| Gene / factor | Functional role in complex IV biogenesis | Typical clinical presentation(s) mentioned in available evidence | Inheritance / notes | Key citations |
|---|---|---|---|---|
| **SURF1** | Assembly factor; proposed heme A transfer/chaperoning to apoCOX1; a common cause of COX-specific Leigh syndrome | Classical **Leigh syndrome** / Leigh spectrum; early infantile neurodegeneration; often complex IV deficiency; hypertrichosis reported in SURF1-associated Leigh syndrome in one cohort | Nuclear gene; inherited forms of COX deficiency are typically AR when due to nuclear assembly genes; strong founder effect for **c.845_846delCT** in Russian cohort | (pqac-00000000, pqac-00000004, pqac-00000023) |
| **SCO1** | Copper-delivery / CuA-site assembly factor for COX2; contains copper-binding motif; part of metallochaperone pathway with COX17/SCO2/COA6 | Historically severe infantile **encephalopathy, hepatopathy, lactic acidosis, cardiomyopathy**; expanded 2024 phenotype includes **developmental and epileptic encephalopathy** with **progressive hypopituitarism** | Nuclear gene; **MC4DN4** due to SCO1 variants; reported as autosomal recessive COX deficiency subtype | (pqac-00000016, pqac-00000019, pqac-00000021, pqac-00000022) |
| **SCO2** | Copper delivery and disulfide-exchange in **CuA-site assembly** on COX2; works with COX17/SCO1/COA6 | **Fatal infantile cardioencephalomyopathy**, hypertrophic cardiomyopathy, hypotonia; can resemble spinal muscular atrophy or axonal neuropathy/CMT; variable severity | Nuclear gene; commonly AR; **E140K** highlighted as recurrent/common pathogenic allele | (pqac-00000016, pqac-00000018, pqac-00000019, pqac-00000022) |
| **COX10** | **Heme O synthase** in heme A biosynthesis (heme B → heme O); required upstream of COX1 hemylation | **Isolated COX deficiency**, **Leigh syndrome**, cardiomyopathy; included among LS genes detected in 2023 cohort | Nuclear gene; AR disease mechanism typical for nuclear COX assembly defects | (pqac-00000002, pqac-00000017, pqac-00000023, pqac-00000004) |
| **COX15** | **Heme A synthase** (heme O → heme A); oligomerization/function linked to PET117 and SURF1-dependent assembly steps | **Isolated COX deficiency**, **Leigh syndrome**, cardiomyopathy, anemia, sensorineural hearing loss | Nuclear gene; AR disease mechanism typical | (pqac-00000002, pqac-00000017, pqac-00000023) |
| **COA6** | Accessory copper-handling / thiol-reductase factor for **CuA metalation**; interacts with SCO proteins and COX2 | Evidence supports COX deficiency with impaired respiration; copper supplementation rescues yeast/model defects; specific human phenotypes not detailed in retrieved excerpts | Nuclear gene; assembly-factor defect | (pqac-00000003, pqac-00000017, pqac-00000018) |
| **COA8** | COX assembly/stability factor (loss-of-function causes isolated complex IV deficiency) | Classically **cavitating leukoencephalopathy** with biphasic course (acute regression then stabilization/improvement); newer familial report expands to **prominent myopathy**, ptosis, hearing loss, neuropathy, cognitive issues | Nuclear gene; biallelic loss-of-function reported | (pqac-00000005) |
| **COX18** | Required for **MT-CO2/COX2 maturation** and complex IV assembly | **Neonatal encephalo-cardio-myopathy** with hypertrophic cardiomyopathy, infantile myopathy, and **axonal sensory neuropathy** | Nuclear gene; biallelic pathogenic variant reported in 2023 case | (pqac-00000006) |
| **COX17** | Copper metallochaperone upstream of SCO1/SCO2/COX11; hands copper to CuA/CuB assembly pathway | No specific standalone phenotype detailed in retrieved excerpts; implicated as candidate/established copper-delivery factor in inherited COX deficiency pathway | Nuclear gene / pathway factor | (pqac-00000016, pqac-00000017, pqac-00000022) |
| **COX11** | Copper delivery to **COX1 CuB site** | COX11 mutations noted in recent literature reviewed; specific phenotype details not expanded in retrieved excerpts | Nuclear gene / pathway factor | (pqac-00000000, pqac-00000017) |
| **COX19** | Copper-handling / assembly accessory factor in COX biogenesis | Specific phenotype not detailed in retrieved excerpts; highlighted as part of copper-delivery/assembly network and candidate in unexplained COX deficiency | Nuclear gene / pathway factor | (pqac-00000000, pqac-00000001) |
| **PET100** | Assembly factor associated with specific COX subassembly complexes | Complex IV deficiency; specific phenotype not detailed in retrieved excerpts | Nuclear gene; assembly-factor defect | (pqac-00000022) |
| **PET117** | Assembly factor linking **COX15 oligomerization/heme A biosynthesis** to COX assembly; also supports COX1 synthesis regulation | **Isolated COX deficiency** reported in affected siblings; broader phenotype details not expanded in retrieved excerpts | Nuclear gene; assembly-factor defect | (pqac-00000000, pqac-00000002) |
| **LRPPRC** | Stabilizes mitochondrial mRNA and supports early **COX1 module** / mitochondrial translation | **French-Canadian Leigh syndrome (LSFC)** with complex IV involvement | Nuclear gene; founder disease in Quebec population noted in broader literature, though not quantified in retrieved excerpts | (pqac-00000017, pqac-00000007) |
| **NDUFA4** | Structural subunit associated with **complex IV** function | **Leigh syndrome** with psychomotor delay, white matter/brainstem changes, lactic and phytanic acidosis in reported child with biallelic deletion | Nuclear gene; ultra-rare cause of mitochondrial complex IV deficiency nuclear type 21 | (pqac-00000004) |


*Table: This table summarizes key genes and assembly pathways implicated in inherited cytochrome c oxidase deficiency using only the retrieved evidence. It highlights how defects in heme A synthesis, copper delivery, and COX1/COX2 assembly map to characteristic phenotypes such as Leigh syndrome, cardioencephalomyopathy, cavitating leukoencephalopathy, and myopathy.*