ALSP is a progressive neurodegenerative disease caused by CSF1R mutations, representing a prototypical primary brain microgliopathy. The disease typically presents in middle adulthood with cognitive decline, motor symptoms, and psychiatric manifestations. While no disease-modifying therapy is currently approved, emerging treatments targeting TREM2 and hematopoietic stem cell transplantation offer potential therapeutic strategies. Early diagnosis through genetic testing and characteristic MRI findings is essential for appropriate management and family counseling. Ongoing research continues to elucidate disease mechanisms and develop targeted therapies for this rare but devastating condition.
Adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP) is a rare, progressive neurodegenerative disorder primarily affecting the cerebral white matter. ALSP is caused by heterozygous loss-of-function mutations in the [CSF1R[/genes/[csf1r[/genes/[csf1r[/genes/[csf1r--TEMP--/genes)--FIX-- (colony stimulating factor 1 receptor) gene, making it the prototypical primary brain microgliopathy—a disease driven by [microglia[/entities/[microglia[/entities/[microglia[/entities/[microglia--TEMP--/entities)--FIX--l dysfunction.
Previously described as two separate entities — hereditary diffuse leukoencephalopathy with spheroids (HDLS) and pigmentary orthochromatic leukodystrophy (POLD) — these conditions were unified under the ALSP designation when [CSF1R[/genes/[csf1r[/genes/[csf1r[/genes/[csf1r--TEMP--/genes)--FIX-- mutations were identified as the shared genetic cause in 2012. ALSP typically manifests in the fourth to fifth decade of life (mean onset ~43 years) and progresses to severe disability and death within 5-10 years of symptom onset. Women appear to have a significantly younger age of onset than men (40 vs. 47 years).
The estimated prevalence is approximately 1 in 100,000, though ALSP is likely underdiagnosed due to clinical overlap with more common conditions including [Alzheimer's Disease[/diseases/[alzheimers[/diseases/[alzheimers[/diseases/[alzheimers--TEMP--/diseases)--FIX--, [Frontotemporal Dementia[/diseases/[ftd[/diseases/[ftd[/diseases/[ftd--TEMP--/diseases)--FIX--, multiple sclerosis, and Vascular Dementia.
ALSP represents a unique category of neurodegenerative disease characterized by:[1]
The [CSF1R[/genes/[csf1r[/genes/[csf1r[/genes/[csf1r--TEMP--/genes)--FIX-- gene, located on chromosome 5q32, encodes a 108 kDa type III receptor tyrosine kinase (RTK) that belongs to the platelet-derived growth factor receptor family. [CSF1R[/genes/[csf1r[/genes/[csf1r[/genes/[csf1r--TEMP--/genes)--FIX-- is the receptor for two ligands: colony stimulating factor 1 (CSF-1/M-CSF) and interleukin-34 (IL-34). The receptor plays a pivotal role in regulating the survival, differentiation, proliferation, and activation of mononuclear phagocytic cells, including [[microglia[/entities/[microglia[/entities/[microglia[/entities/[microglia--TEMP--/entities)--FIX--[/entities/[[microglia[/entities/[microglia[/entities/[[microglia--TEMP--/entities/microglia[//entities//entities/[microglia--TEMP--//entities//entities/[microglia[//entities//entities//entities/[microglia--TEMP--//entities//entities/[microglia[//entities//entities//entities/[microglia](//entities//entities/microglia](//entities//entities/[microglia](//entities//entities//entities/microglia](//entities//entities/[microglia](/entities//entities//entities//entities/microglia](//entities//entities//entities/microglia](//entities//entities/microglia](//entities//entities/[microglia](//entities//entities//entities/microglia](//entities//entities/microglia (//entities//entities)--FIX-- (/entities//entities/microglia) ()--FIX-- (/entities/microglia) ()--FIX--).
Over 100 pathogenic variants in [CSF1R[/genes/[csf1r[/genes/[csf1r[/genes/[csf1r--TEMP--/genes)--FIX-- have been identified in ALSP patients:
ALSP follows autosomal dominant inheritance with high penetrance. De novo mutations account for a significant proportion of cases (estimated 20-40%), and genetic anticipation has not been definitively demonstrated.
Under normal conditions, ligand binding triggers [CSF1R[/genes/[csf1r[/genes/[csf1r[/genes/[csf1r--TEMP--/genes)--FIX-- dimerization and autophosphorylation, activating downstream pathways including:
ALSP is fundamentally a disease of [microglia[/entities/[microglia[/entities/[microglia[/entities/[microglia--TEMP--/entities)--FIX--l homeostasis. [CSF1R[/genes/[csf1r[/genes/[csf1r[/genes/[csf1r--TEMP--/genes)--FIX-- haploinsufficiency leads to:
The most common initial presentation (approximately 55% of cases) involves cognitive decline resembling Frontotemporal Dementia or early-onset Alzheimer's Disease[11]:
The most common initial presentation (approximately 55% of cases) involves cognitive decline resembling [Frontotemporal Dementia[/diseases/[ftd[/diseases/[ftd[/diseases/[ftd--TEMP--/diseases)--FIX-- or early-onset [Alzheimer's Disease[/diseases/[alzheimers[/diseases/[alzheimers[/diseases/[alzheimers--TEMP--/diseases)--FIX--:
Motor involvement occurs in approximately 65-75% of patients during the disease course[12]:
Motor involvement occurs in approximately 65-75% of patients during the disease course:
Depression and anxiety are frequently reported (30-40% of patients), often preceding the recognition of cognitive decline by months to years[13].
Depression and anxiety are frequently reported (30-40% of patients), often preceding the recognition of cognitive decline by months to years. Psychotic symptoms including hallucinations may also occur.
Characteristic neuroimaging findings on MRI are essential for diagnosis[14]:
Characteristic neuroimaging findings on MRI are essential for diagnosis:
Definitive diagnosis requires identification of a pathogenic variant in [CSF1R[/genes/[csf1r[/genes/[csf1r[/genes/[csf1r--TEMP--/genes)--FIX-- through sequencing of exons 12-22 (tyrosine kinase domain) or whole-gene analysis. Genetic testing should be considered in any adult presenting with progressive white matter disease and cognitive decline, particularly when MRI features are suggestive.
In the pre-genetic testing era, brain biopsy was often required for diagnosis. Histopathological findings include axonal spheroids (on neurofilament immunostaining), pigmented macrophages (PAS-positive, autofluorescent), and white matter loss with gliosis. Biopsy is now rarely necessary when genetic testing is available.
ALSP must be distinguished from several more common conditions[15]:
ALSP must be distinguished from several more common conditions:
No disease-modifying therapy is currently approved for ALSP. Management is symptomatic:
Case reports have described stabilization or improvement following allogeneic HSCT, particularly when performed early in the disease course. Donor-derived [microglia[/entities/[microglia[/entities/[microglia[/entities/[microglia--TEMP--/entities)--FIX-- can repopulate the brain, potentially restoring [CSF1R[/genes/[csf1r[/genes/[csf1r[/genes/[csf1r--TEMP--/genes)--FIX---dependent [microglia[/entities/[microglia[/entities/[microglia[/entities/[microglia--TEMP--/entities)--FIX--l functions. However, HSCT carries significant morbidity and mortality risks, and prospective controlled trial data are lacking.
Iluzanebart is a human monoclonal IgG1 agonist antibody targeting [TREM2[/entities/[trem2[/entities/[trem2[/entities/[trem2--TEMP--/entities)--FIX--, developed by Vigil Neuroscience for ALSP treatment. The rationale is that [TREM2[/entities/[trem2[/entities/[trem2[/entities/[trem2--TEMP--/entities)--FIX-- activation can compensate for [CSF1R[/genes/[csf1r[/genes/[csf1r[/genes/[csf1r--TEMP--/genes)--FIX-- dysfunction by activating overlapping downstream signaling pathways.
ALSP is invariably progressive, with median disease duration from symptom onset to death of approximately 6.8 years (range 2-29 years). Rapid cognitive decline, early motor involvement, and younger age at onset are associated with faster progression. The cause of death is most commonly aspiration pneumonia, followed by status epilepticus and general debilitation.
ALSP is a progressive neurodegenerative disease caused by [CSF1R[/genes/[csf1r[/genes/[csf1r[/genes/[csf1r--TEMP--/genes)--FIX-- mutations, representing a prototypical primary brain microgliopathy. The disease typically presents in middle adulthood with cognitive decline, motor symptoms, and psychiatric manifestations. While no disease-modifying therapy is currently approved, emerging treatments targeting [TREM2[/entities/[trem2[/entities/[trem2[/entities/[trem2--TEMP--/entities)--FIX-- and hematopoietic stem cell transplantation offer potential therapeutic strategies. Early diagnosis through genetic testing and characteristic MRI findings is essential for appropriate management and family counseling. Ongoing research continues to elucidate disease mechanisms and develop targeted therapies for this rare but devastating condition.
The study of Adult Onset Leukoencephalopathy With Axonal Spheroids And Pigmented Glia (Alsp) 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.
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