CSF1R mutations identified in three families with autosomal dominantly inherited leukoencephalopathy

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.

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.

A Novel de novo KIF1A Mutation in a Patient with Autism, Hyperactivity, Epilepsy, Sensory Disturbance, and Spastic Paraplegia

Heterozygous mutations in KIF1A have been reported to cause syndromic intellectual disability or pure spastic paraplegia. However, their genotype-phenotype correlations have not been fully elucidated. We herein report a man with autism and hyperactivity along with sensory disturbance and spastic paraplegia, carrying a novel de novo mutation in KIF1A [c.37C>T (p.R13C)]. Autism and hyperactivity have only previously been reported in a patient with c.38 G>A (R13H) mutation. This case suggests that alterations in this arginine at codon 13 might lead to a common clinical spectrum and further expand the genetic and clinical spectra associated with KIF1A mutations.

Harnessing Immunoproteostasis to Treat Neurodegenerative Disorders

Immunoproteostasis is a term used to reflect interactions between the immune system and the proteinopathies that are presumptive "triggers" of many neurodegenerative disorders. The study of immunoproteostasis is bolstered by several observations. Mutations or rare variants in genes expressed in microglial cells, known to regulate immune functions, or both can cause, or alter risk for, various neurodegenerative disorders. Additionally, genetic association studies identify numerous loci harboring genes that encode proteins of known immune function that alter risk of developing Alzheimer's disease (AD) and other neurodegenerative proteinopathies. Further, preclinical studies reveal beneficial effects and liabilities of manipulating immune pathways in various neurodegenerative disease models. Although there are concerns that manipulation of the immune system may cause more harm than good, there is considerable interest in developing immune modulatory therapies for neurodegenerative disorders. Herein, I highlight the promise and challenges of harnessing immunoproteostasis to treat neurodegenerative proteinopathies.

Novel De Novo KCND3 Mutation in a Japanese Patient with Intellectual Disability, Cerebellar Ataxia, Myoclonus, and Dystonia

Spinocerebellar ataxia 19/22 (SCA19/22) is a rare type of autosomal dominant SCA that was previously described in 11 families. We report the case of a 30-year-old Japanese man presenting with intellectual disability, early onset cerebellar ataxia, myoclonus, and dystonia without a family history. MRI showed cerebellar atrophy, and electroencephalograms showed paroxysmal sharp waves during hyperventilation and photic stimulation. Trio whole-exome sequencing analysis of DNA samples from the patient and his parents revealed a de novo novel missense mutation (c.1150G>A, p.G384S) in KCND3, the causative gene of SCA19/22, substituting for evolutionally conserved glycine. The mutation was predicted to be functionally deleterious by bioinformatic analysis. Although pure cerebellar ataxia is the most common clinical feature in SCA19/22 families, extracerebellar symptoms including intellectual disability and myoclonus are reported in a limited number of families, suggesting a genotype-phenotype correlation for particular mutations. Although autosomal recessive diseases are more common in patients with early onset sporadic cerebellar ataxia, the present study emphasizes that such a possibility of de novo mutation should be considered.

Adult-onset leukoencephalopathy with axonal spheroids and pigmented glia: A case report

Adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP) is a rare neurodegenerative disorder characterized by cerebral white matter abnormalities, myelin loss, and axonal swellings. ALSP is caused by mutations in colony stimulating factor 1 receptor gene. We report an ASLP patient with asymptomatic intracranial calcifications distributed in white matter found incidentally in a health screening.

CSF1R mutation presenting as dementia with Lewy bodies

Hereditary diffuse leukoencephalopathy with spheroids (HDLS) is an adult-onset autosomal dominant leukoencephalopathy resulting from mutations affecting the tyrosine kinase domain of the colony stimulating factor receptor 1 protein (encoded by CSF1R). The clinical phenotypes reported with CSF1R mutations are variable. We present a case of a patient with a pathogenic variant in the CSF1R gene with clinical and imaging features suggestive of Dementia with Lewy Bodies (DLB). This case expands the known clinical presentations associated with CSF1R mutations.

Genetic Variation in Genes Underlying Diverse Dementias May Explain a Small Proportion of Cases in the Alzheimer's Disease Sequencing Project

BACKGROUND/AIMS

The Alzheimer's Disease Sequencing Project (ADSP) aims to identify novel genes influencing Alzheimer's disease (AD). Variants within genes known to cause dementias other than AD have previously been associated with AD risk. We describe evidence of co-segregation and associations between variants in dementia genes and clinically diagnosed AD within the ADSP.

METHODS

We summarize the properties of known pathogenic variants within dementia genes, describe the co-segregation of variants annotated as "pathogenic" in ClinVar and new candidates observed in ADSP families, and test for associations between rare variants in dementia genes in the ADSP case-control study. The participants were clinically evaluated for AD, and they represent European, Caribbean Hispanic, and isolate Dutch populations.

RESULTS/CONCLUSIONS

Pathogenic variants in dementia genes were predominantly rare and conserved coding changes. Pathogenic variants within ARSA, CSF1R, and GRN were observed, and candidate variants in GRN and CHMP2B were nominated in ADSP families. An independent case-control study provided evidence of an association between variants in TREM2, APOE, ARSA, CSF1R, PSEN1, and MAPT and risk of AD. Variants in genes which cause dementing disorders may influence the clinical diagnosis of AD in a small proportion of cases within the ADSP.

Adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP): Integrating the literature on hereditary diffuse leukoencephalopathy with spheroids (HDLS) and pigmentary orthochromatic leukodystrophy (POLD)

Adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP) is a progressive degenerative white matter disorder. ALSP was previously recognized as two distinct entities, hereditary diffuse leukoencephalopathy with spheroids (HDLS) and pigmentary orthochromatic leukodystrophy (POLD). However, recent identification of mutations in the tyrosine kinase domain of the colony stimulating factor 1 receptor (CSF1R) gene, which regulates mononuclear cell lineages including microglia, have provided genetic and mechanistic evidence that POLD and HDLS should be regarded as a single clinicopathologic entity. We describe two illustrative cases of ALSP which presented with neuropsychiatric symptoms, progressive cognitive decline, and motor and gait disturbances. Antemortem diagnoses of autopsy-confirmed ALSP vary significantly, and include primary progressive multiple sclerosis, frontotemporal dementia, Alzheimer disease, atypical cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), corticobasal syndrome, and atypical Parkinson disease, suggesting that ALSP may be significantly underdiagnosed. This article presents a systematic review of ALSP in the context of two illustrative cases to help integrate the literature on HDLS and POLD. Consistent use of the term ALSP is suggested for clarity in the literature going forward.

Adult onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP) and Nasu-Hakola disease: lesion staging and dynamic changes of axons and microglial subsets

The brains of 10 Japanese patients with adult onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP) encompassing hereditary diffuse leukoencephalopathy with axonal spheroids (HDLS) and pigmentary orthochromatic leukodystrophy (POLD) and eight Japanese patients with Nasu-Hakola disease (N-HD) and five age-matched Japanese controls were examined neuropathologically with special reference to lesion staging and dynamic changes of microglial subsets. In both diseases, the pathognomonic neuropathological features included spherically swollen axons (spheroids and globules), axon loss and changes of microglia in the white matter. In ALSP, four lesion stages based on the degree of axon loss were discernible: Stage I, patchy axon loss in the cerebral white matter without atrophy; Stage II, large patchy areas of axon loss with slight atrophy of the cerebral white matter and slight dilatation of the lateral ventricles; Stage III, extensive axon loss in the cerebral white matter and dilatation of the lateral and third ventricles without remarkable axon loss in the brainstem and cerebellum; Stage IV, devastated cerebral white matter with marked dilatation of the ventricles and axon loss in the brainstem and/or cerebellum. Internal capsule and pontine base were relatively well preserved in the N-HD, even at Stage IV, and the swollen axons were larger with a higher density in the ALSP. Microglial cells immunopositive for CD68, CD163 or CD204 were far more obvious in ALSP, than in N-HD, and the shape and density of the cells changed in each stage. With progression of the stage, clinical symptoms became worse to apathetic state, and epilepsy was frequently observed in patients at Stages III and IV in both diseases. From these findings, it is concluded that (i) shape, density and subsets of microglia change dynamically along the passage of stages and (ii) increase of IBA-1-, CD68-, CD163- and CD204-immunopositive cells precedes loss of axons in ALSP.

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

Background and purpose

The clinical characteristics of colony stimulating factor 1 receptor (CSF1R) related adult‐onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP) have been only partially elucidated.

Methods

Clinical data from CSF1R mutation carriers who had been seen at our institutions or reported elsewhere were collected and analysed using a specific investigation sheet to standardize the data.

Results

In all, 122 cases from 90 families with CSF1R mutations were identified. The mean age of onset was 43 years (range 18–78 years), the mean age at death was 53 years (range 23–84 years) and the mean disease duration was 6.8 years (range 1–29 years). Women had a significantly younger age of onset than men (40 vs. 47 years, P = 0.0006, 95% confidence interval 3.158–11.177). There was an age‐dependent penetrance that was significantly different between the sexes (P = 0.0013). Motor dysfunctions were the most frequent initial symptom in women whose diseases began in their 20s. Thinning of the corpus callosum, abnormal signalling in pyramidal tracts, diffusion‐restricted lesions and calcifications in the white matter were characteristic imaging findings of ALSP. The calcifications were more frequently reported in our case series than in the literature (54% vs. 3%). Seventy‐nine per cent of the mutations were located in the distal part of the tyrosine kinase domain of CSF1R (102 cases). There were no apparent phenotype−genotype correlations.

Conclusions

The characteristics of ALSP were clarified. The phenotype of ALSP caused by CSF1R mutations is affected by sex.

Hereditary diffuse leukoencephalopathy with axonal spheroids (HDLS): update on molecular genetics

Hereditary diffuse leukoencephalopathy with spheroids (HDLS) is a rare autosomal dominant disease characterized by giant neuroaxonal swellings (spheroids) within the cerebral white matter (WM). Symptoms are variable and can include cognitive, mental and motor dysfunctions. Patients carry mutations in the protein kinase domain of the colony-stimulating factor 1 receptor (CSF1R) which is a tyrosine kinase receptor essential for microglia development. To date, more than 50 pathogenic variants have been reported in patients with HDLS, including missense, frameshift and non-sense mutations, but also deletions and splice-site mutations, all located in the intracellular tyrosine kinase domain, encoded by exons 12-22. The aim of this paper is to review the literature data about the molecular genetic pattern of HDLS.

A family with hereditary diffuse leukoencephalopathy with spheroids caused by a novel c.2442+2T>C mutation in the CSF1R gene

Clinical phenotypes of hereditary diffuse leukoencephalopathy with spheroids (HDLS), a familial progressive neurodegenerative disorder affecting the white matter of the brain, are heterogenous and may include behavioral and personality changes, memory impairment, parkinsonism, seizure, and spasticity. Thus, HDLS is frequently unrecognized and misdiagnosed. Heterozygous mutations located within the kinase domain of the gene encoding the colony-stimulating factor 1 receptor (CSF1R), a cell surface receptor with key roles in development and innate immunity, have been shown in HDLS. These different gene mutations may be related to the various clinical phenotypes. We report here a newly identified family with HDLS harboring a mutation in the CSF1R gene. We examined clinical and neuropathological features in three members of this family. These patients presented with affective incontinence, memory impairment, and executive dysfunction at onset, and revealed nonfluent aphasia, parkinsonism, and seizure as the disease progressed. We identified a novel CSF1R splice site mutation (c.2442+2T>C) in intron 18 for two of the patients. MRI of these patients revealed progressive, frontotemporal-predominant, confluent leukoencephalopathy. We also observed severe myelin loss, axonal degeneration, and abundant axonal spheroids, astrocytes, and microglia in the cerebral white matter, consistent with HDLS neuropathological features. Additionally, we identified atypical neuropathological findings for HDLS, including neuronal loss and gliosis with ballooned neurons and central chromatolysis in the frontal cortex and hippocampus. This report provides further evidence for the clinical and neuropathological heterogeneity of HDLS.

SIFT missense predictions for genomes

The SIFT (sorting intolerant from tolerant) algorithm helps bridge the gap between mutations and phenotypic variations by predicting whether an amino acid substitution is deleterious. SIFT has been used in disease, mutation and genetic studies, and a protocol for its use has been previously published with Nature Protocols. This updated protocol describes SIFT 4G (SIFT for genomes), which is a faster version of SIFT that enables practical computations on reference genomes. Users can get predictions for single-nucleotide variants from their organism of interest using the SIFT 4G annotator with SIFT 4G's precomputed databases. The scope of genomic predictions is expanded, with predictions available for more than 200 organisms. Users can also run the SIFT 4G algorithm themselves. SIFT predictions can be retrieved for 6.7 million variants in 4 min once the database has been downloaded. If precomputed predictions are not available, the SIFT 4G algorithm can compute predictions at a rate of 2.6 s per protein sequence. SIFT 4G is available from http://sift-dna.org/sift4g.

Sporadic adult-onset leucodystrophy with axonal spheroids and pigmented glia with no mutations in the known targeted genes

AIMS

Adult-onset orthochromatic leucodystrophy, associated with pigmented macrophages and hereditary diffuse leucoencephalopathy with spheroids, are two disorders with similar clinical manifestations, radiological characteristics and neuropathological findings. Mutations in the colony-stimulating factor 1 receptor (CSF1R) gene are the hallmark of this spectrum of disease. Furthermore, polycystic membranous lipomembranous osteodysplasia with sclerosing leucoencephalopathy is caused by mutations in two genes, DAP12 and TREM2, which encode proteins involved in the same pathways as CSF1R. We describe a case of sporadic adult-onset orthochromatic leucodystrophy associated with pigmented macrophages diagnosed by biopsy without harbouring mutations in the known targeted genes.

METHODS AND RESULTS

A 51-year-old woman, with no familial history of neurological diseases, developed a progressive neurological deterioration showing inappropriate behaviour, ataxia, spasticity, axial dystonia and agitation. Radiological images and a stereotaxic biopsy were conclusive with adult-onset orthochromatic leucodystrophy associated with pigmented macrophages. Genetic analysis did not show mutations in either CSF1R, DAP12 or TREM2.

CONCLUSIONS

We add support to the idea that all these entities are closely related diseases linked to a convergent metabolic pathway, but caused by different genes or perhaps by the combination of individually non-pathogenic variations of selected genes. Genetic defects are still barely known in a substantial number of adult leucodystrophies.

Common neuropathological features underlie distinct clinical presentations in three siblings with hereditary diffuse leukoencephalopathy with spheroids caused by CSF1R p.Arg782His

Hereditary diffuse leukoencephalopathy with spheroids (HDLS) presents with a variety of clinical phenotypes including motor impairments such as gait dysfunction, rigidity, tremor and bradykinesia as well as cognitive deficits including personality changes and dementia. In recent years, colony stimulating factor 1 receptor gene (CSF1R) has been identified as the primary genetic cause of HDLS. We describe the clinical and neuropathological features in three siblings with HDLS and the CSF1R p.Arg782His (c.2345G > A) pathogenic mutation. Each case had varied motor symptoms and clinical features, but all included slowed movements, poor balance, memory impairment and frontal deficits. Neuroimaging with magnetic resonance imaging revealed atrophy and increased signal in the deep white matter. Abundant white matter spheroids and CD68-positive macrophages were the predominant pathologies in these cases. Similar to other cases reported in the literature, the three cases described here had varied clinical phenotypes with a pronounced, but heterogeneous distribution of axonal spheroids and distinct microglia morphology. Our findings underscore the critical importance of genetic testing for establishing a clinical and pathological diagnosis of HDLS.

Adult-onset leukoencephalopathy with axonal spheroids and pigmented glia linked CSF1R mutation: Report of four Korean cases

We describe detailed clinical, biochemical, neuroimaging and neuropathological features in adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP), encompassing hereditary diffuse leukoencephalopathy with axonal spheroids (HDLS) and pigmentary orthochromatic leukodystrophy (POLD), linked to colony-stimulating factor 1 receptor (CSF1R) mutations in four Korean cases. Clinical, biochemical, neuroimaging and neuropathological findings were obtained by direct evaluation and from previous medical records. The genetic analysis of the CSF1R gene was done in two autopsy-confirmed ALSP cases and two cases where ALSP was suspected based on the clinical and neuroimaging characteristics. We identified two known mutations: c.2342C>T (p.A781V) in one autopsy-proven HDLS and clinically ALSP-suspected case and c.2345G>A (p.R782H) in another autopsy-proven POLD case. We also found a novel mutation (c.2296A>G; p.M766V) in a patient presenting with hand tremor, stuttering and hesitant speech, and abnormal behavior whose father died from a possible diagnosis of spinocerebellar ataxia. To the best of our knowledge, this is the first documented ALSP-linked CSF1R mutation in Korea and supports the suggestion that HDLS and POLD, with pathological characteristics that are somewhat different but which are caused by CSF1R mutations, are the same spectrum of disease, ALSP.

[Clinical and neuroimaging characteristics of patients with hereditary diffuse leukoencephalopathy with spheroids (HDLS)]

Hereditary diffuse leukoencephalopathy with spheroids (HDLS) is an autosomal dominant early-onset dementia that affects the cerebral white matter predominantly. Mutations in colony stimulating factor-1 receptor (CSF-1R) were identified as the genetic cause of HDLS, and this enabled the antemorterm diagnosis of HDLS by genetic testing. This review paper describes clinical and neuroimaging findings in genetically-proven HDLS cases. The mean age at onset was 45 years ranging from 18 to 78 years. The most frequent initial symptom was cognitive decline. A wide range of clinical features including intellectual decline, behavioral and character changes, convulsion, pyramidal signs and motor symptoms have been described. Series of brain MRI study exhibit the white matter changes on FLAIR images, which were occasionally asymmetric in the early phase of the disease. Early MRI features are alteration of corpus callosum and dilatation of lateral ventricles showing central atrophy. Hyperintensity lesions detected by diffusion weighted images were detectable in some cases with HDLS. Brain CT study showed spotty calcification in the affected white matter. HDLS is not rare disease and should be considered as differential diagnosis of early-onset dementia exhibiting the white matter disease.

Phenotypic characterization of a Csf1r haploinsufficient mouse model of adult-onset leukodystrophy with axonal spheroids and pigmented glia (ALSP)

Mutations in the colony stimulating factor-1 receptor (CSF1R) that abrogate the expression of the affected allele or lead to the expression of mutant receptor chains devoid of kinase activity have been identified in both familial and sporadic cases of ALSP. To determine the validity of the Csf1r heterozygous mouse as a model of adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP) we performed behavioral, radiologic, histopathologic, ultrastructural and cytokine expression studies of young and old Csf1r+/- and control Csf1r+/+ mice. Six to 8-month old Csf1r+/- mice exhibit cognitive deficits, and by 9-11 months develop sensorimotor deficits and in male mice, depression and anxiety-like behavior. MRIs of one year-old Csf1r+/- mice reveal lateral ventricle enlargement and thinning of the corpus callosum. Ultrastructural analysis of the corpus callosum uncovers dysmyelinated axons as well as neurodegeneration, evidenced by the presence of axonal spheroids. Histopathological examination of 11-week-old mice reveals increased axonal and myelin staining in the cortex, increase of neuronal cell density in layer V and increase of microglial cell densities throughout the brain, suggesting that early developmental changes contribute to disease. By 10-months of age, the neuronal cell density normalizes, oligodendrocyte precursor cells increase in layers II-III and V and microglial densities remain elevated without an increase in astrocytes. Also, the age-dependent increase in CSF-1R+ neurons in cortical layer V is reduced. Moreover, the expression of Csf2, Csf3, Il27 and Il6 family cytokines is increased, consistent with microglia-mediated inflammation. These results demonstrate that the inactivation of one Csf1r allele is sufficient to cause an ALSP-like disease in mice. The Csf1r+/- mouse is a model of ALSP that will allow the critical events for disease development to be determined and permit rapid evaluation of therapeutic approaches. Furthermore, our results suggest that aberrant activation of microglia in Csf1r+/- mice may play a central role in ALSP pathology.

Enlarging the nosological spectrum of hereditary diffuse leukoencephalopathy with axonal spheroids (HDLS)

Hereditary diffuse leukoencephalopathy with axonal spheroids (HDLS) is an autosomal dominant disease clinically characterized by cognitive decline, personality changes, motor impairment, parkinsonism and seizures. Recently, mutations in the colony-stimulating factor-1 receptor (CSF1R) gene have been shown to be associated with HDLS. We report clinical, neuropathological and molecular genetic findings of patients from a new family with a mutation in the CSF1R gene. Disease onset was earlier and disease progression was more rapid compared with previously reported patients. Psychiatric symptoms including personality changes, alcohol abuse and severe depression were the first symptoms in male patients. In the index, female patient, the initial symptom was cognitive decline. Magnetic resonance imaging (MRI) showed bilateral, confluent white matter lesions in the cerebrum. Stereotactic biopsy revealed loss of myelin and microglial activation as well as macrophage infiltration of the parenchyma. Numerous axonal swellings and spheroids were present. Ultrastructural analysis revealed pigment-containing macrophages. Axonal swellings were detected by electron microscopy not only in the central nervous system (CNS) but also in skin nerves. We identified a heterozygous mutation (c.2330G>A, p.R777Q) in the CSF1R gene. Through this report, we aim to enlarge the nosological spectrum of HDLS, providing new clinical descriptions as well as novel neuropathological findings from the peripheral nervous system.

Molecular epidemiology and clinical spectrum of hereditary spastic paraplegia in the Japanese population based on comprehensive mutational analyses

Hereditary spastic paraplegia (HSP) is one of the most genetically heterogeneous neurodegenerative disorders characterized by progressive spasticity and pyramidal weakness of lower limbs. Because >30 causative genes have been identified, screening of multiple genes is required for establishing molecular diagnosis of individual patients with HSP. To elucidate molecular epidemiology of HSP in the Japanese population, we have conducted mutational analyses of 16 causative genes of HSP (L1CAM, PLP1, ATL1, SPAST, CYP7B1, NIPA1, SPG7, KIAA0196, KIF5A, HSPD1, BSCL2, SPG11, SPG20, SPG21, REEP1 and ZFYVE27) using resequencing microarrays, array-based comparative genomic hybridization and Sanger sequencing. The mutational analysis of 129 Japanese patients revealed 49 mutations in 46 patients, 32 of which were novel. Molecular diagnosis was accomplished for 67.3% (33/49) of autosomal dominant HSP patients. Even among sporadic HSP patients, mutations were identified in 11.1% (7/63) of them. The present study elucidated the molecular epidemiology of HSP in the Japanese population and further broadened the mutational and clinical spectra of HSP.

Haploinsufficiency of CSF-1R and clinicopathologic characterization in patients with HDLS

Objective:

To clarify the genetic, clinicopathologic, and neuroimaging characteristics of patients with hereditary diffuse leukoencephalopathy with spheroids (HDLS) with the colony stimulating factor 1 receptor (CSF-1R) mutation.

Methods:

We performed molecular genetic analysis of CSF-1R in patients with HDLS. Detailed clinical and neuroimaging findings were retrospectively investigated. Five patients were examined neuropathologically.

Results:

We found 6 different CSF-1R mutations in 7 index patients from unrelated Japanese families. The CSF-1R mutations included 3 novel mutations and 1 known missense mutation at evolutionarily conserved amino acids, and 1 novel splice-site mutation. We identified a novel frameshift mutation. Reverse transcription PCR analysis revealed that the frameshift mutation causes nonsense-mediated mRNA decay by generating a premature stop codon, suggesting that haploinsufficiency of CSF-1R is sufficient to cause HDLS. Western blot analysis revealed that the expression level of CSF-1R in the brain from the patients was lower than from control subjects. The characteristic MRI findings were the involvement of the white matter and thinning of the corpus callosum with signal alteration, and sequential analysis revealed that the white matter lesions and cerebral atrophy relentlessly progressed with disease duration. Spotty calcifications in the white matter were frequently observed by CT. Neuropathologic analysis revealed that microglia in the brains of the patients demonstrated distinct morphology and distribution.

Conclusions:

These findings suggest that patients with HDLS, irrespective of mutation type in CSF-1R, show characteristic clinical and neuroimaging features, and that perturbation of CSF-1R signaling by haploinsufficiency may play a role in microglial dysfunction leading to the pathogenesis of HDLS.

M-CSF receptor mutations in hereditary diffuse leukoencephalopathy with spheroids impair not only kinase activity but also surface expression

The tyrosine kinase Fms, the cell surface receptor for M-CSF and IL-34, is critical for microglial proliferation and differentiation in the brain. Recently, a number of mutations have been identified in Fms as a putative genetic cause of hereditary diffuse leukoencephalopathy with spheroids (HDLS), implying an important role of microglial dysfunction in HDLS pathogenesis. In this study, we initially confirmed that 11 mutations, which reside within the ATP-binding or major tyrosine kinase domain, caused a severe impairment of ligand-induced Fms auto-phosphorylation. Intriguingly, we found that 10 of the 11 mutants also showed a weak cell surface expression, which was associated with a concomitant increase in the low molecular weight hypo-N-glycosylated immature gp130Fms-like species. Indeed, the mutant proteins heavily accumulated to the Golgi-like perinuclear regions. These results indicate that all of the Fms mutations tested severely impair the kinase activity and most of the mutations also impair the trafficking to the cell surface, further suggesting that HDLS is caused by the loss of Fms function.

A novel A781V mutation in the CSF1R gene causes hereditary diffuse leucoencephalopathy with axonal spheroids

We report a family with a novel CSF1R mutation causing hereditary diffuse leucoencephalopathy with axonal spheroids. Family members presented with neuropsychiatric and behavioural symptoms, with subsequent development of motor symptoms and gait disturbance. MRI brain showed extensive white matter change with a frontal predominance and associated atrophy in two members of the family. Genetic testing revealed a novel mutation c.2342C > T (p.A781V) in the CSF1R gene in two brothers of the family. This report highlights the difficulties in diagnosing HDLS and discusses the indications for testing for mutations in the CSF1R gene.

A case of hereditary diffuse leukoencephalopathy with axonal spheroids caused by a de novo mutation in CSF1R masquerading as primary progressive multiple sclerosis

We report a sporadic case of hereditary diffuse leukoencephalopathy with axonal spheroids (HDLS) confirmed by biopsy and colony-stimulating factor 1 receptor ( CSF1R) sequencing. A 28-year-old woman developed progressive spastic gait and dysarthria. Brain T2/FLAIR-weighted magnetic resonance imaging showed bilateral high signal intensity lesions in the parietal deep white matter, which subsequently extended anteriorly. Biopsied brain specimens demonstrated demyelinated white matter tissue with axonal spheroids infiltrated with foamy macrophages, and CD8+ and CD4+ T cells. She had a heterozygous mutation, c.2381T>C (p.782 Ile>Thr), in CSF1R. This is the first genetically proven case of HDLS mimicking primary progressive multiple sclerosis.