), and the white matter severity score (20.19 ± 8.47) of female patients was significantly higher than that of male patients (16.00 ± 7.62). There is no statistical difference in age of onset between male and female patients.

CONCLUSIONS

The core manifestations of Chinese CRD patients are progressive cognitive decline, parkinsonism, and bilateral asymmetric white matter changes. Compared to men, women have more severe cognitive impairment and imaging changes. c.2381 T > C/p.I794T is a hotspot mutation in Chinese patients. © 2024 International Parkinson and Movement Disorder Society.

Clinical presentation and diagnosis of adult-onset leukoencephalopathy with axonal spheroids and pigmented glia: a literature analysis of case studies

Introduction

Because adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP) is a rare, rapidly progressive, debilitating, and ultimately fatal neurodegenerative disease, a rapid and accurate diagnosis is critical. This analysis examined the frequency of initial misdiagnosis of ALSP via comprehensive review of peer-reviewed published cases.

Methods

Data were extracted from a MEDLINE search via PubMed (January 1, 1980, through March 22, 2022) from eligible published case reports/series for patients with an ALSP diagnosis that had been confirmed by testing for the colony-stimulating factor-1 receptor gene (CSF1R) mutation. Patient demographics, clinical symptoms, brain imaging, and initial diagnosis data were summarized descriptively. Categorical data for patient demographics, symptoms, and brain imaging were stratified by initial diagnosis category to test for differences in initial diagnosis based on each variable.

Results

Data were extracted from a cohort of 291 patients with ALSP from 93 published case reports and case series. Mean (standard deviation) age of symptom onset was 43.2 (11.6) years. A family history of ALSP was observed in 59.1% of patients. Cognitive impairment (47.1%) and behavioral and psychiatric abnormalities (26.8%) were the most frequently reported initial symptoms. Of 291 total cases, an accurate initial diagnosis of ALSP was made in 72 cases (24.7%) and the most frequent initial misdiagnosis categories were frontotemporal dementia (28 [9.6%]) and multiple sclerosis (21 [7.2%]). Of the 219 cases (75.3%) that were initially mis- or undiagnosed, 206 cases (94.1%) were later confirmed as ALSP by immunohistology, imaging, and/or genetic testing; for the remaining 13 cases, no final diagnosis was reported. Initial diagnosis category varied based on age, family history, geographic region, mode of inheritance, and presenting symptoms of pyramidal or extrapyramidal motor dysfunction, behavioral and psychiatric abnormalities, cognitive impairment, and speech difficulty. Brain imaging abnormalities were common, and initial diagnosis category was significantly associated with white matter hyperintensities, white matter calcifications, and ventricular enlargement.

Discussion

In this literature analysis, ALSP was frequently misdiagnosed. Improving awareness of this condition and distinguishing it from other conditions with overlapping presenting symptoms is important for timely management of a rapidly progressive disease such as ALSP.

Allogenic microglia replacement: A novel therapeutic strategy for neurological disorders

Microglia are resident immune cells in the central nervous system (CNS) that play vital roles in CNS development, homeostasis and disease pathogenesis. Genetic defects in microglia lead to microglial dysfunction, which in turn leads to neurological disorders. The correction of the specific genetic defects in microglia in these disorders can lead to therapeutic effects. Traditional genetic defect correction approaches are dependent on viral vector-based genetic defect corrections. However, the viruses used in these approaches, including adeno-associated viruses, lentiviruses and retroviruses, do not primarily target microglia; therefore, viral vector-based genetic defect corrections are ineffective in microglia. Microglia replacement is a novel approach to correct microglial genetic defects via replacing microglia of genetic defects with allogenic healthy microglia. In this paper, we systematically review the history, rationale and therapeutic perspectives of microglia replacement, which would be a novel strategy for treating CNS disorders.

White matter disorders with cerebral calcification in adulthood

This chapter provides a comprehensive overview of adult-onset leukoencephalopathies with cerebral calcification (CC), emphasizing the importance of age at presentation, systemic clinical features, and neuroimaging patterns for accurate diagnosis. CC is a multifaceted phenomenon associated with various neurologic, developmental, metabolic, and genetic conditions, as well as normal aging. Here, we explore the distinction between primary familial brain calcification (PFBC) and secondary forms, including metabolic and mitochondrial causes. We discuss genetic causes, e.g., SLC20A2, XPR1, PDGFB, PDGFRB, MYORG, NAA60 and JAM2, in the context of autosomal dominant and recessive PFBC and other inherited conditions. The chapter delineates the diagnostic approach involving family history, clinical assessments, and detailed investigations of calcium-phosphate metabolism. Neuroimaging modalities, including computed tomography and magnetic resonance imaging, are crucial for assessing calcification patterns and localizations. Genetic testing, especially next-generation sequencing, plays a pivotal role in providing a final molecular diagnosis. The management of patients with CC encompasses symptomatic treatment and cause-specific approaches, requiring a multidisciplinary care approach. In conclusion, this chapter highlights the complexity of leukoencephalopathies with CC, emphasizing the need for integrated and evolving management to optimize patient care.

Hematopoietic stem cell transplantation in leukodystrophies

More than 50 leukodystrophies have been described. This group of inherited disorders affects myelin development and/or maintenance and can manifest from birth to adulthood. Neuroinflammation is a hallmark of some leukodystrophies, explaining in part the therapeutic benefit of hematopoietic stem cell transplantation (HSCT). Indeed, in addition to supplying the CNS with myelomonocyte donor cells expressing the deficient protein or enzyme, HSCT allows the restoration of normal microglia function, which may act on neuroinflammation. In this chapter, we explore the rationale, indication, and outcome of HSCT in Cerebral Adrenoleukodystrophy (CALD), Metachromatic Leukodystrophy (MLD), Krabbe Disease (KD), and Adult-onset Leukoencephalopathy with Axonal Spheroids and Pigmented Glia (ALSP), which are among the most frequent leukodystrophies. For these leukodystrophies, HSCT may modify notably the natural history and improve CNS-related deficits, provided that the procedure is performed early into the disease course. In addition, we discuss the recent development of ex vivo gene therapy for CALD and MLD as a promising alternative to allograft.

Progress in leukodystrophies with zebrafish

Inherited leukodystrophies are genetic disorders characterized by abnormal white matter in the central nervous system. Although individually rare, there are more than 400 distinct types of leukodystrophies with a cumulative incidence of 1 in 4500 live births. The pathophysiology of most leukodystrophies is poorly understood, there are treatments for only a few, and there is significant morbidity and mortality, suggesting a critical need for improvements in this field. A variety of animal, cell, and induced pluripotent stem cell-derived models have been developed for leukodystrophies, but with significant limitations in all models. Many leukodystrophies lack animal models, and extant models often show no or mixed recapitulation of key phenotypes. Zebrafish (Danio rerio) have become increasingly used as disease models for studying leukodystrophies due to their early onset of disease phenotypes and conservation of molecular and neurobiological mechanisms. Here, we focus on reviewing new zebrafish disease models for leukodystrophy or models with recent progress. This includes discussion of leukodystrophy with vanishing white matter disease, X-linked adrenoleukodystrophy, Zellweger spectrum disorders and peroxisomal disorders, PSAP deficiency, metachromatic leukodystrophy, Krabbe disease, hypomyelinating leukodystrophy-8/4H leukodystrophy, Aicardi-Goutières syndrome, RNASET2-deficient cystic leukoencephalopathy, hereditary diffuse leukoencephalopathy with spheroids-1 (CSF1R-related leukoencephalopathy), and ultra-rare leukodystrophies. Zebrafish models offer important potentials for the leukodystrophy field, including testing of new variants in known genes; establishing causation of newly discovered genes; and early lead compound identification for therapies. There are also unrealized opportunities to use humanized zebrafish models which have been sparsely explored.

MRI pattern recognition in white matter disease

Magnetic resonance imaging (MRI) pattern recognition is a powerful tool for quick diagnosis of genetic and acquired white matter disorders. In many cases, distribution and character of white matter abnormalities directly point to a specific diagnosis and guide confirmatory testing. Knowledge of normal brain development is essential to interpret white matter changes in young children. MRI is also used for disease staging and treatment decisions in leukodystrophies and acquired disorders as multiple sclerosis, and as a biomarker to follow treatment effects.

Adult-onset leukoencephalopathy with axonal spheroids and pigmented glia

Adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP) is an adult-onset, inherited white matter disorder encompassing two previously identified clinicopathologically similar entities: pigmentary orthochromatic leukodystrophy (POLD) and hereditary diffuse leukoencephalopathy with spheroids (HDLS). In this chapter, we discuss how advances in our genetic understanding of the condition have further delineated three distinct clinical entities within ALSP, namely CSF1R-related ALSP, AARS2-related leukoencephalopathy (AARS2-L), and AARS (HDLS-S). We provide descriptions of the clinical, radiologic, pathologic, and pathophysiologic findings in each entity, detailing their similarities and differences, and discuss current and future treatment options where available.

Differential regulation of microglial states by colony stimulating factors

Recent studies have emphasized the role of microglia in the progression of many neurodegenerative diseases. The colony stimulating factors, CSF-1 (M-CSF), granulocyte-macrophage CSF (GM-CSF) and granulocyte CSF (G-CSF) regulate microglia through different cognate receptors. While the receptors for GM-CSF (GM-CSFR) and G-CSF (G-CSFR) are specific for their ligands, CSF-1 shares its receptor, the CSF-1 receptor-tyrosine kinase (CSF-1R), with interleukin-34 (IL-34). All four cytokines are expressed locally in the CNS. Activation of the CSF-1R in macrophages is anti-inflammatory. In contrast, the actions of GM-CSF and G-CSF elicit different activated states. We here review the roles of each of these cytokines in the CNS and how they contribute to the development of disease in a mouse model of CSF-1R-related leukodystrophy. Understanding their roles in this model may illuminate their contribution to the development or exacerbation of other neurodegenerative diseases.

Pearls & Oy-sters: CSF1R-Related Leukoencephalopathy With Spinal Cord Lesions Mimicking Multiple Sclerosis

CSF1R-related leukoencephalopathy is an autosomal dominant neurologic disorder causing microglial dysfunction with a wide range of neurologic complications, including motor dysfunction, dementia, and seizures. This case report highlights an unusual presentation of CSF1R-related leukoencephalopathy with radiographic spinal cord involvement initially diagnosed as multiple sclerosis. This case highlights the importance of considering adult-onset neurogenetic disorders in the setting of white matter disease. Genetic testing provides a confirmatory diagnosis for an expanding number of adult-onset leukoencephalopathies and informs therapeutic decision-making.

Adult-onset leukodystrophies: a practical guide, recent treatment updates, and future directions

Adult-onset leukodystrophies though individually rare are not uncommon. This group includes several disorders with isolated adult presentations, as well as several childhood leukodystrophies with attenuated phenotypes that present at a later age. Misdiagnoses often occur due to the clinical and radiological overlap with common acquired disorders such as infectious, immune, inflammatory, vascular, metabolic, and toxic etiologies. Increased prevalence of non-specific white matter changes in adult population poses challenges during diagnostic considerations. Clinico-radiological spectrum and molecular landscape of adult-onset leukodystrophies have not been completely elucidated at this time. Diagnostic approach is less well-standardized when compared to the childhood counterpart. Absence of family history and reduced penetrance in certain disorders frequently create a dilemma. Comprehensive evaluation and molecular confirmation when available helps in prognostication, early initiation of treatment in certain disorders, enrollment in clinical trials, and provides valuable information for the family for reproductive counseling. In this review article, we aimed to formulate an approach to adult-onset leukodystrophies that will be useful in routine practice, discuss common adult-onset leukodystrophies with usual and unusual presentations, neuroimaging findings, recent advances in treatment, acquired mimics, and provide an algorithm for comprehensive clinical, radiological, and genetic evaluation that will facilitate early diagnosis and consider active treatment options when available. A high index of suspicion, awareness of the clinico-radiological presentations, and comprehensive genetic evaluation are paramount because treatment options are available for several disorders when diagnosed early in the disease course.

Brain abnormalities, neurodegeneration, and dysosteosclerosis (BANDDOS): new cases, systematic literature review, and associations with CSF1R-ALSP

CSF1R mutations cause autosomal-dominant CSF1R-related leukoencephalopathy with axonal spheroids and pigmented glia (CSF1R-ALSP) and autosomal-recessive brain abnormalities, neurodegeneration, and dysosteosclerosis (BANDDOS). The former is increasingly recognized, and disease-modifying therapy was introduced; however, literature is scarce on the latter. This review analyzes BANDDOS and discusses similarities and differences with CSF1R-ALSP.We systematically retrieved and analyzed the clinical, genetic, radiological, and pathological data on the previously reported and our cases with BANDDOS. We identified 19 patients with BANDDOS (literature search according to the PRISMA 2020 guidelines: n = 16, our material: n = 3). We found 11 CSF1R mutations, including splicing (n = 3), missense (n = 3), nonsense (n = 2), and intronic (n = 2) variants and one inframe deletion. All mutations disrupted the tyrosine kinase domain or resulted in nonsense-mediated mRNA decay. The material is heterogenous, and the presented information refers to the number of patients with sufficient data on specific symptoms, results, or performed procedures. The first symptoms occurred in the perinatal period (n = 5), infancy (n = 2), childhood (n = 5), and adulthood (n = 1). Dysmorphic features were present in 7/17 cases. Neurological symptoms included speech disturbances (n = 13/15), cognitive decline (n = 12/14), spasticity/rigidity (n = 12/15), hyperactive tendon reflex (n = 11/14), pathological reflexes (n = 8/11), seizures (n = 9/16), dysphagia (n = 9/12), developmental delay (n = 7/14), infantile hypotonia (n = 3/11), and optic nerve atrophy (n = 2/7). Skeletal deformities were observed in 13/17 cases and fell within the dysosteosclerosis - Pyle disease spectrum. Brain abnormalities included white matter changes (n = 19/19), calcifications (n = 15/18), agenesis of corpus callosum (n = 12/16), ventriculomegaly (n = 13/19), Dandy-Walker complex (n = 7/19), and cortical abnormalities (n = 4/10). Three patients died in infancy, two in childhood, and one case at unspecified age. A single brain autopsy evidenced multiple brain anomalies, absence of corpus callosum, absence of microglia, severe white matter atrophy with axonal spheroids, gliosis, and numerous dystrophic calcifications.In conclusion, BANDDOS presents in the perinatal period or infancy and has a devastating course with congenital brain abnormalities, developmental delay, neurological deficits, osteopetrosis, and dysmorphic features. There is a significant overlap in the clinical, radiological, and neuropathological aspects between BANDDOS and CSF1R-ALSP. As both disorders are on the same continuum, there is a window of opportunity to apply available therapy in CSF1R-ALSP to BANDDOS.

Neuropsychological profile of CSF1R-related leukoencephalopathy

Introduction

The neuropsychological profile of CSF1R-related leukoencephalopathy (CRL) is undefined. This study defines the profile, contrasts it with that of other dementia syndromes, and highlights measures sensitive to cognitive impairment.

Methods

We administered a standardized battery of neuropsychological tests to five consecutive CRL cases.

Results

The neuropsychological profile of CRL reflects impaired general cognitive function, processing speed, executive function, speeded visual problem solving, verbal fluency, and self-reported depression and anxiety. Confrontation naming and memory are preserved. Within cognitive domains, certain measures more frequently identified impairment than others.

Discussion

CRL impairs general cognitive function, processing speed, executive function. Language and visual problem solving may be impaired if processing speed is required. Confrontation naming and memory are uniquely preserved, contrasting CRL to other dementia syndromes. Cognitive screens excluding processing speed and executive function may not detect CRL cognitive manifestations. Findings sharply define cognitive impairment of CRL and inform cognitive test selection.

The genetic and phenotypic spectra of adult genetic leukoencephalopathies in a cohort of 309 patients

Genetic leukoencephalopathies (gLEs) are a highly heterogeneous group of rare genetic disorders. The spectrum of gLEs varies among patients of different ages. Distinct from the relatively more abundant studies of gLEs in children, only a few studies that explore the spectrum of adult gLEs have been published, and it should be noted that the majority of these excluded certain gLEs. Thus, to date, no large study has been designed and conducted to characterize the genetic and phenotypic spectra of gLEs in adult patients. We recruited a consecutive series of 309 adult patients clinically suspected of gLEs from Beijing Tiantan Hospital between January 2014 and December 2021. Whole-exome sequencing, mitochondrial DNA sequencing and repeat analysis of NOTCH2NLC, FMR1, DMPK and ZNF9 were performed for patients. We describe the genetic and phenotypic spectra of the set of patients with a genetically confirmed diagnosis and summarize their clinical and radiological characteristics. A total of 201 patients (65%) were genetically diagnosed, while 108 patients (35%) remained undiagnosed. The most frequent diseases were leukoencephalopathies related to NOTCH3 (25%), NOTCH2NLC (19%), ABCD1 (9%), CSF1R (7%) and HTRA1 (5%). Based on a previously proposed pathological classification, the gLEs in our cohort were divided into leukovasculopathies (35%), leuko-axonopathies (31%), myelin disorders (21%), microgliopathies (7%) and astrocytopathies (6%). Patients with NOTCH3 mutations accounted for 70% of the leukovasculopathies, followed by HTRA1 (13%) and COL4A1/2 (9%). The leuko-axonopathies contained the richest variety of associated genes, of which NOTCH2NLC comprised 62%. Among myelin disorders, demyelinating leukoencephalopathies (61%)-mainly adrenoleukodystrophy and Krabbe disease-accounted for the majority, while hypomyelinating leukoencephalopathies (2%) were rare. CSF1R was the only mutated gene detected in microgliopathy patients. Leukoencephalopathy with vanishing white matter disease due to mutations in EIF2B2-5 accounted for half of the astrocytopathies. We characterized the genetic and phenotypic spectra of adult gLEs in a large Chinese cohort. The most frequently mutated genes were NOTCH3, NOTCH2NLC, ABCD1, CSF1R and HTRA1.

Case report: Treatment of advanced CSF1-receptor associated leukoencephalopathy with hematopoietic stem cell transplant

CSF1 receptor-related leukoencephalopathy is a rare genetic disorder presenting with severe, adult-onset white matter dementia as one of the leading symptoms. Within the central nervous system, the affected CSF1-receptor is expressed exclusively in microglia cells. Growing evidence implicates that replacing the defective microglia with healthy donor cells through hematopoietic stem cell transplant might halt disease progression. Early initiation of that treatment is crucial to limit persistent disability. However, which patients are suitable for this treatment is not clear, and imaging biomarkers that specifically depict lasting structural damage are lacking. In this study, we report on two patients with CSF1R-related leukoencephalopathy in whom allogenic hematopoietic stem cell transplant at advanced disease stages led to clinical stabilization. We compare their disease course with that of two patients admitted in the same timeframe to our hospital, considered too late for treatment, and place our cases in context with the respective literature. We propose that the rate of clinical progression might be a suitable stratification measure for treatment amenability in patients. Furthermore, for the first time we evaluate [18F] florbetaben, a PET tracer known to bind to intact myelin, as a novel MRI-adjunct tool to image white matter damage in CSF1R-related leukoencephalopathy. In conclusion, our data add evidence for allogenic hematopoietic stem cell transplant as a promising treatment in CSF1R-related leukoencephalopathy patients with slow to moderate disease progression.

Hematopoietic Stem Cell Transplantation in CSF1R-Related Leukoencephalopathy: Retrospective Study on Predictors of Outcomes

Mutations in the CSF1R gene are the most common cause of adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP), a neurodegenerative disease with rapid progression and ominous prognosis. Hematopoietic stem cell transplantation (HSCT) has been increasingly offered to patients with CSF1R-ALSP. However, different therapy results were observed, and it was not elucidated which patient should be referred for HSCT. This study aimed to determine predictors of good and bad HSCT outcomes in CSF1R-ALSP. We retrospectively analyzed 15 patients, 14 symptomatic and 1 asymptomatic, with CSF1R-ALSP that underwent HSCT. Median age of onset was 39 years, and the median age of HSCT was 43 years. Cognitive impairment was the most frequent initial manifestation (43%), followed by gait problems (21%) and neuropsychiatric symptoms (21%). Median post-HSCT follow-up was 26 months. Good outcomes were associated with gait problems as initial (p = 0.041) and predominant (p = 0.017) manifestation and younger age at HSCT (p = 0.044). Cognitive impairment as first manifestation was a predictor of a bad outcome (p = 0.016) and worsening of cognition post-HSCT (p = 0.025). In conclusion, gait problems indicated a milder phenotype with better response to HSCT and good therapy outcomes. In contrast, patients with a higher burden of cognitive symptoms were most likely not to benefit from HSCT.

Chitotriosidase is a biomarker for adult-onset leukoencephalopathy with axonal spheroids and pigmented glia

Adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP) leads to rapidly progressive dementia and is caused by mutations in the gene CSF1R. Neurodegeneration is driven by dysfunction of microglia, the predominant cell type expressing CSF1R in the brain. We assessed chitotriosidase, an enzyme secreted by microglia, in serum and cerebrospinal fluid of patients with ALSP. Chitotriosidase activity was highly increased in cerebrospinal fluid of patients and correlated inversely with disease duration. Of interest, presymptomatic CSF1R mutation carriers did not show elevated chitotriosidase levels. This makes chitotriosidase a promising new biomarker of disease activity for this rare disease.

Modeling CSF-1 receptor deficiency diseases - how close are we?

The role of colony-stimulating factor-1 receptor (CSF-1R) in macrophage and organismal development has been extensively studied in mouse. Within the last decade, mutations in the CSF1R have been shown to cause rare diseases of both pediatric (Brain Abnormalities, Neurodegeneration, and Dysosteosclerosis, OMIM #618476) and adult (CSF1R-related leukoencephalopathy, OMIM #221820) onset. Here we review the genetics, penetrance, and histopathological features of these diseases and discuss to what extent the animal models of Csf1r deficiency currently available provide systems in which to study the underlying mechanisms involved.

Case Report: Novel CSF1R Variant in a Patient With Behavioral Variant Frontotemporal Dementia Syndrome With Prodromal Repetitive Scratching Behavior

CSF1R-related leukoencephalopathy is an autosomal dominant neurodegenerative disease caused by mutations in the tyrosine kinase domain of the colony stimulating factor 1 receptor (CSF1R). Several studies have found that hematogenic stem cell transplantation is an effective disease modifying therapy however the literature regarding prodromal and early symptoms CSF1R-related leukoencephalopathy is limited. We describe a 63-year-old patient with 4 years of repetitive scratching and skin picking behavior followed by 10 years of progressive behavioral, cognitive, and motor decline in a pattern suggesting behavioral variant of frontotemporal dementia. Brain MRI demonstrated prominent frontal and parietal atrophy accompanied by underlying bilateral patchy white matter hyperintensities sparing the U fibers and cavum septum pellucidum. Whole-exome sequencing revealed a novel, predicted deleterious missense variant in a highly conserved amino acid in the tyrosine kinase domain of CSF1R (p.Gly872Arg). Given this evidence and the characteristic clinical and radiological findings this novel variant was classified as likely pathogenic according to the American College of Medical Genetics standard guidelines. Detailed description of the prodromal scratching and skin picking behavior and possible underlying mechanisms in this case furthers knowledge about early manifestations of CSF1R-related leukoencephalopathy with the hope that early detection and timely administration of disease modifying therapies becomes possible.

The Primary Microglial Leukodystrophies: A Review

Primary microglial leukodystrophy or leukoencephalopathy are disorders in which a genetic defect linked to microglia causes cerebral white matter damage. Pigmented orthochromatic leukodystrophy, adult-onset orthochromatic leukodystrophy associated with pigmented macrophages, hereditary diffuse leukoencephalopathy with (axonal) spheroids, and adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP) are different terms apparently used to designate the same disease. However, ALSP linked to dominantly inherited mutations in CSF1R (colony stimulating factor receptor 1) cause CSF-1R-related leukoencephalopathy (CRP). Yet, recessive ALSP with ovarian failure linked to AARS2 (alanyl-transfer (t)RNA synthase 2) mutations (LKENP) is a mitochondrial disease and not a primary microglial leukoencephalopathy. Polycystic membranous lipomembranous osteodysplasia with sclerosing leukoencephalopathy (PLOSL; Nasu–Hakola disease: NHD) is a systemic disease affecting bones, cerebral white matter, selected grey nuclei, and adipose tissue The disease is caused by mutations of one of the two genes TYROBP or TREM2, identified as PLOSL1 and PLOSL2, respectively. TYROBP associates with receptors expressed in NK cells, B and T lymphocytes, dendritic cells, monocytes, macrophages, and microglia. TREM2 encodes the protein TREM2 (triggering receptor expressed on myeloid cells 2), which forms a receptor signalling complex with TYROBP in macrophages and dendritic cells. Rather than pure microglial leukoencephalopathy, NHD can be considered a multisystemic “immunological” disease.

Two Novel Intronic Mutations in the CSF1R Gene in Two Families With CSF1R-Microglial Encephalopathy

Objective: To describe two novel heterozygous splicing variants of the CSF1R gene responsible for CSF1R-microglial encephalopathy in two unrelated Han Chinese families and further explore the relationship between the pathological and neuroimaging findings in this disease.

Methods: The demographic data, detailed medical history, and clinical manifestations of two unrelated Han families with CSF1R-microglial encephalopathy were recorded. Some family members also underwent detailed neuropsychological evaluation, neuroimaging, and genetic testing. The probands underwent whole-exome sequencing (WES) or next-generation sequencing (NGS) to confirm the diagnosis. The findings were substantiated using Sanger sequencing, segregation analysis, and phenotypic reevaluation.

Results: Both families presented with a dominant hereditary pattern. Five of 27 individuals (four generations) from the first family, including the proband and his sister, father, uncle, and grandmother, presented with cognitive impairments clinically during their respective lifetimes. Brain magnetic resonance imaging (MRI) depicted symmetric, confluent, and diffuse deep white matter changes, atrophy of the frontoparietal lobes, and thinning of the corpus callosum. The proband’s brother remained asymptomatic; brain MRI revealed minimal white matter changes, but pseudo-continuous arterial spin labeling (pCASL) demonstrated a marked reduction in the cerebral blood flow (CBF) in the bilateral deep white matter and corpus callosum. Seven family members underwent WES, which identified a novel splice-site heterozygous mutation (c.2319+1C>A) in intron 20 of the CSF1R gene in four members. The proband from the second family presented with significant cognitive impairment and indifference; brain MRI depicted symmetric diffuse deep white matter changes and thinning of the corpus callosum. The proband’s mother reported herself to be asymptomatic, while neuropsychological evaluation suggested mild cognitive impairment, and brain MRI demonstrated abnormal signals in the bilateral deep white matter and corpus callosum. NGS of 55 genes related to hereditary leukodystrophy was performed for three members, which confirmed a novel splice-site heterozygous mutation (c.1858+5G>A) in intron 13 of the CSF1R gene in two members.

Conclusions: Our study identified two novel splicing mutation sites in the CSF1R gene within two independent Chinese families with CSF1R-microglial encephalopathy, broadening the genetic spectrum of CSF1R-microglial encephalopathy and emphasizing the value of pCASL for early detection of this disease.

Four Swedish cases of CSF1R-related leukoencephalopathy: Visualization of clinical phenotypes

Colony stimulating factor 1 receptor (CSF1R)‐related leukoencephalopathy is a rare, genetic disease caused by heterozygous mutations in the CSF1R gene with rapidly progressive neurodegeneration, behavioral, cognitive, motor disturbances.

Adult Hereditary White Matter Diseases With Psychiatric Presentation: Clinical Pointers and MRI Algorithm to Guide the Diagnostic Process

OBJECTIVE

The investigators aimed to provide clinical and MRI guidelines for determining when genetic workup should be considered in order to exclude hereditary leukoencephalopathies in affected patients with a psychiatric presentation.

METHODS

A systematic literature review was conducted, and clinical cases are provided. Given the central role of MRI pattern recognition in the diagnosis of white matter disorders, the investigators adapted an MRI algorithm that guides the interpretation of MRI findings and thus directs further investigations, such as genetic testing.

RESULTS

Twelve genetic leukoencephalopathies that can present with psychiatric symptoms were identified. As examples of presentations that can occur in clinical practice, five clinical vignettes from patients assessed at a referral center for adult genetic leukoencephalopathies are provided.

CONCLUSIONS

Features such as drug-resistant symptoms, presence of long-standing somatic features, trigger events, consanguinity, and positive family history should orient the clinician toward diagnostic workup to exclude the presence of a genetic white matter disorder. The identification of MRI white matter abnormalities, especially when presenting a specific pattern of involvement, should prompt genetic testing for known forms of genetic leukoencephalopathies.

A kinase-dead Csf1r mutation associated with adult-onset leukoencephalopathy has a dominant inhibitory impact on CSF1R signalling

Amino acid substitutions in the kinase domain of the human CSF1R gene are associated with autosomal dominant adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP). To model the human disease, we created a disease-associated mutation (pGlu631Lys; E631K) in the mouse Csf1r locus. Homozygous mutation (Csf1rE631K/E631K) phenocopied the Csf1r knockout, with prenatal mortality or severe postnatal growth retardation and hydrocephalus. Heterozygous mutation delayed the postnatal expansion of tissue macrophage populations in most organs. Bone marrow cells from Csf1rE631K/+mice were resistant to CSF1 stimulation in vitro, and Csf1rE631K/+ mice were unresponsive to administration of a CSF1-Fc fusion protein, which expanded tissue macrophage populations in controls. In the brain, microglial cell numbers and dendritic arborisation were reduced in Csf1rE631K/+ mice, as in patients with ALSP. The microglial phenotype is the opposite of microgliosis observed in Csf1r+/- mice. However, we found no evidence of brain pathology or impacts on motor function in aged Csf1rE631K/+ mice. We conclude that heterozygous disease-associated CSF1R mutations compromise CSF1R signalling. We speculate that leukoencephalopathy associated with dominant human CSF1R mutations requires an environmental trigger and/or epistatic interaction with common neurodegenerative disease-associated alleles.

Altered intrinsic brain activity in patients with CSF1R-related leukoencephalopathy

CSF1R-related leukoencephalopathy is an adult-onset white matter disease with high disability and mortality, while little is known about its pathogenesis. This study introduced amplitude of low-frequency fluctuations (ALFF) and regional homogeneity (ReHo) based on resting-state functional magnetic resonance imaging(rsfMRI) to compare the spontaneous brain activities of patients and healthy controls, aiming to enhance our understanding of the disease. RsfMRI was performed on 16 patients and 23 healthy controls, and preprocessed for calculation of ALFF and ReHo. Permutation tests with threshold free cluster enhancement (TFCE) was applied for comparison (number of permutations = 5,000). The TFCE significance threshold was set at [Formula: see text] < 0.05. In addition, 10 was set as the minimum cluster size. Compared to healthy controls, the patient group showed decreased ALFF in right paracentral lobule, and increased ALFF in bilateral insula, hippocampus, thalamus, supramarginal and precentral gyrus, right inferior, middle and superior frontal gyrus, right superior and middle occipital gyrus, as well as left parahippocampal gyrus, fusiform, middle occipital gyrus and angular gyrus. ReHo was decreased in right supplementary motor area, paracentral lobule and precentral gyrus, while increased in right superior occipital gyrus and supramarginal gyrus, left parahippocampal gyrus, hippocampus, fusiform, middle occipital gyrus and angular gyrus, as well as bilateral middle occipital gyrus and midbrain. These results revealed altered spontaneous brain activities in CSF1R-related leukoencephalopathy, especially in limbic system and motor cortex, which may shed light on underlying mechanisms.

Pathogenicity analysis and a novel case report of intronic mutations in CSF1R gene

Colony-stimulating factor 1 receptor-associated leukoencephalopathy (CSF1R-related leukoencephalopathy) is a genetic disorder mutated in a single allele. It is characterized by an adult-onset along with predominantly cognitive impairment, accompanied by neuropsychiatric symptoms as well as motor symptoms such as Parkinsonism. In the current study, we confirmed a case of CSF1R-related leukoencephalopathy pedigree by genetic screening, and a new intron c. 1858 + 5 G > A mutation was detected in affected patients. After reviewing all previous reports of introns, we found that symptoms and clinical manifestations of the patients were typical and met the features of previous intron reports.

Neuroimaging phenotypes of CSF1R-related leukoencephalopathy: Systematic review, meta-analysis, and imaging recommendations

Colony-stimulating factor 1 receptor (CSF1R)-related leukoencephalopathy is a rare but fatal microgliopathy. The diagnosis is often delayed due to multifaceted symptoms that can mimic several other neurological disorders. Imaging provides diagnostic clues that help identify cases. The objective of this study was to integrate the literature on neuroimaging phenotypes of CSF1R-related leukoencephalopathy. A systematic review and meta-analysis were performed for neuroimaging findings of CSF1R-related leukoencephalopathy via PubMed, Web of Science, and Embase on 25 August 2021. The search included cases with confirmed CSF1R mutations reported under the previous terms hereditary diffuse leukoencephalopathy with spheroids, pigmentary orthochromatic leukodystrophy, and adult-onset leukoencephalopathy with axonal spheroids and pigmented glia. In 78 studies providing neuroimaging data, 195 cases were identified carrying CSF1R mutations in 14 exons and five introns. Women had a statistically significant earlier age of onset (p = 0.041, 40 vs 43 years). Mean delay between symptom onset and neuroimaging was 2.3 years. Main magnetic resonance imaging (MRI) findings were frontoparietal white matter lesions, callosal thinning, and foci of restricted diffusion. The hallmark computed tomography (CT) finding was white matter calcifications. Widespread cerebral hypometabolism and hypoperfusion were reported using positron emission tomography and single-photon emission computed tomography. In conclusion, CSF1R-related leukoencephalopathy is associated with progressive white matter lesions and brain atrophy that can resemble other neurodegenerative/-inflammatory disorders. However, long-lasting diffusion restriction and parenchymal calcifications are more specific findings that can aid the differential diagnosis. Native brain CT and brain MRI (with and without a contrast agent) are recommended with proposed protocols and pictorial examples are provided.

Adult-Onset Leukoencephalopathy With Axonal Spheroids and Pigmented Glia: Review of Clinical Manifestations as Foundations for Therapeutic Development

A comprehensive review of published literature was conducted to elucidate the genetics, neuropathology, imaging findings, prevalence, clinical course, diagnosis/clinical evaluation, potential biomarkers, and current and proposed treatments for adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP), a rare, debilitating, and life-threatening neurodegenerative disorder for which disease-modifying therapies are not currently available. Details on potential efficacy endpoints for future interventional clinical trials in patients with ALSP and data related to the burden of the disease on patients and caregivers were also reviewed. The information in this position paper lays a foundation to establish an effective clinical rationale and address the clinical gaps for creation of a robust strategy to develop therapeutic agents for ALSP, as well as design future clinical trials, that have clinically meaningful and convergent endpoints.

Dominant-acting CSF1R variants cause microglial depletion and altered astrocytic phenotype in zebrafish and adult-onset leukodystrophy

Tissue-resident macrophages of the brain, including microglia, are implicated in the pathogenesis of various CNS disorders and are possible therapeutic targets by their chemical depletion or replenishment by hematopoietic stem cell therapy. Nevertheless, a comprehensive understanding of microglial function and the consequences of microglial depletion in the human brain is lacking. In human disease, heterozygous variants in CSF1R, encoding the Colony-stimulating factor 1 receptor, can lead to adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP) possibly caused by microglial depletion. Here, we investigate the effects of ALSP-causing CSF1R variants on microglia and explore the consequences of microglial depletion in the brain. In intermediate- and late-stage ALSP post-mortem brain, we establish that there is an overall loss of homeostatic microglia and that this is predominantly seen in the white matter. By introducing ALSP-causing missense variants into the zebrafish genomic csf1ra locus, we show that these variants act dominant negatively on the number of microglia in vertebrate brain development. Transcriptomics and proteomics on relatively spared ALSP brain tissue validated a downregulation of microglia-associated genes and revealed elevated astrocytic proteins, possibly suggesting involvement of astrocytes in early pathogenesis. Indeed, neuropathological analysis and in vivo imaging of csf1r zebrafish models showed an astrocytic phenotype associated with enhanced, possibly compensatory, endocytosis. Together, our findings indicate that microglial depletion in zebrafish and human disease, likely as a consequence of dominant-acting pathogenic CSF1R variants, correlates with altered astrocytes. These findings underscore the unique opportunity CSF1R variants provide to gain insight into the roles of microglia in the human brain, and the need to further investigate how microglia, astrocytes, and their interactions contribute to white matter homeostasis.

Generation of an human induced pluripotent stem cell JTUi007-A from a patient with CSF1R-related leukoencephalopathy carrying heterozygous p.Ile794Thr mutation in CSF1R gene

CSF1R-related leukoencephalopathy is an adult-onset monogenic microgliopathy causing leukoencephalopathy with high mortality and disabiliity. Here, an human induced pluripotent stem cell (hiPSC) line was generated from peripheral blood mononuclear cells of a 46-year-old female patient carrying heterozygous c.2381 T>C/p.Ile794Thr mutation with episomal plasmids encoding hOCT4, hSOX2, hNANOG, hLIN28, hKLF4 and hMYC. With normal karyotype, pluripotent markers expression and the capability to differentiate into the three germ layers in vivo, the hiPSC line is a promising tool for further study the pathogenic mechanism and potential therapeutic targets of this disease.

Colony stimulating factors in the nervous system

Although traditionally seen as regulators of hematopoiesis, colony-stimulating factors (CSFs) have emerged as important players in the nervous system, both in health and disease. This review summarizes the cellular sources, patterns of expression and physiological roles of the macrophage (CSF-1, IL-34), granulocyte-macrophage (GM-CSF) and granulocyte (G-CSF) colony stimulating factors within the nervous system, with a particular focus on their actions on microglia. CSF-1 and IL-34, via the CSF-1R, are required for the development, proliferation and maintenance of essentially all CNS microglia in a temporal and regional specific manner. In contrast, in steady state, GM-CSF and G-CSF are mainly involved in regulation of microglial function. The alterations in expression of these growth factors and their receptors, that have been reported in several neurological diseases, are described and the outcomes of their therapeutic targeting in mouse models and humans are discussed.

Clinical and genetic characterization of adult-onset leukoencephalopathy caused by CSF1R mutations

Objective

Mutations in the colony‐stimulating factor 1 receptor gene (CSF1R) were identified as a cause of adult‐onset inherited leukoencephalopathy. The present study aims at investigating the frequency, clinical characteristics, and functional effects of CSF1R mutations in Taiwanese patients with adult‐onset leukoencephalopathy.

Methods

Mutational analysis of CSF1R was performed in 149 unrelated individuals with leukoencephalopathy by a targeted resequencing panel covering the entire coding regions of CSF1R. In vitro analysis of the CSF1‐induced autophosphorylation activities of mutant CSF1R proteins was conducted to assess the pathogenicity of the CSF1R mutations.

Results

Among the eight CSF1R variants identified in this study, five mutations led to a loss of CSF1‐induced autophosphorylation of CSF1R proteins. Four mutations (p.K586*, p.G589R, p.R777Q, and p.R782C) located within the tyrosine kinase domain of CSF1R, whereas the p.T79M mutation resided in the immunoglobulin‐like domain. The five patients carrying the CSF1R mutations developed cognitive decline at age 41, 43, 50, 79, and 86 years, respectively. Psychiatric symptoms and behavior changes were observed in four of the five patients. The executive function and processing speed were severely impaired at an early stage, and their cognitive function deteriorated rapidly within 3–4 years. Diffusion‐restricted lesions at the subcortical regions and bilateral corticospinal tracts were found in three patients.

Interpretation

CSF1R mutations account for 3.5% (5/149) of the adult‐onset leukoencephalopathy in Taiwan. CSF1R mutations outside the tyrosine kinase domain may also disturb the CSF1R function and lead to the clinical phenotype. Molecular functional validation is important to determine the pathogenicity of novel CSF1R variants.

A case of CSF1R-related leukoencephalopathy: serial neuroimaging and neuropsychological tests

Colony-stimulating factor 1 receptor (CSF1R)-related leukoencephalopathy is one of the most common causes of adult-onset leukodystrophy and is caused by mutation of the CSF1R gene. Brain magnetic resonance imaging (MRI) findings in asymptomatic patients have not been well recognized. We report on the case of a patient with CSF1R-related leukoencephalopathy who had a novel missense variant of the CSF1R gene with a family history of early onset dementia. This is a representative case of CSF1R-related leukoencephalopathy, which shows the progression of brain MRI and cognitive decline from an asymptomatic state.