| Domain | High-confidence finding | Suggested ontology identifiers/terms | Evidence scope / caveat |
|---|---|---|---|
| Identity / gene | Progressive external ophthalmoplegia with mitochondrial DNA deletions, autosomal recessive 4 is a **DGUOK-related mitochondrial DNA-maintenance disorder** characterized by adult mitochondrial myopathy, variably including progressive external ophthalmoplegia and multiple skeletal-muscle mtDNA deletions. | **MONDO:0014899**; DGUOK; deoxyguanosine kinase; PEO4; autosomal-recessive progressive external ophthalmoplegia | Direct disease-level mapping and human molecular evidence. DGUOK also causes severe hepatocerebral mtDNA-depletion disease, which is broader than PEO4. (pqac-00000000, pqac-00000001) |
| Inheritance | Biallelic germline DGUOK variants cause disease through **autosomal-recessive inheritance**; carrier parents are generally asymptomatic, and recurrence risk is 25% for each pregnancy when both parents are carriers. | Autosomal recessive inheritance; germline variant; genetic carrier | Direct for DGUOK-associated disease; recurrence-risk statement follows Mendelian inheritance. Penetrance among individuals with two definitively pathogenic alleles is not quantified. (pqac-00000005, pqac-00000011) |
| Core ocular phenotypes | Principal ocular findings are slowly progressive external ophthalmoplegia or ophthalmoparesis and usually bilateral ptosis; strabismus can occur. | **HPO labels:** Progressive external ophthalmoplegia; Ptosis; Strabismus | Direct patient-level evidence, but the published DGUOK cohort was very small and some affected individuals lacked ophthalmoplegia. Reliable percentages cannot be assigned. (pqac-00000002, pqac-00000003, pqac-00000010) |
| Other muscle phenotypes | The spectrum includes mitochondrial myopathy, limb-girdle or distal weakness, neck weakness, exercise-related pain or intolerance, cramps, dysphagia, dysphonia, and occasional rhabdomyolysis. | **HPO labels:** Mitochondrial myopathy; Muscle weakness; Proximal muscle weakness; Distal muscle weakness; Exercise intolerance; Muscle cramps; Dysphagia; Dysphonia; Rhabdomyolysis | Direct adult DGUOK case-series evidence; manifestations vary substantially and may represent PEO-plus or non-PEO DGUOK phenotypes. (pqac-00000001, pqac-00000002) |
| Neurologic / systemic phenotypes | Rare reported presentations include adult lower-motor-neuron disease with mild cognitive impairment; diabetes and cataract occurred in an individual patient. Childhood liver disease may precede later myopathy in broader DGUOK deficiency. | **HPO labels:** Lower motor neuron dysfunction; Mild cognitive impairment; Diabetes mellitus; Cataract; Hepatic dysfunction | Patient-level associations do not establish typical PEO4 frequencies or direct causality for every feature. Infantile liver disease belongs to the broader DGUOK spectrum. (pqac-00000001, pqac-00000002, pqac-00000006) |
| Laboratory / pathology | Muscle may show elevated creatine kinase, myopathic EMG, ragged-red fibers, cytochrome-c-oxidase-negative fibers, severe COX deficiency, and multiple mtDNA deletions. Lactate may be normal or moderately increased. | **HPO labels:** Elevated circulating creatine kinase; Ragged-red muscle fibers; Cytochrome-c oxidase deficiency; Abnormality of mitochondrial metabolism; mitochondrial DNA deletion | Direct patient-level clinical, histologic, and molecular evidence. Normal lactate does not exclude disease. (pqac-00000002, pqac-00000003) |
| Molecular mechanism | Mitochondrial DGUOK phosphorylates deoxyguanosine and deoxyadenosine to dGMP and dAMP in the purine-nucleoside salvage pathway. Reduced activity disrupts mitochondrial dNTP supply, impairs mtDNA maintenance, and produces depletion and/or multiple deletions followed by respiratory-chain dysfunction. | **GO labels:** Deoxyguanosine kinase activity; Deoxyadenosine kinase activity; Purine deoxyribonucleoside salvage; Mitochondrial DNA replication; Mitochondrial genome maintenance; Oxidative phosphorylation | The enzyme defect and mtDNA instability are supported directly; the detailed sequence from nucleotide imbalance to selective extraocular-muscle degeneration is partly inferred. (pqac-00000006, pqac-00000009, pqac-00000011) |
| Variants / functional evidence | Reported variants include c.186C>A (p.Tyr62Ter), c.605_606delGA (p.Arg202TyrfsTer12), c.130G>A (p.Glu44Lys), c.137A>G (p.Asn46Ser), c.462T>A (p.Asn154Lys), c.509A>G (p.Gln170Arg), and c.444-11C>G. Patient muscle showed reduced protein or abnormal splicing and residual DGUOK activity of approximately **19%–45%** of control. | DGUOK sequence variant; missense variant; nonsense variant; frameshift variant; splice-region variant; loss of function | Direct functional human-muscle evidence. p.Gln170Arg alone has uncertain significance because it occurred in controls at a reported allele frequency of 1.98%; variants require phase, population, segregation, and ACMG/AMP reassessment rather than blanket pathogenic classification. (pqac-00000006, pqac-00000009, pqac-00000010) |
| Anatomy / cells / compartments | Extraocular and skeletal muscles are primary affected tissues; myofibers contain dysfunctional mitochondria and accumulated mtDNA abnormalities. Bulbar and lower-motor-neuron involvement may occur in broader presentations. DGUOK localizes to the mitochondrial matrix. | **UBERON labels:** Extraocular muscle; Skeletal muscle tissue. **CL labels:** Skeletal muscle fiber; Extraocular muscle cell; Lower motor neuron. **GO labels:** Mitochondrial matrix; Mitochondrion; Mitochondrial nucleoid | Extraocular and skeletal muscle involvement and mitochondrial localization are supported; cell-specific clonal expansion and selective vulnerability are incompletely demonstrated for DGUOK-PEO4. (pqac-00000002, pqac-00000009, pqac-00000010) |
| Diagnosis | Diagnosis integrates ptosis or ophthalmoparesis, CK and lactate testing, EMG, muscle histology, mtDNA deletion/depletion analysis in affected tissue, and demonstration of biallelic pathogenic or likely pathogenic DGUOK variants. Sequencing detects most DGUOK pathogenic variants; deletion/duplication analysis is considered if sequencing is incomplete. | Genetic testing; mitochondrial DNA deletion analysis; mitochondrial DNA copy-number analysis; muscle biopsy; electromyography; DGUOK sequencing; multigene panel; exome sequencing; genome sequencing | Direct PEO4 evidence supports muscle mtDNA analysis plus DGUOK testing; estimated yields of approximately 95% for sequence analysis and 5% for deletion/duplication analysis derive from broader DGUOK deficiency. A VUS does not establish or exclude diagnosis. (pqac-00000005, pqac-00000007, pqac-00000008) |
| Treatment | No curative or DGUOK-PEO4-specific approved therapy is established. Management is individualized and supportive: ptosis and ocular-motility management, physical and occupational therapy, swallowing and nutritional assessment, and surveillance for respiratory, cardiac, neurologic, endocrine, and hepatic complications when indicated. | **NCIT labels:** Supportive care; Physical therapy; Occupational therapy; Ptosis repair; Nutritional support; Genetic counseling | Symptomatic management is extrapolated largely from mitochondrial CPEO practice rather than controlled DGUOK-PEO4 trials. Liver transplantation pertains to selected liver-predominant DGUOK deficiency and is not treatment for isolated adult PEO4; later muscle disease can still emerge. (pqac-00000006, pqac-00000008) |
| Epidemiology | Population prevalence, incidence, carrier frequency, sex ratio, penetrance, and survival for PEO4 are unknown. Biallelic DGUOK variants accounted for **5.6%** of one selected adult cohort with multiple skeletal-muscle mtDNA deletions. More than 100 individuals with all forms of DGUOK deficiency have been reported. | Rare disease; orphan disease | The 5.6% figure is a referral-cohort proportion, not population prevalence. Broader estimates that DGUOK causes 15%–20% of mtDNA-depletion syndromes should not be applied to adult PEO4. (pqac-00000001, pqac-00000005, pqac-00000012) |
| Evidence gaps | No robust PEO4-specific natural-history cohort, validated severity scale, prevalence study, genotype–phenotype model, protective allele, environmental-risk association, epigenetic signature, single-cell or spatial dataset, faithful disease-specific animal model, prognostic biomarker, randomized treatment trial, or DGUOK-specific interventional trial was identified. | Evidence gap; natural history study; biomarker study; clinical trial; single-cell transcriptomics; disease model | Negative finding from the retrieved literature and trial searches, not proof that no unpublished or newly registered evidence exists. Most knowledge rests on a small number of human cases and broader mitochondrial-disease extrapolation. (pqac-00000005, pqac-00000006, pqac-00000012) |


*Table: High-confidence disease, phenotype, mechanism, diagnostic, and management annotations for MONDO:0014899. The table distinguishes direct PEO4 evidence from broader DGUOK-deficiency evidence and highlights major knowledge gaps.*