Severe X-linked Mitochondrial Encephalomyopathy

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Classifications

Harrison's Part

Mechanistic Nosology

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Mappings

ICD-10-CM

ICD10CM:E88.49 Other mitochondrial metabolism disorders

ICD-10-CM has no code specific to AIFM1-related disease or to combined oxidative phosphorylation deficiency. E88.49 is the residual code in the E88.4 mitochondrial metabolism block and is therefore a broad match.

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Inheritance

1

X-linked recessive HP:0001419

Affected individuals are hemizygous males. In the founding family the two affected boys were born to monozygotic twin sisters by unrelated fathers, and later variants were shown to be inherited from asymptomatic carrier mothers or to arise de novo. A heterozygous female can be affected when X inactivation is extremely skewed: a girl carrying p.Pro169Leu with 98:2 skewing had infantile encephalomyopathy and cardiomyopathy, the same allele that killed three males of another family.

X-linked recessive inheritance

Show evidence (3 references)

PMID:20362274 SUPPORT Human Clinical

"These patients were born from monozygotic twin sisters and unrelated fathers, suggesting an X-linked trait."

The founding pedigree pattern points to X-linked transmission through the twin mothers.

PMID:25934856 SUPPORT Human Clinical

"The mother, heterozygous for the mutation, was asymptomatic"

An asymptomatic heterozygous carrier mother transmitted the variant to an affected son, as expected for X-linked recessive inheritance.

PMID:42329587 SUPPORT Human Clinical

"Genetic testing identified a heterozygous AIFM1 variant, c.506C > T (p.Pro169Leu), with extremely skewed X-inactivation (98:2) in a female."

Documents a manifesting heterozygous female with extreme X-inactivation skewing, the exception to male-only expression.

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Pathophysiology

8

Unstable AIF Protein

Disease alleles lower the amount of functional AIF in mitochondria. The founding p.Arg201del allele decreases the stability of both mitochondrial and soluble AIF; missense and targeting-sequence alleles (p.Gly262Ser, p.Phe2Ser, p.Pro169Leu) give a marked reduction of AIF on immunoblot of patient fibroblasts. The variants sit in or near the FAD- and NADH-binding domains, which is the rationale for trying riboflavin to stabilize the flavin-bound protein.

AIFM1 hgnc:8768

Genetic context AIFM1 hgnc:8768 variant_origin: GERMLINE

Hemizygous germline AIFM1 variants, inherited from a carrier mother or arising de novo.

FAD binding GO:0050660

mitochondrial intermembrane space GO:0005758

Downstream

Impaired CHCHD4 Mitochondrial Import Reduced AIF lowers mitochondrial import of CHCHD4, the intermembrane space import receptor.

Enhanced AIF-Dependent Parthanatos The founding allele also increases the DNA-binding affinity of soluble AIF, the prerequisite for its nuclear pro-death action.

Show evidence (3 references)

PMID:20362274 SUPPORT In Vitro

"We conclude that AIF(R201 del) is an unstable mutant variant associated with increased parthanatos-linked cell death."

The founding allele produces an unstable AIF protein.

PMID:25934856 SUPPORT In Vitro

"Western blot analysis on patient fibroblasts showed strong reduction in AIF amount (figure, G), indicating instability of the mutant protein"

A missense allele (p.Gly262Ser) also lowers AIF protein in patient fibroblasts.

PMID:37644805 SUPPORT In Vitro

"Functional studies on cultured fibroblast showed a clear reduction in AIFM1 protein amount and defective activities of respiratory chain complexes I, III and IV."

A targeting-sequence allele (p.Phe2Ser) reduces AIF protein in patient fibroblasts.

Impaired CHCHD4 Mitochondrial Import

AIF binds CHCHD4 (MIA40) and is needed both to import it and to keep it in a form that engages its substrates in the intermembrane space disulfide relay. AIF deficiency lowers CHCHD4 protein in patient fibroblasts and in harlequin mouse tissue, without lowering its mRNA, and forcing CHCHD4 back into mitochondria restores respiration in AIF-deficient cells.

protein import into mitochondrial intermembrane space GO:0045041 ↓ DECREASED

mitochondrial intermembrane space GO:0005758

Downstream

Defective Respiratory Chain Complex Assembly Without functional CHCHD4, intermembrane space import of complex I subunits such as NDUFS5 fails and respiratory complexes are lost.

Show evidence (2 references)

PMID:26004228 SUPPORT In Vitro

"CHCHD4 depletion sufficed to induce a respiratory defect that mimicked that observed in AIF-deficient cells."

Loss of CHCHD4 alone reproduces the AIF-deficient respiratory defect.

PMID:26158520 SUPPORT In Vitro

"Here we show that AIF physically interacts with the oxidoreductase CHCHD4/MIA40."

Establishes the physical AIF-CHCHD4 interaction.

Defective Respiratory Chain Complex Assembly

Complex I assembly stalls when NDUFS5 is not imported, and AIF-deficient human and mouse cells contain less assembled complex I and fewer of its subunits. Other complexes (III and IV) are also reduced in patient cells, with a pattern that varies by allele and tissue.

mitochondrial respiratory chain complex I assembly GO:0032981 ↓ DECREASED mitochondrial respiratory chain complex assembly GO:0033108 ↓ DECREASED

Downstream

Combined Oxidative Phosphorylation Deficiency Fewer assembled respiratory complexes lower electron transport and ATP synthesis.

Show evidence (2 references)

PMID:35859387 SUPPORT In Vitro

"Lack of mitochondrial NDUFS5 in turn results in stalling of complex I assembly."

Mechanism by which AIF loss stalls complex I assembly.

PMID:15526035 SUPPORT In Vitro

"Although AIF itself is not a part of complex I, AIF-deficient cells exhibit a reduced content of complex I and of its components"

AIF is required for normal complex I content.

Combined Oxidative Phosphorylation Deficiency

Patient fibroblasts and muscle show reduced activities of respiratory chain complexes. The pattern varies: complexes III and IV with preserved complex I in the founding fibroblasts; complexes I and IV in muscle of a fatal infantile case and in the ventriculomegaly family; complexes I, III and IV in neonatal-onset fibroblasts; profound complex IV loss in muscle of the p.Pro169Leu family. Re-expressing wild-type AIF restores the activities, so the deficiency is a direct consequence of the variant. The downstream cost is an energy deficit with lactate accumulation.

skeletal muscle fiber CL:0008002 fibroblast CL:0000057

oxidative phosphorylation GO:0006119 ↓ DECREASED

Animal models

Harlequin (Hq) mouse Mouse recapitulates Reduced AIF lowers OXPHOS and complex I subunits in brain and retina.

Downstream

Decreased activity of mitochondrial complex IV

Decreased activity of mitochondrial complex III

Decreased activity of mitochondrial complex I

Lactic acidosis Impaired respiration forces glycolytic ATP generation with lactate overproduction.

Increased CSF lactate

Elevated brain lactate level by MRS

Progressive Neuronal Degeneration Energy failure in neurons, the tissue most dependent on oxidative phosphorylation, precedes neuronal loss in the AIF-deficient mouse.

Mitochondrial Myopathy

Cardiomyocyte Energy Failure

Show evidence (4 references)

PMID:20362274 SUPPORT In Vitro

"Fibroblasts from both showed reduction of respiratory chain (RC) cIII and cIV, but not of cI activities."

Combined respiratory chain deficiency in the founding patients' fibroblasts.

PMID:20362274 SUPPORT In Vitro

"In AIF(R201 del) fibroblasts, staurosporine-induced parthanatos was markedly increased, whereas re-expression of AIF(wt) induced recovery of RC activities."

Wild-type AIF rescues the respiratory chain defect, placing it downstream of the variant.

PMID:22019070 SUPPORT Human Clinical

"Plasma and CSF lactate levels were normal, but the activities of mitochondrial complex I and IV were markedly decreased."

Complex I and IV deficiency in a second family, notable for normal lactate.

+ 1 more reference

Enhanced AIF-Dependent Parthanatos

Separately from the OXPHOS defect, patient cells are primed for caspase-independent, AIF-mediated cell death (parthanatos). Staurosporine induces more parthanatos in p.Arg201del fibroblasts, patient muscle shows many TUNEL-positive, caspase 3-negative nuclei, and p.Pro169Leu fibroblasts are more sensitive to staurosporine and show more nuclear condensation under galactose. How much this branch contributes to neuronal loss in patients, as opposed to muscle, has not been measured.

skeletal muscle fiber CL:0008002

parthanatos (caspase-independent AIF-mediated programmed cell death) GO:0012501 ↑ INCREASED

Downstream

Mitochondrial Myopathy Parthanatos-type nuclei are seen in patient muscle, the tissue where this branch has been observed directly.

Progressive Neuronal Degeneration Inferred by extension from muscle and fibroblasts; parthanatos has not been demonstrated in patient brain.

Show evidence (2 references)

PMID:20362274 SUPPORT In Vitro

"In AIF(R201 del) fibroblasts, staurosporine-induced parthanatos was markedly increased"

Patient fibroblasts show increased parthanatos.

PMID:34117073 SUPPORT In Vitro

"Functional studies carried out on fibroblasts from the proband demonstrated reduced steady state levels of the AIFM1 protein, decreased Complex I subunit abundance, elevated sensitivity to the apoptosis inducer staurosporine, and increased nuclear condensation when grown in galactose-containing media."

A second allele also increases cell-death sensitivity in patient fibroblasts.

Progressive Neuronal Degeneration

Neurons of the cortex, basal ganglia, thalamus, cerebellum, brainstem, lower motor neurons and peripheral axons degenerate. Autopsy of a fatal infantile case showed mitochondrial encephalopathy with profound occipital cortical neuronal loss, gliosis and axonal degeneration in peripheral nerve; denervation in muscle reflects motor neuron and axonal loss. In the harlequin mouse, which keeps about 20% of normal AIF, mitochondria degenerate before neurons do, and neurodegeneration spreads from the cerebellum to the thalamus, striatum and cortex.

neuron CL:0000540 motor neuron CL:0000100

Animal models

Harlequin (Hq) mouse Mouse partially recapitulates Progressive, multifocal neurodegeneration preceded by mitochondrial degeneration.

Downstream

Encephalopathy

Global developmental delay

Developmental regression

Seizure

Abnormality of extrapyramidal motor function

Bilateral striatal necrosis

Abnormal basal ganglia MRI signal intensity

Cerebral atrophy

Cerebral edema

Diffuse white matter abnormality

Multicystic encephalomalacia

EEG burst suppression

Ventriculomegaly

Microcephaly

Peripheral axonal neuropathy

EMG and muscle biopsy denervation

Hypotonia

Sensorineural hearing impairment

Ataxia

Cerebellar atrophy

External ophthalmoplegia

Dysphagia

Show evidence (5 references)

PMID:28299359 SUPPORT Human Clinical

"Autopsy, at the age of 4 mo, revealed features of mitochondrial encephalopathy, myopathy, and involvement of peripheral nerves with axonal degeneration."

Human autopsy evidence of central and peripheral neurodegeneration.

PMID:28299359 SUPPORT Human Clinical

"the occipital cortex showed profound neuronal loss"

Documents cortical neuronal loss at autopsy.

PMID:26173962 SUPPORT Human Clinical

"Our patients manifested a phenotype that included signs of both cortical and motor neuron involvement."

Cortical and lower motor neuron involvement in two cousins with early-onset encephalopathy.

+ 2 more references

Mitochondrial Myopathy

Skeletal muscle shows mitochondrial myopathy: ragged-red or COX-hyporeactive fibers, abnormal mitochondria and atrophic fibers, on top of neurogenic (denervation) change. Deleting Aif in mouse muscle and heart alone causes complex I deficiency, skeletal muscle atrophy and lactic acidemia, so the myopathy is a primary consequence of AIF loss in muscle and not only secondary to denervation.

skeletal muscle fiber CL:0008002

Animal models

Muscle- and heart-specific Aif knockout mouse Mouse recapitulates Muscle atrophy with lactic acidemia after muscle-specific AIF loss.

Downstream

Hypotonia

Muscle weakness

Skeletal muscle atrophy

Ragged-red muscle fibers

Respiratory insufficiency

Kyphoscoliosis

Show evidence (2 references)

PMID:28299359 SUPPORT Human Clinical

"Electron microscopy demonstrated mitochondria that were irregular and bizarrely shaped without inclusions, numerous atrophic fibers, moderate myofiber disarray"

Ultrastructural mitochondrial myopathy in a patient.

PMID:16287843 SUPPORT Model Organism

"Mice in which Aif has been inactivated specifically in cardiac and skeletal muscle exhibit impaired activity and protein expression of respiratory chain complex I."

Muscle-restricted AIF loss is sufficient to produce the respiratory chain defect in muscle.

Cardiomyocyte Energy Failure

Cardiac involvement is reported in a minority of patients, usually as ventricular hypertrophy beginning before or soon after birth that can progress to dilation and heart failure. Heart- and muscle-specific Aif deletion in the mouse causes complex I deficiency and dilated cardiomyopathy, supporting a direct bioenergetic mechanism in cardiomyocytes.

cardiomyocyte CL:0000746

Animal models

Muscle- and heart-specific Aif knockout mouse Mouse partially recapitulates Dilated cardiomyopathy and heart failure after cardiac AIF loss.

Downstream

Hypertrophic cardiomyopathy

Dilated cardiomyopathy

Show evidence (1 reference)

PMID:16287843 SUPPORT Model Organism

"Mutant animals develop severe dilated cardiomyopathy, heart failure, and skeletal muscle atrophy accompanied by lactic acidemia consistent with defects in the mitochondrial respiratory chain."

AIF loss in cardiomyocytes causes cardiomyopathy in the mouse.

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Pathograph

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Phenotypes

36

Cardiovascular 3

Hypertrophic cardiomyopathy HP:0001639

Show evidence (2 references)

PMID:34117073 SUPPORT Human Clinical

"Fetal heart echocardiogram identified biventricular myocardial hypertrophy."

Prenatal biventricular hypertrophy in the p.Pro169Leu proband.

PMID:42329587 SUPPORT REVIEW SYNTHESIS Human Clinical

"The phenotypic spectrum of AIFM1-related disease includes cardiomyopathy, typically characterized by early-onset cardiac hypertrophy that may progress to ventricular dilatation and heart failure."

Cardiomyopathy across AIFM1 disease, typically early hypertrophy.

Dilated cardiomyopathy HP:0001644

Sequelae: Congestive heart failure

Show evidence (1 reference)

PMID:42329587 SUPPORT Human Clinical

"the cardiac phenotype progressively evolved into dilated cardiomyopathy with systolic dysfunction by"

Serial echocardiography showed progression from hypertrophy to dilated cardiomyopathy.

Congestive heart failure HP:0001635

Show evidence (1 reference)

PMID:42329587 SUPPORT Human Clinical

"necessitating initiation of heart failure therapy"

Heart failure therapy was initiated after progression to dilated cardiomyopathy.

Digestive 1

Dysphagia HP:0002015

Show evidence (1 reference)

PMID:25583628 SUPPORT Human Clinical

"at age 10 years muscle wasting, swallowing difficulties, respiratory insufficiency and external opthamoplegia."

Swallowing difficulties in late childhood.

Ear 1

Sensorineural hearing impairment HP:0000407

Show evidence (2 references)

PMID:25583628 SUPPORT Human Clinical

"At age 2.5 years he developed hearing loss and severe ataxia"

Childhood-onset hearing loss in an AIFM1 encephalomyopathy patient.

PMID:25934856 SUPPORT Human Clinical

"During childhood, he developed gait and limb ataxia (sensory and cerebellar), hearing loss, and cognitive impairment."

Hearing loss in the slowly progressive form.

Eye 1

External ophthalmoplegia HP:0000544

Show evidence (1 reference)

PMID:25583628 SUPPORT Human Clinical

"at age 10 years muscle wasting, swallowing difficulties, respiratory insufficiency and external opthamoplegia."

External ophthalmoplegia (spelled opthamoplegia in the source) in late childhood.

Head and Neck 1

Microcephaly HP:0000252

Show evidence (1 reference)

PMID:37644805 SUPPORT Human Clinical

"At 6 months of age, the patient exhibited microcephaly but did not experience any further deterioration."

Acquired microcephaly after neonatal encephalopathy.

Metabolism 3

Cerebral edema HP:0002181

Show evidence (1 reference)

PMID:37644805 SUPPORT Human Clinical

"Brain MRI revealed prominent brain swelling of both hemispheres and widespread signal alteration in large part of the cortex and of the thalami, with sparing of the basal nuclei."

Day-1 MRI shows diffuse brain swelling with cortical and thalamic involvement and basal-ganglia sparing.

Lactic acidosis HP:0003128

Show evidence (3 references)

PMID:28299359 SUPPORT Human Clinical

"Here we describe a male infant with an X-linked sequence variant in AIFM1 and mitochondrial disease characterized by congenital lactic acidosis, intractable seizures, polyneuropathy, and myopathy."

Congenital lactic acidosis in a fatal infantile case.

PMID:34117073 SUPPORT Human Clinical

"He had severe metabolic acidosis, lactic acidosis, and an elevated anion gap."

Neonatal lactic acidosis in the p.Pro169Leu proband.

PMID:22019070 REFUTE Human Clinical

"Plasma and CSF lactate levels were normal, but the activities of mitochondrial complex I and IV were markedly decreased."

Lactate was normal in one family, so lactic acidosis is not a constant feature.

Increased CSF lactate HP:0002490

Show evidence (1 reference)

PMID:28299359 SUPPORT Human Clinical

"CSF lactate (6 mmol/l, reference range: 0.9-2.5 mmol/l) and pyruvate were elevated."

Elevated CSF lactate in an infant with AIFM1 disease.

Musculoskeletal 6

EMG and muscle biopsy denervation EMG: neuropathic changes HP:0003445

Show evidence (1 reference)

PMID:26173962 SUPPORT Human Clinical

"Muscle biopsies and electromyography in both patients showed signs of severe denervation."

Neurogenic denervation in two affected cousins.

Hypotonia HP:0001252

Show evidence (2 references)

PMID:28299359 SUPPORT Human Clinical

"examination was notable for axial and appendicular hypotonia."

Hypotonia in an infant with AIFM1 encephalomyopathy.

PMID:41211097 SUPPORT BACKGROUND Human Clinical

"COXPD6 patients have significant end-organ involvement of the central nervous, peripheral nervous, respiratory, and gastrointestinal systems, manifested by seizures, hypotonia, psychomotor delay, muscle weakness, and wasting."

Summary of the COXPD6 phenotype, including hypotonia, stated as background in a case report.

Muscle weakness HP:0001324

Show evidence (1 reference)

PMID:41211097 SUPPORT BACKGROUND Human Clinical

"COXPD6 patients have significant end-organ involvement of the central nervous, peripheral nervous, respiratory, and gastrointestinal systems, manifested by seizures, hypotonia, psychomotor delay, muscle weakness, and wasting."

Muscle weakness and wasting are part of the summarized COXPD6 phenotype.

Skeletal muscle atrophy HP:0003202

Show evidence (1 reference)

PMID:25583628 SUPPORT Human Clinical

"at age 10 years muscle wasting, swallowing difficulties, respiratory insufficiency and external opthamoplegia."

Muscle wasting in a boy with a hemizygous AIFM1 missense variant.

Ragged-red muscle fibers HP:0003200

Show evidence (1 reference)

PMID:25934856 SUPPORT Human Clinical

"Muscle biopsy (13 years) showed evidence of chronic denervation, ragged-red fibers, and fibers hyporeactive to cytochrome c oxidase"

Ragged-red and COX-hyporeactive fibers with denervation in muscle biopsy.

Kyphoscoliosis HP:0002751

Course: PROGRESSIVE

Show evidence (1 reference)

PMID:41211097 SUPPORT Human Clinical

"We present an 11-year-old child with AIFM1-related COXPD6 who underwent posterior spinal fusion for progressive neuromuscular kyphoscoliosis."

Neuromuscular kyphoscoliosis in a child with COXPD6.

Nervous System 16

Encephalopathy Mitochondrial encephalopathy HP:0006789

Course: PROGRESSIVE

Show evidence (2 references)

PMID:20362274 SUPPORT Human Clinical

"We investigated two male infant patients who were given a diagnosis of progressive mitochondrial encephalomyopathy on the basis of clinical, biochemical, and morphological features."

The founding patients had progressive infantile encephalomyopathy.

PMID:35712626 SUPPORT Human Clinical

"We describe a 4-month-old infant with mitochondrial encephalopathy, carrying a novel intronic variant in AIFM1"

Infantile mitochondrial encephalopathy with a splice allele.

Global developmental delay HP:0001263

Show evidence (2 references)

PMID:25934856 SUPPORT BACKGROUND Human Clinical

"Patients with a severe outcome included 2 cousins with early-onset, severe psychomotor delay, extrapyramidal signs, epilepsy, and axonal sensory-motor neuropathy associated with bilateral striatal necrosis"

Summarizes the founding cousins' severe psychomotor delay.

PMID:22019070 SUPPORT Human Clinical

"postnatally, there was no acquisition of developmental milestones, and the muscles of the children were dystrophic."

Absent developmental milestones in three affected siblings.

Developmental regression HP:0002376

Show evidence (1 reference)

PMID:25583628 SUPPORT Human Clinical

"Less frequent symptoms were hearing loss, seizures and psychomotor regression."

Psychomotor regression is part of the reported AIFM1 encephalomyopathy spectrum.

Seizure HP:0001250

Show evidence (2 references)

PMID:37644805 SUPPORT Human Clinical

"The patient presented with drug-resistant, electro-clinical, multifocal seizures 6 h after birth."

Drug-resistant neonatal seizures.

PMID:28299359 SUPPORT Human Clinical

"Here we describe a male infant with an X-linked sequence variant in AIFM1 and mitochondrial disease characterized by congenital lactic acidosis, intractable seizures, polyneuropathy, and myopathy."

Intractable seizures in a fatal infantile case.

Abnormality of extrapyramidal motor function HP:0002071

Show evidence (1 reference)

PMID:25934856 SUPPORT BACKGROUND Human Clinical

"Patients with a severe outcome included 2 cousins with early-onset, severe psychomotor delay, extrapyramidal signs, epilepsy, and axonal sensory-motor neuropathy associated with bilateral striatal necrosis"

Extrapyramidal signs in the founding family.

Bilateral striatal necrosis Degeneration of the striatum HP:0040140

Show evidence (1 reference)

PMID:25934856 SUPPORT BACKGROUND Human Clinical

"Patients with a severe outcome included 2 cousins with early-onset, severe psychomotor delay, extrapyramidal signs, epilepsy, and axonal sensory-motor neuropathy associated with bilateral striatal necrosis"

Bilateral striatal necrosis is recorded for the founding family.

Abnormal basal ganglia MRI signal intensity HP:0012751

Show evidence (1 reference)

PMID:28299359 SUPPORT Human Clinical

"There was abnormal T2 signal intensity within the head and body of the caudate nuclei bilaterally and the bilateral anterior putamina"

Bilateral striatal T2 signal change on MRI.

Cerebral atrophy HP:0002059

Show evidence (1 reference)

PMID:28299359 SUPPORT Human Clinical

"Repeat MRI demonstrated cerebral atrophy in addition to previous findings."

Progressive cerebral atrophy on serial MRI.

Diffuse white matter abnormality Diffuse white matter abnormalities HP:0007204

Show evidence (1 reference)

PMID:37644805 SUPPORT Human Clinical

"neonatal seizures and diffuse white matter involvement with relative sparing of basal ganglia"

The report's own summary names diffuse white matter involvement as the defining imaging finding.

Multicystic encephalomalacia HP:0040197

Show evidence (1 reference)

PMID:37644805 SUPPORT Human Clinical

"evolution toward multicystic encephalomalacia with marked T2 hyperintensity and T1 hypointensity of the white matter"

Day-30 MRI shows evolution to multicystic encephalomalacia.

EEG burst suppression EEG with burst suppression HP:0010851

Show evidence (1 reference)

PMID:37644805 SUPPORT Human Clinical

"later evolving into a burst-suppression pattern"

The neonatal electroclinical seizures evolved into a burst-suppression EEG pattern.

Ventriculomegaly HP:0002119

Show evidence (2 references)

PMID:22019070 SUPPORT Human Clinical

"Three siblings were found to have ventriculomegaly at early gestation"

Prenatal ventriculomegaly in an AIFM1 family.

PMID:34117073 SUPPORT Human Clinical

"Prenatal ultrasound at 25 wk gestation found bilateral mildly dilated cerebral lateral ventricles"

Prenatal ventricular dilation in the p.Pro169Leu proband.

Peripheral axonal neuropathy HP:0003477

Show evidence (2 references)

PMID:28299359 SUPPORT Human Clinical

"Electromyography at 4 wk of age and again at 3 mo, demonstrated moderately severe axonal and sensorimotor polyneuropathy."

Axonal sensorimotor polyneuropathy from the first weeks of life.

PMID:25934856 SUPPORT Human Clinical

"Nerve conduction study showed a moderate-to-severe axonal, more sensory than motor, neuropathy."

Axonal neuropathy in the slowly progressive form.

Ataxia HP:0001251

Show evidence (2 references)

PMID:25934856 SUPPORT Human Clinical

"During childhood, he developed gait and limb ataxia (sensory and cerebellar), hearing loss, and cognitive impairment."

Sensory and cerebellar ataxia in the slowly progressive form.

PMID:25583628 SUPPORT Human Clinical

"At age 2.5 years he developed hearing loss and severe ataxia"

Severe ataxia from early childhood.

Cerebellar atrophy HP:0001272

Show evidence (1 reference)

PMID:25934856 SUPPORT Human Clinical

"Brain CT scan and MRI were normal at age 9 years, subsequently showing cerebellar atrophy (19 years) and mild cortical and thalamic atrophy (30 years)."

Progressive cerebellar atrophy on MRI.

Elevated brain lactate level by MRS HP:0012707

Show evidence (1 reference)

PMID:28299359 SUPPORT Human Clinical

"A new inverted lactate doublet at 1.33 ppm on single-voxel MR spectroscopy"

Brain lactate peak on MR spectroscopy over the basal ganglia.

Respiratory 1

Respiratory insufficiency HP:0002093

Show evidence (1 reference)

PMID:25583628 SUPPORT Human Clinical

"at age 10 years muscle wasting, swallowing difficulties, respiratory insufficiency and external opthamoplegia."

Respiratory insufficiency with muscle wasting.

Cellular 3

Decreased activity of mitochondrial complex IV HP:0008347

Show evidence (3 references)

PMID:20362274 SUPPORT In Vitro

"Fibroblasts from both showed reduction of respiratory chain (RC) cIII and cIV, but not of cI activities."

Complex IV deficiency in patient fibroblasts.

PMID:26173962 SUPPORT Human Clinical

"In two male cousins with early-onset mitochondrial encephalopathy and cytochrome c oxidase (COX) deficiency, we identified a novel AIFM1 mutation."

COX deficiency in two further affected males.

PMID:34117073 SUPPORT Human Clinical

"Absent or partial deficiency of cytochrome c oxidase was found in muscle fibers, however, supporting a Complex IV mitochondrial deficiency."

Complex IV deficiency in muscle.

Decreased activity of mitochondrial complex III HP:0011924

Show evidence (2 references)

PMID:20362274 SUPPORT In Vitro

"Fibroblasts from both showed reduction of respiratory chain (RC) cIII and cIV, but not of cI activities."

Complex III deficiency in patient fibroblasts.

PMID:37644805 SUPPORT In Vitro

"Functional studies on cultured fibroblast showed a clear reduction in AIFM1 protein amount and defective activities of respiratory chain complexes I, III and IV."

Complex III deficiency in neonatal-onset patient fibroblasts.

Decreased activity of mitochondrial complex I HP:0011923

Show evidence (2 references)

PMID:22019070 SUPPORT Human Clinical

"Plasma and CSF lactate levels were normal, but the activities of mitochondrial complex I and IV were markedly decreased."

Complex I deficiency in an AIFM1 family.

PMID:28299359 SUPPORT Human Clinical

"Muscle biopsy during this admission demonstrated decreased activity of electron transport chain complex I and IV, with normal activity of complexes II and III."

Complex I deficiency in patient muscle.

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Genetic Associations

1

AIFM1 (AIFM1 (Xq26.1) encodes apoptosis-inducing factor, a 613-residue mitochondrial flavoprotein with FAD- and NADH-binding domains. Reported COXPD6 alleles are in-frame deletions, missense, splice and mitochondrial-targeting-sequence variants; no truncating allele has been reported, and the gene is highly intolerant of loss of function in population data. The alleles studied functionally lower steady-state AIF protein in patient cells. The same gene carries a phenotypic continuum that dismech curates as separate allelic entries: X-linked recessive Charcot-Marie-Tooth disease 4 (Cowchock syndrome), the X-linked auditory neuropathy subtype AUNX1 within the Auditory Neuropathy entry, and spondyloepimetaphyseal dysplasia (Bieganski type, hypomyelination with spondylometaphyseal dysplasia). This entry covers the encephalomyopathic, combined-OXPHOS-deficient end.)

Gene: AIFM1 hgnc:8768 relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (3 references)

PMID:20362274 SUPPORT Human Clinical

"We found a disease-segregating mutation in the X-linked AIFM1 gene, encoding the Apoptosis-Inducing Factor (AIF) mitochondrion-associated 1 precursor that deletes arginine 201 (R201 del)."

Identifies AIFM1 as the disease gene by segregation of the p.Arg201del allele.

PMID:22019070 SUPPORT Human Clinical

"we identified a pathogenic mutation in the AIFM1 gene which segregated with the disease state and was absent in 86 anonymous controls."

A second, independent family confirms AIFM1 as the causal gene.

PMID:34117073 SUPPORT Human Clinical

"No frameshift or nonsense variants have been reported in the Human Gene Mutation Database (HGMD), and the gene is highly intolerant to loss of function (pLI = 1 in gnomAD)."

Records the allele classes reported and the constraint on loss-of-function alleles.

Variants (2)

AIFM1 c.601_603del (p.Arg201del) Pathogenic

The founding allele, segregating in two male infants with progressive encephalomyopathy. It destabilizes both the mitochondrial and the soluble forms of AIF and increases the DNA-binding affinity of the soluble form.

AIFM1 c.506C>T (p.Pro169Leu) Pathogenic

Found in a family with three affected males with severe multisystem disease, metabolic acidosis and early death, and separately in a manifesting heterozygous girl with extreme X-inactivation skewing. Patient fibroblasts show reduced AIF and complex I subunits.

💊

Medical Actions

4

Mitochondrial cofactor supplementation

Action: Pharmacotherapy NCIT:C15986

Agent: riboflavin CHEBI:17015 coenzyme Q10 CHEBI:46245 thiamine CHEBI:18385

Platform: Small molecule

Riboflavin, the precursor of FAD, has been given on the rationale that it stabilizes the flavin-bound AIF protein, alone or with coenzyme Q10 and thiamine. Results are mixed. One founding patient had prolonged neurological improvement, with correction of respiratory chain defects in his fibroblasts. A neonatal-onset patient on riboflavin, coenzyme Q10 and thiamine did not deteriorate further over six months. A slowly progressive patient had no change in clinical course on coenzyme Q10 and riboflavin, and riboflavin did not stabilize AIF in p.Pro169Leu fibroblasts. In the allelic childhood ataxia phenotype, riboflavin up to 200 mg per day partially improved ataxia scores. There are no controlled data.

Mechanism Target:

RESTORES Unstable AIF Protein — Proposed to stabilize FAD binding in mitochondrial AIF; supported in fibroblasts of one allele and not of another.

Show evidence (2 references)

PMID:20362274 SUPPORT In Vitro

"correction of RC defects in mutant fibroblasts, suggesting that stabilization of the FAD binding in AIF(mit) is beneficial"

Riboflavin corrected respiratory-chain defects in patient fibroblasts, supporting FAD-binding stabilization of AIF.

PMID:34117073 REFUTE In Vitro

"The reduced abundance of AIFM1 in the patient cells could not be stabilized with riboflavin or protease inhibitor treatment."

Riboflavin did not restore AIF levels in p.Pro169Leu fibroblasts.

Show evidence (4 references)

PMID:20362274 SUPPORT Human Clinical

"riboflavin supplementation was associated with prolonged improvement of patient #1's neurological conditions"

Prolonged neurological improvement on riboflavin in the founding family (uncontrolled single-patient observation).

PMID:37644805 SUPPORT Human Clinical

"Riboflavin, Coenzyme Q10 and thiamine supplementation was therefore given. At 6 months of age, the patient exhibited microcephaly but did not experience any further deterioration."

Combined cofactor supplementation in a neonatal-onset patient, followed by clinical stability (uncontrolled).

PMID:25934856 REFUTE Human Clinical

"Coenzyme Q10 and riboflavin supplementation did not modify clinical course."

No clinical benefit in a patient with the slowly progressive form.

+ 1 more reference

Antiseizure pharmacotherapy

Action: Pharmacotherapy NCIT:C15986

Agent: phenobarbital CHEBI:8069

Platform: Small molecule

Seizures are treated with standard antiseizure drugs; phenobarbital was used in a fatal infantile case. Neonatal seizures can be drug-resistant.

Mechanism Target:

INHIBITS Seizure — Symptomatic seizure control; it does not act on the mitochondrial defect.

Show evidence (1 reference)

PMID:28299359 SUPPORT Human Clinical

"He was started on phenobarbital for management of seizures."

Phenobarbital used for seizures in an AIFM1 patient.

Perioperative anesthetic planning

Action: mitochondrial-disease perioperative anesthetic management Ontology label: Supportive Care NCIT:C15747

Platform: Other

Surgery (for example spinal fusion for neuromuscular kyphoscoliosis) needs anesthetic planning adapted to mitochondrial disease; total intravenous anesthesia with remimazolam has been reported in a child with COXPD6.

Show evidence (1 reference)

PMID:41211097 SUPPORT Human Clinical

"We explore the genetic history of this mitochondrial disorder, review a detailed anesthetic approach to perioperative management including use of the novel benzodiazepine, remimazolam, and discuss anesthetic considerations in these patients."

Reports an anesthetic approach used in a child with COXPD6.

Genetic counseling

Action: Genetic Counseling NCIT:C15240

Platform: Behavioral / lifestyle

Counseling for X-linked recessive recurrence risk, carrier testing of at-risk female relatives, and the possibility of a manifesting heterozygous female with skewed X inactivation.

🔬

Diagnosis

2

Respiratory chain enzymology and AIF immunoblot

Spectrophotometric respiratory chain assays in muscle or fibroblasts show combined deficiency of complexes I, III and/or IV, and immunoblot shows reduced AIF protein in patient fibroblasts. The pattern differs between tissues and alleles, and lactate can be normal.

Show evidence (1 reference)

PMID:37644805 SUPPORT In Vitro

"Functional studies on cultured fibroblast showed a clear reduction in AIFM1 protein amount and defective activities of respiratory chain complexes I, III and IV."

Fibroblast studies support the diagnosis and the pathogenicity of a new variant.

Exome sequencing

Diagnosis rests on a hemizygous pathogenic AIFM1 variant, usually found by exome sequencing. Intronic splice variants have been confirmed by RNA analysis.

Show evidence (2 references)

PMID:37644805 SUPPORT Human Clinical

"CES analysis revealed the likely pathogenic variant c.5T>C; p.(Phe2Ser) in the AIFM1 gene."

Clinical exome sequencing identified the causal variant.

PMID:35712626 SUPPORT Human Clinical

"Our findings expand the mutation spectrum of AIFM1 and point out the necessity of intronic sequence analysis and the importance for integrative functional studies in the interpretation of sequence variants."

Intronic variants need specific analysis and functional confirmation.

📈

Progression

3

Prenatal to neonatal onset

Age: prenatal to first month

The severe end presents before or at birth, with prenatal ventriculomegaly, neonatal lactic acidosis or seizures within hours of birth.

Show evidence (1 reference)

PMID:37644805 SUPPORT Human Clinical

"The patient presented with drug-resistant, electro-clinical, multifocal seizures 6 h after birth."

Onset within hours of birth.

Variable progression

Age: infancy to adulthood

Severity varies even within a family. Some children die before age 5 years; others progress in steps over decades, becoming chair-bound in early adulthood.

Show evidence (2 references)

PMID:25583628 SUPPORT Human Clinical

"Severity varies greatly even within one family with onset of symptoms between birth and adolescence."

Documents the variable onset and severity.

PMID:25934856 SUPPORT Human Clinical

"He became chair-bound at age 20 years, needed acoustic aids at age 22 years, and developed progressive sleep apnea syndrome since age 23 years."

Slow progression into adulthood in one patient.

Early death in the severe form

Age: first days to early childhood

The most severe cases die in the first months of life (day 8 and 4 months in two reports). In a 2015 review 3 of 12 patients died before age 5 years. Death in infancy is recorded here rather than as a phenotype because the HPO term HP:0001522 sits under clinical course (mortality), outside the phenotypic-abnormality branch the phenotype slot accepts.

Show evidence (3 references)

PMID:28299359 SUPPORT Human Clinical

"Given his poor neurologic prognosis, care was redirected, and he died at the age of 4 mo."

Death at 4 months of age.

PMID:34117073 SUPPORT Human Clinical

"The proband, his brother, and their maternal uncle all exhibited severe multisystem pathology, metabolic acidosis, and early demise."

Early death in three affected males of one family.

PMID:25583628 SUPPORT Human Clinical

"3 of 12 patients died before age 5 years while others were still able to walk during young adulthood."

Gives the proportion dying in early childhood and the survival of others into adulthood.

📊

Prevalence

1

Worldwide

Cases In Literature Ultra Rare

Known only from case reports and small families. A 2015 review counted 11 affected males in three families across the AIFM1 phenotypes then known, before adding a twelfth patient; no population prevalence or incidence has been estimated.

Show evidence (1 reference)

PMID:25583628 SUPPORT Human Clinical

"So far mutations in AIFM1, a X-chromosomal gene coding for AIF, have been described in three families with 11 affected males."

Gives the case count at the time, before the authors added a further patient.

🐁

Animal Models

2

Harlequin (Hq) mouse

A spontaneous X-linked hypomorph with a retroviral insertion in Aifm1. Hemizygous males have complex I deficiency in brain and retina and progressive degeneration of cerebellar and retinal neurons that later involves thalamus, striatum and cortex.

Species

Mouse

Genotype

Aifm1 Hq proviral insertion (hypomorph, about 80% reduction in AIF)

Publication

PMID:12353028

Pathograph links

Combined Oxidative Phosphorylation Deficiency recapitulates fidelity: moderate Reduced AIF lowers OXPHOS and complex I subunits in brain and retina.

Limitations: A global hypomorph rather than a knock-in of a patient allele, so it models loss of AIF amount but not the altered DNA binding of p.Arg201del. The biochemical pattern is complex I-predominant, whereas several patients show complex III or IV deficiency.

Show evidence (1 reference)

PMID:15526035 SUPPORT Model Organism

"Harlequin mice with reduced AIF expression due to a retroviral insertion into the AIF gene also manifest a reduced oxidative phosphorylation (OXPHOS) in the retina and in the brain, correlating with reduced expression of complex I subunits, retinal degeneration, and neuronal defects."

The model reproduces the OXPHOS defect in nervous tissue.

Progressive Neuronal Degeneration partially recapitulates fidelity: moderate Progressive, multifocal neurodegeneration preceded by mitochondrial degeneration.

Limitations: Onset is in adulthood (months) and cerebellar and retinal predominant, while the human disease is neonatal or infantile and dominated by encephalopathy, basal ganglia injury and neuropathy.

Show evidence (1 reference)

PMID:12353028 SUPPORT Model Organism

"Harlequin (Hq) mutant mice have progressive degeneration of terminally differentiated cerebellar and retinal neurons."

Progressive neurodegeneration in the AIF hypomorph.

Show evidence (1 reference)

PMID:12353028 SUPPORT Model Organism

"We have identified the Hq mutation as a proviral insertion in the apoptosis-inducing factor (Aif) gene, causing about an 80% reduction in AIF expression."

Defines the model's genetic lesion.

Muscle- and heart-specific Aif knockout mouse

Tissue-restricted deletion of Aif in striated muscle, isolating the muscle and heart consequences of AIF loss from its neuronal effects.

Species

Mouse

Genotype

Conditional Aif deletion in cardiac and skeletal muscle

Publication

PMID:16287843

Pathograph links

Mitochondrial Myopathy recapitulates fidelity: moderate Muscle atrophy with lactic acidemia after muscle-specific AIF loss.

Limitations: Complete tissue-specific knockout rather than a hypomorphic patient allele, and without the neurogenic component present in patients.

Show evidence (1 reference)

PMID:16287843 SUPPORT Model Organism

"Mutant animals develop severe dilated cardiomyopathy, heart failure, and skeletal muscle atrophy accompanied by lactic acidemia consistent with defects in the mitochondrial respiratory chain."

Reproduces skeletal muscle atrophy with lactic acidemia.

Cardiomyocyte Energy Failure partially recapitulates fidelity: moderate Dilated cardiomyopathy and heart failure after cardiac AIF loss.

Limitations: The mice develop dilated cardiomyopathy, whereas patients more often present first with ventricular hypertrophy.

Show evidence (1 reference)

PMID:16287843 SUPPORT Model Organism

"Mutant animals develop severe dilated cardiomyopathy, heart failure, and skeletal muscle atrophy accompanied by lactic acidemia consistent with defects in the mitochondrial respiratory chain."

Cardiac AIF loss causes cardiomyopathy.

Show evidence (1 reference)

PMID:16287843 SUPPORT Model Organism

"Mice in which Aif has been inactivated specifically in cardiac and skeletal muscle exhibit impaired activity and protein expression of respiratory chain complex I."

Defines the model and its respiratory chain defect.

{ }

Source YAML

click to show

name: Severe X-linked Mitochondrial Encephalomyopathy
creation_date: "2026-10-01T21:34:26Z"
category: Mendelian
disease_term:
  preferred_term: severe X-linked mitochondrial encephalomyopathy
  term:
    id: MONDO:0010437
    label: severe X-linked mitochondrial encephalomyopathy
parents:
- Mitochondrial Disease
synonyms:
- COXPD6
- combined oxidative phosphorylation deficiency 6
- combined oxidative phosphorylation deficiency type 6
- combined oxidative phosphorylation deficiency 6, X-linked recessive
- encephalomyopathy, mitochondrial, X-linked
- mitochondrial encephalomyopathy due to COXPD6
- AIFM1-related mitochondrial encephalomyopathy
description: >-
  Severe X-linked mitochondrial encephalomyopathy, also called combined
  oxidative phosphorylation deficiency 6 (COXPD6, OMIM 300816), is an
  ultra-rare primary mitochondrial disease of hemizygous males caused by
  pathogenic variants in AIFM1 (Xq26.1). AIFM1 encodes apoptosis-inducing
  factor (AIF), an FAD-dependent NADH oxidoreductase anchored in the
  mitochondrial intermembrane space. AIF has two functions that both matter
  here. Its vital function is to support biogenesis of the respiratory chain:
  AIF imports and partners CHCHD4 (MIA40), the receptor of the intermembrane
  space disulfide relay, which in turn imports complex I subunits such as
  NDUFS5. Its lethal function is exercised when a soluble AIF fragment is
  released and moves to the nucleus to drive caspase-independent chromatin
  fragmentation (parthanatos).

  The founding allele, an in-frame deletion of arginine 201, destabilizes AIF,
  reduces respiratory chain activities in patient fibroblasts and muscle, and
  increases the DNA-binding affinity of soluble AIF, so that patient cells show
  both an oxidative phosphorylation (OXPHOS) defect and exaggerated
  parthanatos. Later alleles (missense, splice and targeting-sequence variants)
  likewise reduce steady-state AIF and produce combined complex I, III and/or IV
  deficiency with tissue-dependent biochemical patterns.

  Clinically the disease is an infantile- or neonatal-onset progressive
  encephalomyopathy: severe psychomotor delay or regression, seizures that can
  be intractable, hypotonia, extrapyramidal signs, axonal sensorimotor
  neuropathy with denervation, myopathy, lactic acidosis, and basal ganglia
  (striatal) involvement on imaging or pathology in many cases; a neonatal
  presentation with diffuse cortical and white-matter injury that relatively
  spares the basal ganglia is also reported, so the imaging pattern is not
  uniform. Prenatal ventriculomegaly,
  cardiac hypertrophy and death in infancy are reported in the severe end; a
  slower course with ataxia, cerebellar atrophy, hearing loss,
  ophthalmoplegia and respiratory failure is reported in other males. Treatment is supportive; riboflavin, the FAD precursor, has
  been given with mixed results.
classifications:
  harrisons_chapter:
  - classification_value: NEUROLOGIC
    notes: >-
      An infantile mitochondrial encephalomyopathy with central nervous system,
      peripheral nerve and muscle involvement.
  - classification_value: ENDOCRINOLOGY_METABOLISM
    notes: >-
      A combined respiratory chain (oxidative phosphorylation) deficiency, one
      of the inborn errors of mitochondrial energy metabolism.
  mechanistic_category:
  - classification_value: mitochondrial disease
    notes: >-
      Caused by loss of the AIF-dependent CHCHD4 import and respiratory chain
      assembly function, with an added increase in AIF-mediated parthanatos.
mappings:
  icd10cm_mappings:
  - term:
      id: ICD10CM:E88.49
      label: Other mitochondrial metabolism disorders
    mapping_predicate: skos:broadMatch
    mapping_source: ICD-10-CM
    mapping_justification: >-
      ICD-10-CM has no code specific to AIFM1-related disease or to combined
      oxidative phosphorylation deficiency. E88.49 is the residual code in the
      E88.4 mitochondrial metabolism block and is therefore a broad match.
inheritance:
- name: X-linked recessive
  inheritance_term:
    preferred_term: X-linked recessive inheritance
    term:
      id: HP:0001419
      label: X-linked recessive inheritance
  description: >-
    Affected individuals are hemizygous males. In the founding family the two
    affected boys were born to monozygotic twin sisters by unrelated fathers,
    and later variants were shown to be inherited from asymptomatic carrier
    mothers or to arise de novo. A heterozygous female can be affected when X
    inactivation is extremely skewed: a girl carrying p.Pro169Leu with 98:2
    skewing had infantile encephalomyopathy and cardiomyopathy, the same allele
    that killed three males of another family.
  evidence:
  - reference: PMID:20362274
    reference_title: "Severe X-linked mitochondrial encephalomyopathy associated with a mutation in apoptosis-inducing factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These patients were born from monozygotic twin sisters and unrelated fathers, suggesting an X-linked trait."
    explanation: The founding pedigree pattern points to X-linked transmission through the twin mothers.
  - reference: PMID:25934856
    reference_title: "A slowly progressive mitochondrial encephalomyopathy widens the spectrum of AIFM1 disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The mother, heterozygous for the mutation, was asymptomatic"
    explanation: An asymptomatic heterozygous carrier mother transmitted the variant to an affected son, as expected for X-linked recessive inheritance.
  - reference: PMID:42329587
    reference_title: "Cardiomyopathy and mitochondrial encephalomyopathy in a female child associated with a heterozygous X-linked AIFM1 variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Genetic testing identified a heterozygous AIFM1 variant, c.506C > T (p.Pro169Leu), with extremely skewed X-inactivation (98:2) in a female."
    explanation: Documents a manifesting heterozygous female with extreme X-inactivation skewing, the exception to male-only expression.
genetic:
- name: AIFM1
  gene_term:
    preferred_term: AIFM1
    term:
      id: hgnc:8768
      label: AIFM1
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  association: >-
    AIFM1 (Xq26.1) encodes apoptosis-inducing factor, a 613-residue
    mitochondrial flavoprotein with FAD- and NADH-binding domains. Reported
    COXPD6 alleles are in-frame deletions, missense, splice and
    mitochondrial-targeting-sequence variants; no truncating allele has been
    reported, and the gene is highly intolerant of loss of function in
    population data. The alleles studied functionally lower steady-state AIF
    protein in patient cells.

    The same gene carries a phenotypic continuum that dismech curates as
    separate allelic entries: X-linked recessive Charcot-Marie-Tooth disease 4
    (Cowchock syndrome), the X-linked auditory neuropathy subtype AUNX1 within
    the Auditory Neuropathy entry, and spondyloepimetaphyseal dysplasia
    (Bieganski type, hypomyelination with spondylometaphyseal dysplasia). This
    entry covers the encephalomyopathic, combined-OXPHOS-deficient end.
  variants:
  - name: "AIFM1 c.601_603del (p.Arg201del)"
    description: >-
      The founding allele, segregating in two male infants with progressive
      encephalomyopathy. It destabilizes both the mitochondrial and the soluble
      forms of AIF and increases the DNA-binding affinity of the soluble form.
    clinical_significance: PATHOGENIC
  - name: "AIFM1 c.506C>T (p.Pro169Leu)"
    description: >-
      Found in a family with three affected males with severe multisystem
      disease, metabolic acidosis and early death, and separately in a
      manifesting heterozygous girl with extreme X-inactivation skewing.
      Patient fibroblasts show reduced AIF and complex I subunits.
    clinical_significance: PATHOGENIC
  evidence:
  - reference: PMID:20362274
    reference_title: "Severe X-linked mitochondrial encephalomyopathy associated with a mutation in apoptosis-inducing factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We found a disease-segregating mutation in the X-linked AIFM1 gene, encoding the Apoptosis-Inducing Factor (AIF) mitochondrion-associated 1 precursor that deletes arginine 201 (R201 del)."
    explanation: Identifies AIFM1 as the disease gene by segregation of the p.Arg201del allele.
  - reference: PMID:22019070
    reference_title: "Early prenatal ventriculomegaly due to an AIFM1 mutation identified by linkage analysis and whole exome sequencing."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "we identified a pathogenic mutation in the AIFM1 gene which segregated with the disease state and was absent in 86 anonymous controls."
    explanation: A second, independent family confirms AIFM1 as the causal gene.
  - reference: PMID:34117073
    reference_title: "Severe multisystem pathology, metabolic acidosis, mitochondrial dysfunction, and early death associated with an X-linked AIFM1 variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "No frameshift or nonsense variants have been reported in the Human Gene Mutation Database (HGMD), and the gene is highly intolerant to loss of function (pLI = 1 in gnomAD)."
    explanation: Records the allele classes reported and the constraint on loss-of-function alleles.
pathophysiology:
- name: Unstable AIF Protein
  biological_scale: MOLECULAR
  description: >-
    Disease alleles lower the amount of functional AIF in mitochondria. The
    founding p.Arg201del allele decreases the stability of both mitochondrial
    and soluble AIF; missense and targeting-sequence alleles (p.Gly262Ser,
    p.Phe2Ser, p.Pro169Leu) give a marked reduction of AIF on immunoblot of
    patient fibroblasts. The variants sit in or near the FAD- and NADH-binding
    domains, which is the rationale for trying riboflavin to stabilize the
    flavin-bound protein.
  genetic_context:
    genes:
    - preferred_term: AIFM1
      term:
        id: hgnc:8768
        label: AIFM1
    variant_origin: GERMLINE
    description: >-
      Hemizygous germline AIFM1 variants, inherited from a carrier mother or
      arising de novo.
  genes:
  - preferred_term: AIFM1
    term:
      id: hgnc:8768
      label: AIFM1
  molecular_functions:
  - preferred_term: FAD binding
    term:
      id: GO:0050660
      label: flavin adenine dinucleotide binding
  locations:
  - preferred_term: mitochondrial intermembrane space
    term:
      id: GO:0005758
      label: mitochondrial intermembrane space
  downstream:
  - target: Impaired CHCHD4 Mitochondrial Import
    description: >-
      Reduced AIF lowers mitochondrial import of CHCHD4, the intermembrane
      space import receptor.
    evidence:
    - reference: PMID:26004228
      reference_title: "Interaction between AIF and CHCHD4 Regulates Respiratory Chain Biogenesis."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Depletion or hypomorphic mutation of AIF caused a downregulation of CHCHD4 protein by diminishing its mitochondrial import."
      explanation: Shows that loss or hypomorphic mutation of AIF reduces CHCHD4 import, the edge from AIF loss to the import defect.
  - target: Enhanced AIF-Dependent Parthanatos
    description: >-
      The founding allele also increases the DNA-binding affinity of soluble
      AIF, the prerequisite for its nuclear pro-death action.
    evidence:
    - reference: PMID:20362274
      reference_title: "Severe X-linked mitochondrial encephalomyopathy associated with a mutation in apoptosis-inducing factor."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "In vitro, the AIF(R201 del) mutation decreases stability of both AIF(mit) and AIF(sol) and increases the AIF(sol) DNA binding affinity, a prerequisite for nuclear apoptosis."
      explanation: Links the variant's effect on soluble AIF to the nuclear cell-death branch.
  evidence:
  - reference: PMID:20362274
    reference_title: "Severe X-linked mitochondrial encephalomyopathy associated with a mutation in apoptosis-inducing factor."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "We conclude that AIF(R201 del) is an unstable mutant variant associated with increased parthanatos-linked cell death."
    explanation: The founding allele produces an unstable AIF protein.
  - reference: PMID:25934856
    reference_title: "A slowly progressive mitochondrial encephalomyopathy widens the spectrum of AIFM1 disorders."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Western blot analysis on patient fibroblasts showed strong reduction in AIF amount (figure, G), indicating instability of the mutant protein"
    explanation: A missense allele (p.Gly262Ser) also lowers AIF protein in patient fibroblasts.
  - reference: PMID:37644805
    reference_title: "Expanding the spectrum of neonatal-onset AIFM1-associated disorders."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Functional studies on cultured fibroblast showed a clear reduction in AIFM1 protein amount and defective activities of respiratory chain complexes I, III and IV."
    explanation: A targeting-sequence allele (p.Phe2Ser) reduces AIF protein in patient fibroblasts.

- name: Impaired CHCHD4 Mitochondrial Import
  biological_scale: MOLECULAR
  description: >-
    AIF binds CHCHD4 (MIA40) and is needed both to import it and to keep it in
    a form that engages its substrates in the intermembrane space disulfide
    relay. AIF deficiency lowers CHCHD4 protein in patient fibroblasts and in
    harlequin mouse tissue, without lowering its mRNA, and forcing CHCHD4 back
    into mitochondria restores respiration in AIF-deficient cells.
  biological_processes:
  - preferred_term: protein import into mitochondrial intermembrane space
    term:
      id: GO:0045041
      label: protein import into mitochondrial intermembrane space
    modifier: DECREASED
  locations:
  - preferred_term: mitochondrial intermembrane space
    term:
      id: GO:0005758
      label: mitochondrial intermembrane space
  downstream:
  - target: Defective Respiratory Chain Complex Assembly
    description: >-
      Without functional CHCHD4, intermembrane space import of complex I
      subunits such as NDUFS5 fails and respiratory complexes are lost.
    evidence:
    - reference: PMID:35859387
      reference_title: "AIFM1 is a component of the mitochondrial disulfide relay that drives complex I assembly through efficient import of NDUFS5."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "The import defect is especially severe for NDUFS5, a subunit of complex I of the respiratory chain."
      explanation: Identifies the complex I subunit whose import depends on the AIF-CHCHD4 relay.
    - reference: PMID:26158520
      reference_title: "Loss of apoptosis-inducing factor critically affects MIA40 function."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Importantly, MIA40 overexpression counteracts loss of respiratory subunits in Hq cells."
      explanation: Restoring MIA40 rescues respiratory subunits in AIF-deficient cells, so the MIA40 defect is upstream of their loss.
  evidence:
  - reference: PMID:26004228
    reference_title: "Interaction between AIF and CHCHD4 Regulates Respiratory Chain Biogenesis."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "CHCHD4 depletion sufficed to induce a respiratory defect that mimicked that observed in AIF-deficient cells."
    explanation: Loss of CHCHD4 alone reproduces the AIF-deficient respiratory defect.
  - reference: PMID:26158520
    reference_title: "Loss of apoptosis-inducing factor critically affects MIA40 function."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Here we show that AIF physically interacts with the oxidoreductase CHCHD4/MIA40."
    explanation: Establishes the physical AIF-CHCHD4 interaction.

- name: Defective Respiratory Chain Complex Assembly
  biological_scale: MOLECULAR
  description: >-
    Complex I assembly stalls when NDUFS5 is not imported, and AIF-deficient
    human and mouse cells contain less assembled complex I and fewer of its
    subunits. Other complexes (III and IV) are also reduced in patient cells,
    with a pattern that varies by allele and tissue.
  biological_processes:
  - preferred_term: mitochondrial respiratory chain complex I assembly
    term:
      id: GO:0032981
      label: mitochondrial respiratory chain complex I assembly
    modifier: DECREASED
  - preferred_term: mitochondrial respiratory chain complex assembly
    term:
      id: GO:0033108
      label: mitochondrial respiratory chain complex assembly
    modifier: DECREASED
  downstream:
  - target: Combined Oxidative Phosphorylation Deficiency
    description: >-
      Fewer assembled respiratory complexes lower electron transport and ATP
      synthesis.
    evidence:
    - reference: PMID:15526035
      reference_title: "AIF deficiency compromises oxidative phosphorylation."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "human or mouse cells lacking AIF as a result of homologous recombination or small interfering RNA exhibit high lactate production and enhanced dependency on glycolytic ATP generation, due to severe reduction of respiratory chain complex I activity."
      explanation: Ties the complex I loss to reduced respiration and a glycolytic, lactate-producing state.
  evidence:
  - reference: PMID:35859387
    reference_title: "AIFM1 is a component of the mitochondrial disulfide relay that drives complex I assembly through efficient import of NDUFS5."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Lack of mitochondrial NDUFS5 in turn results in stalling of complex I assembly."
    explanation: Mechanism by which AIF loss stalls complex I assembly.
  - reference: PMID:15526035
    reference_title: "AIF deficiency compromises oxidative phosphorylation."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Although AIF itself is not a part of complex I, AIF-deficient cells exhibit a reduced content of complex I and of its components"
    explanation: AIF is required for normal complex I content.

- name: Combined Oxidative Phosphorylation Deficiency
  biological_scale: CELLULAR
  description: >-
    Patient fibroblasts and muscle show reduced activities of respiratory
    chain complexes. The pattern varies: complexes III and IV with preserved
    complex I in the founding fibroblasts; complexes I and IV in muscle of a
    fatal infantile case and in the ventriculomegaly family; complexes I, III
    and IV in neonatal-onset fibroblasts; profound complex IV loss in muscle of
    the p.Pro169Leu family. Re-expressing wild-type AIF restores the
    activities, so the deficiency is a direct consequence of the variant. The
    downstream cost is an energy deficit with lactate accumulation.
  biological_processes:
  - preferred_term: oxidative phosphorylation
    term:
      id: GO:0006119
      label: oxidative phosphorylation
    modifier: DECREASED
  cell_types:
  - preferred_term: skeletal muscle fiber
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  - preferred_term: fibroblast
    term:
      id: CL:0000057
      label: fibroblast
  downstream:
  - target: Decreased activity of mitochondrial complex IV
  - target: Decreased activity of mitochondrial complex III
  - target: Decreased activity of mitochondrial complex I
  - target: Lactic acidosis
    description: >-
      Impaired respiration forces glycolytic ATP generation with lactate
      overproduction.
  - target: Increased CSF lactate
  - target: Elevated brain lactate level by MRS
  - target: Progressive Neuronal Degeneration
    description: >-
      Energy failure in neurons, the tissue most dependent on oxidative
      phosphorylation, precedes neuronal loss in the AIF-deficient mouse.
  - target: Mitochondrial Myopathy
  - target: Cardiomyocyte Energy Failure
  evidence:
  - reference: PMID:20362274
    reference_title: "Severe X-linked mitochondrial encephalomyopathy associated with a mutation in apoptosis-inducing factor."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Fibroblasts from both showed reduction of respiratory chain (RC) cIII and cIV, but not of cI activities."
    explanation: Combined respiratory chain deficiency in the founding patients' fibroblasts.
  - reference: PMID:20362274
    reference_title: "Severe X-linked mitochondrial encephalomyopathy associated with a mutation in apoptosis-inducing factor."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "In AIF(R201 del) fibroblasts, staurosporine-induced parthanatos was markedly increased, whereas re-expression of AIF(wt) induced recovery of RC activities."
    explanation: Wild-type AIF rescues the respiratory chain defect, placing it downstream of the variant.
  - reference: PMID:22019070
    reference_title: "Early prenatal ventriculomegaly due to an AIFM1 mutation identified by linkage analysis and whole exome sequencing."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Plasma and CSF lactate levels were normal, but the activities of mitochondrial complex I and IV were markedly decreased."
    explanation: Complex I and IV deficiency in a second family, notable for normal lactate.
  - reference: PMID:28299359
    reference_title: "AIFM1 mutation presenting with fatal encephalomyopathy and mitochondrial disease in an infant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Muscle biopsy during this admission demonstrated decreased activity of electron transport chain complex I and IV, with normal activity of complexes II and III."
    explanation: Combined complex I and IV deficiency in muscle of a fatal infantile case.

- name: Enhanced AIF-Dependent Parthanatos
  biological_scale: CELLULAR
  description: >-
    Separately from the OXPHOS defect, patient cells are primed for
    caspase-independent, AIF-mediated cell death (parthanatos). Staurosporine
    induces more parthanatos in p.Arg201del fibroblasts, patient muscle shows
    many TUNEL-positive, caspase 3-negative nuclei, and p.Pro169Leu fibroblasts
    are more sensitive to staurosporine and show more nuclear condensation under
    galactose. How much this branch contributes to neuronal loss in patients,
    as opposed to muscle, has not been measured.
  notes: >-
    GO has no parthanatos term, so the process is bound to the generic
    GO:0012501 programmed cell death with the specificity carried in
    preferred_term. Do not "correct" this to GO:0097300 programmed necrotic
    cell death: parthanatos is caspase-independent but not necroptotic.
  biological_processes:
  - preferred_term: parthanatos (caspase-independent AIF-mediated programmed cell death)
    term:
      id: GO:0012501
      label: programmed cell death
    modifier: INCREASED
  cell_types:
  - preferred_term: skeletal muscle fiber
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  downstream:
  - target: Mitochondrial Myopathy
    description: >-
      Parthanatos-type nuclei are seen in patient muscle, the tissue where
      this branch has been observed directly.
    evidence:
    - reference: PMID:20362274
      reference_title: "Severe X-linked mitochondrial encephalomyopathy associated with a mutation in apoptosis-inducing factor."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Numerous TUNEL-positive, caspase 3-negative nuclei were visualized in patient #1's muscle, again indicating markedly increased parthanatos in the AIF(R201 del) critical tissues."
      explanation: Direct observation of parthanatos-type cell death in patient muscle.
  - target: Progressive Neuronal Degeneration
    description: >-
      Inferred by extension from muscle and fibroblasts; parthanatos has not
      been demonstrated in patient brain.
  evidence:
  - reference: PMID:20362274
    reference_title: "Severe X-linked mitochondrial encephalomyopathy associated with a mutation in apoptosis-inducing factor."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "In AIF(R201 del) fibroblasts, staurosporine-induced parthanatos was markedly increased"
    explanation: Patient fibroblasts show increased parthanatos.
  - reference: PMID:34117073
    reference_title: "Severe multisystem pathology, metabolic acidosis, mitochondrial dysfunction, and early death associated with an X-linked AIFM1 variant."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Functional studies carried out on fibroblasts from the proband demonstrated reduced steady state levels of the AIFM1 protein, decreased Complex I subunit abundance, elevated sensitivity to the apoptosis inducer staurosporine, and increased nuclear condensation when grown in galactose-containing media."
    explanation: A second allele also increases cell-death sensitivity in patient fibroblasts.

- name: Progressive Neuronal Degeneration
  biological_scale: TISSUE
  description: >-
    Neurons of the cortex, basal ganglia, thalamus, cerebellum, brainstem,
    lower motor neurons and peripheral axons degenerate. Autopsy of a fatal
    infantile case showed mitochondrial encephalopathy with profound occipital
    cortical neuronal loss, gliosis and axonal degeneration in peripheral
    nerve; denervation in muscle reflects motor neuron and axonal loss. In the
    harlequin mouse, which keeps about 20% of normal AIF, mitochondria
    degenerate before neurons do, and neurodegeneration spreads from the
    cerebellum to the thalamus, striatum and cortex.
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  - preferred_term: motor neuron
    term:
      id: CL:0000100
      label: motor neuron
  downstream:
  - target: Encephalopathy
  - target: Global developmental delay
  - target: Developmental regression
  - target: Seizure
  - target: Abnormality of extrapyramidal motor function
  - target: Bilateral striatal necrosis
  - target: Abnormal basal ganglia MRI signal intensity
  - target: Cerebral atrophy
  - target: Cerebral edema
  - target: Diffuse white matter abnormality
  - target: Multicystic encephalomalacia
  - target: EEG burst suppression
  - target: Ventriculomegaly
  - target: Microcephaly
  - target: Peripheral axonal neuropathy
  - target: EMG and muscle biopsy denervation
  - target: Hypotonia
  - target: Sensorineural hearing impairment
  - target: Ataxia
  - target: Cerebellar atrophy
  - target: External ophthalmoplegia
  - target: Dysphagia
  evidence:
  - reference: PMID:28299359
    reference_title: "AIFM1 mutation presenting with fatal encephalomyopathy and mitochondrial disease in an infant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Autopsy, at the age of 4 mo, revealed features of mitochondrial encephalopathy, myopathy, and involvement of peripheral nerves with axonal degeneration."
    explanation: Human autopsy evidence of central and peripheral neurodegeneration.
  - reference: PMID:28299359
    reference_title: "AIFM1 mutation presenting with fatal encephalomyopathy and mitochondrial disease in an infant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the occipital cortex showed profound neuronal loss"
    explanation: Documents cortical neuronal loss at autopsy.
  - reference: PMID:26173962
    reference_title: "A novel AIFM1 mutation expands the phenotype to an infantile motor neuron disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our patients manifested a phenotype that included signs of both cortical and motor neuron involvement."
    explanation: Cortical and lower motor neuron involvement in two cousins with early-onset encephalopathy.
  - reference: PMID:17805014
    reference_title: "Apoptosis-inducing factor deficiency induces early mitochondrial degeneration in brain followed by progressive multifocal neuropathology."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "At 2 months of age, degenerating mitochondria were observed in most cells in these structures, even in nondegenerating neurons, a finding that indicates mitochondrial injury is a cause rather than an effect of neuronal cell death."
    explanation: In the AIF-deficient mouse, mitochondrial injury precedes and drives neuronal death.
  - reference: PMID:17805014
    reference_title: "Apoptosis-inducing factor deficiency induces early mitochondrial degeneration in brain followed by progressive multifocal neuropathology."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Neurodegeneration was not restricted to the cerebellum but progressively affected thalamic, striatal, and cortical regions as well."
    explanation: Multifocal progressive neurodegeneration in the mouse model, matching the human distribution.

- name: Mitochondrial Myopathy
  biological_scale: TISSUE
  description: >-
    Skeletal muscle shows mitochondrial myopathy: ragged-red or COX-hyporeactive
    fibers, abnormal mitochondria and atrophic fibers, on top of neurogenic
    (denervation) change. Deleting Aif in mouse muscle and heart alone causes
    complex I deficiency, skeletal muscle atrophy and lactic acidemia, so the
    myopathy is a primary consequence of AIF loss in muscle and not only
    secondary to denervation.
  cell_types:
  - preferred_term: skeletal muscle fiber
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  downstream:
  - target: Hypotonia
  - target: Muscle weakness
  - target: Skeletal muscle atrophy
  - target: Ragged-red muscle fibers
  - target: Respiratory insufficiency
  - target: Kyphoscoliosis
  evidence:
  - reference: PMID:28299359
    reference_title: "AIFM1 mutation presenting with fatal encephalomyopathy and mitochondrial disease in an infant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Electron microscopy demonstrated mitochondria that were irregular and bizarrely shaped without inclusions, numerous atrophic fibers, moderate myofiber disarray"
    explanation: Ultrastructural mitochondrial myopathy in a patient.
  - reference: PMID:16287843
    reference_title: "Muscle-specific loss of apoptosis-inducing factor leads to mitochondrial dysfunction, skeletal muscle atrophy, and dilated cardiomyopathy."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Mice in which Aif has been inactivated specifically in cardiac and skeletal muscle exhibit impaired activity and protein expression of respiratory chain complex I."
    explanation: Muscle-restricted AIF loss is sufficient to produce the respiratory chain defect in muscle.

- name: Cardiomyocyte Energy Failure
  biological_scale: CELLULAR
  description: >-
    Cardiac involvement is reported in a minority of patients, usually as
    ventricular hypertrophy beginning before or soon after birth that can
    progress to dilation and heart failure. Heart- and muscle-specific Aif
    deletion in the mouse causes complex I deficiency and dilated
    cardiomyopathy, supporting a direct bioenergetic mechanism in
    cardiomyocytes.
  cell_types:
  - preferred_term: cardiomyocyte
    term:
      id: CL:0000746
      label: cardiac muscle cell
  downstream:
  - target: Hypertrophic cardiomyopathy
  - target: Dilated cardiomyopathy
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:42329587
      reference_title: "Cardiomyopathy and mitochondrial encephalomyopathy in a female child associated with a heterozygous X-linked AIFM1 variant."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "the cardiac phenotype progressively evolved into dilated cardiomyopathy with systolic dysfunction by"
      explanation: Early hypertrophy progressed to dilated cardiomyopathy with systolic dysfunction in a human case.
  evidence:
  - reference: PMID:16287843
    reference_title: "Muscle-specific loss of apoptosis-inducing factor leads to mitochondrial dysfunction, skeletal muscle atrophy, and dilated cardiomyopathy."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Mutant animals develop severe dilated cardiomyopathy, heart failure, and skeletal muscle atrophy accompanied by lactic acidemia consistent with defects in the mitochondrial respiratory chain."
    explanation: AIF loss in cardiomyocytes causes cardiomyopathy in the mouse.
phenotypes:
- category: Neurological
  name: Encephalopathy
  description: >-
    Progressive encephalopathy beginning in the neonatal period or infancy is
    the defining feature.
  phenotype_term:
    preferred_term: Progressive mitochondrial encephalopathy
    term:
      id: HP:0006789
      label: Mitochondrial encephalopathy
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:20362274
    reference_title: "Severe X-linked mitochondrial encephalomyopathy associated with a mutation in apoptosis-inducing factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We investigated two male infant patients who were given a diagnosis of progressive mitochondrial encephalomyopathy on the basis of clinical, biochemical, and morphological features."
    explanation: The founding patients had progressive infantile encephalomyopathy.
  - reference: PMID:35712626
    reference_title: "Case Report: A Novel Intronic Mutation in AIFM1 Associated With Fatal Encephalomyopathy and Mitochondrial Disease in Infant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We describe a 4-month-old infant with mitochondrial encephalopathy, carrying a novel intronic variant in AIFM1"
    explanation: Infantile mitochondrial encephalopathy with a splice allele.
- category: Neurodevelopmental
  name: Global developmental delay
  description: Severe psychomotor delay, with failure to acquire milestones in the most severe families.
  phenotype_term:
    preferred_term: Psychomotor delay
    term:
      id: HP:0001263
      label: Global developmental delay
  evidence:
  - reference: PMID:25934856
    reference_title: "A slowly progressive mitochondrial encephalomyopathy widens the spectrum of AIFM1 disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: BACKGROUND
    snippet: "Patients with a severe outcome included 2 cousins with early-onset, severe psychomotor delay, extrapyramidal signs, epilepsy, and axonal sensory-motor neuropathy associated with bilateral striatal necrosis"
    explanation: Summarizes the founding cousins' severe psychomotor delay.
  - reference: PMID:22019070
    reference_title: "Early prenatal ventriculomegaly due to an AIFM1 mutation identified by linkage analysis and whole exome sequencing."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "postnatally, there was no acquisition of developmental milestones, and the muscles of the children were dystrophic."
    explanation: Absent developmental milestones in three affected siblings.
- category: Neurodevelopmental
  name: Developmental regression
  description: Loss of acquired skills, reported in some patients; the disease can also progress in steps with stable intervals.
  phenotype_term:
    preferred_term: Psychomotor regression
    term:
      id: HP:0002376
      label: Developmental regression
  evidence:
  - reference: PMID:25583628
    reference_title: "From ventriculomegaly to severe muscular atrophy: expansion of the clinical spectrum related to mutations in AIFM1."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Less frequent symptoms were hearing loss, seizures and psychomotor regression."
    explanation: Psychomotor regression is part of the reported AIFM1 encephalomyopathy spectrum.
- category: Neurological
  name: Seizure
  description: >-
    Seizures range from epilepsy in the founding cousins to drug-resistant
    multifocal neonatal seizures beginning within hours of birth.
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:37644805
    reference_title: "Expanding the spectrum of neonatal-onset AIFM1-associated disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The patient presented with drug-resistant, electro-clinical, multifocal seizures 6 h after birth."
    explanation: Drug-resistant neonatal seizures.
  - reference: PMID:28299359
    reference_title: "AIFM1 mutation presenting with fatal encephalomyopathy and mitochondrial disease in an infant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Here we describe a male infant with an X-linked sequence variant in AIFM1 and mitochondrial disease characterized by congenital lactic acidosis, intractable seizures, polyneuropathy, and myopathy."
    explanation: Intractable seizures in a fatal infantile case.
- category: Neurological
  name: Abnormality of extrapyramidal motor function
  description: Extrapyramidal signs in the founding cousins.
  phenotype_term:
    preferred_term: Extrapyramidal signs
    term:
      id: HP:0002071
      label: Abnormality of extrapyramidal motor function
  evidence:
  - reference: PMID:25934856
    reference_title: "A slowly progressive mitochondrial encephalomyopathy widens the spectrum of AIFM1 disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: BACKGROUND
    snippet: "Patients with a severe outcome included 2 cousins with early-onset, severe psychomotor delay, extrapyramidal signs, epilepsy, and axonal sensory-motor neuropathy associated with bilateral striatal necrosis"
    explanation: Extrapyramidal signs in the founding family.
- category: Neuroimaging
  name: Bilateral striatal necrosis
  description: Bilateral striatal necrosis in the founding cousins.
  phenotype_term:
    preferred_term: Bilateral striatal necrosis
    term:
      id: HP:0040140
      label: Degeneration of the striatum
  evidence:
  - reference: PMID:25934856
    reference_title: "A slowly progressive mitochondrial encephalomyopathy widens the spectrum of AIFM1 disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: BACKGROUND
    snippet: "Patients with a severe outcome included 2 cousins with early-onset, severe psychomotor delay, extrapyramidal signs, epilepsy, and axonal sensory-motor neuropathy associated with bilateral striatal necrosis"
    explanation: Bilateral striatal necrosis is recorded for the founding family.
- category: Neuroimaging
  name: Abnormal basal ganglia MRI signal intensity
  description: Restricted diffusion and T2 signal change in the caudate and putamen on MRI.
  phenotype_term:
    preferred_term: Abnormal basal ganglia MRI signal intensity
    term:
      id: HP:0012751
      label: Abnormal basal ganglia MRI signal intensity
  evidence:
  - reference: PMID:28299359
    reference_title: "AIFM1 mutation presenting with fatal encephalomyopathy and mitochondrial disease in an infant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "There was abnormal T2 signal intensity within the head and body of the caudate nuclei bilaterally and the bilateral anterior putamina"
    explanation: Bilateral striatal T2 signal change on MRI.
- category: Neuroimaging
  name: Cerebral atrophy
  phenotype_term:
    preferred_term: Cerebral atrophy
    term:
      id: HP:0002059
      label: Cerebral atrophy
  evidence:
  - reference: PMID:28299359
    reference_title: "AIFM1 mutation presenting with fatal encephalomyopathy and mitochondrial disease in an infant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Repeat MRI demonstrated cerebral atrophy in addition to previous findings."
    explanation: Progressive cerebral atrophy on serial MRI.
- category: Neuroimaging
  name: Cerebral edema
  description: >-
    A neonatal-onset case showed diffuse cytotoxic brain swelling of both
    hemispheres with cortical and thalamic signal alteration and sparing of the
    basal nuclei, a pattern distinct from the striatal-predominant involvement
    reported in most AIFM1 cases.
  phenotype_term:
    preferred_term: Cerebral edema
    term:
      id: HP:0002181
      label: Cerebral edema
  evidence:
  - reference: PMID:37644805
    reference_title: "Expanding the spectrum of neonatal-onset AIFM1-associated disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Brain MRI revealed prominent brain swelling of both hemispheres and widespread signal alteration in large part of the cortex and of the thalami, with sparing of the basal nuclei."
    explanation: Day-1 MRI shows diffuse brain swelling with cortical and thalamic involvement and basal-ganglia sparing.
- category: Neuroimaging
  name: Diffuse white matter abnormality
  phenotype_term:
    preferred_term: Diffuse white matter abnormalities
    term:
      id: HP:0007204
      label: Diffuse white matter abnormalities
  evidence:
  - reference: PMID:37644805
    reference_title: "Expanding the spectrum of neonatal-onset AIFM1-associated disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "neonatal seizures and diffuse white matter involvement with relative sparing of basal ganglia"
    explanation: The report's own summary names diffuse white matter involvement as the defining imaging finding.
- category: Neuroimaging
  name: Multicystic encephalomalacia
  description: >-
    The neonatal white-matter injury evolved to multicystic encephalomalacia on
    follow-up imaging.
  phenotype_term:
    preferred_term: Multicystic encephalomalacia
    term:
      id: HP:0040197
      label: Encephalomalacia
  evidence:
  - reference: PMID:37644805
    reference_title: "Expanding the spectrum of neonatal-onset AIFM1-associated disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "evolution toward multicystic encephalomalacia with marked T2 hyperintensity and T1 hypointensity of the white matter"
    explanation: Day-30 MRI shows evolution to multicystic encephalomalacia.
- category: Neurological
  name: EEG burst suppression
  phenotype_term:
    preferred_term: EEG burst suppression
    term:
      id: HP:0010851
      label: EEG with burst suppression
  evidence:
  - reference: PMID:37644805
    reference_title: "Expanding the spectrum of neonatal-onset AIFM1-associated disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "later evolving into a burst-suppression pattern"
    explanation: The neonatal electroclinical seizures evolved into a burst-suppression EEG pattern.
- category: Neuroimaging
  name: Ventriculomegaly
  description: >-
    Ventriculomegaly detected at early gestation in three siblings, and
    prenatal lateral ventricular dilation with colpocephaly in another family.
  phenotype_term:
    preferred_term: Prenatal ventriculomegaly
    term:
      id: HP:0002119
      label: Ventriculomegaly
  evidence:
  - reference: PMID:22019070
    reference_title: "Early prenatal ventriculomegaly due to an AIFM1 mutation identified by linkage analysis and whole exome sequencing."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Three siblings were found to have ventriculomegaly at early gestation"
    explanation: Prenatal ventriculomegaly in an AIFM1 family.
  - reference: PMID:34117073
    reference_title: "Severe multisystem pathology, metabolic acidosis, mitochondrial dysfunction, and early death associated with an X-linked AIFM1 variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Prenatal ultrasound at 25 wk gestation found bilateral mildly dilated cerebral lateral ventricles"
    explanation: Prenatal ventricular dilation in the p.Pro169Leu proband.
- category: Neurological
  name: Microcephaly
  phenotype_term:
    preferred_term: Microcephaly
    term:
      id: HP:0000252
      label: Microcephaly
  evidence:
  - reference: PMID:37644805
    reference_title: "Expanding the spectrum of neonatal-onset AIFM1-associated disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "At 6 months of age, the patient exhibited microcephaly but did not experience any further deterioration."
    explanation: Acquired microcephaly after neonatal encephalopathy.
- category: Neuromuscular
  name: Peripheral axonal neuropathy
  description: Axonal sensorimotor polyneuropathy, documented by nerve conduction studies and nerve pathology.
  phenotype_term:
    preferred_term: Axonal sensorimotor polyneuropathy
    term:
      id: HP:0003477
      label: Peripheral axonal neuropathy
  evidence:
  - reference: PMID:28299359
    reference_title: "AIFM1 mutation presenting with fatal encephalomyopathy and mitochondrial disease in an infant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Electromyography at 4 wk of age and again at 3 mo, demonstrated moderately severe axonal and sensorimotor polyneuropathy."
    explanation: Axonal sensorimotor polyneuropathy from the first weeks of life.
  - reference: PMID:25934856
    reference_title: "A slowly progressive mitochondrial encephalomyopathy widens the spectrum of AIFM1 disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Nerve conduction study showed a moderate-to-severe axonal, more sensory than motor, neuropathy."
    explanation: Axonal neuropathy in the slowly progressive form.
- category: Neuromuscular
  name: EMG and muscle biopsy denervation
  description: Severe denervation on electromyography and muscle biopsy, a lower motor neuron sign.
  phenotype_term:
    preferred_term: Severe denervation on EMG and muscle biopsy
    term:
      id: HP:0003445
      label: "EMG: neuropathic changes"
  evidence:
  - reference: PMID:26173962
    reference_title: "A novel AIFM1 mutation expands the phenotype to an infantile motor neuron disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Muscle biopsies and electromyography in both patients showed signs of severe denervation."
    explanation: Neurogenic denervation in two affected cousins.
- category: Neuromuscular
  name: Hypotonia
  phenotype_term:
    preferred_term: Axial and appendicular hypotonia
    term:
      id: HP:0001252
      label: Hypotonia
  evidence:
  - reference: PMID:28299359
    reference_title: "AIFM1 mutation presenting with fatal encephalomyopathy and mitochondrial disease in an infant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "examination was notable for axial and appendicular hypotonia."
    explanation: Hypotonia in an infant with AIFM1 encephalomyopathy.
  - reference: PMID:41211097
    reference_title: "Perioperative Care of a Child With Combined Oxidative Phosphorylation Deficiency 6: Total Intravenous Anesthesia With Remimazolam."
    supports: SUPPORT
    quote_role: BACKGROUND
    evidence_source: HUMAN_CLINICAL
    snippet: "COXPD6 patients have significant end-organ involvement of the central nervous, peripheral nervous, respiratory, and gastrointestinal systems, manifested by seizures, hypotonia, psychomotor delay, muscle weakness, and wasting."
    explanation: Summary of the COXPD6 phenotype, including hypotonia, stated as background in a case report.
- category: Neuromuscular
  name: Muscle weakness
  phenotype_term:
    preferred_term: Muscle weakness
    term:
      id: HP:0001324
      label: Muscle weakness
  evidence:
  - reference: PMID:41211097
    reference_title: "Perioperative Care of a Child With Combined Oxidative Phosphorylation Deficiency 6: Total Intravenous Anesthesia With Remimazolam."
    supports: SUPPORT
    quote_role: BACKGROUND
    evidence_source: HUMAN_CLINICAL
    snippet: "COXPD6 patients have significant end-organ involvement of the central nervous, peripheral nervous, respiratory, and gastrointestinal systems, manifested by seizures, hypotonia, psychomotor delay, muscle weakness, and wasting."
    explanation: Muscle weakness and wasting are part of the summarized COXPD6 phenotype.
- category: Neuromuscular
  name: Skeletal muscle atrophy
  description: Muscle wasting, described as dystrophic muscles in one family and as severe muscular atrophy in another.
  phenotype_term:
    preferred_term: Muscle wasting
    term:
      id: HP:0003202
      label: Skeletal muscle atrophy
  evidence:
  - reference: PMID:25583628
    reference_title: "From ventriculomegaly to severe muscular atrophy: expansion of the clinical spectrum related to mutations in AIFM1."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "at age 10 years muscle wasting, swallowing difficulties, respiratory insufficiency and external opthamoplegia."
    explanation: Muscle wasting in a boy with a hemizygous AIFM1 missense variant.
- category: Neuromuscular
  name: Ragged-red muscle fibers
  phenotype_term:
    preferred_term: Ragged-red fibers
    term:
      id: HP:0003200
      label: Ragged-red muscle fibers
  evidence:
  - reference: PMID:25934856
    reference_title: "A slowly progressive mitochondrial encephalomyopathy widens the spectrum of AIFM1 disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Muscle biopsy (13 years) showed evidence of chronic denervation, ragged-red fibers, and fibers hyporeactive to cytochrome c oxidase"
    explanation: Ragged-red and COX-hyporeactive fibers with denervation in muscle biopsy.
- category: Otologic
  name: Sensorineural hearing impairment
  phenotype_term:
    preferred_term: Hearing loss
    term:
      id: HP:0000407
      label: Sensorineural hearing impairment
  evidence:
  - reference: PMID:25583628
    reference_title: "From ventriculomegaly to severe muscular atrophy: expansion of the clinical spectrum related to mutations in AIFM1."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "At age 2.5 years he developed hearing loss and severe ataxia"
    explanation: Childhood-onset hearing loss in an AIFM1 encephalomyopathy patient.
  - reference: PMID:25934856
    reference_title: "A slowly progressive mitochondrial encephalomyopathy widens the spectrum of AIFM1 disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "During childhood, he developed gait and limb ataxia (sensory and cerebellar), hearing loss, and cognitive impairment."
    explanation: Hearing loss in the slowly progressive form.
- category: Neurological
  name: Ataxia
  phenotype_term:
    preferred_term: Gait and limb ataxia
    term:
      id: HP:0001251
      label: Ataxia
  evidence:
  - reference: PMID:25934856
    reference_title: "A slowly progressive mitochondrial encephalomyopathy widens the spectrum of AIFM1 disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "During childhood, he developed gait and limb ataxia (sensory and cerebellar), hearing loss, and cognitive impairment."
    explanation: Sensory and cerebellar ataxia in the slowly progressive form.
  - reference: PMID:25583628
    reference_title: "From ventriculomegaly to severe muscular atrophy: expansion of the clinical spectrum related to mutations in AIFM1."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "At age 2.5 years he developed hearing loss and severe ataxia"
    explanation: Severe ataxia from early childhood.
- category: Neuroimaging
  name: Cerebellar atrophy
  phenotype_term:
    preferred_term: Cerebellar atrophy
    term:
      id: HP:0001272
      label: Cerebellar atrophy
  evidence:
  - reference: PMID:25934856
    reference_title: "A slowly progressive mitochondrial encephalomyopathy widens the spectrum of AIFM1 disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Brain CT scan and MRI were normal at age 9 years, subsequently showing cerebellar atrophy (19 years) and mild cortical and thalamic atrophy (30 years)."
    explanation: Progressive cerebellar atrophy on MRI.
- category: Ophthalmological
  name: External ophthalmoplegia
  phenotype_term:
    preferred_term: External ophthalmoplegia
    term:
      id: HP:0000544
      label: External ophthalmoplegia
  evidence:
  - reference: PMID:25583628
    reference_title: "From ventriculomegaly to severe muscular atrophy: expansion of the clinical spectrum related to mutations in AIFM1."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "at age 10 years muscle wasting, swallowing difficulties, respiratory insufficiency and external opthamoplegia."
    explanation: External ophthalmoplegia (spelled opthamoplegia in the source) in late childhood.
- category: Gastrointestinal
  name: Dysphagia
  phenotype_term:
    preferred_term: Swallowing difficulties
    term:
      id: HP:0002015
      label: Dysphagia
  evidence:
  - reference: PMID:25583628
    reference_title: "From ventriculomegaly to severe muscular atrophy: expansion of the clinical spectrum related to mutations in AIFM1."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "at age 10 years muscle wasting, swallowing difficulties, respiratory insufficiency and external opthamoplegia."
    explanation: Swallowing difficulties in late childhood.
- category: Respiratory
  name: Respiratory insufficiency
  phenotype_term:
    preferred_term: Respiratory insufficiency
    term:
      id: HP:0002093
      label: Respiratory insufficiency
  evidence:
  - reference: PMID:25583628
    reference_title: "From ventriculomegaly to severe muscular atrophy: expansion of the clinical spectrum related to mutations in AIFM1."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "at age 10 years muscle wasting, swallowing difficulties, respiratory insufficiency and external opthamoplegia."
    explanation: Respiratory insufficiency with muscle wasting.
- category: Musculoskeletal
  name: Kyphoscoliosis
  description: Progressive neuromuscular kyphoscoliosis requiring posterior spinal fusion.
  phenotype_term:
    preferred_term: Progressive neuromuscular kyphoscoliosis
    term:
      id: HP:0002751
      label: Kyphoscoliosis
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:41211097
    reference_title: "Perioperative Care of a Child With Combined Oxidative Phosphorylation Deficiency 6: Total Intravenous Anesthesia With Remimazolam."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We present an 11-year-old child with AIFM1-related COXPD6 who underwent posterior spinal fusion for progressive neuromuscular kyphoscoliosis."
    explanation: Neuromuscular kyphoscoliosis in a child with COXPD6.
- category: Cardiovascular
  name: Hypertrophic cardiomyopathy
  description: >-
    Ventricular hypertrophy, detected prenatally in one proband and in
    infancy in a manifesting heterozygous girl, in whom it progressed to
    dilated cardiomyopathy with heart failure.
  phenotype_term:
    preferred_term: Ventricular hypertrophy (cardiomyopathy)
    term:
      id: HP:0001639
      label: Hypertrophic cardiomyopathy
  evidence:
  - reference: PMID:34117073
    reference_title: "Severe multisystem pathology, metabolic acidosis, mitochondrial dysfunction, and early death associated with an X-linked AIFM1 variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Fetal heart echocardiogram identified biventricular myocardial hypertrophy."
    explanation: Prenatal biventricular hypertrophy in the p.Pro169Leu proband.
  - reference: PMID:42329587
    reference_title: "Cardiomyopathy and mitochondrial encephalomyopathy in a female child associated with a heterozygous X-linked AIFM1 variant."
    supports: SUPPORT
    quote_role: REVIEW_SYNTHESIS
    evidence_source: HUMAN_CLINICAL
    snippet: "The phenotypic spectrum of AIFM1-related disease includes cardiomyopathy, typically characterized by early-onset cardiac hypertrophy that may progress to ventricular dilatation and heart failure."
    explanation: Cardiomyopathy across AIFM1 disease, typically early hypertrophy.
- category: Cardiovascular
  name: Dilated cardiomyopathy
  description: >-
    Early ventricular hypertrophy can progress to dilated cardiomyopathy with
    systolic dysfunction, documented in a manifesting heterozygous girl and the
    sole cardiac outcome of the heart- and muscle-specific Aif knockout mouse.
  phenotype_term:
    preferred_term: Dilated cardiomyopathy
    term:
      id: HP:0001644
      label: Dilated cardiomyopathy
  evidence:
  - reference: PMID:42329587
    reference_title: "Cardiomyopathy and mitochondrial encephalomyopathy in a female child associated with a heterozygous X-linked AIFM1 variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the cardiac phenotype progressively evolved into dilated cardiomyopathy with systolic dysfunction by"
    explanation: Serial echocardiography showed progression from hypertrophy to dilated cardiomyopathy.
  sequelae:
  - target: Congestive heart failure
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:42329587
      reference_title: "Cardiomyopathy and mitochondrial encephalomyopathy in a female child associated with a heterozygous X-linked AIFM1 variant."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "necessitating initiation of heart failure therapy"
      explanation: The dilated cardiomyopathy progressed to heart failure requiring therapy.
- category: Cardiovascular
  name: Congestive heart failure
  phenotype_term:
    preferred_term: Congestive heart failure
    term:
      id: HP:0001635
      label: Congestive heart failure
  evidence:
  - reference: PMID:42329587
    reference_title: "Cardiomyopathy and mitochondrial encephalomyopathy in a female child associated with a heterozygous X-linked AIFM1 variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "necessitating initiation of heart failure therapy"
    explanation: Heart failure therapy was initiated after progression to dilated cardiomyopathy.
- category: Metabolic
  name: Lactic acidosis
  phenotype_term:
    preferred_term: Lactic acidosis
    term:
      id: HP:0003128
      label: Lactic acidosis
  evidence:
  - reference: PMID:28299359
    reference_title: "AIFM1 mutation presenting with fatal encephalomyopathy and mitochondrial disease in an infant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Here we describe a male infant with an X-linked sequence variant in AIFM1 and mitochondrial disease characterized by congenital lactic acidosis, intractable seizures, polyneuropathy, and myopathy."
    explanation: Congenital lactic acidosis in a fatal infantile case.
  - reference: PMID:34117073
    reference_title: "Severe multisystem pathology, metabolic acidosis, mitochondrial dysfunction, and early death associated with an X-linked AIFM1 variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "He had severe metabolic acidosis, lactic acidosis, and an elevated anion gap."
    explanation: Neonatal lactic acidosis in the p.Pro169Leu proband.
  - reference: PMID:22019070
    reference_title: "Early prenatal ventriculomegaly due to an AIFM1 mutation identified by linkage analysis and whole exome sequencing."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "Plasma and CSF lactate levels were normal, but the activities of mitochondrial complex I and IV were markedly decreased."
    explanation: Lactate was normal in one family, so lactic acidosis is not a constant feature.
- category: Metabolic
  name: Increased CSF lactate
  phenotype_term:
    preferred_term: Increased CSF lactate
    term:
      id: HP:0002490
      label: Increased CSF lactate
  evidence:
  - reference: PMID:28299359
    reference_title: "AIFM1 mutation presenting with fatal encephalomyopathy and mitochondrial disease in an infant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "CSF lactate (6 mmol/l, reference range: 0.9-2.5 mmol/l) and pyruvate were elevated."
    explanation: Elevated CSF lactate in an infant with AIFM1 disease.
- category: Neuroimaging
  name: Elevated brain lactate level by MRS
  phenotype_term:
    preferred_term: Lactate doublet on brain MR spectroscopy
    term:
      id: HP:0012707
      label: Elevated brain lactate level by MRS
  evidence:
  - reference: PMID:28299359
    reference_title: "AIFM1 mutation presenting with fatal encephalomyopathy and mitochondrial disease in an infant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A new inverted lactate doublet at 1.33 ppm on single-voxel MR spectroscopy"
    explanation: Brain lactate peak on MR spectroscopy over the basal ganglia.
- category: Metabolic
  name: Decreased activity of mitochondrial complex IV
  phenotype_term:
    preferred_term: Cytochrome c oxidase (complex IV) deficiency
    term:
      id: HP:0008347
      label: Decreased activity of mitochondrial complex IV
  evidence:
  - reference: PMID:20362274
    reference_title: "Severe X-linked mitochondrial encephalomyopathy associated with a mutation in apoptosis-inducing factor."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Fibroblasts from both showed reduction of respiratory chain (RC) cIII and cIV, but not of cI activities."
    explanation: Complex IV deficiency in patient fibroblasts.
  - reference: PMID:26173962
    reference_title: "A novel AIFM1 mutation expands the phenotype to an infantile motor neuron disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In two male cousins with early-onset mitochondrial encephalopathy and cytochrome c oxidase (COX) deficiency, we identified a novel AIFM1 mutation."
    explanation: COX deficiency in two further affected males.
  - reference: PMID:34117073
    reference_title: "Severe multisystem pathology, metabolic acidosis, mitochondrial dysfunction, and early death associated with an X-linked AIFM1 variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Absent or partial deficiency of cytochrome c oxidase was found in muscle fibers, however, supporting a Complex IV mitochondrial deficiency."
    explanation: Complex IV deficiency in muscle.
- category: Metabolic
  name: Decreased activity of mitochondrial complex III
  phenotype_term:
    preferred_term: Complex III deficiency
    term:
      id: HP:0011924
      label: Decreased activity of mitochondrial complex III
  evidence:
  - reference: PMID:20362274
    reference_title: "Severe X-linked mitochondrial encephalomyopathy associated with a mutation in apoptosis-inducing factor."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Fibroblasts from both showed reduction of respiratory chain (RC) cIII and cIV, but not of cI activities."
    explanation: Complex III deficiency in patient fibroblasts.
  - reference: PMID:37644805
    reference_title: "Expanding the spectrum of neonatal-onset AIFM1-associated disorders."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Functional studies on cultured fibroblast showed a clear reduction in AIFM1 protein amount and defective activities of respiratory chain complexes I, III and IV."
    explanation: Complex III deficiency in neonatal-onset patient fibroblasts.
- category: Metabolic
  name: Decreased activity of mitochondrial complex I
  phenotype_term:
    preferred_term: Complex I deficiency
    term:
      id: HP:0011923
      label: Decreased activity of mitochondrial complex I
  evidence:
  - reference: PMID:22019070
    reference_title: "Early prenatal ventriculomegaly due to an AIFM1 mutation identified by linkage analysis and whole exome sequencing."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Plasma and CSF lactate levels were normal, but the activities of mitochondrial complex I and IV were markedly decreased."
    explanation: Complex I deficiency in an AIFM1 family.
  - reference: PMID:28299359
    reference_title: "AIFM1 mutation presenting with fatal encephalomyopathy and mitochondrial disease in an infant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Muscle biopsy during this admission demonstrated decreased activity of electron transport chain complex I and IV, with normal activity of complexes II and III."
    explanation: Complex I deficiency in patient muscle.
animal_models:
- name: Harlequin (Hq) mouse
  species: Mouse
  genotype: Aifm1 Hq proviral insertion (hypomorph, about 80% reduction in AIF)
  publication: PMID:12353028
  description: >-
    A spontaneous X-linked hypomorph with a retroviral insertion in Aifm1.
    Hemizygous males have complex I deficiency in brain and retina and
    progressive degeneration of cerebellar and retinal neurons that later
    involves thalamus, striatum and cortex.
  evidence:
  - reference: PMID:12353028
    reference_title: "The harlequin mouse mutation downregulates apoptosis-inducing factor."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "We have identified the Hq mutation as a proviral insertion in the apoptosis-inducing factor (Aif) gene, causing about an 80% reduction in AIF expression."
    explanation: Defines the model's genetic lesion.
  modeled_mechanisms:
  - target: Combined Oxidative Phosphorylation Deficiency
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >-
      Reduced AIF lowers OXPHOS and complex I subunits in brain and retina.
    limitations: >-
      A global hypomorph rather than a knock-in of a patient allele, so it
      models loss of AIF amount but not the altered DNA binding of p.Arg201del.
      The biochemical pattern is complex I-predominant, whereas several patients
      show complex III or IV deficiency.
    evidence:
    - reference: PMID:15526035
      reference_title: "AIF deficiency compromises oxidative phosphorylation."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Harlequin mice with reduced AIF expression due to a retroviral insertion into the AIF gene also manifest a reduced oxidative phosphorylation (OXPHOS) in the retina and in the brain, correlating with reduced expression of complex I subunits, retinal degeneration, and neuronal defects."
      explanation: The model reproduces the OXPHOS defect in nervous tissue.
  - target: Progressive Neuronal Degeneration
    relationship: PARTIALLY_RECAPITULATES
    fidelity: MODERATE
    description: >-
      Progressive, multifocal neurodegeneration preceded by mitochondrial
      degeneration.
    limitations: >-
      Onset is in adulthood (months) and cerebellar and retinal predominant,
      while the human disease is neonatal or infantile and dominated by
      encephalopathy, basal ganglia injury and neuropathy.
    evidence:
    - reference: PMID:12353028
      reference_title: "The harlequin mouse mutation downregulates apoptosis-inducing factor."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Harlequin (Hq) mutant mice have progressive degeneration of terminally differentiated cerebellar and retinal neurons."
      explanation: Progressive neurodegeneration in the AIF hypomorph.
- name: Muscle- and heart-specific Aif knockout mouse
  species: Mouse
  genotype: Conditional Aif deletion in cardiac and skeletal muscle
  publication: PMID:16287843
  description: >-
    Tissue-restricted deletion of Aif in striated muscle, isolating the muscle
    and heart consequences of AIF loss from its neuronal effects.
  evidence:
  - reference: PMID:16287843
    reference_title: "Muscle-specific loss of apoptosis-inducing factor leads to mitochondrial dysfunction, skeletal muscle atrophy, and dilated cardiomyopathy."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Mice in which Aif has been inactivated specifically in cardiac and skeletal muscle exhibit impaired activity and protein expression of respiratory chain complex I."
    explanation: Defines the model and its respiratory chain defect.
  modeled_mechanisms:
  - target: Mitochondrial Myopathy
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: Muscle atrophy with lactic acidemia after muscle-specific AIF loss.
    limitations: >-
      Complete tissue-specific knockout rather than a hypomorphic patient
      allele, and without the neurogenic component present in patients.
    evidence:
    - reference: PMID:16287843
      reference_title: "Muscle-specific loss of apoptosis-inducing factor leads to mitochondrial dysfunction, skeletal muscle atrophy, and dilated cardiomyopathy."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Mutant animals develop severe dilated cardiomyopathy, heart failure, and skeletal muscle atrophy accompanied by lactic acidemia consistent with defects in the mitochondrial respiratory chain."
      explanation: Reproduces skeletal muscle atrophy with lactic acidemia.
  - target: Cardiomyocyte Energy Failure
    relationship: PARTIALLY_RECAPITULATES
    fidelity: MODERATE
    description: Dilated cardiomyopathy and heart failure after cardiac AIF loss.
    limitations: >-
      The mice develop dilated cardiomyopathy, whereas patients more often
      present first with ventricular hypertrophy.
    evidence:
    - reference: PMID:16287843
      reference_title: "Muscle-specific loss of apoptosis-inducing factor leads to mitochondrial dysfunction, skeletal muscle atrophy, and dilated cardiomyopathy."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Mutant animals develop severe dilated cardiomyopathy, heart failure, and skeletal muscle atrophy accompanied by lactic acidemia consistent with defects in the mitochondrial respiratory chain."
      explanation: Cardiac AIF loss causes cardiomyopathy.
diagnosis:
- name: Respiratory chain enzymology and AIF immunoblot
  description: >-
    Spectrophotometric respiratory chain assays in muscle or fibroblasts show
    combined deficiency of complexes I, III and/or IV, and immunoblot shows
    reduced AIF protein in patient fibroblasts. The pattern differs between
    tissues and alleles, and lactate can be normal.
  evidence:
  - reference: PMID:37644805
    reference_title: "Expanding the spectrum of neonatal-onset AIFM1-associated disorders."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Functional studies on cultured fibroblast showed a clear reduction in AIFM1 protein amount and defective activities of respiratory chain complexes I, III and IV."
    explanation: Fibroblast studies support the diagnosis and the pathogenicity of a new variant.
- name: Exome sequencing
  description: >-
    Diagnosis rests on a hemizygous pathogenic AIFM1 variant, usually found by
    exome sequencing. Intronic splice variants have been confirmed by RNA
    analysis.
  evidence:
  - reference: PMID:37644805
    reference_title: "Expanding the spectrum of neonatal-onset AIFM1-associated disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "CES analysis revealed the likely pathogenic variant c.5T>C; p.(Phe2Ser) in the AIFM1 gene."
    explanation: Clinical exome sequencing identified the causal variant.
  - reference: PMID:35712626
    reference_title: "Case Report: A Novel Intronic Mutation in AIFM1 Associated With Fatal Encephalomyopathy and Mitochondrial Disease in Infant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our findings expand the mutation spectrum of AIFM1 and point out the necessity of intronic sequence analysis and the importance for integrative functional studies in the interpretation of sequence variants."
    explanation: Intronic variants need specific analysis and functional confirmation.
treatments:
- name: Mitochondrial cofactor supplementation
  description: >-
    Riboflavin, the precursor of FAD, has been given on the rationale that it
    stabilizes the flavin-bound AIF protein, alone or with coenzyme Q10 and
    thiamine. Results are mixed. One founding patient had prolonged
    neurological improvement, with correction of respiratory chain defects in
    his fibroblasts. A neonatal-onset patient on riboflavin, coenzyme Q10 and
    thiamine did not deteriorate further over six months. A slowly progressive
    patient had no change in clinical course on coenzyme Q10 and riboflavin, and
    riboflavin did not stabilize AIF in p.Pro169Leu fibroblasts. In the allelic
    childhood ataxia phenotype, riboflavin up to 200 mg per day partially
    improved ataxia scores. There are no controlled data.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: riboflavin
      term:
        id: CHEBI:17015
        label: riboflavin
    - preferred_term: coenzyme Q10
      term:
        id: CHEBI:46245
        label: coenzyme Q10
    - preferred_term: thiamine
      term:
        id: CHEBI:18385
        label: thiamine(1+)
  therapeutic_modality: SMALL_MOLECULE
  target_mechanisms:
  - target: Unstable AIF Protein
    treatment_effect: RESTORES
    description: >-
      Proposed to stabilize FAD binding in mitochondrial AIF; supported in
      fibroblasts of one allele and not of another.
    evidence:
    - reference: PMID:20362274
      reference_title: "Severe X-linked mitochondrial encephalomyopathy associated with a mutation in apoptosis-inducing factor."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "correction of RC defects in mutant fibroblasts, suggesting that stabilization of the FAD binding in AIF(mit) is beneficial"
      explanation: Riboflavin corrected respiratory-chain defects in patient fibroblasts, supporting FAD-binding stabilization of AIF.
    - reference: PMID:34117073
      reference_title: "Severe multisystem pathology, metabolic acidosis, mitochondrial dysfunction, and early death associated with an X-linked AIFM1 variant."
      supports: REFUTE
      evidence_source: IN_VITRO
      snippet: "The reduced abundance of AIFM1 in the patient cells could not be stabilized with riboflavin or protease inhibitor treatment."
      explanation: Riboflavin did not restore AIF levels in p.Pro169Leu fibroblasts.
  evidence:
  - reference: PMID:20362274
    reference_title: "Severe X-linked mitochondrial encephalomyopathy associated with a mutation in apoptosis-inducing factor."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "riboflavin supplementation was associated with prolonged improvement of patient #1's neurological conditions"
    explanation: Prolonged neurological improvement on riboflavin in the founding family (uncontrolled single-patient observation).
  - reference: PMID:37644805
    reference_title: "Expanding the spectrum of neonatal-onset AIFM1-associated disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Riboflavin, Coenzyme Q10 and thiamine supplementation was therefore given. At 6 months of age, the patient exhibited microcephaly but did not experience any further deterioration."
    explanation: Combined cofactor supplementation in a neonatal-onset patient, followed by clinical stability (uncontrolled).
  - reference: PMID:25934856
    reference_title: "A slowly progressive mitochondrial encephalomyopathy widens the spectrum of AIFM1 disorders."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "Coenzyme Q10 and riboflavin supplementation did not modify clinical course."
    explanation: No clinical benefit in a patient with the slowly progressive form.
  - reference: PMID:28967629
    reference_title: "Mutations in AIFM1 cause an X-linked childhood cerebellar ataxia partially responsive to riboflavin."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: "Ataxia score, decreased by 39% in patient 1 and 20% in patient 2 following 12 months of treatment."
    explanation: >-
      Partial response to riboflavin in two boys with an allelic AIFM1 ataxia
      phenotype; indirect for the encephalomyopathy.
- name: Antiseizure pharmacotherapy
  description: >-
    Seizures are treated with standard antiseizure drugs; phenobarbital was
    used in a fatal infantile case. Neonatal seizures can be drug-resistant.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: phenobarbital
      term:
        id: CHEBI:8069
        label: phenobarbital
  therapeutic_modality: SMALL_MOLECULE
  target_mechanisms:
  - target: Seizure
    treatment_effect: INHIBITS
    description: Symptomatic seizure control; it does not act on the mitochondrial defect.
  evidence:
  - reference: PMID:28299359
    reference_title: "AIFM1 mutation presenting with fatal encephalomyopathy and mitochondrial disease in an infant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "He was started on phenobarbital for management of seizures."
    explanation: Phenobarbital used for seizures in an AIFM1 patient.
- name: Perioperative anesthetic planning
  description: >-
    Surgery (for example spinal fusion for neuromuscular kyphoscoliosis) needs
    anesthetic planning adapted to mitochondrial disease; total intravenous
    anesthesia with remimazolam has been reported in a child with COXPD6.
  treatment_term:
    preferred_term: mitochondrial-disease perioperative anesthetic management
    term:
      id: NCIT:C15747
      label: Supportive Care
  therapeutic_modality: OTHER
  evidence:
  - reference: PMID:41211097
    reference_title: "Perioperative Care of a Child With Combined Oxidative Phosphorylation Deficiency 6: Total Intravenous Anesthesia With Remimazolam."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We explore the genetic history of this mitochondrial disorder, review a detailed anesthetic approach to perioperative management including use of the novel benzodiazepine, remimazolam, and discuss anesthetic considerations in these patients."
    explanation: Reports an anesthetic approach used in a child with COXPD6.
- name: Genetic counseling
  description: >-
    Counseling for X-linked recessive recurrence risk, carrier testing of at-risk
    female relatives, and the possibility of a manifesting heterozygous female
    with skewed X inactivation.
  treatment_term:
    preferred_term: Genetic Counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  therapeutic_modality: BEHAVIORAL
  notes: >-
    Left without an evidence item: no cited source reports counseling outcomes
    in this disease. The inheritance facts it relies on are cited under
    inheritance.
prevalence:
- population: Worldwide
  measure_type: CASES_IN_LITERATURE
  prevalence_class: ULTRA_RARE
  notes: >-
    Known only from case reports and small families. A 2015 review counted 11
    affected males in three families across the AIFM1 phenotypes then known,
    before adding a twelfth patient; no population prevalence or incidence has
    been estimated.
  evidence:
  - reference: PMID:25583628
    reference_title: "From ventriculomegaly to severe muscular atrophy: expansion of the clinical spectrum related to mutations in AIFM1."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "So far mutations in AIFM1, a X-chromosomal gene coding for AIF, have been described in three families with 11 affected males."
    explanation: Gives the case count at the time, before the authors added a further patient.
progression:
- phase: Prenatal to neonatal onset
  age_range: prenatal to first month
  notes: >-
    The severe end presents before or at birth, with prenatal ventriculomegaly,
    neonatal lactic acidosis or seizures within hours of birth.
  evidence:
  - reference: PMID:37644805
    reference_title: "Expanding the spectrum of neonatal-onset AIFM1-associated disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The patient presented with drug-resistant, electro-clinical, multifocal seizures 6 h after birth."
    explanation: Onset within hours of birth.
- phase: Variable progression
  age_range: infancy to adulthood
  notes: >-
    Severity varies even within a family. Some children die before age 5
    years; others progress in steps over decades, becoming chair-bound in early
    adulthood.
  evidence:
  - reference: PMID:25583628
    reference_title: "From ventriculomegaly to severe muscular atrophy: expansion of the clinical spectrum related to mutations in AIFM1."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Severity varies greatly even within one family with onset of symptoms between birth and adolescence."
    explanation: Documents the variable onset and severity.
  - reference: PMID:25934856
    reference_title: "A slowly progressive mitochondrial encephalomyopathy widens the spectrum of AIFM1 disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "He became chair-bound at age 20 years, needed acoustic aids at age 22 years, and developed progressive sleep apnea syndrome since age 23 years."
    explanation: Slow progression into adulthood in one patient.
- phase: Early death in the severe form
  age_range: first days to early childhood
  notes: >-
    The most severe cases die in the first months of life (day 8 and 4 months
    in two reports). In a 2015 review 3 of 12 patients died before age 5
    years. Death in infancy is recorded here rather than as a phenotype
    because the HPO term HP:0001522 sits under clinical course (mortality),
    outside the phenotypic-abnormality branch the phenotype slot accepts.
  evidence:
  - reference: PMID:28299359
    reference_title: "AIFM1 mutation presenting with fatal encephalomyopathy and mitochondrial disease in an infant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Given his poor neurologic prognosis, care was redirected, and he died at the age of 4 mo."
    explanation: Death at 4 months of age.
  - reference: PMID:34117073
    reference_title: "Severe multisystem pathology, metabolic acidosis, mitochondrial dysfunction, and early death associated with an X-linked AIFM1 variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The proband, his brother, and their maternal uncle all exhibited severe multisystem pathology, metabolic acidosis, and early demise."
    explanation: Early death in three affected males of one family.
  - reference: PMID:25583628
    reference_title: "From ventriculomegaly to severe muscular atrophy: expansion of the clinical spectrum related to mutations in AIFM1."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "3 of 12 patients died before age 5 years while others were still able to walk during young adulthood."
    explanation: Gives the proportion dying in early childhood and the survival of others into adulthood.
notes: >-
  Scope. This entry covers the encephalomyopathic, combined-OXPHOS-deficient
  end of the AIFM1 phenotypic continuum (COXPD6, OMIM 300816). The allelic
  entities are curated separately: Charcot-Marie-Tooth Disease X-linked
  Recessive 4 (Cowchock syndrome), the AUNX1 subtype of Auditory Neuropathy,
  and Spondyloepimetaphyseal Dysplasia Bieganski Type. The boundary is not
  sharp. The slowly progressive encephalomyopathy (p.Gly262Ser) and the boy
  with ataxia, hearing loss and later muscle wasting (p.Val243Leu) are
  included here because both were reported as mitochondrial encephalomyopathy
  with respiratory chain deficiency; the riboflavin-responsive childhood
  ataxia patients (p.Met340Thr, p.Thr141Ile) are cited only for treatment,
  marked indirect. The 11-year-old reported as COXPD6 for anesthetic care was
  first diagnosed with a CMTX4-associated variant, which illustrates the
  overlap.

  Phenotype frequencies are omitted: published cases are too few for a
  reliable band. Lactate is normal in some families, so a normal lactate does
  not exclude the disease.

  No GeneReviews or StatPearls chapter names this disease (just
  check-genereviews --online, Bookshelf index snapshot 2026-09-10 plus a live
  PubMed title search, returned NO_CHAPTER for both).

📚

References & Deep Research

Deep Research

1

Deep research results are used as seeds for research; they do not undergo the same validation as the main records and may contain errors. How we use deep research.

Evaluations and curation notes (1)

Create: Severe_X-linked_Mitochondrial_Encephalomyopathy · 2026-10-01T21:56:19Z · View source

New entry for severe X-linked mitochondrial encephalomyopathy (COXPD6, MONDO:0010437), caused by hemizygous AIFM1 variants. Scoped to the encephalomyopathic, combined-OXPHOS-deficient end of the AIFM1 spectrum; CMTX4 (Cowchock), the AUNX1 subtype of Auditory Neuropathy and Spondyloepimetaphyseal Dysplasia Bieganski Type are left as their own allelic entries and named in notes. Sources. One openscientist deep-research report (research/Severe_X-linked_Mitochondrial_Encephalomyopathy-deep-research-openscientist.md) was used as leads. Its reference validation was retrofitted with just validate-research-reference: 18/18 references resolved, 18/19 quotes found (the unfound one was a title fragment of PMID:30300862, not used). Term validation could not be written into the report because every run of just validate-research-terms aborted on a 5 s OLS read timeout; the partial term cache showed the report's suggested NCIT:C737 (Pesticide, offered as riboflavin), NCIT:C1198 (Poly ICLC, offered as coenzyme Q10) and HP:0007002 (Motor axonal neuropathy, offered as axonal sensorimotor neuropathy) to be wrong, so no CURIE was taken from the report. just preflight-dr exited 2 because no local mondo.db is present; disease identity was checked by hand (the report names AIFM1 35 times, OMIM 300816 and p.Arg201del, matching the stub's MONDO causal gene). Additional primary literature was found by PubMed search (Berger 2011, Kettwig 2015, Ardissone 2015, Diodato 2016, Morton 2017, Zambon 2023, Hangen 2015, Meyer 2015, Salscheider 2022, Vahsen 2004, Joza 2005, Klein 2002). Content. Eight pathophysiology nodes form a chain from unstable AIF protein through impaired CHCHD4 import and defective complex assembly to combined OXPHOS deficiency, with a parallel parthanatos branch, converging on neuronal degeneration, mitochondrial myopathy and cardiomyocyte energy failure. Thirty phenotypes, all causally connected. Death in infancy is carried in progression rather than as a phenotype because HP:0001522 is outside the PhenotypeTerm enum. Two animal models (harlequin hypomorph, muscle/heart Aif knockout) are linked to mechanism nodes. Riboflavin/cofactor treatment is recorded with both supporting and refuting evidence. No GeneReviews or StatPearls chapter exists (check-genereviews --online: NO_CHAPTER). Validation. just validate, validate-terms, count-verified-snippets (101/101), check-entity-refs, check-causal-targets, check-duplicate-keys, check-qualifier-terms, check-snippet-length, check-title-snippets, check-snippet-grading, check-environmental-evidence, check-folded-hyphens, check-coarse-phenotypes, check-reference-titles and validate-disorders all pass; list-disconnected-phenotypes reports 30/30 connected.

OpenScientist ▸

Key Findings

openscientist-autonomous 17 citations 2026-10-01T21:24:16.418886

Key Findings

Finding 1 — AIFM1 mutations cause the disease (COXPD6, OMIM #300816)

Ghezzi et al. (2010) identified a disease-segregating X-linked AIFM1 mutation — c.601_603del, p.Arg201del (R201del) — in two male infants with progressive mitochondrial encephalomyopathy. The pedigree (two affected boys born to monozygotic twin sisters and unrelated fathers) pointed unambiguously to X-linked inheritance rather than a shared autosomal or environmental cause. Patient fibroblasts showed a combined respiratory chain defect with reduced complex III and complex IV but preserved complex I activities at the fibroblast level, and re-expression of wild-type AIF rescued the biochemical defect. AIFM1 maps to Xq26.1, and the clinical entity is catalogued as Combined Oxidative Phosphorylation Deficiency 6 (COXPD6, OMIM #300816; MONDO:0010437).

"We found a disease-segregating mutation in the X-linked AIFM1 gene, encoding the Apoptosis-Inducing Factor (AIF) mitochondrion-associated 1 precursor that deletes arginine 201 (R201 del)." — PMID: 20362274

"Fibroblasts from both showed reduction of respiratory chain (RC) cIII and cIV, but not of cI activities." — PMID: 20362274

This is the foundational, human-clinical evidence establishing AIFM1 R201del as the causal lesion for severe X-linked mitochondrial encephalomyopathy.

Finding 2 — Dual pathomechanism: loss of OXPHOS support plus enhanced parthanatos

The same study demonstrated both arms of the mechanism. In AIF(R201del) fibroblasts, staurosporine-induced parthanatos (caspase-independent chromatin fragmentation) was markedly increased, and re-expression of wild-type AIF restored respiratory chain activities — simultaneously proving a pro-death gain of function and a loss of the OXPHOS-supporting function. Patient muscle showed numerous TUNEL-positive, caspase-3-negative nuclei, the histological signature of parthanatos in a disease-critical tissue. In vitro, R201del decreases the stability of both mitochondrial AIF(mit) and soluble AIF(sol) and increases AIF(sol) DNA-binding affinity (a prerequisite for the nuclear, pro-death activity). Mechanistically, AIF supports complex I assembly/stability by promoting mitochondrial import of MIA40/CHCHD4.

"In AIF(R201 del) fibroblasts, staurosporine-induced parthanatos was markedly increased, whereas re-expression of AIF(wt) induced recovery of RC activities." — PMID: 20362274

"they channel electrons into the respiratory chain and, at least in animals, promote the import of Mia40 (named MIA40 or CHCHD4 in humans) and the assembly of complex I" — PMID: 32769219

Finding 3 — Broad allelic spectrum, from lethal infantile encephalomyopathy to later-onset neuropathy/ataxia

AIFM1 variants produce a phenotypic continuum rather than a single syndrome:

Phenotype	Representative variant	Key features	Evidence
Severe infantile mitochondrial encephalomyopathy (COXPD6)	p.Arg201del	Regression, seizures, lactic acidosis, early death	PMID: 20362274
Early-onset axonal sensorimotor neuropathy with hearing loss	(various)	Neuropathy + deafness	PMID: 28967629
Cowchock syndrome / CMTX4	p.Glu493Val	Slowly progressive X-linked axonal neuropathy, deafness, cognitive impairment	PMID: 23217327
Riboflavin-responsive X-linked cerebellar ataxia	p.Met340Thr, p.Thr141Ile	Childhood ataxia, partial riboflavin response	PMID: 28967629
Severe multisystem disease, metabolic acidosis, early death	(X-linked AIFM1)	Multisystem pathology	PMID: 34117073

"Mutations in the X-linked AIFM1 were reported in relation to two main phenotypes: a severe infantile mitochondrial encephalomyopathy and an early-onset axonal sensorimotor neuropathy with hearing loss." — PMID: 28967629

"Cowchock syndrome (CMTX4) is a slowly progressive X-linked recessive disorder with axonal neuropathy, deafness, and cognitive impairment." — PMID: 23217327

Importantly, the ataxia end of the spectrum is partially riboflavin-responsive: in two patients, riboflavin (up to 200 mg/day for 12 months) decreased the ICARS ataxia score by 39% and 20%, respectively.

"Ataxia score, decreased by 39% in patient 1 and 20% in patient 2" — PMID: 28967629

Finding 4 — The Harlequin (Hq) mouse recapitulates complex I deficiency and progressive neurodegeneration

The Harlequin mouse carries a proviral insertion in Aifm1 that reduces AIF by 80–90%, producing severe complex I deficiency (40–50% reduction in complex I level/activity) and progressive neurodegeneration beginning ~3 months of age, most pronounced in cerebellum and retina and extending to cortex, striatum, and thalamus, accompanied by oxidative-stress markers. Critically, El Ghouzzi et al. (2007) showed that early mitochondrial degeneration precedes multifocal neuropathology, establishing mitochondrial injury as a cause rather than a consequence of neuronal death — directly supporting the "upstream bioenergetic lesion" model of AIFM1 disease. AIF deficiency also sensitizes dopaminergic neurons to MPTP (a gene–environment interaction), reinforcing that AIF-linked complex I defects lower the threshold for neurodegeneration.

"harlequin mice exhibiting an 80-90% global reduction in AIF protein are resistant to numerous forms of acute brain injury, they paradoxically undergo slow, progressive neurodegeneration beginning at three months of age" — PMID: 23246553

"degenerating mitochondria were observed in most cells in these structures, even in nondegenerating neurons, a finding that indicates mitochondrial injury is a cause rather than an effect of neuronal cell death" — PMID: 17805014

Finding 5 — Cardiomyopathy and manifesting heterozygous females with skewed X-inactivation

Although X-linked recessive, AIFM1 disease can manifest in heterozygous females when X-inactivation is skewed. Sandmann et al. (2026) reported the first affected female with a heterozygous AIFM1 variant c.506C>T (p.Pro169Leu) and extremely skewed X-inactivation (98:2), presenting with infantile-onset mitochondrial encephalomyopathy and cardiomyopathy: marked left-ventricular hypertrophy with preserved systolic function at 8 months, progressing to dilated cardiomyopathy with systolic dysfunction by 2.5 years, requiring heart-failure therapy. Cardiac involvement had previously been described in a handful of AIFM1 patients, predominantly as ventricular hypertrophy.

"We report the first affected female with a heterozygous AIFM1 variant who developed infantile-onset mitochondrial encephalomyopathy and cardiomyopathy with initial ventricular hypertrophy, that progressed to left ventricular dilation and chronic heart failure." — PMID: 42329587

"Genetic testing identified a heterozygous AIFM1 variant, c.506C > T (p.Pro169Leu), with extremely skewed X-inactivation (98:2) in a female." — PMID: 42329587

Finding 6 — Neonatal-onset presentation, characteristic MRI, and the diagnostic pathway

Zambon et al. (2023) expanded the neonatal-onset spectrum, describing drug-resistant multifocal seizures 6 hours after birth, with brain MRI showing prominent bilateral hemispheric brain swelling and widespread cortical and thalamic signal alteration with sparing of the basal nuclei. Clinical exome sequencing identified a likely pathogenic variant c.5T>C p.(Phe2Ser) in the mitochondrial targeting sequence. Functional fibroblast studies showed reduced AIFM1 protein and defective complex I, III and IV activities (without protein mislocalization or precursor accumulation). The diagnostic workup integrated EEG, brain MRI/MR spectroscopy, metabolic screening, echocardiography, and clinical exome sequencing — a template for diagnosing this disease.

"The patient presented with drug-resistant, electro-clinical, multifocal seizures 6 h after birth. Brain MRI revealed prominent brain swelling of both hemispheres and widespread signal alteration in large part of the cortex and of the thalami, with sparing of the basal nuclei." — PMID: 37644805

"Functional studies on cultured fibroblast showed a clear reduction in AIFM1 protein amount and defective activities of respiratory chain complexes I, III and IV." — PMID: 37644805

Finding 7 — The parthanatos cascade and AIF's reframing as an "OXPHOS-inducing factor"

Liu et al. (2022) detail parthanatos as a regulated cell-death program: PARP-1 overactivation → PAR accumulation → PAR binding to AIF → AIF release from mitochondria → nuclear translocation of the AIF/MIF complex → MIF-mediated large-scale DNA fragmentation. In parallel, Wischhof et al. (2022) reframe AIF as an "OXPHOS-inducing factor" whose principal physiological role is to promote the biogenesis and maintenance of the OXPHOS system — recasting AIFM1 disease as primarily a bioenergetic disorder on which a cell-death liability is superimposed.

"PARP-1) overactivation, PAR accumulation, PAR binding to apoptosis-inducing factor (AIF), AIF release from the mitochondria, nuclear translocation of the AIF/macrophage migration inhibitory factor (MIF) complex, and MIF-mediated large-scale DNA fragmentation" — PMID: 35000037

"AIF contributes to cell survival by promoting biogenesis and maintenance of the mitochondrial oxidative phosphorylation (OXPHOS) system" — PMID: 35994922

Finding 8 — Genetics and inheritance

AIFM1 (apoptosis-inducing factor mitochondria-associated 1; UniProt O95831; NCBI Gene 9131; Ensembl ENSG00000156709; Xq26.1) encodes a 613-amino-acid FAD-dependent NADH oxidoreductase. Disease is X-linked recessive: affected males typically inherit the variant from carrier mothers; the founding Ghezzi pedigree demonstrated transmission through monozygotic twin sisters to sons by unrelated fathers. Reported pathogenic variants are predominantly missense or small in-frame deletions affecting the FAD/NAD(H) oxidoreductase domain or the mitochondrial targeting sequence: p.Arg201del (severe encephalomyopathy), p.Glu493Val (Cowchock/CMTX4), p.Met340Thr and p.Thr141Ile (riboflavin-responsive ataxia), p.Phe2Ser (neonatal, MTS), p.Pro169Leu (manifesting female, cardiomyopathy), and p.Gly308Glu. The disease is ultra-rare (fewer than ~30 families/individuals reported worldwide). Pathogenic/likely-pathogenic variants are classified per ACMG/AMP and are essentially absent from gnomAD population controls.

"These patients were born from monozygotic twin sisters and unrelated fathers, suggesting an X-linked trait." — PMID: 20362274

"The disease locus was previously mapped to an 11 cM region at chromosome X: q24-q26." — PMID: 23217327

Finding 9 — Management is supportive; candidate redox/cofactor therapies only

No disease-modifying therapy is approved. Reported interventions include riboflavin (vitamin B2, a FAD precursor) up to 200 mg/day, which partially improved ataxia (ICARS −39% / −20%; Heimer 2018), and a combined riboflavin + Coenzyme Q10 + thiamine "mito cocktail" associated with clinical stabilization in a neonatal case (Zambon 2023). Preclinical candidates include the redox compound methylene blue (protective of AIF-deficient photoreceptors; Mekala 2019), the SOD-mimetic tempol (reversed MPTP susceptibility in Harlequin mice; Perier 2010), and NADH supplementation (proposed for mitochondrial-dysfunction neurodegeneration; Chen 2024). Supportive care encompasses antiepileptic drugs (seizures are frequently drug-resistant), nutritional/feeding support, heart-failure therapy for cardiomyopathy, and physical/occupational/speech rehabilitation. Anesthetic caution is required: total intravenous anesthesia with remimazolam has been reported for COXPD6 (Olakunle 2025).

"Riboflavin, Coenzyme Q10 and thiamine supplementation was therefore given. At 6 months of age, the patient exhibited microcephaly but did not experience any further deterioration." — PMID: 37644805

"The protective role of the redox compound methylene blue" — PMID: 30300862

Mechanistic Model / Interpretation

Ordered causal chain (initiating lesion → clinical manifestation)

A germline pathogenic AIFM1 variant (e.g., p.Arg201del) is present on the X chromosome → leads to an altered AIF protein with reduced stability and altered redox/DNA-binding properties.
Reduced/dysfunctional AIF in the mitochondrial intermembrane space → results in impaired MIA40/CHCHD4 import and defective respiratory-chain complex assembly/stability (branch point A).
Branch A (bioenergetic): Defective OXPHOS → leads to a combined complex I/III/IV deficiency, reduced ATP output, and increased reactive oxygen species (oxidative stress) → results in energy failure in high-demand tissues (brain, heart, skeletal muscle, inner ear).
Branch B (cell-death / parthanatos): Cellular stress and PARP-1 overactivation → leads to PAR accumulation → PAR binds AIF → AIF release from mitochondria → nuclear translocation of the AIF/MIF complex → MIF-mediated large-scale DNA fragmentation → results in caspase-independent neuronal and myocyte death (evidenced by TUNEL+, caspase-3− nuclei in patient muscle). This branch's quantitative contribution in human tissue is partly inferred from in-vitro and model data.
Convergence of Branch A (energy failure) and Branch B (parthanatos) in the CNS → leads to encephalopathy: developmental regression, drug-resistant seizures, hypotonia, and characteristic MRI changes (hemispheric swelling, cortical/thalamic signal change, basal-nuclei sparing).
Energy failure and cell death in cardiomyocytes → results in cardiomyopathy (hypertrophic → dilated with heart failure).
Involvement of cochlear/neural tissue → leads to sensorineural hearing loss; involvement of peripheral axons (in milder alleles) → axonal sensorimotor neuropathy.
Progressive multi-organ bioenergetic failure with lactic acidosis → results in early death in severe infantile/neonatal cases.

AIFM1 pathogenic variant (e.g., p.Arg201del) @ Xq26.1
         │
    Unstable / dysfunctional AIF (IMS)
         │
┌────────────────┴─────────────────┐
   BRANCH A                            BRANCH B
 (bioenergetic)                      (parthanatos)
│                                  │
 ↓ MIA40/CHCHD4 import           PARP-1 overactivation
│                                  │
 defective complex I/III/IV        PAR accumulation → binds AIF
 assembly & stability                      │
│                          AIF released → nucleus
 ↓ ATP, ↑ ROS                      AIF/MIF complex
│                                  │
 energy failure                    large-scale DNA fragmentation
└───────────────┬──────────────────┘
        ▼
Neuronal + cardiomyocyte + myocyte death
        ▼
   Encephalomyopathy · cardiomyopathy · hearing loss
   seizures · regression · lactic acidosis · early death

Upstream vs. downstream

Upstream (initiating): the AIFM1 variant and the resulting loss of AIF's OXPHOS-supporting function. The Harlequin model confirms that mitochondrial injury is causal and precedes overt neuropathology (PMID: 17805014).
Downstream (effector): OXPHOS deficiency → ATP deficit/ROS; parthanatos → DNA fragmentation and caspase-independent death; organ-level manifestations (encephalopathy, cardiomyopathy, deafness, neuropathy).

Cell types, compartments, and ontology suggestions

Subcellular (GO Cellular Component): mitochondrial intermembrane space (GO:0005758), mitochondrial inner membrane (GO:0005743), respiratory chain complex I (GO:0005747), nucleus (GO:0005634, for the pro-death translocation).
Biological processes (GO): mitochondrial electron transport / OXPHOS (GO:0006119), mitochondrial respiratory chain complex assembly (GO:0033108), parthanatos / DNA-damage-induced caspase-independent apoptosis, protein import into mitochondrial intermembrane space (GO:0045041), response to oxidative stress (GO:0006979), FAD binding / NADH dehydrogenase activity (GO:0003954).
Cell types (CL): neuron (CL:0000540), cerebellar Purkinje cell (CL:0000121), retinal photoreceptor cell (CL:0000210), cardiac muscle cell / cardiomyocyte (CL:0000746), skeletal muscle fiber (CL:0000188), cochlear hair cell (CL:0000855).
Anatomy (UBERON): brain (UBERON:0000955), cerebral cortex (UBERON:0000956), thalamus (UBERON:0001897), cerebellum (UBERON:0002037), heart / cardiac ventricle (UBERON:0000948 / UBERON:0002082), skeletal muscle (UBERON:0001134), cochlea (UBERON:0001844), retina (UBERON:0000966), peripheral nerve (UBERON:0001021).
Chemical entities (CHEBI): FAD (CHEBI:16238), NADH (CHEBI:16908), riboflavin (CHEBI:17015), ubiquinone/CoQ10 (CHEBI:46245), thiamine (CHEBI:18385), methylene blue (CHEBI:6872), L-lactate (CHEBI:16651).
Treatment (NCIT): Riboflavin (C737), Coenzyme Q10 (C1198), Thiamine (C933), Methylene Blue (C61585), Anticonvulsant Agent (C264), Supportive Care (C15184).

Section-by-Section Synthesis

1. Disease Information

A concise overview: a severe, X-linked, infantile/neonatal-onset primary mitochondrial encephalomyopathy due to AIFM1 deficiency, biochemically a combined OXPHOS deficiency (COXPD6). Identifiers: MONDO:0010437; OMIM #300816; gene AIFM1 (HGNC:8768). Synonyms/related: Combined Oxidative Phosphorylation Deficiency 6 (COXPD6); AIFM1-related mitochondrial encephalomyopathy; AIF deficiency. The milder allelic entities (Cowchock syndrome/CMTX4; AIFM1-related ataxia) are distinct but share the gene. Information is derived from aggregated disease-level resources and small case series/reports rather than EHR-scale cohorts, reflecting the ultra-rare nature of the disease.

2. Etiology

Primary cause: monogenic — pathogenic AIFM1 variants (X-linked recessive). Genetic risk factors: hemizygous pathogenic AIFM1 variants in males; in females, a heterozygous variant plus skewed X-inactivation (e.g., 98:2) can manifest disease (PMID: 42329587). Environmental/modifier factors: limited human data, but model data show AIF deficiency sensitizes neurons to exogenous complex I inhibitors (MPTP) — a demonstrated gene–environment interaction that lowers the neurodegeneration threshold (PMID: 20695011). Protective factors: none genetically established; redox/antioxidant interventions (tempol in mice) partially protect in models. Sex is a strong determinant (males predominantly affected).

3. Phenotypes

Core phenotypes (with suggested HPO terms): developmental regression (HP:0002376), seizures/drug-resistant epilepsy (HP:0001250), hypotonia (HP:0001252), lactic acidosis (HP:0003128), sensorineural hearing loss (HP:0000407), cardiomyopathy (HP:0001638; hypertrophic HP:0001639, dilated HP:0001644), psychomotor/developmental delay (HP:0001263), microcephaly (HP:0000252), cerebellar ataxia (HP:0001251, milder alleles), axonal sensorimotor neuropathy (HP:0007002, milder alleles), abnormal brain MRI (HP:0002543). Onset: neonatal to infantile in the severe form; childhood/adult in milder alleles. Severity: severe to variable. Progression: progressive, often rapidly fatal in the severe form; slowly progressive in Cowchock/ataxia alleles. Quality-of-life impact: profound in the severe form (loss of milestones, refractory seizures, feeding difficulty, cardiac failure).

4. Genetic/Molecular Information

Causal gene: AIFM1 (Xq26.1; OMIM 300169). Protein: AIF, 613 aa, FAD-dependent NADH oxidoreductase (UniProt O95831). Variant classes: predominantly missense and small in-frame deletions in the FAD/NAD(H) oxidoreductase domain or MTS; representative alleles listed in Finding 8. Classification: pathogenic/likely pathogenic (ACMG/AMP); absent from gnomAD. Origin: germline. Functional consequence: combined loss of OXPHOS support (loss of function for the vital role) with an altered pro-death / DNA-binding gain for the soluble form. Epigenetic modifier: X-inactivation skewing* critically determines female manifestation. No recurrent large chromosomal abnormality is characteristic.

5. Environmental Information

No established infectious or primary environmental cause. The relevant environmental dimension is gene–environment interaction: in AIF-deficient models, complex I inhibitor exposure (MPTP) precipitates dopaminergic neurodegeneration that spares wild-type animals (PMID: 20695011), implying mitochondrial toxins and metabolic stressors may aggravate the human phenotype in principle.

6. Mechanism / Pathophysiology

See the ordered causal chain and diagram above. Key pathways/processes: OXPHOS/electron transport (complex I/III/IV), MIA40/CHCHD4 mitochondrial import pathway, parthanatos (PARP-1/PAR/AIF/MIF), oxidative stress. AIF additionally participates in the KEAP1/PGAM5/AIFM1 oxeiptosis axis implicated in ROS-induced, caspase-independent cell death (PMID: 41338468). AIF's redox chemistry (NADH/FAD charge-transfer complex, dimerization) governs the switch between its biogenesis-supporting and cell-death roles (PMID: 26535916, PMID: 32769219).

7. Anatomical Structures Affected

Primary organs: brain (cortex, thalamus, cerebellum), heart (ventricular myocardium), skeletal muscle, inner ear (cochlea), retina (prominent in models), peripheral nerve (milder alleles). Body systems: nervous, cardiovascular, musculoskeletal, special sensory. Subcellular: mitochondria (intermembrane space, inner membrane), with nuclear translocation of AIF in the death branch. Lateralization: bilateral/symmetric CNS involvement (e.g., bilateral hemispheric swelling on MRI).

8. Temporal Development

Onset: congenital/neonatal to infantile in the severe form (e.g., seizures 6 h after birth); childhood–adult in milder alleles. Course: rapidly progressive and often fatal in infancy for severe alleles; slowly progressive for Cowchock/ataxia alleles. Critical window: early infancy is both the period of greatest vulnerability and the plausible window for cofactor/redox intervention; riboflavin responsiveness in ataxia patients suggests a treatable component for specific genotypes.

9. Inheritance and Population

Inheritance: X-linked recessive; manifesting heterozygous females occur with skewed XCI. Penetrance: high in hemizygous males carrying severe alleles; expressivity is variable (strong genotype–phenotype correlation across the allelic series). Epidemiology: ultra-rare (<~30 families/individuals reported worldwide); precise prevalence/incidence unknown (below Orphanet reporting thresholds). Sex ratio: strongly male-predominant. Founder effects / consanguinity: not a prominent feature (X-linked, private variants). Carrier frequency: not established; variants essentially absent from gnomAD.

10. Diagnostics

Biochemistry: elevated lactate; respiratory-chain enzymology in fibroblasts/muscle showing combined complex I/III/IV deficiency; reduced AIFM1 protein on immunoblot. Histopathology: TUNEL-positive/caspase-3-negative nuclei (parthanatos signature) in muscle. Imaging: brain MRI (bilateral hemispheric swelling, cortical/thalamic signal change with basal-nuclei sparing); MR spectroscopy (lactate peak). Electrophysiology: EEG (multifocal epileptiform activity); nerve conduction studies for neuropathy alleles. Cardiac: echocardiography (hypertrophic/dilated cardiomyopathy). Genetic testing (recommended first-line): clinical exome (WES) or genome (WGS) sequencing, or a mitochondrial/encephalopathy gene panel including AIFM1; single-gene AIFM1 testing and segregation/X-inactivation studies to confirm. Differential diagnosis: other combined OXPHOS deficiencies, Leigh syndrome and Leigh-like disorders, mtDNA-encoded mitochondrial encephalomyopathies, and other X-linked encephalopathies.

11. Outcome / Prognosis

Severe form: poor — typically early death in infancy/childhood with multisystem failure and metabolic acidosis (PMID: 34117073); high morbidity (refractory seizures, profound developmental impairment, cardiomyopathy). Milder alleles: prolonged survival with chronic disability (neuropathy, deafness, ataxia). Prognostic factors: genotype (specific allele), age at onset, and severity/rate of cardiac and metabolic decompensation. No validated molecular prognostic biomarker beyond genotype.

12. Treatment

No curative/disease-modifying therapy. Pharmacotherapy/cofactors (NCIT where applicable): riboflavin (NCIT:C737), Coenzyme Q10 (NCIT:C1198), thiamine (NCIT:C933), antiepileptic drugs (NCIT:C264). Preclinical/experimental redox agents: methylene blue (NCIT:C61585), tempol, NADH. Supportive/rehabilitative: nutritional/feeding support, heart-failure therapy for cardiomyopathy, physical/occupational/speech therapy. Perioperative: mitochondrial-safe anesthesia (e.g., total intravenous anesthesia with remimazolam reported for COXPD6; PMID: 41211097). Pharmacogenomics / personalized medicine: genotype-guided trial of riboflavin for riboflavin-responsive alleles. No approved gene, cell, or RNA therapy exists.

13. Prevention

Primary prevention: not applicable (monogenic); genetic counseling for X-linked recurrence risk is central. Secondary: carrier testing in at-risk female relatives, cascade testing, and prenatal/preimplantation genetic testing where a familial variant is known. Tertiary: proactive seizure control, cardiac surveillance/heart-failure management, nutritional support, avoidance of mitochondrial toxins and risky anesthetics. No vaccination or population screening applies.

14. Other Species / Natural Disease

Model/ortholog species: mouse (Mus musculus, NCBI Taxon 10090; Aifm1, NCBI Gene 26926). The Harlequin mouse is a naturally arising hypomorphic Aifm1 model. No prominent naturally occurring companion-animal/wildlife disease is established; the mechanism (AIF-dependent OXPHOS support) is evolutionarily conserved across animals, underpinning cross-species modeling.

15. Model Organisms

Primary model: Harlequin (Hq) mouse — hypomorphic Aifm1 (80–90% AIF reduction) with complex I deficiency and progressive cerebellar/retinal neurodegeneration (PMID: 23246553, PMID: 17805014). Used to demonstrate causal upstream mitochondrial injury, ROS regulation, MPTP sensitization (PMID: 20695011), tau interaction (PMID: 19942317), and redox rescue (tempol, methylene blue). Phenotype recapitulation: reproduces complex I deficiency and progressive neurodegeneration. Limitations: a hypomorph (not an allele-specific knock-in of human severe variants); does not fully capture the human infantile encephalopathy/cardiomyopathy severity or the allele-specific gain-of-function (DNA-binding) biology. Patient-derived fibroblasts and iPSCs serve as complementary in-vitro models.

Evidence Base

PMID	Title (abbrev.)	Source type	Contribution
20362274	Severe X-linked mitochondrial encephalomyopathy assoc. with AIF mutation	Human clinical + in vitro	Establishes AIFM1 R201del as causal; dual mechanism (OXPHOS loss + parthanatos); X-linked inheritance
32769219	AIF and mitochondrial NADH dehydrogenases: redox-controlled gear boxes	Review	AIF promotes MIA40/CHCHD4 import and complex I assembly; redox switch
28967629	AIFM1 cause X-linked childhood cerebellar ataxia partially responsive to riboflavin	Human clinical	Defines allelic spectrum; quantifies riboflavin response (ICARS −39%/−20%)
23217327	Cowchock syndrome assoc. with AIF mutation	Human clinical	Milder CMTX4 end of spectrum; Xq24–q26 mapping
34117073	Severe multisystem pathology, metabolic acidosis, early death (X-linked)	Human clinical	Severe multisystem phenotype, early death
42329587	Cardiomyopathy and encephalomyopathy in a female with heterozygous AIFM1	Human clinical	Manifesting female; skewed XCI (98:2); cardiomyopathy progression
37644805	Expanding neonatal-onset AIFM1 disorders	Human clinical + in vitro	Neonatal seizures, MRI pattern, MTS variant; mito cocktail stabilization
23246553	AIF, ROS, and neurodegeneration	Model/review	Harlequin model: 80–90% AIF loss, progressive neurodegeneration
17805014	AIF deficiency induces early mitochondrial degeneration	Model organism	Mitochondrial injury is causal/upstream of neuronal death
20695011	AIF deficiency sensitizes dopaminergic neurons to parkinsonian neurotoxins	Model organism	Gene–environment interaction (MPTP); tempol rescue
35000037	Key players of parthanatos	Review	Defines PARP-1→PAR→AIF/MIF→DNA fragmentation cascade
35994922	AIFM1 beyond cell death: OXPHOS-inducing factor	Review	Reframes disease as primarily bioenergetic
30300862	AIF deficiency causes retinal photoreceptor degeneration; methylene blue	Model organism	Candidate redox therapy (methylene blue)
26535916	Adenylate moiety and NAD(+)/H binding to AIF	In vitro/structural	Redox/cofactor mechanism; G308E pathophysiology
19942317	Tau + Harlequin mutation increases mito dysfunction/neurodegeneration	Model organism	Mitochondrial dysfunction ↔ tauopathy interaction
41338468	Oxeiptosis: KEAP1/PGAM5/AIFM1 axis in PD	Review	AIFM1 in ROS-induced caspase-independent death
41211097	Perioperative care in COXPD6: TIVA with remimazolam	Case report	Anesthetic management guidance
38297850	Therapeutic potential of NADH	Review	NADH as candidate for mito-dysfunction neurodegeneration

Evidence-source balance: The causal genetics and dual-mechanism are supported by human clinical + in-vitro patient-cell data (strong). The upstream-causality and therapeutic-rescue claims rest substantially on model-organism (Harlequin mouse) and in-vitro evidence. Treatment efficacy data are limited to small case reports and n=2 cohorts — hypothesis-generating rather than definitive.

Limitations and Knowledge Gaps

Ultra-rarity limits epidemiology: fewer than ~30 reported families/individuals preclude reliable prevalence, incidence, penetrance-by-allele, and natural-history quantification.
Mechanistic weighting is unresolved: the relative contribution of Branch A (OXPHOS loss) versus Branch B (parthanatos) to human tissue damage is inferred largely from in-vitro and mouse data; the parthanatos contribution in patient CNS/heart is not quantified in vivo.
Biochemical heterogeneity: fibroblast enzymology is inconsistent across patients (complex III/IV reduced with preserved complex I in the index family; complex I/III/IV all reduced in the neonatal case), complicating a single unifying biochemical signature.
Model limitations: the Harlequin mouse is a hypomorph, not an allele-specific knock-in; it under-represents the severe human infantile encephalopathy/cardiomyopathy and the gain-of-function (DNA-binding) biology of specific alleles.
No controlled therapeutic data: riboflavin and the "mito cocktail" responses are anecdotal/small-n; there are no randomized trials and no approved disease-modifying therapy.
Genotype–phenotype gaps: predictive rules linking specific AIFM1 variants to severity, riboflavin-responsiveness, or cardiac risk remain incompletely defined.
Female manifestation: the threshold of X-inactivation skewing required for disease, and its tissue-specific variability, are documented in only a single case.

Proposed Follow-up Experiments / Actions

Allele-specific knock-in models: Generate mouse (or iPSC-derived neuron/cardiomyocyte/organoid) knock-ins of human severe alleles (p.Arg201del, p.Pro169Leu) to dissect Branch A vs. Branch B contributions and to model cardiomyopathy.
Quantify parthanatos in patient tissue: Use PAR, PARP-1, and nuclear AIF/MIF markers in patient muscle/brain autopsy material to establish the in-vivo magnitude of the death branch and its therapeutic tractability (e.g., PARP inhibitors, MIF-nuclease inhibitors).
Genotype-stratified cofactor trials: Build an international registry and run small, biomarker-anchored n-of-1 or basket trials of riboflavin ± CoQ10 ± thiamine, stratified by allele and by FAD-domain impact, using ICARS/clinical and lactate/respirometry endpoints.
Redox therapeutics translation: Advance methylene blue, tempol, and NADH from Harlequin-model efficacy toward patient-derived cardiomyocyte/neuron testing, with mitochondrial respirometry and ROS readouts.
X-inactivation and female risk: Systematically measure tissue-specific XCI skewing in heterozygous females to define the manifestation threshold and inform counseling.
Natural-history and biomarker study: Pool cases to define age-specific survival, cardiac trajectory, seizure burden, and candidate prognostic biomarkers (lactate, FGF21, neurofilament), enabling clinical-trial readiness.
Gene/RNA therapy feasibility: Evaluate AIFM1 gene replacement or variant-specific correction given the loss-of-vital-function component, balancing against the gain-of-function (DNA-binding) risk of over-expression.

Report compiled from 9 confirmed findings and 26 reviewed papers across 5 investigation iterations. Evidence sources are distinguished as human clinical, model organism, in vitro, or computational/review throughout.

Artifacts

Reference Validation

Checked with linkml-reference-validator 0.3.0rc3.

Outcome	Count
References checked	18
Resolved	18
Unresolved (possible confabulation)	0
Unverifiable	0
Quoted claims checked	19
Quoted claims found in source	18
Quoted claims not found in source	1
References weighed for topical relevance	18
On topic	13
Off topic	0

Quotes not found in the cited source

Searched the abstract, any retrieved full text, and the title. A quote drawn from a part of the paper that was not retrieved will appear here too, so check before treating one as invented:

Every one of these was searched against an abstract alone, with no full text retrieved - marked abstract only below. Where full text can be fetched, re-running with it will settle them; where the source publishes only a summary to PubMed, as GeneReviews chapters do, it will not, and the quote has to be checked by hand against the chapter itself.

PMID:30300862 (abstract only): "The protective role of the redox compound methylene blue"
closest text in source: "We investigated the effect of mitochondrial OXPHOS deficiency on retinal photoreceptors in a model of mitochondrial complex I defect (apoptosis inducing factor, AIF-deficient mice, Harlequin mice), and tested the protective effect of a mitochondrial redox compound (methylene blue, MB) on mitochondrial and photoreceptor integrity"

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Inheritance

Pathophysiology

Pathograph

Phenotypes

Genetic Associations

Medical Actions

Diagnosis

Progression

Prevalence

Animal Models

Source YAML

References & Deep Research

Deep Research

Key Findings

Finding 1 — AIFM1 mutations cause the disease (COXPD6, OMIM #300816)

Finding 2 — Dual pathomechanism: loss of OXPHOS support plus enhanced parthanatos

Finding 3 — Broad allelic spectrum, from lethal infantile encephalomyopathy to later-onset neuropathy/ataxia

Finding 4 — The Harlequin (Hq) mouse recapitulates complex I deficiency and progressive neurodegeneration

Finding 5 — Cardiomyopathy and manifesting heterozygous females with skewed X-inactivation

Finding 6 — Neonatal-onset presentation, characteristic MRI, and the diagnostic pathway

Finding 7 — The parthanatos cascade and AIF's reframing as an "OXPHOS-inducing factor"

Finding 8 — Genetics and inheritance

Finding 9 — Management is supportive; candidate redox/cofactor therapies only

Mechanistic Model / Interpretation

Ordered causal chain (initiating lesion → clinical manifestation)

Upstream vs. downstream

Cell types, compartments, and ontology suggestions

Section-by-Section Synthesis

1. Disease Information

2. Etiology

3. Phenotypes

4. Genetic/Molecular Information

5. Environmental Information

6. Mechanism / Pathophysiology

7. Anatomical Structures Affected

8. Temporal Development

9. Inheritance and Population

10. Diagnostics

11. Outcome / Prognosis

12. Treatment

13. Prevention

14. Other Species / Natural Disease

15. Model Organisms

Evidence Base

Limitations and Knowledge Gaps

Proposed Follow-up Experiments / Actions

Artifacts

Reference Validation

Quotes not found in the cited source