This is a mechanism module, not a specific disease. Disorder entries reference individual nodes via conforms_to (e.g., "complex_iv_assembly_deficiency#Impaired Terminal Electron Transfer and ATP Synthesis"). The module defines the expected pathophysiology structure; conforming nodes should include the corresponding biological processes and causal edges, specialized to their genetic and tissue context. Sub-step substitutions: copper delivery to the CuA/CuB centers (SCO1, SCO2, COX17, COX11, COA6); heme A biosynthesis (COX10 heme O synthase, COX15 heme A synthase); COX2 maturation/insertion (COX18); early/general assembly (SURF1, COA8, PET100, PET117); structural subunits (MT-CO1, MT-CO2, MT-CO3, NDUFA4). Tissue substitutions: brain/Leigh (SURF1), heart (SCO2), liver/endocrine (SCO1), skeletal muscle (COA8).
MONDO anchoring (verified 2026-08-01, see issue #3544): the nuclear-encoded arm of this module is represented in dismech by the Grouping "Mitochondrial Complex IV Deficiency", which maps to MONDO:0033885 (mitochondrial complex IV deficiency, nuclear-type) with skos:exactMatch. There is no separate umbrella *disease* entry for the module. Note that MONDO:0033885 is labelled nuclear-type but is asserted directly under MONDO:0000066 and carries the pan-form umbrella cross-references (OMIMPS:220110, Orphanet:254905 "isolated COX deficiency", MESH:D030401, NCIT:C98910, DOID:3762, GARD:0000048), because MONDO has no pan-form Complex IV parent class of its own (the historical umbrella MONDO:0009068 is obsolete) and no "mitochondrial type" sibling. Complex I is modelled with the full triple that Complex IV lacks: MONDO:0100133 (pan-form) over MONDO:0100223 (nuclear type) and MONDO:0100134 (mitochondrial type). Until the Complex IV counterparts exist upstream, the mtDNA-encoded structural subunit causes named above (MT-CO1, MT-CO2, MT-CO3) have no MONDO class to anchor a disorder leaf to; the New Term Requests are collected in issue #3544.
Complex IV Biogenesis Failure
trigger
Pathogenic variants in a Complex IV structural subunit, assembly factor, copper-delivery metallochaperone, or heme A biosynthesis enzyme prevent correct assembly and cofactor insertion, so a mature, catalytically competent COX holoenzyme cannot form. More than 30 genes converge on this step.
Downstream
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Impaired Terminal Electron Transfer and ATP Synthesis
Without a mature holoenzyme, the terminal step of the respiratory chain cannot proceed.
Show evidence (3 references)
"COX biosynthesis requires numerous assembly factors that do not form part of the final complex but participate in prosthetic group synthesis and metal delivery in addition to membrane insertion and maturation of COX subunits."
Describes the assembly-factor-dependent biogenesis step whose failure defines this node.
"More than 30 genes have been linked to COX deficiency"
Documents the large number of genes (subunits, assembly factors, cofactor machinery) that converge on this biogenesis-failure step.
"Mutations in copper transporters and chaperones that perturb mitochondrial copper homeostasis result in fatal genetic disorders."
Supports the copper-delivery sub-step (SCO1/SCO2 etc.) of Complex IV biogenesis failure.
Impaired Terminal Electron Transfer and ATP Synthesis
central effector
Loss of functional COX blocks transfer of electrons from reduced cytochrome c to molecular oxygen and abolishes the associated proton pumping across the inner mitochondrial membrane, collapsing the proton-motive force and oxidative ATP synthesis.
Downstream
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Lactic Acidosis and Metabolic Decompensation
Failure of oxidative ATP synthesis forces a shift to anaerobic glycolysis.
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High-Energy Tissue Dysfunction
The bioenergetic deficit is most damaging in tissues with high oxidative demand.
Show evidence (1 reference)
"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."
Defines the terminal electron-transfer and proton-pumping function that is lost when COX is deficient.
High-Energy Tissue Dysfunction
consequence
Energy failure manifests in high-demand tissues, producing the organ-specific phenotypes of COX deficiency: encephalopathy/Leigh syndrome (brain), cardiomyopathy (heart), myopathy (skeletal muscle), and hepatopathy (liver). Conforming disorder entries substitute the dominant tissue and its cell types.
Show evidence (2 references)
"COX deficiency results in severe muscle weakness, heart, liver, and kidney disorders, as well as brain damage in infants and adolescents"
Summarizes the multi-organ, high-energy-tissue dysfunction produced by COX deficiency.
"affect the whole organism or specific tissues"
Supports the variable, tissue-specific expression of the bioenergetic deficit that conforming entries specialize.