SURF1-Related Leigh Syndrome

name: SURF1-Related Leigh Syndrome
category: Mendelian
creation_date: "2026-05-30T00:00:00Z"
synonyms:
- SURF1 deficiency
- Mitochondrial complex IV deficiency, nuclear type 1
- MC4DN1
- SURF1-related cytochrome c oxidase deficiency
description: >
  SURF1-related Leigh syndrome is the most common nuclear cause of isolated
  cytochrome c oxidase (COX, Complex IV) deficiency. Biallelic loss-of-function
  variants in SURF1, which encodes an early COX assembly factor, abolish
  maturation of the Complex IV holoenzyme. Affected children typically present
  in infancy with subacute necrotizing encephalomyelopathy (Leigh syndrome):
  psychomotor regression, brainstem and basal ganglia lesions on MRI, hypotonia,
  and lactic acidosis. It is the prototypical assembly-factor COX deficiency and
  conforms to the conserved Complex IV assembly deficiency mechanism.
disease_term:
  preferred_term: SURF1-related Leigh syndrome
  term:
    id: MONDO:0700250
    label: mitochondrial complex IV deficiency, nuclear type 1
parents:
- Leigh Syndrome
- Mitochondrial Disease
references:
- reference: PMID:26425749
  title: "Nuclear Gene-Encoded Leigh Syndrome Spectrum Overview."
  tags:
  - GeneReviews
prevalence:
- notes: >
    In Leigh syndrome cohorts, SURF1 is the single most common identifiable
    cause; a founder SURF1 variant is widespread in Eastern Europe.
  evidence:
  - reference: PMID:36675121
    reference_title: "Leigh syndrome: spectrum of molecular defects and clinical features in Russia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The most common cause of LS in Russian patients are pathogenic variants in the SURF1 gene (44.3% of patients).
    explanation: SURF1 was the single most common cause of Leigh syndrome in a 219-patient cohort.
pathophysiology:
- name: SURF1 Loss and Defective Complex IV Assembly
  conforms_to: "complex_iv_assembly_deficiency#Complex IV Biogenesis Failure"
  description: >
    Biallelic SURF1 loss-of-function variants remove an early COX assembly
    factor, preventing maturation of the Complex IV holoenzyme.
  biological_processes:
  - preferred_term: mitochondrial respiratory chain complex IV assembly
    term:
      id: GO:0033617
      label: mitochondrial respiratory chain complex IV assembly
    modifier: DECREASED
  evidence:
  - reference: PMID:39632678
    reference_title: "SURF1 Deficiency: Expanding on Disease Phenotype and Assessing Disease Burden by Describing Clinical and Biochemical Phenotype."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: SURF1 deficiency leads to dysfunction of Cytochrome C Oxidase (COX) activity, which is crucial for mitochondrial oxidative phosphorylation.
    explanation: Confirms SURF1 loss causes COX (Complex IV) dysfunction, the basis of this assembly defect.
  downstream:
  - target: Impaired Terminal Electron Transfer and ATP Synthesis
    causal_link_type: DIRECT
    description: Failure to assemble a mature holoenzyme abolishes terminal electron transfer.
- name: Impaired Terminal Electron Transfer and ATP Synthesis
  conforms_to: "complex_iv_assembly_deficiency#Impaired Terminal Electron Transfer and ATP Synthesis"
  description: >
    Loss of functional COX blocks transfer of electrons from cytochrome c to
    oxygen and proton pumping, collapsing oxidative ATP synthesis.
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  biological_processes:
  - preferred_term: mitochondrial electron transport, cytochrome c to oxygen
    term:
      id: GO:0006123
      label: mitochondrial electron transport, cytochrome c to oxygen
    modifier: DECREASED
  - preferred_term: ATP synthesis coupled electron transport
    term:
      id: GO:0042775
      label: mitochondrial ATP synthesis coupled electron transport
    modifier: DECREASED
  evidence:
  - reference: PMID:10545952
    reference_title: "Fatal infantile cardioencephalomyopathy with COX deficiency and mutations in SCO2, a COX assembly gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Mammalian cytochrome c oxidase (COX) catalyses the transfer of reducing equivalents from cytochrome c to molecular oxygen and pumps protons across the inner mitochondrial membrane.
    explanation: Defines the terminal electron-transfer and proton-pumping function lost in SURF1-related COX deficiency.
  downstream:
  - target: Lactic Acidosis from Reduced Oxidative Metabolism
    causal_link_type: DIRECT
    description: Failure of oxidative ATP synthesis forces anaerobic glycolysis.
  - target: Encephalopathy
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Energy deficit in brainstem and basal ganglia produces the necrotizing Leigh lesions.
- name: Lactic Acidosis from Reduced Oxidative Metabolism
  conforms_to: "complex_iv_assembly_deficiency#Lactic Acidosis and Metabolic Decompensation"
  description: >
    Impaired oxidative phosphorylation increases pyruvate-to-lactate conversion,
    producing lactic acidosis.
  biological_processes:
  - preferred_term: lactate biosynthetic process
    term:
      id: GO:0019249
      label: lactate biosynthetic process
    modifier: INCREASED
  downstream:
  - target: Lactic acidosis
    causal_link_type: DIRECT
    description: Increased lactate production manifests as lactic acidosis in blood and CSF.
phenotypes:
- name: Developmental regression
  description: Loss of acquired motor and developmental milestones (motor regression in 92.3% of a SURF1 cohort).
  phenotype_term:
    preferred_term: Developmental regression
    term:
      id: HP:0002376
      label: Developmental regression
  evidence:
  - reference: PMID:39632678
    reference_title: "SURF1 Deficiency: Expanding on Disease Phenotype and Assessing Disease Burden by Describing Clinical and Biochemical Phenotype."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Common clinical features included brainstem abnormalities (93.3%), motor regression (92.3%)
    explanation: Motor regression occurred in 92.3% of SURF1 Leigh syndrome patients.
- name: Delayed growth and development
  description: Delayed growth/development, reported in 35.7% of a SURF1 cohort and clinically distinct from developmental regression (failure to reach milestones rather than loss of acquired ones).
  phenotype_term:
    preferred_term: Delayed growth and development
    term:
      id: HP:0001263
      label: Global developmental delay
  evidence:
  - reference: PMID:39632678
    reference_title: "SURF1 Deficiency: Expanding on Disease Phenotype and Assessing Disease Burden by Describing Clinical and Biochemical Phenotype."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: delayed growth/development (35.7%)
    explanation: Delayed growth/development occurred in 35.7% of SURF1 Leigh syndrome patients, distinct from motor regression.
- name: Abnormal brainstem morphology
  description: Brainstem lesions on MRI, present in 93.3% of a SURF1 cohort.
  phenotype_term:
    preferred_term: Brainstem abnormalities
    term:
      id: HP:0002363
      label: Abnormal brainstem morphology
  evidence:
  - reference: PMID:39632678
    reference_title: "SURF1 Deficiency: Expanding on Disease Phenotype and Assessing Disease Burden by Describing Clinical and Biochemical Phenotype."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Common clinical features included brainstem abnormalities (93.3%), motor regression (92.3%)
    explanation: Brainstem abnormalities occurred in 93.3% of SURF1 Leigh syndrome patients.
- name: Lactic acidosis
  description: Elevated blood and CSF lactate due to impaired oxidative metabolism.
  phenotype_term:
    preferred_term: Lactic acidosis
    term:
      id: HP:0003128
      label: Lactic acidosis
  evidence:
  - reference: PMID:20301352
    reference_title: "Mitochondrial DNA-Associated Leigh Syndrome Spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Decompensation (often with elevated lactate levels in blood and/or cerebrospinal fluid) is typically associated with developmental delay and/or regression.
    explanation: Elevated blood/CSF lactate is characteristic of the Leigh syndrome spectrum.
- name: Encephalopathy
  description: Subacute necrotizing encephalopathy with basal ganglia and brainstem involvement.
  phenotype_term:
    preferred_term: Encephalopathy
    term:
      id: HP:0001298
      label: Encephalopathy
  evidence:
  - reference: PMID:39632678
    reference_title: "SURF1 Deficiency: Expanding on Disease Phenotype and Assessing Disease Burden by Describing Clinical and Biochemical Phenotype."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Leigh syndrome, a severe neurological disorder is commonly caused by homozygous or bi-allelic pathogenic variants in the SURF1 gene.
    explanation: SURF1 variants cause Leigh syndrome, a severe neurological disorder (subacute necrotizing encephalopathy).
- name: Muscular hypotonia
  description: Generalized low muscle tone, common in infantile Leigh syndrome.
  phenotype_term:
    preferred_term: Muscular hypotonia
    term:
      id: HP:0001252
      label: Hypotonia
  evidence:
  - reference: PMID:20301352
    reference_title: "Mitochondrial DNA-Associated Leigh Syndrome Spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Neurologic features include hypotonia, spasticity, seizures, movement disorders, cerebellar ataxia, and peripheral neuropathy.
    explanation: Hypotonia is a core neurologic feature of the Leigh syndrome spectrum.
biochemical:
- name: Reduced cytochrome c oxidase (Complex IV) enzyme activity
  presence: DECREASED
  context: >
    Markedly reduced COX activity in patient fibroblasts and tissues is the
    defining biochemical feature; in a SURF1 cohort residual activity averaged
    32% of controls.
  evidence:
  - reference: PMID:39632678
    reference_title: "SURF1 Deficiency: Expanding on Disease Phenotype and Assessing Disease Burden by Describing Clinical and Biochemical Phenotype."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: Patient COX activity was at most 50% of controls, averaging 32%
    explanation: Quantifies reduced COX (Complex IV) activity in SURF1-deficient patient fibroblasts.
  - reference: PMID:38154062
    reference_title: "Cytochrome c oxidase deficiency detection in human fibroblasts using scanning electrochemical microscopy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: This study demonstrates the applicability of scanning electrochemical microscopy to quantify COX activity in living human fibroblast cells.
    explanation: Emerging less-invasive method to quantify reduced COX activity in patient fibroblasts.
    images:
    - Cytochrome_c_Oxidase_Deficiency-deep-research-falcon_artifacts/image-1.png
genetic:
- name: SURF1 pathogenic variants causing Leigh syndrome
  gene_term:
    preferred_term: SURF1
    term:
      id: hgnc:11474
      label: SURF1
  inheritance:
  - name: Autosomal recessive
    evidence:
    - reference: PMID:39632678
      reference_title: "SURF1 Deficiency: Expanding on Disease Phenotype and Assessing Disease Burden by Describing Clinical and Biochemical Phenotype."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Leigh syndrome, a severe neurological disorder is commonly caused by homozygous or bi-allelic pathogenic variants in the SURF1 gene.
      explanation: Documents biallelic (autosomal recessive) SURF1 variants as the cause of SURF1 Leigh syndrome.
  variants:
  - name: SURF1 c.845_846delCT founder variant
    description: >
      A recurrent SURF1 frameshift variant widespread in Eastern Europe,
      accounting for the majority of mutant alleles in a Russian cohort.
    gene:
      preferred_term: SURF1
      term:
        id: hgnc:11474
        label: SURF1
    evidence:
    - reference: PMID:36675121
      reference_title: "Leigh syndrome: spectrum of molecular defects and clinical features in Russia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The most frequent pathogenic variant is c.845_846delCT (66.0% of mutant alleles; 128/192), which is also widespread in Eastern Europe."
      explanation: Documents the SURF1 c.845_846delCT founder variant and its frequency.
  features: >
    Biallelic loss-of-function variants in SURF1 (an early COX assembly factor)
    are the most common nuclear cause of isolated COX deficiency and Leigh
    syndrome.
treatments:
- name: Supportive and Metabolic Care
  description: >
    No curative therapy exists; management is supportive, including treatment of
    lactic acidosis, anti-seizure medication, nutritional support, and avoidance
    of metabolic decompensation.
  treatment_term:
    preferred_term: supportive care
    term:
      id: MAXO:0000950
      label: supportive care
  evidence:
  - reference: PMID:20301352
    reference_title: "Mitochondrial DNA-Associated Leigh Syndrome Spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Treatment is supportive."
    explanation: Management of the Leigh syndrome spectrum is supportive.