Nasu-Hakola Disease (PLOSL)

Nasu-Hakola Disease (PLOSL)

Introduction

Nasu Hakola Disease (Plosl) is a progressive neurodegenerative disorder characterized by the gradual loss of neuronal function. This page provides comprehensive information about the disease, including its pathophysiology, clinical presentation, diagnosis, and current therapeutic approaches.

Overview

Nasu-Hakola disease, also known as Polycystic Lipomembranous Osteodysplasia with Sclerosing Leukoencephalopathy (PLOSL), is a rare autosomal recessive disorder characterized by a combination of progressive dementia and bone abnormalities.<a href="#references">¹</a> The disease typically presents in early adulthood with bone pain and cystic lesions, followed by progressive neurological deterioration leading to premature death. Nasu-Hakola disease represents a unique intersection between skeletal and neuropsychiatric pathology, making it a fascinating model for understanding the relationship between immune system dysfunction and neurodegeneration. [@paloneva2003]

The disease exists in two genetic subtypes: PLOSL1 (caused by mutations in the TYROBP gene) and PLOSL2 (caused by mutations in the [TREM2](/proteins/trem2-protein) gene).<a href="#references">²</a> Both genes encode proteins critical for immune signaling in [microglia](/cell-types/microglia), the resident immune cells of the brain. This connection has placed Nasu-Hakola disease at the center of [Alzheimer's Disease](/diseases/alzheimers-disease) research, as [TREM2](/proteins/trem2-protein) variants are strong genetic risk factors for late-onset AD. [@omim]

Nasu-Hakola Disease (PLOSL)

Introduction

Nasu Hakola Disease (Plosl) is a progressive neurodegenerative disorder characterized by the gradual loss of neuronal function. This page provides comprehensive information about the disease, including its pathophysiology, clinical presentation, diagnosis, and current therapeutic approaches.

Overview

Nasu-Hakola disease, also known as Polycystic Lipomembranous Osteodysplasia with Sclerosing Leukoencephalopathy (PLOSL), is a rare autosomal recessive disorder characterized by a combination of progressive dementia and bone abnormalities.<a href="#references">¹</a> The disease typically presents in early adulthood with bone pain and cystic lesions, followed by progressive neurological deterioration leading to premature death. Nasu-Hakola disease represents a unique intersection between skeletal and neuropsychiatric pathology, making it a fascinating model for understanding the relationship between immune system dysfunction and neurodegeneration. [@paloneva2003]

The disease exists in two genetic subtypes: PLOSL1 (caused by mutations in the TYROBP gene) and PLOSL2 (caused by mutations in the [TREM2](/proteins/trem2-protein) gene).<a href="#references">²</a> Both genes encode proteins critical for immune signaling in [microglia](/cell-types/microglia), the resident immune cells of the brain. This connection has placed Nasu-Hakola disease at the center of [Alzheimer's Disease](/diseases/alzheimers-disease) research, as [TREM2](/proteins/trem2-protein) variants are strong genetic risk factors for late-onset AD. [@omim]

Genetics

PLOSL1 (TYROBP)

The classic form of Nasu-Hakola disease (PLOSL1) is caused by homozygous or compound heterozygous loss-of-function mutations in the TYROBP gene (also known as DAP12) on chromosome 19q13.12.<a href="#references">³</a> TYROBP encodes a transmembrane signaling adapter protein that couples with activating receptors in the immune system, particularly the [TREM2](/genes/trem2) receptor on [microglia](/cell-types/microglia). The disease results from complete loss of TYROBP function, leading to impaired microglial activation and defective immune surveillance in the brain. [@guerreiro2013]

PLOSL2 (TREM2)

A genetically distinct form (PLOSL2) results from homozygous mutations in the [TREM2](/genes/trem2) gene on chromosome 6p21.<a href="#references">⁴</a> TREM2 (Triggering Receptor Expressed on Myeloid Cells 2) is a surface receptor primarily expressed on [microglia](/cell-types/microglia) that recognizes lipid ligands, [Amyloid-Beta](/proteins/amyloid-beta), and cellular debris. Pathogenic TREM2 mutations impair microglial phagocytosis, metabolic fitness, and the ability to form neurodegenerative disease-associated [microglia](/cell-types/microglia) (DAM). [@jonsson2013]

Inheritance Pattern

Both forms follow autosomal recessive inheritance. Carriers of heterozygous TYROBP or TREM2 mutations are typically asymptomatic but may have slightly increased risk for certain conditions. Notably, heterozygous TREM2 variants (particularly the R47H variant) are associated with approximately 2-4-fold increased risk for late-onset Alzheimer's Disease.<a href="#references">⁵</a> [@nasu1973]

Pathophysiology

Central Nervous System

The hallmark neuropathological feature of Nasu-Hakola disease is a sclerosing leukoencephalopathy characterized by widespread demyelination and gliosis of cerebral white matter.<a href="#references">⁶</a> Research indicates that severe chronic vasogenic brain edema is the primary pathogenetic mechanism, with basement membranes of blood vessels becoming thickened and often multiplied, particularly in white matter regions. This [Blood-Brain Barrier](/entities/blood-brain-barrier) dysfunction leads to accumulation of fluid in the brain parenchyma. [@matsumoto1999]

Neuropathological studies reveal: [@verloes1997]

• Diffuse white matter degeneration with loss of myelin
• Axonal destruction
• Reactive astrocytosis
• Microglial activation with inadequate phagocytic response
• Cerebral atrophy, particularly in frontal and temporal lobes
• Basal ganglia calcifications

Skeletal System

The bone abnormalities in Nasu-Hakola disease result from abnormal bone metabolism. Patients develop Painless cystic lesions (polycystic osteolysis) in the phalanges, metacarpals, carpals, metatarsals, tarsals, patella, and ends of long bones.<a href="#references">⁷</a> These lesions lead to pathologic fractures and progressive bone loss. The combination of bone cysts and neurological symptoms is unique among human diseases. [@genereviews]

Clinical Presentation

Early Stage (Typically Age 20-30)

The disease typically begins with skeletal manifestations: [@deczkowska2016]

• Pain and swelling in wrists and ankles, often following minor trauma
• Development of bone cysts in the hands and feet
• Pathologic fractures
• Progressive joint deformities
• Gait abnormalities due to lower extremity involvement

Neurological Stage (Typically Age 30-40)

Progressive neurological decline follows the skeletal manifestations: [@hakola1992]

• Cognitive decline: Progressive presenile dementia resembling Alzheimer's Disease
• Behavioral changes: Frontal lobe syndrome with personality alterations, loss of social inhibitions, aggressive behavior
• Mood disturbances: Euphoria, apathy, depression
• Speech disorders: Dysarthria, eventual mutism
• Motor symptoms: Upper motor neuron signs including spasticity, myoclonus, gait disturbance
• Seizures: Generalized tonic-clonic seizures
• Agnosia and apraxia: Loss of sensory and motor planning abilities
• Memory impairment: Progressive forgetfulness and cognitive deficits

Disease Progression

The disease follows a relentless progressive course. Most patients become completely disabled within 5-10 years of neurological symptom onset. The median age of death is between 35-45 years, with most patients dying by age 50.<a href="#references">⁸</a> Death typically results from complications of immobility, seizures, or aspiration. [@ulrich2016]

Diagnosis

Clinical Diagnosis

Diagnosis is based on the characteristic combination of:

Neuroimaging

MRI findings are critical for diagnosis:

• Diffuse white matter hyperintensities on T2-weighted imaging
• Cerebral atrophy, particularly frontal and temporal lobes
• Basal ganglia calcifications
• Thinning of the corpus callosum
• Caudate nucleus atrophy

Genetic Testing

Molecular genetic testing confirms the diagnosis:

• Sequencing of TYROBP gene for PLOSL1
• Sequencing of TREM2 gene for PLOSL2
• Identifies pathogenic variants in affected individuals
• Enables carrier testing for at-risk family members

Laboratory Findings

• Elevated CSF protein
• Abnormal EEG patterns
• Standard blood work typically unremarkable

Treatment

Current Management

There is no cure for Nasu-Hakola disease. Management is entirely supportive and focuses on symptom relief:<a href="#references">⁹</a>

Research Directions

The discovery of the TREM2-Alzheimer's Disease link has spurred interest in TREM2-targeted therapies:<a href="#references">¹⁰</a>

• TREM2 agonistic antibodies: Promoting microglial activation
• Small molecule TREM2 activators: Enhancing receptor signaling
• Gene therapy approaches: Delivering functional TREM2
• Stem cell transplantation: Replacing defective microglia

Epidemiology

Nasu-Hakola disease is extremely rare, with estimated prevalence of approximately 2 × 10⁻⁶ in Finnish populations.<a href="#references">¹¹</a> Cases have been reported globally, with higher concentrations in Finland and Japan due to founder effects. Both sexes are equally affected.

Relationship to Alzheimer's Disease

The identification of TREM2 mutations causing Nasu-Hakola disease revolutionized Alzheimer's Disease research. Heterozygous TREM2 variants (particularly R47H, R62H, and D87N) increase Alzheimer's Disease risk by 2-4 fold.<a href="#references">¹²</a> This discovery highlighted the critical role of microglia in Alzheimer's pathogenesis and led to the concept of disease-associated microglia (DAM). Understanding how TREM2 dysfunction leads to neurodegeneration may yield therapeutic strategies for both conditions.

External Links

• [OMIM: Nasu-Hakola Disease](https://omim.org/entry/221770)
• [GeneReviews: TREM2-Related Neurodegeneration](https://www.ncbi.nlm.nih.gov/books/NBK546262/)
• [Alzheimer's Disease Information: TREM2 Research](https://www.alz.org/)
• [Diseases Index](/diseases/diseases)
• [microglia](/cell-types/microglia)/entities/microglia
• [Gene Therapy for Neurodegenerative Diseases/therapeutics/gene-therapy)](/genes/th)

Background

The study of Nasu Hakola Disease (Plosl) has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.

Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.

Recent Research (2024-2026)

Recent advances in Nasu-Hakola Disease (PLOSL) have focused on understanding disease mechanisms, identifying biomarkers, and developing novel therapeutic approaches. Key developments include:

• Genetic studies: Identification of new genetic risk factors and mechanistic insights
• Biomarker research: Development of diagnostic and prognostic biomarkers
• Therapeutic approaches: Investigation of novel treatment strategies
• Clinical trials: Ongoing Phase I-III trials for new therapies

Allen Brain Atlas Resources

• [Allen Brain Atlas - Gene Expression](https://human.brain-map.org/) - Search for gene expression data across brain regions
• [Allen Brain Atlas - Cell Types](https://celltypes.brain-map.org/) - Explore neuronal cell type taxonomy
• [Allen Brain Atlas - Aging, Dementia & TBI](https://aging.brain-map.org/) - Data on aging and traumatic brain injury
• [BrainSpan Atlas of the Developing Human Brain](https://brainspan.org/) - Developmental gene expression data

References