Complex IV Assembly Deficiency Module

Module complex_iv_assembly_deficiency 7 disorders Pathograph 4

A conserved mechanism module representing isolated cytochrome c oxidase (COX, mitochondrial respiratory chain Complex IV) deficiency. Loss of a structural subunit, an assembly/maturation factor, a copper-delivery metallochaperone, or a heme A biosynthesis enzyme prevents maturation of a functional COX holoenzyme. The resulting block in terminal electron transfer (cytochrome c to molecular oxygen) and proton pumping collapses oxidative ATP synthesis, forcing anaerobic glycolysis (lactic acidosis) and producing energy failure in high-demand tissues (brain, heart, skeletal muscle, liver). The module captures the gene-agnostic core shared across the many nuclear and mtDNA causes of isolated COX deficiency; conforming disorder entries substitute the specific gene, the affected assembly sub-step, and the organ/tissue tropism while preserving this causal chain.

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Pathophysiology Nodes

4 shared nodes are defined in this module.

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Cell Types

No cell types are annotated for this module.

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Biological Processes

Notes

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 lacks a non-obsolete pan-form Complex IV grouping class, so the umbrella disease entry that conforms to this module uses MONDO:0033885 (nuclear-type) as the closest available term.

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Used By Disorder Entries

COA8-Related COX Deficiency via COA8 Loss and Defective Complex IV Assembly → Complex IV Biogenesis Failure , Impaired Terminal Electron Transfer and ATP Synthesis

COX10-Related COX Deficiency via COX10 Loss and Defective Heme A Biosynthesis → Complex IV Biogenesis Failure , Impaired Terminal Electron Transfer and ATP Synthesis

COX15-Related COX Deficiency via COX15 Loss and Defective Heme A Biosynthesis → Complex IV Biogenesis Failure , Impaired Terminal Electron Transfer and ATP Synthesis

COX18-Related COX Deficiency via COX18 Loss and Defective COX2 Maturation → Complex IV Biogenesis Failure , Impaired Terminal Electron Transfer and ATP Synthesis

SCO1-Related COX Deficiency via SCO1 Loss and Defective Copper Delivery to COX → Complex IV Biogenesis Failure , Impaired Terminal Electron Transfer and ATP Synthesis

SCO2-Related Fatal Infantile Cardioencephalomyopathy via SCO2 Loss and Defective Copper Delivery to COX → Complex IV Biogenesis Failure , Impaired Terminal Electron Transfer and ATP Synthesis

SURF1-Related Leigh Syndrome via SURF1 Loss and Defective Complex IV Assembly → Complex IV Biogenesis Failure , Impaired Terminal Electron Transfer and ATP Synthesis , Lactic Acidosis from Reduced Oxidative Metabolism → Lactic Acidosis and Metabolic Decompensation

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Pathograph

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Pathophysiology

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.

mitochondrial respiratory chain complex IV assembly link DECREASED copper ion transport link DECREASED heme A biosynthetic process link DECREASED

Used by disorders

COA8-Related COX Deficiency as COA8 Loss and Defective Complex IV Assembly

COX10-Related COX Deficiency as COX10 Loss and Defective Heme A Biosynthesis

COX15-Related COX Deficiency as COX15 Loss and Defective Heme A Biosynthesis

COX18-Related COX Deficiency as COX18 Loss and Defective COX2 Maturation

SCO1-Related COX Deficiency as SCO1 Loss and Defective Copper Delivery to COX

SCO2-Related Fatal Infantile Cardioencephalomyopathy as SCO2 Loss and Defective Copper Delivery to COX

SURF1-Related Leigh Syndrome as SURF1 Loss and Defective Complex IV Assembly

Downstream

Impaired Terminal Electron Transfer and ATP Synthesis Without a mature holoenzyme, the terminal step of the respiratory chain cannot proceed.

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.

mitochondrial electron transport, cytochrome c to oxygen link DECREASED ATP synthesis coupled electron transport link DECREASED aerobic respiration link DECREASED

Used by disorders

COA8-Related COX Deficiency

COX10-Related COX Deficiency

COX15-Related COX Deficiency

COX18-Related COX Deficiency

SCO1-Related COX Deficiency

SCO2-Related Fatal Infantile Cardioencephalomyopathy

SURF1-Related Leigh Syndrome

Downstream

Lactic Acidosis and Metabolic Decompensation Failure of oxidative ATP synthesis forces a shift to anaerobic glycolysis.
High-Energy Tissue Dysfunction The bioenergetic deficit is most damaging in tissues with high oxidative demand.

Lactic Acidosis and Metabolic Decompensation

consequence

The shift to anaerobic glycolysis increases pyruvate-to-lactate conversion, elevating lactate in blood and cerebrospinal fluid; metabolic stressors can precipitate acute decompensation.

lactate biosynthetic process link INCREASED

Used by disorders

SURF1-Related Leigh Syndrome as Lactic Acidosis from Reduced Oxidative Metabolism

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.

aerobic respiration link DECREASED