Nasu-Hakola Disease Research Articles

Homozygous TREM2 c.549del; p.(Leu184Serfs*5) variant causing Nasu-Hakola disease in three siblings in a consanguineous Iraqi family: Case report and review of literature.

The Triggering Receptor Expressed on Myeloid Cells 2 protein (TREM2) plays a crucial role in various biological processes, including osteoclast differentiation, and disease-associated microglia (DAM) activation to regulate neuroinflammation, and phagocytosis in the brain. Genetic variations in TREM2 are implicated in neurodegenerative disorders, such as Nasu-hakola disease (NHD), characterized by bone lesions, neuropsychiatric disorders, and early-onset dementia. We studied 3 siblings with suspected NHD. Whole-exome sequencing was conducted on the proband to identify the possible genetic cause(s) and by Sanger sequencing to validate the identified variants in the two other affected siblings, a healthy sister, and the parents. We identified a novel homozygous deletion (c.549del; p.(Leu184Serfs*5)) in TREM2. Our literature review reveals 16 TREM2 mutations causing early-onset dementia and bone lesions. These findings, alongside previous research, elucidate the clinical spectrum of TREM2-related diseases, aiding accurate diagnosis and patient care. This knowledge is vital for understanding TREM2-dependent DAM and its involvement in the pathogenesis of neurodevelopmental disorders which can help to develop targeted therapies and improve outcomes for TREM2-affected individuals.

TREM2 variants that cause early dementia and increase Alzheimer's disease risk affect gene splicing.

Loss-of-function variants in the triggering receptor expressed on myeloid cells 2 (TREM2) are responsible for a spectrum of neurodegenerative disorders. In the homozygous state, they cause severe pathologies with early onset dementia, such as Nasu-Hakola disease and behavioural variants of frontotemporal dementia (FTD), whereas heterozygous variants increase the risk of late-onset Alzheimer's disease (AD) and FTD. For over half of TREM2 variants found in families with recessive early onset dementia, the defect occurs at the transcript level via premature termination codons or aberrant splicing. The remaining variants are missense alterations thought to affect the protein; however, the underlying pathogenic mechanism is less clear. In this work, we tested whether these disease-associated TREM2 variants contribute to the pathology via altered splicing. Variants scored by SpliceAI algorithm were tested by a full-size TREM2 splicing reporter assay in different cell lines. The effect of variants was quantified by qRT-/RT-PCR and western blots. Nanostring nCounter was used to measure TREM2 RNA in the brains of NHD patients who carried spliceogenic variants. Exon skipping events were analysed from brain RNA-Seq datasets available through the Accelerating Medicines Partnership for Alzheimer's Disease Consortium. We found that for some Nasu-Hakola disease and early onset FTD-causing variants, splicing defects were the primary cause (D134G) or likely contributor to pathogenicity (V126G and K186N). Similar but milder effects on splicing of exons 2 and 3 were demonstrated for A130V, L133L and R136W enriched in patients with dementia. Moreover, the two most frequent missense variants associated with AD/FTD risk in European and African ancestries (R62H, 1% in Caucasians and T96K, 12% in Africans) had splicing defects via excessive skipping of exon 2 and overproduction of a potentially antagonistic TREM2 protein isoform. The effect of R62H on exon 2 skipping was confirmed in three independent brain RNA-Seq datasets. Our findings revealed an unanticipated complexity of pathogenic variation in TREM2, in which effects on post-transcriptional gene regulation and protein function often coexist. This necessitates the inclusion of computational and experimental analyses of splicing and mRNA processing for a better understanding of genetic variation in disease.

Behavioral variant of frontotemporal dementia in carriers of biallelic TREM2 variants: cases study.

First reports associated mutations in triggering receptors expressed on myeloid cells 2 (TREM2) with autosomal recessive Nasu-Hakola disease characterized by painful bone cysts and progressive presenile dementia with psychotic symptoms; however, recent TREM2 biallelic rare variants are suggested to be causative also for the behavioral variant of frontotemporal dementia (bvFTD) without bone involvement. Clinical data of three unrelated bvFTD patients carrying TREM2 biallelic variants were evaluated. All patients underwent neurological, psychiatric, and cognitive evaluation and neuroimaging. A full neuropsychological assessment was performed in two cases. Two patients carried compound heterozygous TREM2 variants, p.R62C and p.T66M, and one carried the homozygous p.D87N variant. Based on all obtained clinical and neuroimaging data, a behavioral variant of frontotemporal dementia was diagnosed in all cases. Their clinical manifestation was typical with neuropsychiatric and cognitive features, without bone abnormalities. Despite all three subjects partially resembling clinical manifestations of Nasu-Hakola disease with TREM2 mutations, we reveal some distinct features, including age of onset, neuroimaging findings, or disease course.

Microglia in Neurodegenerative Diseases.

Neurodegenerative diseases are manifested by a progressive death of neural cells, resulting in the deterioration of central nervous system (CNS) functions, ultimately leading to specific behavioural and cognitivesymptoms associated with affected brain regions. Several neurodegenerative disorders are caused by genetic variants or mutations, although the majority of cases are sporadic and linked to various environmental risk factors, with yet an unknown aetiology. Neuroglial changes are fundamental and often lead to the pathophysiology of neurodegenerative diseases. In particular, microglial cells, which are essential for maintaining CNS health, become compromised in their physiological functions with the exposure to environmental risk factors, genetic variants or mutations, as well as disease pathology. In this chapter, we cover the contribution of neuroglia, especially microglia, to several neurodegenerative diseases, including Nasu-Hakola disease, Parkinson's disease, amyotrophic lateral sclerosis, Alzheimer's disease, Huntington's disease, infectious disease-associated neurodegeneration, and metal-precipitated neurodegeneration. Future research perspectives for the field pertaining to the therapeutic targeting of microglia across these disease conditions are also discussed.

Effect of disease‐associated variants in TREM2 on splicing and gene dosage

AbstractBackgroundLoss‐of‐function variants in the triggering receptor expressed on myeloid cells 2 (TREM2) are responsible for a spectrum of neurodegenerative disorders. In the homozygous state, they cause severe pathologies with early onset dementia, such as Nasu‐Hakola disease (NHD) and behavioral variants of frontotemporal dementia (FTD), while heterozygous variants increase risk of late onset Alzheimer’s disease (AD) and FTD. In over half of TREM2 variants found in families with recessive early onset dementia, the defect occurs at the transcript level, via premature termination codons or via aberrant splicing. The remaining ones are missense variants thought to inactivate the protein; however, the underlying pathogenic mechanism is less clear. In this work we tested whether disease‐associated TREM2 variants may contribute to the pathology via altered splicingMethodSpliceAI prediction algorithm was used to screen 56 disease‐associated/risk‐modifying variants for potential effect on splicing. Variants scored by SpliceAI were tested in the splicing reporter assay with full‐length TREM2. Constructs with the common TREM2 variant or the spliceogenic SNP allele were nucleofected into THP‐1, HMC3 and BV2 cell lines. qRT‐/RT‐PCR and western blots were used to quantify the effect of variants at the transcript and protein levels. Nanostring nCounter analysis was used to measure TREM2 RNA in brains of NHD patients who carried spliceogenic variants.ResultWe demonstrated that multiple variants causative for NHD or associated with AD/FTD affect gene splicing reduced dosage of functional transcript and protein.ConclusionOur findings point to the complex character of pathogenicity of TREM2 variants, in which effects on post‐transcriptional gene regulation and protein function are often combined. This hidden layer of complexity necessitates inclusion of computational and experimental analyses of splicing and mRNA processing for better understanding of genetic variation in disease.

Computational saturation mutagenesis to explore the effect of pathogenic mutations on extra-cellular domains of TREM2 associated with Alzheimer’s and Nasu-Hakola disease

Computational saturation mutagenesis to explore the effect of pathogenic mutations on extra-cellular domains of TREM2 associated with Alzheimer’s and Nasu-Hakola disease

Proximal Humerus and Proximal Femur Fractures with Nasu-Hakola Disease Treated with Prosthetic Replacements: A Case Report

Proximal Humerus and Proximal Femur Fractures with Nasu-Hakola Disease Treated with Prosthetic Replacements: A Case Report

A mild type of Nasu-Hakola disease - a case of a woman with presenile dementia and cystic bone lesions.

A mild type of Nasu-Hakola disease - a case of a woman with presenile dementia and cystic bone lesions.

Microglia and Brain Disorders: The Role of Vitamin D and Its Receptor.

Accounting for 5-20% of the total glial cells present in the adult brain, microglia are involved in several functions: maintenance of the neural environment, response to injury and repair, immunesurveillance, cytokine secretion, regulation of phagocytosis, synaptic pruning, and sculpting postnatal neural circuits. Microglia contribute to some neurodevelopmental disorders, such as Nasu-Hakola disease (NHD), Tourette syndrome (TS), autism spectrum disorder (ASD), and schizophrenia. Moreover, microglial involvement in neurodegenerative diseases, such as Alzheimer's (AD) and Parkinson's (PD) diseases, has also been well established. During the last two decades, epidemiological and research studies have demonstrated the involvement of vitamin D3 (VD3) in the brain's pathophysiology. VD3 is a fat-soluble metabolite that is required for the proper regulation of many of the body's systems, as well as for normal human growth and development, and shows neurotrophic and neuroprotective actions and influences on neurotransmission and synaptic plasticity, playing a role in various neurological diseases. In order to better understand the exact mechanisms behind the diverse actions of VD3 in the brain, a large number of studies have been performed on isolated cells or tissues of the central nervous system (CNS). Here, we discuss the involvement of VD3 and microglia on neurodegeneration- and aging-related diseases.

Etiology Understanding Is the Core of Skeletal Diagnosis

Background: The term idiopathic is a non-specific disease label, which fails account for proper etiological understanding. The frequent usage of the term idiopathic may indicate clinical incompetence. We describe a number of patients from our practice with a history of complex bone disorders who were falsely given the term idiopathic by other Institutes. The sole tool used by other Institutes to conclude osteoporosis as a diagnosis is the bone mineral density. Material and Methods: Two Austrian families and one unrelated adult female patient (total number of 12 subjects) have been referred to our department with referral letters confirming the diagnosis of idiopathic osteoporosis. All patients manifested a diverse constellation of skeletal deformities. In all these patients, regular courses of anti-resorptive treatment plus calcium and vitamin D supplements. These have been excessively prescribed. Results: Our diagnostic process which is based heavily on detailed clinical and radiological phenotypic characterizations, we refuted the diagnosis of idiopathic osteoporosis for all patients because of the clear-cut clinical features. For the first family, we suggested the diagnosis of a novel type of mucopolysaccharidosis (the genetic results confirmed the diagnosis of a novel subtype of mucopolysaccharidosis (through the identification of arylsulfatase K ARSK). For the second family which has been subjected to a lengthy useless investigation for almost more than a decade, we refuted the diagnosis of idiopathic osteoporosis and the whole exome sequencing was consistent with the phenotypic diagnosis Nasu-Hakola disease (heterozygous missense mutations in TYROBP gene). The other unrelated 42-year-old- female patient was correctly diagnosed with Nasu-Hakola disease. Conclusion: The objective of this study is to minimize and suppress the usage of the term idiopathic. It has been imperative to understand the sequence of pathological events that occurred in these families. The core for diagnosis is the etiological understanding, which stemmed from professional conscientiousness. Patients underwent misdiagnosis of idiopathic osteoporosis and were treated extensively with anti-resorptive agents, calcium supplements and vitamin D. Strikingly, these medications resulted in a combination of serious cranial and cerebral lesions because of massive pathological calcifications. Imaging analysis via conventional radiographs, MRI and CT scan showed massive calcifications of the cranial sutures, inter-clinoid ligaments and hyper-calcification of the skull base. Sadly speaking, early onset dementia emerged in connection with sclerosing leukoencephalopathy. We believe that the exogenous toxic effects of the huge amounts of bone supplements consumed by these patients enhanced the pre-existing metabolic bone and cerebral disorders. Our findings can ameliorate the etiological understanding of early onset dementia and other correlated cranial and skeletal lesions.

Defects in lysosomal function and lipid metabolism in human microglia harboring a TREM2 loss of function mutation

TREM2 is an innate immune receptor expressed by microglia in the adult brain. Genetic variation in the TREM2 gene has been implicated in risk for Alzheimer’s disease and frontotemporal dementia, while homozygous TREM2 mutations cause a rare leukodystrophy, Nasu-Hakola disease (NHD). Despite extensive investigation, the role of TREM2 in NHD pathogenesis remains poorly understood. Here, we investigate the mechanisms by which a homozygous stop-gain TREM2 mutation (p.Q33X) contributes to NHD. Induced pluripotent stem cell (iPSC)-derived microglia (iMGLs) were generated from two NHD families: three homozygous TREM2 p.Q33X mutation carriers (termed NHD), two heterozygous mutation carriers, one related non-carrier, and two unrelated non-carriers. Transcriptomic and biochemical analyses revealed that iMGLs from NHD patients exhibited lysosomal dysfunction, downregulation of cholesterol genes, and reduced lipid droplets compared to controls. Also, NHD iMGLs displayed defective activation and HLA antigen presentation. This defective activation and lipid droplet content were restored by enhancing lysosomal biogenesis through mTOR-dependent and independent pathways. Alteration in lysosomal gene expression, such as decreased expression of genes implicated in lysosomal acidification (ATP6AP2) and chaperone mediated autophagy (LAMP2), together with reduction in lipid droplets were also observed in post-mortem brain tissues from NHD patients, thus closely recapitulating in vivo the phenotype observed in iMGLs in vitro. Our study provides the first cellular and molecular evidence that the TREM2 p.Q33X mutation in microglia leads to defects in lysosomal function and that compounds targeting lysosomal biogenesis restore a number of NHD microglial defects. A better understanding of how microglial lipid metabolism and lysosomal machinery are altered in NHD and how these defects impact microglia activation may provide new insights into mechanisms underlying NHD and other neurodegenerative diseases.

A polarizing answer - microglia in Nasu-Hakola disease.

A polarizing answer - microglia in Nasu-Hakola disease.

Human early-onset dementia caused by DAP12 deficiency reveals a unique signature of dysregulated microglia.

The TREM2-DAP12 receptor complex sustains microglia functions. Heterozygous hypofunctional TREM2 variants impair microglia, accelerating late-onset Alzheimer's disease. Homozygous inactivating variants of TREM2 or TYROBP-encoding DAP12 cause Nasu-Hakola disease (NHD), an early-onset dementia characterized by cerebral atrophy, myelin loss and gliosis. Mechanisms underpinning NHD are unknown. Here, single-nucleus RNA-sequencing analysis of brain specimens from DAP12-deficient NHD individuals revealed a unique microglia signature indicating heightened RUNX1, STAT3 and transforming growth factor-β signaling pathways that mediate repair responses to injuries. This profile correlated with a wound healing signature in astrocytes and impaired myelination in oligodendrocytes, while pericyte profiles indicated vascular abnormalities. Conversely, single-nuclei signatures in mice lacking DAP12 signaling reflected very mild microglial defects that did not recapitulate NHD. We envision that DAP12 signaling in microglia attenuates wound healing pathways that, if left unchecked, interfere with microglial physiological functions, causing pathology in human. The identification of a dysregulated NHD microglia signature sparks potential therapeutic strategies aimed at resetting microglia signaling pathways.

Lipomembranous fat necrosis: A distinctive and unique morphology (Review).

Lipomembranous fat necrosis (LFN) is an uncommon but distinct form of fat necrosis, which is characterized by eosinophilic, crenulated and/or serpiginous membranes. LFN exhibits macrocystic, microcystic and/or crushed features. LFN is routinely detectable on hematoxylin and eosin (H&E)-stained sections, and is present both in the acute phase and in the later or fibrous stage of necrotic fatty lesions. Smaller crushed LFN embedded within fibrous tissues may be difficult to recognize on H&E-stained sections, but can be highlighted by some staining techniques, including Masson trichrome, periodic acid-Schiff, orcein, long Ziehl-Neelsen stain, silver impregnation, phosphotungstic acid-hematoxylin and luxol fast blue staining. LFN was initially considered a specific feature of Nasu-Hakola disease, but has since been identified in various subcutaneous or intraabdominal lesions related to ischemic conditions or venous insufficiency. In addition, LFN is detectable in intra-articular loose bodies and aortic valves with or without dysfunction, suggesting that LFN is also associated with ischemia-like hypoxic conditions or malnutrition. LFN is considered to be a histological hallmark of hidden ischemic or hypoxic/malnourished conditions in various diseases; however, the exact mechanisms of LFN remain poorly understood. The present review described the clinicopathological features of this interesting, but poorly characterized, condition.

Soluble triggering receptor expressed on myeloid cells 2 (sTREM2) positively regulates lipopolysaccharide-induced expression of CXC chemokine ligand 10 and 11 in mouse macrophages

TREM2 (Triggering receptor expressed on myeloid cells 2) is the causative gene for Nasu-Hakola disease, which is characterized by multiple bone cysts and leukoencephalopathy. In addition, mutations in this gene have been found to be correlated with the onset of Alzheimer's disease. TREM2 is an immunoreceptor expressed on dendritic cells, microglia, osteoclasts, and macrophages. TREM2 on the cell membrane is shed by some proteases and released as soluble TREM2 (sTREM2). Meanwhile, several TREM2 ligands have been reported, and lipopolysaccharide (LPS) is one of the candidates. Using RNA interference to examine TREM2-mediated LPS response in macrophages, we identified five chemokines whose expression was induced via TREM2. Furthermore, we showed that LPS-induced expression of CXC-motif chemokine ligand (Cxcl10) and Cxcl11 among the five chemokines was mediated in part through sTREM2. These results suggest that sTREM2 has cytokine-like functions in macrophages.

TREM2 Gene Compound Heterozygosity in Neurodegenerative Disorders.

Homozygous variants of the TREM2 and TYROBP genes have been shown to be causative for multiple bone cysts and neurodegeneration leading to progressive dementia (NHD, Nasu-Hakola disease). To determine if biallelic variants of these genes and/or oligogenic inheritance could be responsible for a wider spectrum of neurodegenerative conditions. We analyzed 52 genes associated with neurodegenerative disorders using targeted next generation sequencing in a selected group of 29 patients (n = 14 Alzheimer's disease, n = 8 frontotemporal dementia, n = 7 amyotrophic lateral sclerosis) carrying diverse already determined rare variants in exon 2 of TREM2. Molecular modeling was used to get an insight into the potential effects of the mutation. We identified a novel mutation c.401_406delinsTCTAT; p.(Asp134Valfs*55) in exon 3 of TREM2 in an Alzheimer's disease patient also carrying the p.Arg62His TREM2 variant. Molecular modeling revealed that the identified mutation prevents anchoring of the TREM2 protein in the membrane, leaving the core of the Ig-like domain intact. Our results expand the spectrum of neurodegenerative diseases, where the carriers of biallelic mutations in TREM2 have been described for Alzheimer's disease, and highlight the impact of variant burden in other genes on phenotypic heterogeneity.

Dynamic insights into the effects of nonsynonymous polymorphisms (nsSNPs) on loss of TREM2 function

Single nucleotide variations in Triggering Receptor Expressed on Myeloid Cells 2 (TREM2) are associated with many neurodegenerative diseases, including Nasu-Hakola disease (NHD), frontotemporal dementia (FTD), and late-onset Alzheimer's disease because they disrupt ligand binding to the extracellular domain of TREM2. However, the effects of nonsynonymous single nucleotide polymorphisms (nsSNPs) in TREM2 on disease progression remain unknown. In this study, we identified several high-risk nsSNPs in the TREM2 gene using various deleterious SNP predicting algorithms and analyzed their destabilizing effects on the ligand recognizing region of the TREM2 immunoglobulin (Ig) domain by molecular dynamics (MD) simulation. Cumulative prediction by all tools employed suggested the three most deleterious nsSNPs involved in loss of TREM2 function are rs549402254 (W50S), rs749358844 (R52C), and rs1409131974 (D104G). MD simulation showed that these three variants cause substantial structural alterations and conformational remodeling of the apical loops of the TREM2 Ig domain, which is responsible for ligand recognition. Detailed analysis revealed that these variants substantially increased distances between apical loops and induced conformation remodeling by changing inter-loop nonbonded contacts. Moreover, all nsSNPs changed the electrostatic potentials near the putative ligand-interacting region (PLIR), which suggested they might reduce specificity or loss of binding affinity for TREM2 ligands. Overall, this study identifies three potential high-risk nsSNPs in the TREM2 gene. We propose further studies on the molecular mechanisms responsible for loss of TREM2 function and the associations between TREM2 nsSNPs and neurodegenerative diseases.

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.

Downregulation of m6A Methyltransferase in the Hippocampus of Tyrobp -/- Mice and Implications for Learning and Memory Deficits.

Loss-of-function mutations in the gene that encodes TYRO protein kinase-binding protein (TYROBP) cause Nasu-Hakola disease, a heritable disease resembling Alzheimer’s disease (AD). Methylation of N6 methyl-adenosine (m6A) in mRNA plays essential roles in learning and memory. Aberrant m6A methylation has been detected in AD patients and animal models. In the present study, Tyrobp–/– mice showed learning and memory deficits in the Morris water maze, which worsened with age. Tyrobp–/– mice also showed elevated levels of total tau, Ser202/Thr205-phosphorylated tau and amyloid β in the hippocampus and cerebrocortex, which worsened with aging. The m6A methyltransferase components METTL3, METTL14, and WTAP were downregulated in Tyrobp–/– mice, while expression of demethylases that remove the m6A modification (e.g., FTO and ALKBH5) were unaltered. Methylated RNA immunoprecipitation sequencing identified 498 m6A peaks that were upregulated in Tyrobp–/– mice, and 312 m6A peaks that were downregulated. Bioinformatic analysis suggested that most of these m6A peaks occur in sequences near stop codons and 3′-untranslated regions. These findings suggest an association between m6A RNA methylation and pathological TYROBP deficiency.

Nasu-Hakola Disease - A Rare Type of Presenile Dementia.

Nasu-Hakola Disease - A Rare Type of Presenile Dementia.