Identification and functional characterization of novel mutations including frameshift mutation in exon 4 of CSF1R in patients with adult-onset leukoencephalopathy with axonal spheroids and pigmented glia

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.

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.

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.

Elevated granulocyte colony stimulating factor (CSF) causes cerebellar deficits and anxiety in a model of CSF-1 receptor related leukodystrophy

Colony stimulating factor (CSF) receptor-1 (CSF-1R)-related leukoencephalopathy (CRL) is an adult-onset, demyelinating and neurodegenerative disease caused by autosomal dominant mutations in CSF1R, modeled by the Csf1r+/- mouse. The expression of Csf2, encoding granulocyte-macrophage CSF (GM-CSF) and of Csf3, encoding granulocyte CSF (G-CSF), are elevated in both mouse and human CRL brains. While monoallelic targeting of Csf2 has been shown to attenuate many behavioral and histological deficits of Csf1r+/- mice, including cognitive dysfunction and demyelination, the contribution of Csf3 has not been explored. In the present study, we investigate the behavioral, electrophysiological and histopathological phenotypes of Csf1r+/- mice following monoallelic targeting of Csf3. We show that Csf3 heterozygosity normalized the Csf3 levels in Csf1r+/- mouse brains and ameliorated anxiety-like behavior, motor coordination and social interaction deficits, but not the cognitive impairment of Csf1r+/- mice. Csf3 heterozygosity failed to prevent callosal demyelination. However, consistent with its effects on behavior, Csf3 heterozygosity normalized microglial morphology in the cerebellum and in the ventral, but not in the dorsal hippocampus. Csf1r+/- mice exhibited altered firing activity in the deep cerebellar nuclei (DCN) associated with increased engulfment of glutamatergic synapses by DCN microglia and increased deposition of the complement factor C1q on glutamatergic synapses. These phenotypes were significantly ameliorated by monoallelic deletion of Csf3. Our current and earlier findings indicate that G-CSF and GM-CSF play largely non-overlapping roles in CRL-like disease development in Csf1r+/- mice.

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.

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.

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.

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.

Identification of a de novo splicing mutation in the CSF1R gene in a Chinese patient with hereditary diffuse leukoencephalopathy with spheroids

Objective

To report a de novo splicing mutation in the CSF1R gene in a patient with hereditary diffuse leukoencephalopathy with spheroids (HDLS).

Methods

A 42-year-old Chinese woman with constant weakness on her left lower extremity was recruited in the current study. Detail medical history and clinical characteristics were reviewed. Brain magnetic resonance imaging (MRI), whole-exome sequencing, and Sanger sequencing were performed with bioinformatics analysis.

Results

The Chinese HDLS patient with no HDLS family history exhibited a de novo splicing mutation (c.1754-10 T > A) in the CSF1R gene. This mutation was located at the splice site of intron 12 and resulted in the skipping of exon 13 from the CSF1R mRNA. This finding constitutes the first de novo splicing mutation ever reported in HDLS. Furthermore, MRI abnormalities had been reported at least 6 months prior to the onset of the patient’s clinical phenotype.

Conclusion

Our study indicates that the diagnosis of HDLS should be considered even in the absence of a family history and can help deepen the clinical and genetic understanding of HDLS.

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.

Pathologic basis of the preferential thinning of thecorpus callosum in adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP)

Background

Adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP) is an early onset dementia characterized by axonal loss in the cerebral white matter with swollen axons (spheroids). It had been reported that the preferential thinning and “focal lesions” of the corpus callosum were observed on T2-weighted MRI in ALSP patients. The present study aimed to reveal the pathologic basis of them in relation to brain lesion staging (I ~ IV: Oyanagi et al. 2017).

Methods

Seven autopsied brains of ALSP and five controls were neuropathologically examined.

Results

Even at Stage I, corpus callosum body showed evident atrophy, and the atrophy advanced with stage progression. Spheroid size and density were maximal at Stage II in both centrum semiovale and corpus callosum body, but spheroids were larger in corpus callosum body than in centrum semiovale. Microglia in the body at Stage II had a larger cytoplasm than those in centrum semiovale. But spheroids and microglia in the “focal lesions” were identical with those of centrum semiovale.

Conclusion

Preferential thinning of corpus callosum was considered to be formed in relation to peculiar morphological alteration of microglia there in ALSP. Instead, “focal lesions” were formed in connection with the lesions in centrum semiovale.

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Preferential thinning and “focal lesions” of corpus callosum in ALSP.

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Seven autopsied brains of ALSP and five controls were neuropathologically examined.

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Larger spheroids and more microglial alteration in corpus callosum than centrum semiovale.

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“Focal lesions” were formed in connection with the lesions in the centrum semiovale.

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Peculiar morphological change of microglia leads to the preferential thinning of corpus callosum.

[Loss of homeostatic microglia in rare neurological disorders: implications for cell transplantation]

Microglia originating from yolk sac exert various functions to maintain the homeostasis in the brain, and their functional breakdown appears to be involved in the pathophysiology of various neurological diseases. In this review article, loss of homeostatic microglia and new therapeutic approaches for rare neurological disorders are discussed. ASLP (adult-onset leukoencephalopathy with axonal spheroids and pigmented glia) known as a primary microgliopathy is an adult-onset leukoencephalopathy caused by CSF1R mutation. CSF1 receptor encoded by CSF1R plays an important role in the function of microglia. In brain of ALSP patients, homeostatic microglia are significantly reduced. The biallelic mutations for CSF1R cause childhood-onset severe phenotype and elimination of microglia from the brain parenchyma. Since microglia also almost disappear in CSF1R-deficient mice and rats, CSF1R deficiency and loss of microglia appear to be tightly associated across species. Based on the underlying mechanism of homeostatic microglia loss, novel approaches using cell transplantation of normal microglia-like cells have been attempted. Transplantation of wild-type bone marrow cells into Csf1r-/- mice results in replacement by donor-derived microglial-like cells in the recipient's brain. The concept of "microglial niche" may explain the rationale behind the microglial cell transplantation in disease condition(s). Hematopoietic stem cell transplantation (HSCT) has been attempted in 4 patients with ALSP. Beneficial effects by showing stabilization of the disease course have been observed. Although the effectiveness of HSCT for ALSP patients warrants further investigation, the approach of cell transplantation that replaces ruptured homeostatic microglia with normal microglia-like cells seems to be promising.

A Novel Missense Mutation of the CSF1R Gene Causes Incurable CSF1R-Related Leukoencephalopathy: Case Report and Review of Literature

CSF1R-related leukoencephalopathy, mainly caused by the mutation of the colony stimulating factor 1 receptor (CSF1R) gene on chromosome 5, is an underestimated neurological disease typically presenting as early-onset cognitive decline and personality changes. Currently, there is no specific treatment for CSF1R-related leukoencephalopathy. Most clinicians failed to recognize this disease during an early disease stage, leading to a high rate of misdiagnosis. Although rare, an increasing amount of CSF1R-related leukoencephalopathy cases have been reported recently. In this study, we first report a 35-year-old woman with CSF1R-related leukoencephalopathy carrying a novel missense mutation c.2463G >C (p.W821C) of CSF1R. An extensive literature research was performed in order to better understand the broader genetic and clinical characteristics of CSF1R-related leukoencephalopathy. A total of 147 patients with CSF1R-related leukoencephalopathy confirmed either by the genetic test or brain biopsy were identified. Among them, 49 patients were sporadic, and the rest of individuals had a family history originating from 46 different families. Our study indicated that the average age of CSF1R-related leukoencephalopathy onset was 41.4 years. Typical clinical symptoms of CSF1R-related leukoencephalopathy include cognitive decline, movement disorders, behavior changes and mental disorders. Genetic studies have reported 93 missense mutations, 13 splicing mutations, 6 deletion/insertion mutations, 1 code shift mutation and 1 nonsense mutation of the CSF1R gene in patients with CSF1R-related leukoencephalopathy. Early genetic detection and brain biopsy would be helpful for a confirmed diagnosis, and more translational studies are needed to combat this devastating disease.

Deep White Matter Lesions with Persistent Diffusion Restriction on MRI as a Diagnostic Clue: Neuroimaging of a Turkish Family with Hereditary Diffuse Leukoencephalopathy with Spheroids and Literature Review

Background:

Hereditary diffuse leukoencephalopathy with spheroids (HDLS), first described in 1984 is a rare disorder. Generally, it presents at adulthood with dementia, motor impairment, extrapyramidal abnormalities, and epilepsy. Definitive diagnosis is made by brain biopsy. Neuroimaging studies have revealed confluent white matter lesions predominantly in the frontal lobes, corpus callosum, and corticospinal tracts on conventional magnetic resonance imaging. Only a few reports showed diffusion restriction in the cerebral white matter; furthermore, rarer reports emphasized persistent foci of diffusion restriction as a diagnostic imaging marker.

Objective:

Herein, we have aimed to illustrate the first biopsy-proven Turkish HDLS pedigree consisting of 18 persons in 3 generations which contained 4 affected individuals.

Materials and Methods:

Four individuals in the pedigree of HDLS [two affected patients (patient III-1 and patient III-2) and two unaffected individuals (patient II-4 and patient III-5)] were investigated with conventional MRI and Diffusion-weighted imaging (DWI) using 1.5 Tesla (T) scanner. All four individuals were evaluated via neurological examinations and Mini-Mental State Examination. Brain biopsy study was performed on patient III-2. Finally, an extensive literature review involving pathology investigations and neuroimaging studies of HDLS patients was conducted.

Results:

DWIs of two investigated patients showed deep white matter lesions with persistent diffusion restriction. Computed tomography imaging showed punctate mineralization in the lesions. Biopsy specimens of patient III-2 demonstrated axonal spheroids which were typical for HDLS.

Conclusions:

Via the presentation of our pedigree and literature review, we suggest HDSL as a first-line differential diagnosis in patients with undiagnosed adult-onset familial leukoencephalopathy, in particular, those with MRI lesions of frontal white matter and centrum semiovale associated with foci of diffusion restriction and mineralization. Finally, we think that the persistence of the diffusion restriction in deep white matter lesions should be kept in mind as a crucial neuroimaging sign for HDLS.

Clinicopathologic characterization and abnormal autophagy of CSF1R-related leukoencephalopathy

Background

CSF1R-related leukoencephalopathy, also known as hereditary diffuse leukoencephalopathy with spheroids (HDLS), is a rare white-matter encephalopathy characterized by motor and neuropsychiatric symptoms due to colony-stimulating factor 1 receptor (CSF1R) gene mutation. Few of CSF1R mutations have been functionally testified and the pathogenesis remains unknown.

Methods

In order to investigate clinical and pathological characteristics of patients with CSF1R-related leukoencephalopathy and explore the potential impact of CSF1R mutations, we analyzed clinical manifestations of 15 patients from 10 unrelated families and performed brain biopsy in 2 cases. Next generation sequencing was conducted for 10 probands to confirm the diagnosis. Sanger sequencing, segregation analysis and phenotypic reevaluation were utilized to substantiate findings. Functional examination of identified mutations was further explored.

Results

Clinical and neuroimaging characteristics were summarized. The average age at onset was 35.9 ± 6.4 years (range 24–46 years old). Younger age of onset was observed in female than male (34.2 vs. 39.2 years). The most common initial symptoms were speech dysfunction, cognitive decline and parkinsonian symptoms. One patient also had marked peripheral neuropathy. Brain biopsy of two cases showed typical pathological changes, including myelin loss, axonal spheroids, phosphorylated neurofilament and activated macrophages. Electron microscopy disclosed increased mitochondrial vacuolation and disorganized neurofilaments in ballooned axons. A total of 7 pathogenic variants (4 novel, 3 documented) were identified with autophosphorylation deficiency, among which c.2342C > T remained partial function of autophosphorylation. Western blotting disclosed the significantly lower level of c.2026C > T (p.R676*) than wild type. The level of microtubule associated protein 1 light chain 3-II (LC3-II), a classical marker of autophagy, was significantly lower in mutants expressed cells than wild type group by western blotting and immunofluorescence staining.

Conclusions

Our findings support the loss-of-function and haploinsufficiency hypothesis in pathogenesis. Autophagy abnormality may play a role in the disease. Repairing or promoting the phosphorylation level of mutant CSF1R may shed light on therapeutic targets in the future. However, whether peripheral polyneuropathy potentially belongs to CSF1R-related spectrum deserves further study with longer follow-up and more patients enrolled.

Trial registration

ChiCTR, ChiCTR1800015295. Registered 21 March 2018.

Electronic supplementary material

The online version of this article (10.1186/s40035-019-0171-y) contains supplementary material, which is available to authorized users.

A novel dominant-negative mutation of the CSF1R gene causes adult-onset leukoencephalopathy with axonal spheroids and pigmented glia

Adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP) is a rare autosomal dominant disorder that is caused by mutations in the colony-stimulating factor 1 receptor (CSF1R) gene. Functional haplo-insufficiency of the CSF1R gene has been considered for the underlying genetic mechanisms. A novel mutation of CSF1R and its effects on CSF1R expression or clinical characteristics were explored in an ALSP family. Clinical data and imaging data were collected from the family members with ALSP. Peripheral blood samples were collected for DNA and RNA extraction. Whole-exome sequencing and quantitative PCR were used to identify mutations and to determine the expression of CSF1R. The family had a history of a dominant hereditary pattern. Patients in this family presented motor symptoms, emotional abnormality, or memory impairment at onset. MRI findings showed high hyperintensity signals of T2-weighted imaging in the white matter and atrophy of the corpus callosum. NOTCH3 gene sequencing ruled out the diagnosis of CADASIL. Whole-exome sequencing identified a novel splice-site mutation (c.2319+1C>A) in intron 16 of the CSF1R gene. CSF1R mRNA was significantly decreased (~15%) in the peripheral blood samples of affected patients, which was much lower than the expected 50%. Our findings not only supported the pathological implication of this splice-site mutation but also demonstrated for the first time a dominant-negative effect on CSF1R expression. This report extends the genetic spectrum of ALSP with CSF1R mutations and provides evidence for the clinical heterogeneity of ALSP.

Phenotypic impacts of CSF1R deficiencies in humans and model organisms

Mϕ proliferation, differentiation, and survival are controlled by signals from the Mϕ CSF receptor (CSF1R). Mono-allelic gain-of-function mutations in CSF1R in humans are associated with an autosomal-dominant leukodystrophy and bi-allelic loss-of-function mutations with recessive skeletal dysplasia, brain disorders, and developmental anomalies. Most of the phenotypes observed in these human disease states are also observed in mice and rats with loss-of-function mutations in Csf1r or in Csf1 encoding one of its two ligands. Studies in rodent models also highlight the importance of genetic background and likely epistatic interactions between Csf1r and other loci. The impacts of Csf1r mutations on the brain are usually attributed solely to direct impacts on microglial number and function. However, analysis of hypomorphic Csf1r mutants in mice and several other lines of evidence suggest that primary hydrocephalus and loss of the physiological functions of Mϕs in the periphery contribute to the development of brain pathology. In this review, we outline the evidence that CSF1R is expressed exclusively in mononuclear phagocytes and explore the mechanisms linking CSF1R mutations to pleiotropic impacts on postnatal growth and development.

A Novel Splicing Mutation in the CSF1R Gene in a Family With Hereditary Diffuse Leukoencephalopathy With Axonal Spheroids

Hereditary diffuse leukoencephalopathy with axonal spheroids (HDLS) is a rare autosomal dominant disorder that typically presents with early-onset cognitive decline or personality change. The disease is associated with heterozygous mutations in the colony stimulating factor-1 receptor (CSF1R) gene. CSF1R activation regulates microglial survival, proliferation, and differentiation. The different gene mutations may be related to the various clinical phenotypes. Here, we described comprehensive clinical, neuroimaging, neuropathological, and genetic analyses of a family with HDLS. A novel splicing mutation in intron 13 (c.1858+1G>T) of CSF1R was found in this family. It is located at the splice site of intron 13, resulting in a splice donor site leading to exon 13 skipping from the CSF1R mRNA. The mother and two elderly siblings of the proband had the same CSF1R mutation as the proband but showed very mild neuroimaging abnormalities and mild memory loss, which did not affect daily life, indicating very uneven penetrance and distinctly different disease progression among family members. This report provides diverse neuroimaging and clinical characteristics of a novel CSF1R mutation with different disease penetrance. The large clinical heterogeneity in the same family who all had the same mutation indicates that modifying genes and environmental factors may play a role in the pathogenesis of HDLS.