Lebers hereditary optic neuropathy

Overview of Leber's Hereditary Optic Neuropathy (LHON)

  • LHON is a hereditary optic neuropathy characterized by vision loss.

  • Discovered by a German ophthalmologist in 1871; originally thought to be X-linked due to its male dominance.

  • In 1988, linked to mitochondrial DNA mutations by Douglas Wallace.

  • Specific mutations identified in 1992.

Symptoms and Onset

  • Main Symptom: Bilateral vision loss, which is progressive (gets worse over time).

  • Usually presents suddenly between ages 20-30, worsening over 6 months to a year, eventually plateauing.

  • Central scotoma: a dark spot in central vision that enlarges over time.

  • Asynchronous vision loss: often starts in one eye before the other.

  • Associated conditions:

    • Death of retinal ganglion cells (RGCs).

    • Optic neuropathy (issues with the optic nerve).

    • Retinal nerve fiber and optic disc edema.

    • Blood vessel tortuosity (curled blood vessels).

Specific Conditions Related to LHON

  • Leber's Plus: A variant where visual symptoms are accompanied by neurological issues like dystonia and ataxia.

Common Genetic Mutations Associated with LHON

  • Three common mutations linked with LHON affecting complex I of the mitochondrial electron transport chain (ETC):

    1. mtdn1 (3460): Guanine to adenine; least severe, minimal respiratory chain effect.

    2. mtdn4 (11778): Guanine to adenine; lowest chance of visual improvement, associated with color blindness.

    3. mtdn6 (14484): Cytosine mutation; highest chance of visual recovery, spontaneous recovery possible.

Mode of Inheritance

  • LHON is inherited via mitochondrial DNA (mtDNA), always maternal.

  • Homoplasmy vs. Heteroplasmy:

    • Homoplasmy: Same mutation in all mitochondria.

    • Heteroplasmy: A mixture of mutated and normal mtDNA in different mitochondria.

Mitochondrial Function

  • Mitochondrial DNA encodes proteins critical for ATP production via the ETC (electron transport chain).

  • Complex I initiates the process by oxidizing NADH to produce energy.

  • Dysfunction in ETC leads to the production of reactive oxygen species (ROS), which can damage tissues and cells, particularly RGCs.

Impact of LHON Mutations on ETC

  • Mutations disrupt complex I formation and function, leading to reduced ATP production and increased ROS.

  • This causes death of RGCs as they depend on ATP, resulting in vision loss due to impaired signal transmission to the brain.

Case Study: Hormone Replacement Therapy (2019)

  • Case of a 48-year-old woman with bilateral vision loss post hormone discontinuation, initially misdiagnosed with optic neuritis.

  • Treatment included Idebenone, Vitamin C, restarting hormonal birth control, and reducing alcohol intake.

  • Visual field examinations showed significant improvements over time, indicating Idebenone's effectiveness for vision recovery.

Factors Influencing Vision Loss in LHON

  • Estrogen Influence: Possible protective effects from estrogen, especially in postmenopausal women.

  • Alcohol Consumption: High alcohol intake linked to increased ROS, potentially exacerbating vision loss.

  • Higher rates of LHON observed in males; potential reasons:

    • Estrogen's protective mechanism.

    • Underdiagnosis in females due to misidentification with more common conditions like optic neuritis or multiple sclerosis.

The Role of Environmental Factors

  • Environmental ROS from lifestyle choices (e.g., alcohol and smoking) can contribute to vision loss in LHON.

  • Patients with lifestyle habits less likely to produce high ROS levels tend to have better outcomes.

Diagnosis Challenges

  • Misdiagnosis common due to symptom similarity with optic neuritis (painful condition), whereas LHON is painless.

  • Importance of differentiation based on symptom profiles and genetic testing.