LMNB1-related Autosomal Dominant Leukodystrophy

Pathophysiology

• Caused by duplication of the LMNB1 gene on chromosome 5q23.2
• LMNB1 encodes lamin B1, a component of the nuclear lamina
• Overexpression of lamin B1 leads to:
  • Disruption of nuclear envelope structure
  • Altered gene expression
  • Impaired oligodendrocyte function and myelin maintenance

Demographics

• Adult-onset disorder, typically presenting in the 4th to 6th decade of life
• No significant gender predilection
• Prevalence estimated at <1/1,000,000
• Originally described in families of French-Canadian descent, but now reported worldwide

Diagnosis

• Clinical presentation:
  • Progressive gait disturbance
  • Autonomic dysfunction (e.g., orthostatic hypotension, bladder dysfunction)
  • Cognitive decline
  • Cerebellar ataxia
  • Pyramidal signs
• Genetic testing:
  • Identification of LMNB1 gene duplication using array comparative genomic hybridisation (aCGH) or multiplex ligation-dependent probe amplification (MLPA)
• Differential diagnosis:
  • Other adult-onset leukodystrophies (e.g., cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy - CADASIL)
  • Multiple sclerosis
  • Vascular dementia

Imaging

• MRI findings:
  • Symmetric white matter hyperintensities on T2-weighted and FLAIR sequences
  • Predominant involvement of:
  • Cerebellar white matter
  • Periventricular regions
  • Corpus callosum
  • Relative sparing of U-fibres and subcortical white matter
  • Progressive atrophy of affected regions
• DTI (Diffusion Tensor Imaging):
  • Reduced fractional anisotropy in affected white matter
  • Increased mean diffusivity
• MR spectroscopy:
  • Reduced N-acetylaspartate (NAA) in affected white matter
  • Elevated choline and myo-inositol levels

Treatment

• No curative treatment available
• Management focuses on symptomatic relief and supportive care:
  • Physical therapy for gait and balance issues
  • Occupational therapy for activities of daily living
  • Speech therapy for dysarthria
  • Medications for autonomic dysfunction (e.g., fludrocortisone for orthostatic hypotension)
  • Cognitive rehabilitation
• Genetic counselling for affected individuals and family members
• Ongoing research into potential therapies:
  • Gene therapy approaches targeting LMNB1 expression
  • Neuroprotective agents to slow disease progression

Differential diagnosis