Leigh Syndrome

Leigh Syndrome

[Leigh syndrome](/diseases/leigh-syndrome) (also known as subacute necrotizing encephalomyelopathy) is a rare, devastating neurodegenerative disorder characterized by bilateral, symmetric lesions in the brainstem, basal ganglia, and cerebellum. The disease typically presents in infancy or early childhood with progressive neurological deterioration, including loss of motor skills, respiratory failure, and metabolic crises. Leigh syndrome represents the most common inherited mitochondrial disorder and serves as a paradigm for understanding the relationship between mitochondrial dysfunction and neurodegeneration.

Overview

Leigh syndrome was first described by the British neurologist Denis Leigh in 1951, who reported cases of infants with progressive encephalopathy, lactic acidosis, and characteristic neuropathological findings of necrotizing lesions in specific brain regions. The disease results from defects in mitochondrial energy metabolism, leading to impaired ATP production and progressive neuronal death. [@natural2020]

The hallmark neuropathological finding is bilateral, symmetric necrotizing lesions with spongiform changes, neuronal loss, and capillary proliferation in the brainstem, basal ganglia, and cerebellum. These lesions are thought to result from episodes of severe metabolic decompensation, leading to energy failure and cell death in vulnerable brain regions. [@epidemiology2019]

Genetics and Molecular Biology

Inheritance Patterns

Leigh Syndrome

[Leigh syndrome](/diseases/leigh-syndrome) (also known as subacute necrotizing encephalomyelopathy) is a rare, devastating neurodegenerative disorder characterized by bilateral, symmetric lesions in the brainstem, basal ganglia, and cerebellum. The disease typically presents in infancy or early childhood with progressive neurological deterioration, including loss of motor skills, respiratory failure, and metabolic crises. Leigh syndrome represents the most common inherited mitochondrial disorder and serves as a paradigm for understanding the relationship between mitochondrial dysfunction and neurodegeneration.

Overview

Leigh syndrome was first described by the British neurologist Denis Leigh in 1951, who reported cases of infants with progressive encephalopathy, lactic acidosis, and characteristic neuropathological findings of necrotizing lesions in specific brain regions. The disease results from defects in mitochondrial energy metabolism, leading to impaired ATP production and progressive neuronal death. [@natural2020]

The hallmark neuropathological finding is bilateral, symmetric necrotizing lesions with spongiform changes, neuronal loss, and capillary proliferation in the brainstem, basal ganglia, and cerebellum. These lesions are thought to result from episodes of severe metabolic decompensation, leading to energy failure and cell death in vulnerable brain regions. [@epidemiology2019]

Genetics and Molecular Biology

Inheritance Patterns

[Leigh syndrome](/diseases/leigh-syndrome) can result from pathogenic variants in over 100 different genes, with inheritance patterns including: [@neuroinflammation2019]

• Autosomal recessive: Most common (e.g., SURF1, PDHA1, NDUFS1)
• Maternal inheritance: MT-ATP6, MT-ND genes (mitochondrial DNA)
• X-linked: PDHA1 (most common X-linked form)

Causal Genes

Nuclear DNA-Encoded Genes

• Complex I genes: NDUFS1, NDUFS2, NDUFS4, NDUFAF6
• Complex IV genes: SURF1, COX10, COX15, SCO1
• Complex V genes: ATP5F1A (MTATP1)
• Pyruvate dehydrogenase genes: PDHA1, PDHB, DLAT
• Coenzyme Q genes: COQ8A (ADCK3), COQ9
• Assembly factors: Various complex-specific factors

Mitochondrial DNA-Encoded Genes

• MT-ATP6: ATP synthase subunit 6
• MT-ND1, MT-ND5, MT-ND6: Complex I subunits
• MT-CO1, MT-CO2, MT-CO3: Complex IV subunits
• MT-CYB: Cytochrome b (Complex III)

Mitochondrial Dysfunction

The underlying pathophysiology involves impaired mitochondrial energy metabolism: [@coenzyme2019]

Clinical Features

Age of Onset

[Leigh syndrome](/diseases/leigh-syndrome) typically presents in: [@clinical2018]

• Infancy: Most common (6-18 months)
• Early childhood: Can present up to age 5-6
• Adolescence/adulthood: Rare, milder variants

Initial Symptoms

Early signs often include: [@mitochondrial2018]

• Developmental delay: Failure to meet milestones
• Hypotonia: Low muscle tone
• Feeding difficulties: Poor suck, difficulty feeding
• Lethargy: Unusual tiredness
• Vomiting: Recurrent episodes

Core Neurological Features

Motor Regression

• Loss of previously acquired motor skills
• Progressive spasticity
• Ataxia and incoordination
• Dystonia
• Hypotonia (in some)

Respiratory Abnormalities

• Apneustic breathing: Abnormal breathing pattern
• Central hypoventilation: Respiratory failure
• Episodes of respiratory crisis: Often during illness

Ocular Abnormalities

• Ophthalmoplegia: Eye movement paralysis
• Optic atrophy: Vision loss
• Nystagmus: Involuntary eye movements
• Strabismus: Misaligned eyes

Metabolic Crises

Episodes of acute metabolic decompensation: [@targeted2017]

• Triggers: Illness, stress, fasting
• Features: Lethargy, vomiting, acidosis
• Outcome: Often leads to neurological deterioration
• Lactic acidosis: Elevated blood and CSF lactate

Other Features

• Seizures: Can occur, particularly during crises
• Cardiomyopathy: In some genetic forms
• Peripheral neuropathy: In some variants
• Growth failure: Poor weight gain

Diagnosis

Clinical Diagnosis

The diagnosis is suspected based on: [@stem2017]

Neuroimaging

MRI findings are characteristic: [@future2016]

• Bilateral symmetric lesions: In brainstem, basal ganglia, cerebellum
• T2 hyperintensity: Abnormal signal in affected regions
• Basal ganglia involvement: Putamen, caudate, globus pallidus
• Brainstem lesions: Particularly in midbrain and medulla
• Cerebellar involvement: In some cases

• SURF1: White matter spongiform changes
• MT-ATP6: basal ganglia lesions often with diffuse cerebral involvement

Laboratory Findings

• Lactic acidosis: Elevated blood lactate (2-15 mmol/L)
• Elevated CSF lactate: Even when blood lactate normal
• Abnormal organic acids: Urine analysis may show pattern
• Ketones: Elevated during metabolic crises

Enzyme Testing

• Pyruvate dehydrogenase activity: In PDH-deficient forms
• Complex I-V activities: In OXPHOS deficiencies
• Fibroblast testing: Can confirm some forms

Molecular Genetic Testing

Genetic testing provides definitive diagnosis:

• Targeted panels: Mitochondrial disease gene panels
• Whole exome sequencing: Often identifies causal variant
• Mitochondrial genome sequencing: For mtDNA mutations
• Whole genome sequencing: In complex cases

Muscle Biopsy

May show:

• Ragged-red fibers: In some forms
• Reduced complex activities: On enzyme histochemistry
• Abnormal mitochondria: On electron microscopy

Treatment and Management

Current Treatment

No cure exists. Management focuses on:

Acute Crisis Management

• Supportive care: ICU-level support during crises
• Metabolic interventions: Bicarbonate for acidosis
• Seizure control: Anticonvulsant medications
• Nutritional support: IV fluids, feeding as needed

Chronic Management

• Dietary modifications: Ketogenic diet in some forms
• Coenzyme Q10: Supplementation in some cases
• L-carnitine: For carnitine deficiency
• Thiamine: May help in PDH deficiency
• Sodium bicarbonate: For chronic acidosis

Supportive Care

• Physical therapy: Maintain function
• Occupational therapy: Daily activity support
• Speech therapy: If swallowing difficulties
• Nutritional support: May require gastrostomy
• Respiratory support: May require BiPAP or ventilator

Experimental Approaches

Gene Therapy

• AAV vectors: For nuclear-encoded genes
• Mitochondrial gene therapy: Novel approaches being developed
• Allotopic expression: Mitochondrial gene replacement

Small Molecules

• EZH2 inhibitors: Being studied
• NAC and cysteine prodrugs: For glutathione deficiency
• Bypassing OXPHOS defects: Metabolic intermediates

Stem Cell Therapy

• Neural stem cells: In development
• Mesenchymal stem cells: Being studied

Mitochondrial Donation

Pre-implantation genetic diagnosis options:

• Mitochondrial replacement therapy: For mtDNA mutations
• Embryo selection: For couples at risk

Prognosis

Disease Course

[Leigh syndrome](/diseases/leigh-syndrome) typically shows:

• Progressive decline: Over months to years
• Plateau periods: May have periods of stability
• Episodic crises: Leading to stepwise deterioration
• Variable rate: Some forms slower than others

Survival

Prognosis varies by genetic form:

• Most severe: Death within 2-3 years of onset (common)
• Milder variants: Survival into adolescence or adulthood
• MT-ATP6: Often survive to adulthood with support

Factors Influencing Prognosis

• Age of onset: Earlier onset often worse
• Genetic form: Specific variant influences course
• Residual enzyme activity: Higher activity often better
• Treatment response: Ketogenic diet helps some
• Supportive care quality: Affects outcomes

Neuropathology

Characteristic Findings

The neuropathological hallmark is bilateral, symmetric necrotizing lesions:

• Spongiform changes: Vacuolization of neuropil
• Neuronal loss: Death of neurons in affected regions
• Astrocytic gliosis: Proliferation of astrocytes
• Capillary proliferation: New blood vessel formation
• Microglial activation: Inflammatory response

Affected Regions

Commonly involved:

• Basal ganglia: Putamen, caudate, globus pallidus
• Brainstem: Midbrain, pons, medulla
• Cerebellum: Particularly deep nuclei
• Spinal cord: Often involved
• Dorsal root ganglia: May be affected

Epidemiology

Prevalence

[Leigh syndrome](/diseases/leigh-syndrome) is the most common mitochondrial disorder:

• Incidence: 1 in 30,000-40,000 births
• Carrier frequency: Higher in consanguineous populations
• Accounts for: ~30% of childhood mitochondrial disease

Geographic Distribution

Cases reported worldwide with:

• Founder mutations: In specific populations
• Higher in: Regions with consanguinity

Inheritance Patterns

• Autosomal recessive: ~75% of cases
• Mitochondrial (maternal): ~20-25%
• X-linked: ~5% (mostly PDHA1)

Animal Models

Several models have been developed:

• Mouse models: Ndufs4 knockout, Surf1 knockout
• Zebrafish models: For high-throughput screening
• Drosophila models: For genetic studies
• Induced models: iPSC-derived neurons

Research Directions

Understanding Pathogenesis

Current research focuses on:

• Mechanisms of selective neuronal vulnerability
• Role of metabolic crises in lesion formation
• Neuroinflammation in disease progression
• Relationship to other mitochondrial diseases

Therapeutic Development

Key areas include:

• Gene therapy for specific genetic forms
• Small molecule approaches to bypass OXPHOS defects
• Neuroprotective agents
• Metabolic modulators

Biomarker Development

Priorities include:

• Disease progression markers
• Treatment response biomarkers
• Pre-symptomatic detection

See Also

• [Mitochondrial Disorders](/mechanisms/mitochondrial-disorders)
• [OXPHOS Defects](/mechanisms/oxidative-stress-neurodegeneration)
• [Pyruvate Dehydrogenase](/proteins/pdha1-protein)
• [Complex I Deficiency](/mechanisms/complex-i-deficiency)
• [Subacute Necrotizing Encephalomyelopathy](/mechanisms/snes)
• [Metabolic Encephalopathies](/mechanisms/metabolic-encephalopathies)
• [Lactic Acidosis](/mechanisms/lactic-acidosis)
• [Mitochondrial DNA Mutations](/mechanisms/mitochondrial-dna-mutations)

References