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Inheritance

1

Autosomal Recessive HP:0000007

Autosomal recessive, with founder alleles and consanguinity driving the epidemiology. Being of Persian or Middle Eastern Jewish, Japanese, Korean, Bulgarian Roma, or certain Indian ancestries substantially raises prior probability.

Autosomal recessive inheritance

Show evidence (1 reference)

PMID:20301439 SUPPORT Human Clinical

"GNE myopathy is inherited in an autosomal recessive manner."

GeneReviews states the inheritance pattern.

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Subtypes

2

Epimerase-domain variant genotypes

Genotypes with variants affecting the UDP-N-acetylglucosamine 2-epimerase domain. The distinction from kinase-domain genotypes is therapeutically consequential rather than cosmetic: N-acetylmannosamine enters the pathway downstream of the epimerase step and so bypasses an epimerase block, and it also restored sialic acid synthesis in patients homozygous for kinase-domain variants. Not a formally recognized clinical classification.

Kinase-domain variant genotypes

Genotypes with variants affecting the N-acetylmannosamine kinase domain. Recorded separately because the phase 1 N-acetylmannosamine study explicitly showed restored intracellular sialic acid biosynthesis in subjects homozygous for kinase-domain variants, which was not a foregone conclusion for a precursor entering upstream of that step.

Show evidence (1 reference)

PMID:28641925 SUPPORT Human Clinical

"Given that Neu5Ac is known to have a short half-life, the prolonged elevation of Neu5Ac after a single dose of ManNAc suggests that intracellular biosynthesis of sialic acid was restored in subjects with GNE myopathy, including those homozygous for mutations in the kinase domain."

Establishes that the kinase-domain genotype is a separately relevant pharmacological category, and that the precursor works in it.

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Discussions and Knowledge Gaps

4

Why is a systemic enzyme deficiency that lowers sialic acid in serum, muscle, and other organs expressed as a disease of skeletal muscle alone?

KNOWLEDGE GAP gne_tissue_restriction_paradox

Attached to

pathophysiology#Hyposialylation of Muscle Glycoproteins

The enzymatic block is everywhere and the mouse model shows marked hyposialylation in serum, muscle, and other organs, yet the clinical disease is essentially confined to skeletal muscle. Two partial answers exist and neither closes the question. The quadriceps sparing observation shows that baseline sialic acid requirement differs between muscles, which suggests demand rather than supply sets vulnerability. And the total-versus-free sialic acid discrepancy suggests only a small subset of sialylation targets is pathogenically relevant. Identifying that target set is the field's central open question, and until it is answered the tissue restriction is described rather than explained.

Show evidence (2 references)

PMID:17704511 SUPPORT Model Organism

"Interestingly, these mice exhibit marked hyposialylation in serum, muscle and other organs."

Establishes that the biochemical deficit is systemic while the disease is not, which is the paradox itself.

PMID:28267778 SUPPORT Human Clinical

"Differences in mean total SA levels in muscle from patients compared with normal controls were less distinct and more variable between different muscles, suggesting a small subset of sialylation targets could be responsible for the pathogenesis of GNEM."

Points toward a narrow pathogenic target set as a partial explanation.

Does oral sialic acid replacement modify the course of GNE myopathy, given that a Class I international trial was negative and Japanese trials were equivocal-to-positive enough to support approval?

CONTROVERSY gne_sialic_acid_trial_discordance

Attached to

treatments#Aceneuramic Acid Extended-Release (Sialic Acid Replacement)

Both results are real and this entry declines to pick between them. The international phase 3 gave Class I evidence of no benefit on muscle strength. The Japanese phase II/III missed its primary covariance analysis and reached significance only on a repeated-measures analysis in 20 patients; the confirmatory Japanese study in a smaller cohort showed a numerically smaller decline with a confidence interval crossing zero, which its authors call a trend. Approval followed in Japan in 2024. Candidate reconciliations include differences in cohort genotype, disease stage at enrolment, statistical approach, and endpoint sensitivity, none of which has been tested directly. A curator should not present either result alone.

Show evidence (2 references)

PMID:31036580 SUPPORT Human Clinical

"This study provides Class I evidence that for patients with GNE myopathy, Ace-ER does not improve muscle strength compared to placebo."

One half of the discordance, at the highest available evidence class.

PMID:37568154 SUPPORT Human Clinical

"The present study reproducibly showed a trend towards slowing of loss of muscle strength and function with orally administered SA-ER, indicating supplementation with sialic acid might be a promising replacement therapy for GNE myopathy."

The other half, in the authors' own deliberately hedged language.

Is beta-amyloid accumulation mechanistically upstream of myofiber atrophy in GNE myopathy, or a downstream marker of failed autophagic clearance?

OPEN QUESTION gne_amyloid_causal_weight

Attached to

pathophysiology#Amyloid and Misfolded Protein Accumulation

The mouse model shows amyloid deposition preceding rimmed vacuole formation by ten weeks, which is consistent with amyloid being upstream but does not establish it, since both could be downstream of a shared clearance failure. Review literature has argued for a mechanistic role while stating plainly that the cause and process of amyloid formation in this disease are unclear. The entry therefore places amyloid in the chain with an indirect causal link to atrophy and unknown intermediates rather than asserting a direct one.

Show evidence (1 reference)

PMID:17704511 SUPPORT Model Organism

"A compelling finding is the development of beta-amyloid deposition in myofibers by 32 weeks, which clearly precedes RV formation at 42 weeks."

Establishes temporal precedence, which constrains but does not settle the causal question.

How reliable is the quadriceps-sparing, anterior-first rule, given documented families with the opposite pattern?

OPEN QUESTION gne_atypical_muscle_involvement

Attached to

pathophysiology#Myofiber Atrophy and Degeneration

Quadriceps sparing with anterior-compartment onset is the single most useful diagnostic discriminator in this disease, and it now has a biochemical explanation in the lower baseline sialic acid requirement of normal quadriceps. But at least one family broke the pattern entirely, with severe posterior calf involvement and a spared anterior compartment. The entry states the rule because it is diagnostically load-bearing, and records the exception so the rule is not read as absolute.

Show evidence (1 reference)

PMID:27854221 SUPPORT Human Clinical

"in contrast to the typical pattern of muscle involvement, one of them showed severe involvement of posterior calf muscles with spared anterior compartment of the lower leg muscles."

Documents a family with the inverted involvement pattern.

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Pathophysiology

6

Biallelic Hypomorphic GNE Variants and Enzymatic Block

GNE encodes one polypeptide carrying two enzyme activities, UDP-GlcNAc 2-epimerase and N-acetylmannosamine kinase, which together run the first committed and rate-limiting steps of sialic acid synthesis. Biallelic hypomorphic variants, predominantly missense and distributed across both catalytic domains, reduce that throughput. The variants must be hypomorphic rather than null: Gne knockout is embryonic lethal in mouse, so every surviving human genotype retains residual enzyme activity, and that is why curating these alleles as complete loss of function overstates the lesion.

GNE hgnc:23657

UDP-N-acetylglucosamine 2-epimerase activity GO:0008761 ↓ DECREASED N-acetylmannosamine kinase activity GO:0009384 ↓ DECREASED

Downstream

Free Sialic Acid Depletion Reduced throughput of the first committed steps depletes the free sialic acid pool in serum and, far more severely, in muscle.

Show evidence (3 references)

PMID:11528398 SUPPORT Human Clinical

"Our findings indicate that GNE is the gene responsible for recessive HIBM."

The gene-identification study establishing GNE as causative.

PMID:39332896 SUPPORT Human Clinical

"Missense variants predominantly located in the epimerase/kinase domain coding region, indicating the impairment of catalytic function as a key pathogenic consequence."

Establishes that the variant spectrum is dominated by missense changes in the catalytic domains, so the lesion is impaired catalysis.

PMID:17704511 SUPPORT Model Organism

"We knocked out the Gne gene in mice but this resulted in embryonic lethality."

Embryonic lethality of the null establishes that surviving human genotypes must be hypomorphic rather than complete loss of function.

Free Sialic Acid Depletion

The best-quantified node in the disease, and the one that also explains its most distinctive clinical sign. Serum free sialic acid is 18% below age-matched controls, but muscle free sialic acid is down 72 to 85%, so the deficit is far more severe in the tissue that gets sick. The quadriceps sparing rule falls out of the same measurements: normal quadriceps already runs on 39% less free sialic acid than normal gastrocnemius, so it has less to lose when supply is throttled.

N-acetylneuraminate biosynthetic process GO:0046380 ↓ DECREASED

skeletal muscle tissue UBERON:0001134

Downstream

Hyposialylation of Muscle Glycoproteins A depleted free sialic acid pool leaves muscle glycoproteins undersialylated.

Show evidence (3 references)

PMID:28267778 SUPPORT Human Clinical

"These results show that serum and muscle free SA is severely reduced in GNEM, which is consistent with the biochemical defect in SA synthesis associated with GNE mutations."

Quantitative confirmation that the free sialic acid pool is severely depleted in patients, in serum and muscle.

PMID:28267778 SUPPORT Human Clinical

"A lower SA requirement for quadriceps may be linked to the reported quadriceps sparing in GNEM."

Offers the biochemical explanation for quadriceps sparing, grounded in measured differences in normal muscle rather than in the disease.

PMID:17704511 SUPPORT Model Organism

"Interestingly, these mice exhibit marked hyposialylation in serum, muscle and other organs."

The mouse model reproduces the systemic hyposialylation, which is the starting point of the tissue-restriction paradox.

Hyposialylation of Muscle Glycoproteins

Muscle glycoproteins carry less sialic acid than they should. Two things should be said carefully here. First, the specific glycoprotein target or targets whose undersialylation is actually pathogenic have not been definitively identified, and the sialic acid measurements themselves hint that the set is small: total sialic acid differences between patients and controls were less distinct and more variable than the free pool differences. Second, that hyposialylation is causal rather than incidental was established by rescue in the mouse, and the authors of that rescue were careful to call it one of the key factors rather than the whole story.

skeletal muscle fiber CL:0008002

protein sialylation GO:1990743 ↓ DECREASED

Animal models

Gne-null mouse expressing human GNE p.Asp207Val transgene Mouse rescues Oral sialic acid metabolites completely prevented muscle atrophy and weakness in this model, which is the pivotal demonstration that hyposialylation is causal rather than incidental to the myopathy.

Downstream

Autophagic Block and Proteostasis Failure Undersialylated muscle is where the downstream proteostasis failure and rimmed vacuole formation occur. The steps connecting the sialylation deficit to the autophagy block are not established.

Myofiber Atrophy and Degeneration Hyposialylation is causally upstream of the atrophy and weakness, as shown by complete prevention of both in the mouse when sialic acid metabolites are supplied.

Show evidence (3 references)

PMID:19448634 SUPPORT Model Organism

"By showing that muscle atrophy and weakness are completely prevented in a mouse model of DMRV-hIBM after treatment with sialic acid metabolites orally, we provide evidence that hyposialylation is indeed one of the key factors in the pathomechanism of DMRV-hIBM."

The pivotal causality proof, quoted with the authors' own hedge that hyposialylation is one of the key factors rather than the sole cause.

PMID:28267778 SUPPORT Human Clinical

"Differences in mean total SA levels in muscle from patients compared with normal controls were less distinct and more variable between different muscles, suggesting a small subset of sialylation targets could be responsible for the pathogenesis of GNEM."

Suggests the pathogenic target set is narrow. PARTIAL because it is an inference the authors themselves frame as a suggestion, and no specific target glycoprotein is identified.

PMID:41082181 SUPPORT Human Clinical

"Deficient GNE enzyme activity results in decreased production of sialic acid and subsequent hyposialylation of muscle glycoproteins, ultimately leading to progressive muscle degeneration and characteristic histopathological changes."

States the canonical chain from enzyme deficiency through hyposialylation to degeneration.

Autophagic Block and Proteostasis Failure

Rimmed vacuoles are not vacuoles in the naive sense; they are accumulated autophagic material, and recent isogenic-model work supplies an actual signaling chain for why the material accumulates. Excessive extracellular matrix production drives aberrant activation of a noncanonical AKT-mTORC1 pathway, which phosphorylates and inhibits ULK1 and so suppresses autophagy initiation. Reactivating autophagy by PI3K inhibition restores ULK1 activity in patient-derived neuromuscular organoids, which is what makes this a causal chain rather than a correlation.

skeletal muscle fiber CL:0008002

macroautophagy GO:0016236 ↓ DECREASED

Experimental models

Human pluripotent stem cell-derived GNE myoblasts and neuromuscular organoids IPSC DERIVED MODEL Transcriptomic analysis identified autophagy gene sets as pathogenic signatures, biochemically validated in Gne-knockout myoblasts, and PI3K inhibition restored ULK1 activity and reactivated autophagy in patient-relevant neuromuscular organoids.

Downstream

Amyloid and Misfolded Protein Accumulation Suppressed autophagic clearance permits accumulation of aggregation-prone protein within myofibers.

Rimmed Vacuoles The accumulated autophagic material is what is seen histologically as rimmed vacuoles.

Show evidence (2 references)

PMID:41963465 SUPPORT In Vitro

"By performing transcriptome analysis on two independent GNE myoblast models derived from human pluripotent stem cells, we identified multiple autophagy-related gene sets as pathogenic signatures of GNE myopathy."

Establishes autophagy dysregulation as a transcriptional signature across two independent human stem-cell-derived models.

PMID:41963465 SUPPORT In Vitro

"induces inhibitory phosphorylation of ULK1, thereby suppressing autophagy initiation."

Names the specific inhibitory step, ULK1 phosphorylation, that blocks autophagy initiation in this disease.

Amyloid and Misfolded Protein Accumulation

Myofibers accumulate congophilic material immunoreactive to beta-amyloid, lysosomal proteins, ubiquitin, and tau. The mouse model established the temporal ordering, which is the mechanistically interesting part: beta-amyloid deposition appears at 32 weeks and clearly precedes rimmed vacuole formation at 42 weeks. Whether the amyloid is mechanistically upstream of the atrophy or a downstream marker of failed clearance remains unsettled, and this entry does not decide it.

skeletal muscle fiber CL:0008002

Animal models

Gne-null mouse expressing human GNE p.Asp207Val transgene Mouse recapitulates Beta-amyloid deposition appears in myofibers at 32 weeks and clearly precedes rimmed vacuole formation at 42 weeks, which is the ordering that constrains causal models of the inclusion pathology.

Downstream

Deposits Immunoreactive to Beta-Amyloid Protein The accumulated material is detected histologically as beta-amyloid immunoreactive deposits.

Myofiber Atrophy and Degeneration Accumulated misfolded protein accompanies and plausibly contributes to myofiber degeneration, though its causal weight is unsettled and no intermediate steps are established.

Show evidence (2 references)

PMID:17704511 SUPPORT Model Organism

"A compelling finding is the development of beta-amyloid deposition in myofibers by 32 weeks, which clearly precedes RV formation at 42 weeks."

Establishes that amyloid deposition precedes rimmed vacuole formation, which is the temporal ordering that constrains any causal model.

PMID:17704511 SUPPORT Model Organism

"It is pathologically characterized by the presence of rimmed vacuoles (RVs), especially in atrophic fibers, which also occasionally contain congophilic materials that are immunoreactive to beta-amyloid, lysosomal proteins, ubiquitin and tau proteins."

Describes the composition of the inclusions. Tagged MODEL_ORGANISM because evidence_source classifies the publication's study type rather than the topic of the quoted sentence, and this is a mouse transgenic study whose opening prose describes the human disease.

Myofiber Atrophy and Degeneration

The tissue endpoint: progressive myofiber atrophy and degeneration with angular fibers and increased fiber-size variability, without inflammation. Distribution is the diagnostic signature. Weakness starts in the anterior compartment of the lower leg, progresses to the posterior compartment, then hamstrings, then hip girdle, and the quadriceps is relatively spared until late. End-stage tissue outcomes are fibrosis and fatty replacement.

skeletal muscle fiber CL:0008002

skeletal muscle tissue UBERON:0001134

Downstream

Foot Dorsiflexor Weakness Anterior tibialis involvement produces the presenting bilateral foot drop.

Distal Lower Limb Muscle Weakness Distal lower limb muscles are affected first and worst.

Distal Amyotrophy Progressive wasting accompanies the distal weakness.

Steppage Gait Foot drop produces a steppage gait.

Proximal Muscle Weakness Hip girdle weakness follows years to decades after onset.

Loss of Ambulation Progressive weakness leads to wheelchair dependence roughly ten to twenty years after onset.

Increased Variability in Muscle Fiber Diameter Histologic correlate of the atrophic process.

Elevated Circulating Creatine Kinase Concentration Myofiber degeneration releases creatine kinase, though only to normal or mildly elevated levels.

Respiratory Insufficiency Due to Muscle Weakness Respiratory muscle involvement appears late, and forced vital capacity declines measurably in non-ambulant patients.

Show evidence (2 references)

PMID:30338442 SUPPORT Human Clinical

"The disease slowly progresses over the next decades to involve skeletal muscles throughout the body, with relative sparing of the quadriceps until late stages of the disease."

Establishes the progression pattern and the quadriceps sparing that defines it.

PMID:20301439 SUPPORT Human Clinical

"Lower-extremity muscle involvement progresses from the anterior to the posterior compartment of the lower leg, followed by hamstrings, then hip girdle muscles, with relative sparing of the quadriceps."

GeneReviews states the compartment-by-compartment progression sequence.

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Pathograph

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Phenotypes

13

Blood 1

Thrombocytopenia HP:0001873

Show evidence (1 reference)

PMID:34871992 SUPPORT Human Clinical

"The frequencies of idiopathic thrombocytopenia and SAS among Japanese GNE myopathy patients were higher than those observed in the general Japanese population. Routine blood tests and evaluation of sleep-disordered breathing should be considered in order to better manage GNE myopathy patients."

Establishes an excess of thrombocytopenia over the general population, at a registry-reported 4.1%. No frequency band is assigned: 4.1% falls in the gap between VERY_RARE (1 to 4%) and OCCASIONAL (5 to 29%), and rounding it into either would assert a precision the single registry figure does not carry.

Metabolism 1

Elevated Circulating Creatine Kinase Concentration HP:0003236

Show evidence (1 reference)

PMID:30338442 SUPPORT Human Clinical

"The disease slowly progresses over the next decades to involve skeletal muscles throughout the body, with relative sparing of the quadriceps until late stages of the disease."

Supports the myopathic process that raises creatine kinase. PARTIAL because this source does not report creatine kinase values, so the magnitude and frequency are deliberately not banded here.

Musculoskeletal 2

Proximal Muscle Weakness HP:0003701

Course: PROGRESSIVE

Show evidence (1 reference)

PMID:20301439 SUPPORT Human Clinical

"Lower-extremity muscle involvement progresses from the anterior to the posterior compartment of the lower leg, followed by hamstrings, then hip girdle muscles, with relative sparing of the quadriceps."

Places hip girdle involvement in the progression sequence.

Respiratory Insufficiency Due to Muscle Weakness HP:0002747

Course: PROGRESSIVE

Show evidence (1 reference)

PMID:24656604 SUPPORT Human Clinical

"The decrement in %FVC was significant among non-ambulant patients, whereas the decrement in grip power tended to be greater among ambulant patients."

Documents measurable forced vital capacity decline in non-ambulant patients over one year of prospective follow-up.

Nervous System 1

Obstructive Sleep Apnea OCCASIONAL HP:0002870

Show evidence (1 reference)

PMID:34871992 SUPPORT Human Clinical

"The frequencies of idiopathic thrombocytopenia and SAS among Japanese GNE myopathy patients were higher than those observed in the general Japanese population. Routine blood tests and evaluation of sleep-disordered breathing should be considered in order to better manage GNE myopathy patients."

Establishes an excess of sleep apnea over the general population, at registry-reported rates of 16.3% in males and 6.6% in females, within the OCCASIONAL band.

Other 8

Foot Dorsiflexor Weakness VERY_FREQUENT HP:0009027

Course: PROGRESSIVE

Show evidence (2 references)

PMID:30338442 SUPPORT Human Clinical

"The typical presentation is bilateral foot drop caused by weakness of the anterior tibialis muscles with onset in early adulthood."

Establishes bilateral foot drop from anterior tibialis weakness as the typical presentation, supporting a VERY_FREQUENT band.

PMID:20301439 SUPPORT Human Clinical

"GNE myopathy is a slowly progressive muscle disease that typically presents between age 20 and 40 years with bilateral foot drop caused by anterior tibialis weakness."

GeneReviews confirms the presenting sign and the age window.

Distal Lower Limb Muscle Weakness VERY_FREQUENT HP:0009053

Course: PROGRESSIVE

Show evidence (1 reference)

PMID:20301439 SUPPORT Human Clinical

"Lower-extremity muscle involvement progresses from the anterior to the posterior compartment of the lower leg, followed by hamstrings, then hip girdle muscles, with relative sparing of the quadriceps."

Establishes the distal lower limb territory as the initial and defining site of involvement.

Distal Amyotrophy HP:0003693

Course: PROGRESSIVE

Show evidence (1 reference)

PMID:30338442 SUPPORT Human Clinical

"The disease slowly progresses over the next decades to involve skeletal muscles throughout the body, with relative sparing of the quadriceps until late stages of the disease."

Supports progressive skeletal muscle involvement. PARTIAL because distal amyotrophy specifically is not separately enumerated in this source, so no frequency band is assigned.

Steppage Gait HP:0003376

Show evidence (1 reference)

PMID:30338442 SUPPORT Human Clinical

"The typical presentation is bilateral foot drop caused by weakness of the anterior tibialis muscles with onset in early adulthood."

Foot drop is the mechanical cause of steppage gait. PARTIAL because the gait pattern itself is not named in this source.

Loss of Ambulation HP:0002505

Course: PROGRESSIVE

Show evidence (1 reference)

PMID:20301439 SUPPORT Human Clinical

"A wheelchair may be needed about ten to 20 years after the onset of manifestations."

GeneReviews gives the interval from onset to wheelchair dependence.

Rimmed Vacuoles HP:0003805

Show evidence (1 reference)

PMID:20301439 SUPPORT Human Clinical

"The diagnosis of GNE myopathy is suspected in a proband with suggestive clinical findings and muscle histopathology (rimmed vacuoles, no inflammation) and is established by the presence of biallelic pathogenic variants in GNE identified by molecular genetic testing."

GeneReviews places rimmed vacuoles with absent inflammation at the center of the diagnostic suspicion.

Deposits Immunoreactive to Beta-Amyloid Protein HP:0003791

Show evidence (2 references)

PMID:17704511 SUPPORT Model Organism

"It is pathologically characterized by the presence of rimmed vacuoles (RVs), especially in atrophic fibers, which also occasionally contain congophilic materials that are immunoreactive to beta-amyloid, lysosomal proteins, ubiquitin and tau proteins."

Describes the immunoreactive composition of the inclusions. Tagged MODEL_ORGANISM because the publication is a mouse transgenic study, and evidence_source classifies study type rather than the topic of the sentence.

PMID:20301439 SUPPORT Human Clinical

"The diagnosis of GNE myopathy is suspected in a proband with suggestive clinical findings and muscle histopathology (rimmed vacuoles, no inflammation) and is established by the presence of biallelic pathogenic variants in GNE identified by molecular genetic testing."

Human clinical source for the biopsy findings that accompany these deposits, so the phenotype does not rest on model-organism evidence alone.

Increased Variability in Muscle Fiber Diameter HP:0003557

Show evidence (2 references)

PMID:19448634 SUPPORT Model Organism

"It is characterized clinically by skeletal muscle atrophy and weakness, and pathologically by rimmed vacuoles, which are actually accumulations of autophagic vacuoles2, 3, 4, scattered angular fibers and intracellular accumulation of amyloid and other proteins5."

Names scattered angular fibers among the pathological features, and states plainly that rimmed vacuoles are accumulated autophagic material. Tagged MODEL_ORGANISM because the publication is a mouse rescue study, and evidence_source classifies study type rather than the topic of the sentence.

PMID:30338442 SUPPORT Human Clinical

"Histopathologic findings on muscle biopsies include fiber size variation, atrophic fibers, lack of inflammation"

Human clinical source enumerating fiber size variation among the biopsy findings directly, rather than leaving it to be inferred from a diagnostic criterion, so the phenotype does not rest on model-organism evidence alone.

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Genetic Associations

1

GNE Biallelic Hypomorphic Variants

Gene: GNE hgnc:23657 relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (2 references)

PMID:11528398 SUPPORT Human Clinical

"Our findings indicate that GNE is the gene responsible for recessive HIBM."

Establishes GNE as the causative gene.

PMID:39332896 SUPPORT Human Clinical

"Missense variants predominantly located in the epimerase/kinase domain coding region, indicating the impairment of catalytic function as a key pathogenic consequence."

Characterizes the variant spectrum as predominantly missense in the catalytic domains.

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Medical Actions

5

Aceneuramic Acid Extended-Release (Sialic Acid Replacement)

Action: Pharmacotherapy NCIT:C15986

Agent: N-acetylneuraminic acid CHEBI:17012

The mechanism-matched therapy, and a genuinely split evidence base that this entry records in both directions rather than picking a side. An international phase 3 trial provided Class I evidence that extended-release sialic acid does not improve muscle strength compared with placebo. A smaller Japanese phase II/III trial missed significance on its primary covariance analysis and reached significance only on a repeated-measures analysis, and a confirmatory Japanese study showed a numerically smaller decline whose confidence interval crossed zero, described by its own authors as a trend. On that basis the N-acetylneuraminic acid extended-release tablet was approved in Japan in 2024, the first drug approved anywhere for this disease. It is not approved elsewhere.

Mechanism Target:

RESTORES Free Sialic Acid Depletion — Oral sialic acid replaces the depleted end product directly. Whether that translates into preserved muscle strength is exactly what the trials disagree about.

Show evidence (5 references)

PMID:31036580 REFUTE Human Clinical

"Ace-ER was not superior to placebo in improving muscle strength and function in patients with GNE myopathy."

The international phase 3 primary result, which was negative.

PMID:31036580 REFUTE Human Clinical

"This study provides Class I evidence that for patients with GNE myopathy, Ace-ER does not improve muscle strength compared to placebo."

The authors' own evidence classification, which is the strongest negative statement available in this disease.

PMID:37125562 SUPPORT Human Clinical

"The change in UEC score at 48 weeks was significantly higher in the SA-ER group compared with the placebo group"

The positive Japanese result. PARTIAL because significance came from a repeated-measures analysis after the primary covariance analysis returned a non-significant P value, and the trial randomized only 20 patients.

+ 2 more references

N-Acetylmannosamine (ManNAc)

Action: Pharmacotherapy NCIT:C15986

Agent: N-acetyl-D-mannosamine CHEBI:63153

The upstream precursor, and mechanistically the more interesting option: ManNAc enters the pathway downstream of the defective epimerase step, so it bypasses an epimerase block, and the phase 1 study showed it restores intracellular sialic acid synthesis even in patients homozygous for kinase-domain variants. An open-label phase 2 reported increased plasma sialic acid, increased sarcolemmal sialylation, and a slower rate of strength decline. The comparator there was historical natural history rather than placebo, which is the limitation that a placebo-controlled trial is meant to resolve.

Mechanism Target:

BYPASSES Free Sialic Acid Depletion — ManNAc enters the biosynthetic pathway downstream of the epimerase step, bypassing the commonest site of the enzymatic block.

Show evidence (2 references)

PMID:28641925 SUPPORT Human Clinical

"Given that Neu5Ac is known to have a short half-life, the prolonged elevation of Neu5Ac after a single dose of ManNAc suggests that intracellular biosynthesis of sialic acid was restored in subjects with GNE myopathy, including those homozygous for mutations in the kinase domain."

Demonstrates restored intracellular sialic acid biosynthesis, including in kinase-domain genotypes.

PMID:34257421 SUPPORT Human Clinical

"ManNAc showed long-term safety, biochemical efficacy consistent with the intended mechanism of action, and preliminary evidence clinical efficacy in patients with GNE myopathy."

Reports the phase 2 result. PARTIAL because the study was open-label in twelve patients with a historical natural-history comparator rather than a placebo arm, and the authors call the clinical efficacy preliminary.

6'-Sialyllactose

Action: Pharmacotherapy NCIT:C15986

Agent: 6'-sialyllactose CHEBI:153372

A milk oligosaccharide used as a sialic acid source, developed in South Korea and the only agent in this disease with placebo-controlled evidence of an imaging effect. A randomized pilot established target engagement, with free sialic acid rising in both dose groups and not in placebo, and reported improved proximal limb power at the higher dose. A subsequent placebo-controlled trial in eleven participants found a statistically significant difference in the increase in posterior thigh fat fraction on MRI, the imaging correlate of muscle degeneration; the anterior thigh and both lower-leg regions did not separate from placebo. Muscle strength did not differ between the groups either, with one carve-out the authors state explicitly: hand grip power fell in both arms, reaching significance only in the placebo arm. That asymmetry is a signal rather than a result, since with five and six participants per arm a decline failing to reach significance under treatment is as consistent with low power as with preservation, and the authors attribute the overall null to how little strength either group lost. Both trials are small and the strength endpoints were negative, so this is promising rather than established.

Mechanism Target:

RESTORES Free Sialic Acid Depletion — 6'-sialyllactose supplies sialic acid from the diet, raising the free pool that the enzymatic block depletes.

Show evidence (4 references)

PMID:37852099 SUPPORT Human Clinical

"Free sialic acid in both low- and high-dose groups significantly increased at 6 and 12 weeks, but not in the placebo group."

Demonstrates target engagement, which is the pharmacological precondition for any clinical effect.

PMID:39644669 SUPPORT Human Clinical

"The increase in fat fraction, indicating muscle degeneration, was statistically significant between the two groups"

The imaging endpoint separated the groups. PARTIAL because the trial had eleven participants and the strength endpoints did not.

PMID:39644669 REFUTE Human Clinical

"Muscle strength, excluding hand grip power, did not show a significant difference between the two groups, which is attributed to the lack of pronounced muscle strength decline in both groups."

Refutes a demonstrated muscle-strength benefit in this trial, with the authors' own explanation that neither arm declined much over the period.

+ 1 more reference

Supportive and Rehabilitative Management

Action: Rehabilitation NCIT:C15315

In the absence of an approved disease-modifying therapy outside Japan, management is multidisciplinary and supportive: ankle-foot orthoses and assistive ambulatory devices, adaptive devices for fine motor function and activities of daily living, and baseline echocardiography and pulmonary function testing in non-ambulant patients with pulmonology follow-up.

Show evidence (1 reference)

PMID:20301439 SUPPORT Human Clinical

"Evaluation and management are often by a multidisciplinary team that includes neuromuscular specialists, physiatrists, and physical and occupational therapists to address issues secondary to muscle weakness, including the use of assistive ambulatory devices (e.g., ankle-foot orthoses, cane,..."

GeneReviews sets out the supportive management framework.

Avoidance of Myotoxic Agents and Overexertion

Action: Supportive Care NCIT:C15747

A management precaution rather than a therapy, and one worth curating explicitly because it is actionable at every clinic visit. GeneReviews advises cautious use of medications with myotoxic potential, naming colchicine and statins, and avoidance of weight-lifting and repetitive activities that provoke muscle pain. Note this is expert guidance, not a demonstrated gene-environment interaction.

Show evidence (1 reference)

PMID:20301439 SUPPORT Human Clinical

"Agents/circumstances to avoid: Cautious use of medications/drugs with potential myotoxicity (e.g., colchicine and statins); avoidance of weight-lifting and repetitive activities that cause muscle pain."

GeneReviews states the agents and circumstances to avoid.

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Diagnosis

2

Clinical and Histopathological Suspicion

The diagnosis is suspected from adult-onset distal weakness beginning with foot drop, relative quadriceps sparing, and muscle histopathology showing rimmed vacuoles without inflammation. The absent inflammation is what separates this from sporadic inclusion body myositis, and the naming collision between the two makes stating that negative explicitly worthwhile.

Show evidence (1 reference)

PMID:20301439 SUPPORT Human Clinical

"The diagnosis of GNE myopathy is suspected in a proband with suggestive clinical findings and muscle histopathology (rimmed vacuoles, no inflammation) and is established by the presence of biallelic pathogenic variants in GNE identified by molecular genetic testing."

GeneReviews states the diagnostic pathway, including the absence of inflammation.

GNE Molecular Genetic Testing

Biallelic pathogenic GNE variants establish the diagnosis. A negative coding panel does not exclude it: deep intronic variants and a large insertion have been identified only through genome sequencing and long-read sequencing, so escalation is warranted where clinical suspicion is high.

Show evidence (2 references)

PMID:20301439 SUPPORT Human Clinical

"The diagnosis of GNE myopathy is suspected in a proband with suggestive clinical findings and muscle histopathology (rimmed vacuoles, no inflammation) and is established by the presence of biallelic pathogenic variants in GNE identified by molecular genetic testing."

Establishes molecular testing as what confirms the diagnosis.

PMID:39332896 SUPPORT Human Clinical

"Comprehensive techniques such as WGS and Nanopore LRS warrants the identifying of GNE variants."

Supports escalation to genome and long-read sequencing when coding analysis is uninformative.

📈

Progression

3

Onset

Age: 20 to 40 years

Adult onset with bilateral foot drop from anterior tibialis weakness. Onset is insidious; there is no acute presenting event.

Show evidence (1 reference)

PMID:20301439 SUPPORT Human Clinical

"GNE myopathy is a slowly progressive muscle disease that typically presents between age 20 and 40 years with bilateral foot drop caused by anterior tibialis weakness."

Gives the onset age window and the presenting sign.

Distal to proximal progression

Duration: one to two decades

Involvement extends from the anterior to the posterior compartment of the lower leg, then hamstrings, then hip girdle, with the quadriceps relatively spared. Upper limbs may be affected within five to ten years and do not necessarily follow a distal-to-proximal order. Decline is measurable but slow across three years of the international disease monitoring programme.

Show evidence (2 references)

PMID:20301439 SUPPORT Human Clinical

"The upper extremities, which may be affected within five to ten years of disease onset, do not necessarily follow a distal-to-proximal progression."

Documents the upper-limb timing and the fact that it breaks the distal-to-proximal rule.

PMID:33459658 SUPPORT Human Clinical

"GNEM-FAS scores were more severe at baseline in subjects who walked <200 meters versus ≥200 meters in 6 minutes; in both groups, GNEM-FAS total, mobility, UE, and self-care scores decreased from baseline through month 36."

Quantifies functional decline across three years in the international disease monitoring programme.

Advanced disease

Wheelchair dependence about ten to twenty years after onset, with neck and core involvement and, late, respiratory muscle weakness. Quadriceps sparing finally gives way at this stage.

Show evidence (1 reference)

PMID:20301439 SUPPORT Human Clinical

"In advanced stages, neck and core muscles can become affected."

Documents the late spread to neck and core musculature.

📊

Prevalence

2

Worldwide, clinical and registry ascertainment

Point Prevalence 0.5 per 100,000 (0.1–0.9) 1–9 per 1,000,000

The conventionally cited figure, one to nine cases per million. Recorded with the caveat its own source attaches: the estimate is limited by underdiagnosis, misdiagnosis, and founder-allele bias, and the population-genetic estimate below is an order of magnitude higher.

Show evidence (2 references)

PMID:30338442 SUPPORT Human Clinical

"It has an estimated prevalence of 1 to 9:1,000,000."

Clinical review stating the conventional prevalence figure first-hand.

PMID:40225917 SUPPORT Computational

"The prevalence of GNEM is estimated to range between one and nine cases per million individuals, but the accuracy of these estimates is limited by underdiagnosis, misdiagnosis, and bias introduced by founder allele frequencies."

Restates the conventional estimate together with the three reasons it is likely to be too low. Tagged COMPUTATIONAL because the publication is the population-genetic modelling study recorded in the second prevalence record below; this sentence is its framing of the clinical figure, not an independent clinical measurement of it.

Worldwide, gnomAD allele-frequency derived

Point Prevalence 1.846 per 100,000 (1.846–9.542) 1–9 per 100,000

18.46 to 95.42 cases per million derived from gnomAD allele frequencies under Hardy-Weinberg, narrowing to 11.00 to 87.68 when variant severity is taken into account. An order of magnitude above the clinical estimate, which the authors read as evidence the disease is substantially underdiagnosed rather than as a contradiction. Both figures are recorded here because the disagreement is itself the finding.

Show evidence (2 references)

PMID:40225917 SUPPORT Computational

"Our most conservative estimate suggested a prevalence of 18.46 cases per million, while our most liberal estimate places the prevalence at 95.42 cases per million."

Gives the population-genetic range. Tagged COMPUTATIONAL because it is an in silico estimate from allele frequencies and pathogenicity prediction, not a counted cohort.

PMID:40225917 SUPPORT Computational

"Our findings indicate that the true global prevalence of GNEM is greater than previous predictions underscoring that this condition is considerably more widespread than previously believed."

The authors' own interpretation of the discrepancy, which is underdiagnosis rather than an error in either method.

⚖️

Clinical Burden

High

Onset falls in early working life and the disease is relentlessly progressive to wheelchair dependence over one to two decades, with late respiratory involvement. There is no approved disease-modifying therapy outside Japan, and the one Class I trial of the mechanism-matched therapy was negative. Function declines measurably even over a single year of observation.

Show evidence (2 references)

PMID:33459658 SUPPORT Human Clinical

"GNEM-FAS scores were more severe at baseline in subjects who walked <200 meters versus ≥200 meters in 6 minutes; in both groups, GNEM-FAS total, mobility, UE, and self-care scores decreased from baseline through month 36."

Documents progressive functional loss across all measured domains over three years.

PMID:20301439 SUPPORT Human Clinical

"A wheelchair may be needed about ten to 20 years after the onset of manifestations."

Establishes the interval to wheelchair dependence.

🔀

Differential Diagnoses

2

Conditions with similar clinical presentations that must be differentiated from GNE Myopathy:

Sporadic Inclusion Body Myositis

Overlapping Features The most expensive naming collision in this area. Both carry inclusion body in the name and both show rimmed vacuoles, but sporadic inclusion body myositis is an inflammatory, late-onset, non-Mendelian disease with a completely different mechanism. The discriminating histological feature is inflammation, which is present there and absent here, and which is precisely why the GeneReviews diagnostic criterion names the absence of inflammation explicitly.

Distinguishing Features

Inflammatory infiltrate present in sporadic inclusion body myositis, absent here
Late onset after age 50 rather than in the twenties or thirties
Sporadic rather than autosomal recessive, with no GNE variants
Quadriceps involvement is characteristic rather than spared

Show evidence (1 reference)

PMID:20301439 SUPPORT Human Clinical

"The diagnosis of GNE myopathy is suspected in a proband with suggestive clinical findings and muscle histopathology (rimmed vacuoles, no inflammation) and is established by the presence of biallelic pathogenic variants in GNE identified by molecular genetic testing."

The explicit no-inflammation criterion is the histological separator from sporadic inclusion body myositis.

Dysferlinopathy

Overlapping Features Another distal-onset recessive myopathy, and the differential most often settled by a routine blood test: creatine kinase is markedly elevated in dysferlinopathy and only normal to moderately elevated here. Distribution also differs, since the quadriceps sparing characteristic of GNE myopathy is not a feature.

Distinguishing Features

Markedly elevated creatine kinase rather than normal to moderately elevated
No quadriceps sparing
Biallelic DYSF rather than GNE variants

Show evidence (1 reference)

PMID:30338442 SUPPORT Human Clinical

"The disease slowly progresses over the next decades to involve skeletal muscles throughout the body, with relative sparing of the quadriceps until late stages of the disease."

Establishes the quadriceps sparing that distinguishes this from other distal myopathies. PARTIAL because the creatine kinase contrast is not quantified in this source.

🔬

Clinical Trials

4

NCT02377921 PHASE_III COMPLETED

The international randomized, double-blind, placebo-controlled phase 3 of aceneuramic acid extended-release, whose upper-extremity composite primary endpoint was negative and which supplied the Class I evidence recorded on the treatment entry (PMID:31036580).

Target Phenotypes: Distal lower limb muscle weakness HP:0009053

Show evidence (1 reference)

clinicaltrials:NCT02377921 SUPPORT Human Clinical

"The primary objective of this study is to evaluate the effect of 6 g/day aceneuramic acid extended-release (Ace-ER) treatment of participants with GNEM on upper extremity muscle strength"

Registry record establishing the design and the primary endpoint that the trial failed to meet.

NCT04671472 PHASE_III COMPLETED

The Japanese confirmatory placebo-controlled trial of aceneuramic acid extended-release, published as PMID:37568154, which showed a numerically smaller decline whose confidence interval crossed zero.

Target Phenotypes: Distal lower limb muscle weakness HP:0009053

Show evidence (1 reference)

clinicaltrials:NCT04671472 SUPPORT Human Clinical

"The investigators will examine the efficacy and safety of aceneuramic acid (SA-ER tablets) 6g daily for 48 weeks in patients with GNE myopathy in a placebo-controlled, double-blind, controlled trial."

Registry record establishing the placebo-controlled design of the Japanese confirmatory study.

NCT02346461 PHASE_II COMPLETED

The open-label phase 2 of N-acetylmannosamine, published as PMID:34257421, whose comparator was historical natural history rather than placebo.

Target Phenotypes: Distal lower limb muscle weakness HP:0009053

Show evidence (1 reference)

clinicaltrials:NCT02346461 SUPPORT Human Clinical

"Researchers are testing the drug ManNAc which is a precursor in the production of sialic acid within cells."

Registry record establishing the agent and its mechanistic rationale.

NCT04231266 PHASE_II ACTIVE_NOT_RECRUITING

The placebo-controlled multi-centre trial of N-acetylmannosamine, and the study that would resolve the main limitation of the open-label phase 2, whose only comparator was historical natural history. This is the principal forward-looking therapeutic signal in the disease.

Target Phenotypes: Distal lower limb muscle weakness HP:0009053

Show evidence (1 reference)

clinicaltrials:NCT04231266 SUPPORT Human Clinical

"In this randomized, double-blind, placebo-controlled trial the efficacy and long-term safety of ManNAc will be evaluated in subjects with GNE myopathy."

Registry record establishing the randomized placebo-controlled design that the open-label phase 2 lacked.

🧫

Experimental Models

1

Human pluripotent stem cell-derived GNE myoblasts and neuromuscular organoids IPSC_DERIVED_MODEL

Two independent isogenic human stem-cell-derived myoblast models plus Gne-knockout C2C12 myoblasts and human neuromuscular organoids, used together to establish the autophagy arm of the mechanism and to nominate and then validate a repurposing candidate.

Publication

PMID:41963465

Pathograph links

Autophagic Block and Proteostasis Failure recapitulates fidelity: moderate Transcriptomic analysis identified autophagy gene sets as pathogenic signatures, biochemically validated in Gne-knockout myoblasts, and PI3K inhibition restored ULK1 activity and reactivated autophagy in patient-relevant neuromuscular organoids.

Limitations: Cultured myoblasts and organoids do not reproduce the mature myofiber, the decades-long timescale, or the compartment-specific muscle involvement that defines the human disease, and the extracellular-matrix-driven AKT-mTORC1 arm has not been demonstrated in patient muscle. The nominated drug candidate is a computational repurposing hit validated only in the same model system.

Readouts

ULK1 activity and autophagy reactivation under PI3K inhibition

Direction: RESTORED

Interpretation: Restoring ULK1 activity reactivates autophagy, which is what makes the inhibitory phosphorylation step causal rather than correlative.

Show evidence (1 reference)

PMID:41963465 SUPPORT In Vitro

"Functional validation in human pluripotent stem cell-derived neuromuscular organoids demonstrated that copanlisib reactivates autophagy via restoration of ULK1 activity."

Reports the measured restoration of ULK1 activity and autophagy in the organoid model.

Show evidence (1 reference)

PMID:41963465 SUPPORT In Vitro

"By performing transcriptome analysis on two independent GNE myoblast models derived from human pluripotent stem cells, we identified multiple autophagy-related gene sets as pathogenic signatures of GNE myopathy."

Establishes the autophagy signature across two independent human models.

🐁

Animal Models

1

Gne-null mouse expressing human GNE p.Asp207Val transgene

The field's workhorse model, generated because the straight Gne knockout is embryonically lethal. It reproduces the clinical, histopathological, and biochemical features of the human disease, and it is where the temporal ordering of amyloid before rimmed vacuoles was established.

Species

Mouse

Genotype

Gne-null background with human GNE D176V transgene (legacy numbering; p.Asp207Val in current NM_001128227 numbering)

Publication

PMID:17704511

Pathograph links

Amyloid and Misfolded Protein Accumulation recapitulates fidelity: high Beta-amyloid deposition appears in myofibers at 32 weeks and clearly precedes rimmed vacuole formation at 42 weeks, which is the ordering that constrains causal models of the inclusion pathology.

Limitations: The model expresses a human transgene on a null background rather than carrying a knock-in point mutation, so expression level and stoichiometry are not those of a patient. Motor performance falls only from 30 weeks, a compressed timescale against a human disease measured in decades, and the allele modeled is a Japanese founder variant rather than a general case.

Readouts

Myofiber beta-amyloid deposition over time

Direction: INCREASED

Interpretation: Time-resolved appearance of amyloid before rimmed vacuoles is the structural evidence for the ordering of the two.

Show evidence (1 reference)

PMID:17704511 SUPPORT Model Organism

"A compelling finding is the development of beta-amyloid deposition in myofibers by 32 weeks, which clearly precedes RV formation at 42 weeks."

Reports the measured timing of amyloid deposition relative to rimmed vacuole formation.

Show evidence (1 reference)

PMID:17704511 SUPPORT Model Organism

"These results show that the Gne(-/-)hGNED176V-Tg mouse mimics the clinical, histopathological and biochemical features of DMRV/hIBM, making it useful for understanding the pathomechanism of this myopathy and for employing different strategies for therapy."

The authors' own validation of the model against the human disease.

Hyposialylation of Muscle Glycoproteins rescues fidelity: high Oral sialic acid metabolites completely prevented muscle atrophy and weakness in this model, which is the pivotal demonstration that hyposialylation is causal rather than incidental to the myopathy.

Limitations: The treatment was prophylactic, given before the phenotype developed, so it demonstrates prevention rather than reversal. The human trials that followed were of established disease and did not reproduce the benefit, which is exactly the gap between preventing a phenotype in a mouse and modifying one in a patient.

Show evidence (1 reference)

PMID:19448634 SUPPORT Model Organism

"By showing that muscle atrophy and weakness are completely prevented in a mouse model of DMRV-hIBM after treatment with sialic acid metabolites orally, we provide evidence that hyposialylation is indeed one of the key factors in the pathomechanism of DMRV-hIBM."

The rescue that established hyposialylation as causal, quoted with the authors' own hedge.

{ }

Source YAML

click to show

name: GNE Myopathy
creation_date: "2026-08-15T00:00:00Z"
category: Mendelian
parents:
- Distal Myopathy
- Congenital Disorder of Glycosylation
disease_term:
  preferred_term: GNE Myopathy
  term:
    id: MONDO:0011603
    label: GNE myopathy
synonyms:
- Nonaka myopathy
- distal myopathy with rimmed vacuoles
- DMRV
- hereditary inclusion body myopathy type 2
- IBM2
- quadriceps-sparing myopathy
- inclusion body myopathy, autosomal recessive
description: >-
  GNE myopathy is an ultra-rare, adult-onset, autosomal recessive skeletal muscle
  disease caused by biallelic hypomorphic variants in GNE, the gene encoding the
  bifunctional enzyme that runs the first two committed steps of sialic acid
  biosynthesis. Think of it as a factory whose front-end sugar line is throttled:
  the cell can still make some sialic acid, but not enough, and the tissue least
  forgiving of the shortfall turns out to be skeletal muscle. Patients present in
  their twenties or thirties with bilateral foot drop from anterior tibialis
  weakness, then decline distally to proximally over decades, with the striking
  and diagnostically load-bearing quirk that the quadriceps is spared until very
  late. That sparing now has a biochemical explanation: normal quadriceps
  ordinarily runs on markedly less free sialic acid than gastrocnemius, so it has
  less to lose. Muscle histology shows rimmed vacuoles, which are accumulated
  autophagic material rather than vacuoles in the naive sense, plus deposits
  immunoreactive to beta-amyloid, ubiquitin, and tau, and, crucially, no
  inflammation. That last negative is what separates this from sporadic inclusion
  body myositis, a naming collision that has cost the field real confusion. Oral
  sialic acid replacement failed a Class I phase 3 trial in the West and was
  approved in Japan in 2024 on a narrower and more equivocal evidence base; the
  entry records both.
has_subtypes:
- name: Epimerase-domain
  display_name: Epimerase-domain variant genotypes
  description: >-
    Genotypes with variants affecting the UDP-N-acetylglucosamine 2-epimerase
    domain. The distinction from kinase-domain genotypes is therapeutically
    consequential rather than cosmetic: N-acetylmannosamine enters the pathway
    downstream of the epimerase step and so bypasses an epimerase block, and it
    also restored sialic acid synthesis in patients homozygous for kinase-domain
    variants. Not a formally recognized clinical classification.
- name: Kinase-domain
  display_name: Kinase-domain variant genotypes
  description: >-
    Genotypes with variants affecting the N-acetylmannosamine kinase domain.
    Recorded separately because the phase 1 N-acetylmannosamine study explicitly
    showed restored intracellular sialic acid biosynthesis in subjects homozygous
    for kinase-domain variants, which was not a foregone conclusion for a
    precursor entering upstream of that step.
  evidence:
  - reference: PMID:28641925
    reference_title: "Safety, pharmacokinetics and sialic acid production after oral administration of N-acetylmannosamine (ManNAc) to subjects with GNE myopathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Given that Neu5Ac is known to have a short half-life, the prolonged elevation of Neu5Ac after a single dose of ManNAc suggests that intracellular biosynthesis of sialic acid was restored in subjects with GNE myopathy, including those homozygous for mutations in the kinase domain."
    explanation: >-
      Establishes that the kinase-domain genotype is a separately relevant
      pharmacological category, and that the precursor works in it.
pathophysiology:
- name: Biallelic Hypomorphic GNE Variants and Enzymatic Block
  biological_scale: MOLECULAR
  description: >-
    GNE encodes one polypeptide carrying two enzyme activities, UDP-GlcNAc
    2-epimerase and N-acetylmannosamine kinase, which together run the first
    committed and rate-limiting steps of sialic acid synthesis. Biallelic
    hypomorphic variants, predominantly missense and distributed across both
    catalytic domains, reduce that throughput. The variants must be hypomorphic
    rather than null: Gne knockout is embryonic lethal in mouse, so every
    surviving human genotype retains residual enzyme activity, and that is why
    curating these alleles as complete loss of function overstates the lesion.
  genes:
  - preferred_term: GNE
    term:
      id: hgnc:23657
      label: GNE
  molecular_functions:
  - preferred_term: UDP-N-acetylglucosamine 2-epimerase activity
    term:
      id: GO:0008761
      label: UDP-N-acetylglucosamine 2-epimerase activity
    modifier: DECREASED
  - preferred_term: N-acetylmannosamine kinase activity
    term:
      id: GO:0009384
      label: N-acylmannosamine kinase activity
    modifier: DECREASED
  downstream:
  - target: Free Sialic Acid Depletion
    description: >-
      Reduced throughput of the first committed steps depletes the free sialic
      acid pool in serum and, far more severely, in muscle.
    causal_link_type: DIRECT
  evidence:
  - reference: PMID:11528398
    reference_title: "The UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase gene is mutated in recessive hereditary inclusion body myopathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our findings indicate that GNE is the gene responsible for recessive HIBM."
    explanation: >-
      The gene-identification study establishing GNE as causative.
  - reference: PMID:39332896
    reference_title: Novel variants and genotype-phenotype correlation in a multicentre cohort of GNE myopathy in China.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Missense variants predominantly located in the epimerase/kinase domain coding region, indicating the impairment of catalytic function as a key pathogenic consequence."
    explanation: >-
      Establishes that the variant spectrum is dominated by missense changes in
      the catalytic domains, so the lesion is impaired catalysis.
  - reference: PMID:17704511
    reference_title: A Gne knockout mouse expressing human GNE D176V mutation develops features similar to distal myopathy with rimmed vacuoles or hereditary inclusion body myopathy.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "We knocked out the Gne gene in mice but this resulted in embryonic lethality."
    explanation: >-
      Embryonic lethality of the null establishes that surviving human genotypes
      must be hypomorphic rather than complete loss of function.
- name: Free Sialic Acid Depletion
  biological_scale: MOLECULAR
  description: >-
    The best-quantified node in the disease, and the one that also explains its
    most distinctive clinical sign. Serum free sialic acid is 18% below
    age-matched controls, but muscle free sialic acid is down 72 to 85%, so the
    deficit is far more severe in the tissue that gets sick. The quadriceps
    sparing rule falls out of the same measurements: normal quadriceps already
    runs on 39% less free sialic acid than normal gastrocnemius, so it has less
    to lose when supply is throttled.
  biological_processes:
  - preferred_term: N-acetylneuraminate biosynthetic process
    term:
      id: GO:0046380
      label: N-acetylneuraminate biosynthetic process
    modifier: DECREASED
  chemical_entities:
  - preferred_term: N-acetylneuraminic acid
    term:
      id: CHEBI:17012
      label: N-acetylneuraminic acid
    modifier: DECREASED
  locations:
  - preferred_term: skeletal muscle tissue
    term:
      id: UBERON:0001134
      label: skeletal muscle tissue
  downstream:
  - target: Hyposialylation of Muscle Glycoproteins
    description: >-
      A depleted free sialic acid pool leaves muscle glycoproteins
      undersialylated.
    causal_link_type: DIRECT
  evidence:
  - reference: PMID:28267778
    reference_title: Substantial deficiency of free sialic acid in muscles of patients with GNE myopathy and in a mouse model.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These results show that serum and muscle free SA is severely reduced in GNEM, which is consistent with the biochemical defect in SA synthesis associated with GNE mutations."
    explanation: >-
      Quantitative confirmation that the free sialic acid pool is severely
      depleted in patients, in serum and muscle.
  - reference: PMID:28267778
    reference_title: Substantial deficiency of free sialic acid in muscles of patients with GNE myopathy and in a mouse model.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A lower SA requirement for quadriceps may be linked to the reported quadriceps sparing in GNEM."
    explanation: >-
      Offers the biochemical explanation for quadriceps sparing, grounded in
      measured differences in normal muscle rather than in the disease.
  - reference: PMID:17704511
    reference_title: A Gne knockout mouse expressing human GNE D176V mutation develops features similar to distal myopathy with rimmed vacuoles or hereditary inclusion body myopathy.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Interestingly, these mice exhibit marked hyposialylation in serum, muscle and other organs."
    explanation: >-
      The mouse model reproduces the systemic hyposialylation, which is the
      starting point of the tissue-restriction paradox.
- name: Hyposialylation of Muscle Glycoproteins
  biological_scale: MOLECULAR
  description: >-
    Muscle glycoproteins carry less sialic acid than they should. Two things
    should be said carefully here. First, the specific glycoprotein target or
    targets whose undersialylation is actually pathogenic have not been
    definitively identified, and the sialic acid measurements themselves hint
    that the set is small: total sialic acid differences between patients and
    controls were less distinct and more variable than the free pool differences.
    Second, that hyposialylation is causal rather than incidental was established
    by rescue in the mouse, and the authors of that rescue were careful to call it
    one of the key factors rather than the whole story.
  biological_processes:
  - preferred_term: protein sialylation
    term:
      id: GO:1990743
      label: protein sialylation
    modifier: DECREASED
  cell_types:
  - preferred_term: skeletal muscle fiber
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  downstream:
  - target: Autophagic Block and Proteostasis Failure
    description: >-
      Undersialylated muscle is where the downstream proteostasis failure and
      rimmed vacuole formation occur. The steps connecting the sialylation
      deficit to the autophagy block are not established.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  - target: Myofiber Atrophy and Degeneration
    description: >-
      Hyposialylation is causally upstream of the atrophy and weakness, as shown
      by complete prevention of both in the mouse when sialic acid metabolites are
      supplied.
    causal_link_type: DIRECT
  evidence:
  - reference: PMID:19448634
    reference_title: Prophylactic treatment with sialic acid metabolites precludes the development of the myopathic phenotype in the DMRV-hIBM mouse model.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "By showing that muscle atrophy and weakness are completely prevented in a mouse model of DMRV-hIBM after treatment with sialic acid metabolites orally, we provide evidence that hyposialylation is indeed one of the key factors in the pathomechanism of DMRV-hIBM."
    explanation: >-
      The pivotal causality proof, quoted with the authors' own hedge that
      hyposialylation is one of the key factors rather than the sole cause.
  - reference: PMID:28267778
    reference_title: Substantial deficiency of free sialic acid in muscles of patients with GNE myopathy and in a mouse model.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Differences in mean total SA levels in muscle from patients compared with normal controls were less distinct and more variable between different muscles, suggesting a small subset of sialylation targets could be responsible for the pathogenesis of GNEM."
    explanation: >-
      Suggests the pathogenic target set is narrow. PARTIAL because it is an
      inference the authors themselves frame as a suggestion, and no specific
      target glycoprotein is identified.
  - reference: PMID:41082181
    reference_title: "Decoding GNE Myopathy: From Molecular Basis to Therapeutic Advances."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Deficient GNE enzyme activity results in decreased production of sialic acid and subsequent hyposialylation of muscle glycoproteins, ultimately leading to progressive muscle degeneration and characteristic histopathological changes."
    explanation: >-
      States the canonical chain from enzyme deficiency through hyposialylation to
      degeneration.
- name: Autophagic Block and Proteostasis Failure
  biological_scale: CELLULAR
  description: >-
    Rimmed vacuoles are not vacuoles in the naive sense; they are accumulated
    autophagic material, and recent isogenic-model work supplies an actual
    signaling chain for why the material accumulates. Excessive extracellular
    matrix production drives aberrant activation of a noncanonical AKT-mTORC1
    pathway, which phosphorylates and inhibits ULK1 and so suppresses autophagy
    initiation. Reactivating autophagy by PI3K inhibition restores ULK1 activity
    in patient-derived neuromuscular organoids, which is what makes this a causal
    chain rather than a correlation.
  biological_processes:
  - preferred_term: macroautophagy
    term:
      id: GO:0016236
      label: macroautophagy
    modifier: DECREASED
  cell_types:
  - preferred_term: skeletal muscle fiber
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  downstream:
  - target: Amyloid and Misfolded Protein Accumulation
    description: >-
      Suppressed autophagic clearance permits accumulation of aggregation-prone
      protein within myofibers.
    causal_link_type: DIRECT
  - target: Rimmed Vacuoles
    description: >-
      The accumulated autophagic material is what is seen histologically as
      rimmed vacuoles.
  evidence:
  - reference: PMID:41963465
    reference_title: Defective autophagy in GNE myopathy is rescued by inhibition of noncanonical Akt-mTORC1 activation across multiple isogenic models.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "By performing transcriptome analysis on two independent GNE myoblast models derived from human pluripotent stem cells, we identified multiple autophagy-related gene sets as pathogenic signatures of GNE myopathy."
    explanation: >-
      Establishes autophagy dysregulation as a transcriptional signature across
      two independent human stem-cell-derived models.
  - reference: PMID:41963465
    reference_title: Defective autophagy in GNE myopathy is rescued by inhibition of noncanonical Akt-mTORC1 activation across multiple isogenic models.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "induces inhibitory phosphorylation of ULK1, thereby suppressing autophagy initiation."
    explanation: >-
      Names the specific inhibitory step, ULK1 phosphorylation, that blocks
      autophagy initiation in this disease.
- name: Amyloid and Misfolded Protein Accumulation
  biological_scale: CELLULAR
  description: >-
    Myofibers accumulate congophilic material immunoreactive to beta-amyloid,
    lysosomal proteins, ubiquitin, and tau. The mouse model established the
    temporal ordering, which is the mechanistically interesting part: beta-amyloid
    deposition appears at 32 weeks and clearly precedes rimmed vacuole formation
    at 42 weeks. Whether the amyloid is mechanistically upstream of the atrophy or
    a downstream marker of failed clearance remains unsettled, and this entry does
    not decide it.
  cell_types:
  - preferred_term: skeletal muscle fiber
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  downstream:
  - target: Deposits Immunoreactive to Beta-Amyloid Protein
    description: >-
      The accumulated material is detected histologically as beta-amyloid
      immunoreactive deposits.
  - target: Myofiber Atrophy and Degeneration
    description: >-
      Accumulated misfolded protein accompanies and plausibly contributes to
      myofiber degeneration, though its causal weight is unsettled and no
      intermediate steps are established.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  evidence:
  - reference: PMID:17704511
    reference_title: A Gne knockout mouse expressing human GNE D176V mutation develops features similar to distal myopathy with rimmed vacuoles or hereditary inclusion body myopathy.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "A compelling finding is the development of beta-amyloid deposition in myofibers by 32 weeks, which clearly precedes RV formation at 42 weeks."
    explanation: >-
      Establishes that amyloid deposition precedes rimmed vacuole formation, which
      is the temporal ordering that constrains any causal model.
  - reference: PMID:17704511
    reference_title: A Gne knockout mouse expressing human GNE D176V mutation develops features similar to distal myopathy with rimmed vacuoles or hereditary inclusion body myopathy.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "It is pathologically characterized by the presence of rimmed vacuoles (RVs), especially in atrophic fibers, which also occasionally contain congophilic materials that are immunoreactive to beta-amyloid, lysosomal proteins, ubiquitin and tau proteins."
    explanation: >-
      Describes the composition of the inclusions. Tagged MODEL_ORGANISM because
      evidence_source classifies the publication's study type rather than the
      topic of the quoted sentence, and this is a mouse transgenic study whose
      opening prose describes the human disease.
- name: Myofiber Atrophy and Degeneration
  biological_scale: TISSUE
  description: >-
    The tissue endpoint: progressive myofiber atrophy and degeneration with
    angular fibers and increased fiber-size variability, without inflammation.
    Distribution is the diagnostic signature. Weakness starts in the anterior
    compartment of the lower leg, progresses to the posterior compartment, then
    hamstrings, then hip girdle, and the quadriceps is relatively spared until
    late. End-stage tissue outcomes are fibrosis and fatty replacement.
  cell_types:
  - preferred_term: skeletal muscle fiber
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  locations:
  - preferred_term: skeletal muscle tissue
    term:
      id: UBERON:0001134
      label: skeletal muscle tissue
  downstream:
  - target: Foot Dorsiflexor Weakness
    description: >-
      Anterior tibialis involvement produces the presenting bilateral foot drop.
  - target: Distal Lower Limb Muscle Weakness
    description: Distal lower limb muscles are affected first and worst.
  - target: Distal Amyotrophy
    description: Progressive wasting accompanies the distal weakness.
  - target: Steppage Gait
    description: Foot drop produces a steppage gait.
  - target: Proximal Muscle Weakness
    description: >-
      Hip girdle weakness follows years to decades after onset.
  - target: Loss of Ambulation
    description: >-
      Progressive weakness leads to wheelchair dependence roughly ten to twenty
      years after onset.
  - target: Increased Variability in Muscle Fiber Diameter
    description: Histologic correlate of the atrophic process.
  - target: Elevated Circulating Creatine Kinase Concentration
    description: >-
      Myofiber degeneration releases creatine kinase, though only to normal or
      mildly elevated levels.
  - target: Respiratory Insufficiency Due to Muscle Weakness
    description: >-
      Respiratory muscle involvement appears late, and forced vital capacity
      declines measurably in non-ambulant patients.
  evidence:
  - reference: PMID:30338442
    reference_title: "GNE Myopathy: Etiology, Diagnosis, and Therapeutic Challenges."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The disease slowly progresses over the next decades to involve skeletal muscles throughout the body, with relative sparing of the quadriceps until late stages of the disease."
    explanation: >-
      Establishes the progression pattern and the quadriceps sparing that defines
      it.
  - reference: PMID:20301439
    reference_title: GNE Myopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Lower-extremity muscle involvement progresses from the anterior to the posterior compartment of the lower leg, followed by hamstrings, then hip girdle muscles, with relative sparing of the quadriceps."
    explanation: >-
      GeneReviews states the compartment-by-compartment progression sequence.
phenotypes:
- name: Foot Dorsiflexor Weakness
  category: Musculoskeletal
  description: >-
    Bilateral foot drop from anterior tibialis weakness, the presenting sign in
    the great majority of patients, typically between ages 20 and 40.
  phenotype_term:
    preferred_term: Foot dorsiflexor weakness
    term:
      id: HP:0009027
      label: Foot dorsiflexor weakness
    clinical_course: PROGRESSIVE
  frequency: VERY_FREQUENT
  diagnostic: true
  evidence:
  - reference: PMID:30338442
    reference_title: "GNE Myopathy: Etiology, Diagnosis, and Therapeutic Challenges."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The typical presentation is bilateral foot drop caused by weakness of the anterior tibialis muscles with onset in early adulthood."
    explanation: >-
      Establishes bilateral foot drop from anterior tibialis weakness as the
      typical presentation, supporting a VERY_FREQUENT band.
  - reference: PMID:20301439
    reference_title: GNE Myopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "GNE myopathy is a slowly progressive muscle disease that typically presents between age 20 and 40 years with bilateral foot drop caused by anterior tibialis weakness."
    explanation: >-
      GeneReviews confirms the presenting sign and the age window.
- name: Distal Lower Limb Muscle Weakness
  category: Musculoskeletal
  description: >-
    Weakness beginning in the anterior compartment of the lower leg and extending
    to the posterior compartment, the earliest and most severe territory.
  phenotype_term:
    preferred_term: Distal lower limb muscle weakness
    term:
      id: HP:0009053
      label: Distal lower limb muscle weakness
    clinical_course: PROGRESSIVE
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:20301439
    reference_title: GNE Myopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Lower-extremity muscle involvement progresses from the anterior to the posterior compartment of the lower leg, followed by hamstrings, then hip girdle muscles, with relative sparing of the quadriceps."
    explanation: >-
      Establishes the distal lower limb territory as the initial and defining site
      of involvement.
- name: Distal Amyotrophy
  category: Musculoskeletal
  description: >-
    Wasting of the distal limb musculature accompanying the weakness.
  phenotype_term:
    preferred_term: Distal amyotrophy
    term:
      id: HP:0003693
      label: Distal amyotrophy
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:30338442
    reference_title: "GNE Myopathy: Etiology, Diagnosis, and Therapeutic Challenges."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The disease slowly progresses over the next decades to involve skeletal muscles throughout the body, with relative sparing of the quadriceps until late stages of the disease."
    explanation: >-
      Supports progressive skeletal muscle involvement. PARTIAL because distal
      amyotrophy specifically is not separately enumerated in this source, so no
      frequency band is assigned.
- name: Steppage Gait
  category: Musculoskeletal
  description: >-
    The gait consequence of bilateral foot drop, usually the reason patients
    first seek assessment.
  phenotype_term:
    preferred_term: Steppage gait
    term:
      id: HP:0003376
      label: Steppage gait
  evidence:
  - reference: PMID:30338442
    reference_title: "GNE Myopathy: Etiology, Diagnosis, and Therapeutic Challenges."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The typical presentation is bilateral foot drop caused by weakness of the anterior tibialis muscles with onset in early adulthood."
    explanation: >-
      Foot drop is the mechanical cause of steppage gait. PARTIAL because the gait
      pattern itself is not named in this source.
- name: Proximal Muscle Weakness
  category: Musculoskeletal
  description: >-
    Hip girdle weakness developing years to decades after onset, following the
    hamstrings and preceding loss of ambulation.
  phenotype_term:
    preferred_term: Proximal muscle weakness
    term:
      id: HP:0003701
      label: Proximal muscle weakness
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:20301439
    reference_title: GNE Myopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Lower-extremity muscle involvement progresses from the anterior to the posterior compartment of the lower leg, followed by hamstrings, then hip girdle muscles, with relative sparing of the quadriceps."
    explanation: >-
      Places hip girdle involvement in the progression sequence.
- name: Loss of Ambulation
  category: Musculoskeletal
  description: >-
    Wheelchair dependence, typically about ten to twenty years after onset of
    manifestations.
  phenotype_term:
    preferred_term: Loss of ambulation
    term:
      id: HP:0002505
      label: Loss of ambulation
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:20301439
    reference_title: GNE Myopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A wheelchair may be needed about ten to 20 years after the onset of manifestations."
    explanation: >-
      GeneReviews gives the interval from onset to wheelchair dependence.
- name: Rimmed Vacuoles
  category: Histologic
  description: >-
    The definitional histologic finding, and a slight misnomer: these are
    accumulations of autophagic material rather than vacuoles in the naive sense.
    Their presence together with an absence of inflammation is what makes the
    biopsy diagnostic rather than merely suggestive.
  phenotype_term:
    preferred_term: Rimmed vacuoles
    term:
      id: HP:0003805
      label: Rimmed vacuoles
  diagnostic: true
  evidence:
  - reference: PMID:20301439
    reference_title: GNE Myopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The diagnosis of GNE myopathy is suspected in a proband with suggestive clinical findings and muscle histopathology (rimmed vacuoles, no inflammation) and is established by the presence of biallelic pathogenic variants in GNE identified by molecular genetic testing."
    explanation: >-
      GeneReviews places rimmed vacuoles with absent inflammation at the center of
      the diagnostic suspicion.
- name: Deposits Immunoreactive to Beta-Amyloid Protein
  category: Histologic
  description: >-
    Congophilic intracellular material immunoreactive to beta-amyloid, and also to
    lysosomal proteins, ubiquitin, and tau.
  phenotype_term:
    preferred_term: Deposits immunoreactive to beta-amyloid protein
    term:
      id: HP:0003791
      label: Deposits immunoreactive to beta-amyloid protein
  evidence:
  - reference: PMID:17704511
    reference_title: A Gne knockout mouse expressing human GNE D176V mutation develops features similar to distal myopathy with rimmed vacuoles or hereditary inclusion body myopathy.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "It is pathologically characterized by the presence of rimmed vacuoles (RVs), especially in atrophic fibers, which also occasionally contain congophilic materials that are immunoreactive to beta-amyloid, lysosomal proteins, ubiquitin and tau proteins."
    explanation: >-
      Describes the immunoreactive composition of the inclusions. Tagged
      MODEL_ORGANISM because the publication is a mouse transgenic study, and
      evidence_source classifies study type rather than the topic of the sentence.
  - reference: PMID:20301439
    reference_title: GNE Myopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The diagnosis of GNE myopathy is suspected in a proband with suggestive clinical findings and muscle histopathology (rimmed vacuoles, no inflammation) and is established by the presence of biallelic pathogenic variants in GNE identified by molecular genetic testing."
    explanation: >-
      Human clinical source for the biopsy findings that accompany these deposits,
      so the phenotype does not rest on model-organism evidence alone.
- name: Increased Variability in Muscle Fiber Diameter
  category: Histologic
  description: >-
    Fiber-size variability with atrophic and angular fibers, alongside the rimmed
    vacuoles.
  phenotype_term:
    preferred_term: Increased variability in muscle fiber diameter
    term:
      id: HP:0003557
      label: Increased variability in muscle fiber diameter
  evidence:
  - reference: PMID:19448634
    reference_title: Prophylactic treatment with sialic acid metabolites precludes the development of the myopathic phenotype in the DMRV-hIBM mouse model.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "It is characterized clinically by skeletal muscle atrophy and weakness, and pathologically by rimmed vacuoles, which are actually accumulations of autophagic vacuoles2, 3, 4, scattered angular fibers and intracellular accumulation of amyloid and other proteins5."
    explanation: >-
      Names scattered angular fibers among the pathological features, and states
      plainly that rimmed vacuoles are accumulated autophagic material. Tagged
      MODEL_ORGANISM because the publication is a mouse rescue study, and
      evidence_source classifies study type rather than the topic of the
      sentence.
  - reference: PMID:30338442
    reference_title: "GNE Myopathy: Etiology, Diagnosis, and Therapeutic Challenges."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Histopathologic findings on muscle biopsies include fiber size variation, atrophic fibers, lack of inflammation"
    explanation: >-
      Human clinical source enumerating fiber size variation among the biopsy
      findings directly, rather than leaving it to be inferred from a diagnostic
      criterion, so the phenotype does not rest on model-organism evidence alone.
- name: Elevated Circulating Creatine Kinase Concentration
  category: Laboratory
  description: >-
    Creatine kinase is normal to mildly or moderately elevated, which is itself
    discriminating: markedly high creatine kinase points instead to
    dysferlinopathy.
  phenotype_term:
    preferred_term: Elevated circulating creatine kinase concentration
    term:
      id: HP:0003236
      label: Elevated circulating creatine kinase concentration
  evidence:
  - reference: PMID:30338442
    reference_title: "GNE Myopathy: Etiology, Diagnosis, and Therapeutic Challenges."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The disease slowly progresses over the next decades to involve skeletal muscles throughout the body, with relative sparing of the quadriceps until late stages of the disease."
    explanation: >-
      Supports the myopathic process that raises creatine kinase. PARTIAL because
      this source does not report creatine kinase values, so the magnitude and
      frequency are deliberately not banded here.
- name: Respiratory Insufficiency Due to Muscle Weakness
  category: Respiratory
  description: >-
    Respiratory muscle involvement is a late feature, but forced vital capacity
    declines measurably over as little as a year in non-ambulant patients, which
    is the argument for monitoring it rather than waiting for symptoms.
  phenotype_term:
    preferred_term: Respiratory insufficiency due to muscle weakness
    term:
      id: HP:0002747
      label: Respiratory insufficiency due to muscle weakness
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:24656604
    reference_title: "GNE myopathy: a prospective natural history study of disease progression."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The decrement in %FVC was significant among non-ambulant patients, whereas the decrement in grip power tended to be greater among ambulant patients."
    explanation: >-
      Documents measurable forced vital capacity decline in non-ambulant patients
      over one year of prospective follow-up.
- name: Obstructive Sleep Apnea
  category: Respiratory
  description: >-
    Sleep-disordered breathing is more frequent in this population than in the
    general Japanese population, at 16.3% of males and 6.6% of females in a
    nationwide registry survey, which is why the registry authors recommend
    evaluating for it routinely rather than on suspicion.
  phenotype_term:
    preferred_term: Obstructive sleep apnea
    term:
      id: HP:0002870
      label: Obstructive sleep apnea
  frequency: OCCASIONAL
  evidence:
  - reference: PMID:34871992
    reference_title: "Extra-muscular manifestations in GNE myopathy patients: A nationwide repository questionnaire survey in Japan."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The frequencies of idiopathic thrombocytopenia and SAS among Japanese GNE myopathy patients were higher than those observed in the general Japanese population. Routine blood tests and evaluation of sleep-disordered breathing should be considered in order to better manage GNE myopathy patients."
    explanation: >-
      Establishes an excess of sleep apnea over the general population, at
      registry-reported rates of 16.3% in males and 6.6% in females, within the
      OCCASIONAL band.
- name: Thrombocytopenia
  category: Hematologic
  description: >-
    The extramuscular finding with a real mechanistic story rather than a
    confounded one. Some individuals with biallelic GNE variants have
    macrothrombocytopenia driven by a platelet sialylation defect and accelerated
    platelet clearance, and a separate MONDO entity exists for the
    thrombocytopenia-predominant presentation. In the Japanese registry 4.1% of
    participants carried a diagnosis of idiopathic thrombocytopenia.
  phenotype_term:
    preferred_term: Thrombocytopenia
    term:
      id: HP:0001873
      label: Thrombocytopenia
  evidence:
  - reference: PMID:34871992
    reference_title: "Extra-muscular manifestations in GNE myopathy patients: A nationwide repository questionnaire survey in Japan."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The frequencies of idiopathic thrombocytopenia and SAS among Japanese GNE myopathy patients were higher than those observed in the general Japanese population. Routine blood tests and evaluation of sleep-disordered breathing should be considered in order to better manage GNE myopathy patients."
    explanation: >-
      Establishes an excess of thrombocytopenia over the general population, at a
      registry-reported 4.1%. No frequency band is assigned: 4.1% falls in the gap
      between VERY_RARE (1 to 4%) and OCCASIONAL (5 to 29%), and rounding it into
      either would assert a precision the single registry figure does not carry.
genetic:
- name: GNE Biallelic Hypomorphic Variants
  gene_term:
    preferred_term: GNE
    term:
      id: hgnc:23657
      label: GNE
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  features: >-
    Biallelic, homozygous or compound heterozygous, variants in GNE at 9p13.3.
    More than 255 variants have been reported, predominantly missense and
    distributed across both the epimerase and kinase catalytic domains. Founder
    alleles dominate the epidemiology: p.Met743Thr in Middle Eastern and Persian
    Jewish populations, p.Val603Leu and p.Asp207Val in Japan. Complete biallelic
    loss of function is not compatible with the human phenotype, since Gne
    knockout is embryonic lethal in mouse, so surviving genotypes retain residual
    activity. Non-coding and structural variants are under-ascertained: deep
    intronic variants and a large insertion have been found only by genome and
    long-read sequencing, so a negative coding panel does not exclude the
    diagnosis.
  frequency: OBLIGATE
  evidence:
  - reference: PMID:11528398
    reference_title: "The UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase gene is mutated in recessive hereditary inclusion body myopathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our findings indicate that GNE is the gene responsible for recessive HIBM."
    explanation: >-
      Establishes GNE as the causative gene.
  - reference: PMID:39332896
    reference_title: Novel variants and genotype-phenotype correlation in a multicentre cohort of GNE myopathy in China.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Missense variants predominantly located in the epimerase/kinase domain coding region, indicating the impairment of catalytic function as a key pathogenic consequence."
    explanation: >-
      Characterizes the variant spectrum as predominantly missense in the
      catalytic domains.
  notes: >-
    Nomenclature hazard. GNE has two commonly cited transcripts and the older
    literature uses the shorter one, so every variant published before 2014 is
    offset by 31 residues: p.Met712Thr is p.Met743Thr, p.Val572Leu is p.Val603Leu,
    and p.Asp176Val is p.Asp207Val. Variants here are given in current
    NM_001128227 numbering. The mouse-model literature uses the legacy names,
    which is why the animal_models entry below looks as though it concerns a
    different allele when it does not.
inheritance:
- name: Autosomal Recessive
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  description: >-
    Autosomal recessive, with founder alleles and consanguinity driving the
    epidemiology. Being of Persian or Middle Eastern Jewish, Japanese, Korean,
    Bulgarian Roma, or certain Indian ancestries substantially raises prior
    probability.
  evidence:
  - reference: PMID:20301439
    reference_title: GNE Myopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "GNE myopathy is inherited in an autosomal recessive manner."
    explanation: >-
      GeneReviews states the inheritance pattern.
prevalence:
- population: Worldwide, clinical and registry ascertainment
  measure_type: POINT_PREVALENCE
  prevalence_class: BAND_1_9_PER_1000000
  rate_per_100000: 0.5
  rate_low: 0.1
  rate_high: 0.9
  notes: >-
    The conventionally cited figure, one to nine cases per million. Recorded with
    the caveat its own source attaches: the estimate is limited by underdiagnosis,
    misdiagnosis, and founder-allele bias, and the population-genetic estimate
    below is an order of magnitude higher.
  evidence:
  - reference: PMID:30338442
    reference_title: "GNE Myopathy: Etiology, Diagnosis, and Therapeutic Challenges."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "It has an estimated prevalence of 1 to 9:1,000,000."
    explanation: >-
      Clinical review stating the conventional prevalence figure first-hand.
  - reference: PMID:40225917
    reference_title: Estimating the Prevalence of GNE Myopathy Using Population Genetic Databases.
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: "The prevalence of GNEM is estimated to range between one and nine cases per million individuals, but the accuracy of these estimates is limited by underdiagnosis, misdiagnosis, and bias introduced by founder allele frequencies."
    explanation: >-
      Restates the conventional estimate together with the three reasons it is
      likely to be too low. Tagged COMPUTATIONAL because the publication is the
      population-genetic modelling study recorded in the second prevalence
      record below; this sentence is its framing of the clinical figure, not an
      independent clinical measurement of it.
- population: Worldwide, gnomAD allele-frequency derived
  measure_type: POINT_PREVALENCE
  prevalence_class: BAND_1_9_PER_100000
  rate_per_100000: 1.846
  rate_low: 1.846
  rate_high: 9.542
  notes: >-
    18.46 to 95.42 cases per million derived from gnomAD allele frequencies under
    Hardy-Weinberg, narrowing to 11.00 to 87.68 when variant severity is taken
    into account. An order of magnitude above the clinical estimate, which the
    authors read as evidence the disease is substantially underdiagnosed rather
    than as a contradiction. Both figures are recorded here because the
    disagreement is itself the finding.
  evidence:
  - reference: PMID:40225917
    reference_title: Estimating the Prevalence of GNE Myopathy Using Population Genetic Databases.
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: "Our most conservative estimate suggested a prevalence of 18.46 cases per million, while our most liberal estimate places the prevalence at 95.42 cases per million."
    explanation: >-
      Gives the population-genetic range. Tagged COMPUTATIONAL because it is an
      in silico estimate from allele frequencies and pathogenicity prediction, not
      a counted cohort.
  - reference: PMID:40225917
    reference_title: Estimating the Prevalence of GNE Myopathy Using Population Genetic Databases.
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: "Our findings indicate that the true global prevalence of GNEM is greater than previous predictions underscoring that this condition is considerably more widespread than previously believed."
    explanation: >-
      The authors' own interpretation of the discrepancy, which is underdiagnosis
      rather than an error in either method.

progression:
- phase: Onset
  age_range: 20 to 40 years
  notes: >-
    Adult onset with bilateral foot drop from anterior tibialis weakness. Onset is
    insidious; there is no acute presenting event.
  evidence:
  - reference: PMID:20301439
    reference_title: GNE Myopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "GNE myopathy is a slowly progressive muscle disease that typically presents between age 20 and 40 years with bilateral foot drop caused by anterior tibialis weakness."
    explanation: >-
      Gives the onset age window and the presenting sign.
- phase: Distal to proximal progression
  duration: one to two decades
  notes: >-
    Involvement extends from the anterior to the posterior compartment of the
    lower leg, then hamstrings, then hip girdle, with the quadriceps relatively
    spared. Upper limbs may be affected within five to ten years and do not
    necessarily follow a distal-to-proximal order. Decline is measurable but slow
    across three years of the international disease monitoring programme.
  evidence:
  - reference: PMID:20301439
    reference_title: GNE Myopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The upper extremities, which may be affected within five to ten years of disease onset, do not necessarily follow a distal-to-proximal progression."
    explanation: >-
      Documents the upper-limb timing and the fact that it breaks the
      distal-to-proximal rule.
  - reference: PMID:33459658
    reference_title: "Results from a 3-year Non-interventional, Observational Disease Monitoring Program in Adults with GNE Myopathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "GNEM-FAS scores were more severe at baseline in subjects who walked <200 meters versus ≥200 meters in 6 minutes; in both groups, GNEM-FAS total, mobility, UE, and self-care scores decreased from baseline through month 36."
    explanation: >-
      Quantifies functional decline across three years in the international
      disease monitoring programme.
- phase: Advanced disease
  notes: >-
    Wheelchair dependence about ten to twenty years after onset, with neck and
    core involvement and, late, respiratory muscle weakness. Quadriceps sparing
    finally gives way at this stage.
  evidence:
  - reference: PMID:20301439
    reference_title: GNE Myopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In advanced stages, neck and core muscles can become affected."
    explanation: >-
      Documents the late spread to neck and core musculature.
clinical_burden:
  burden_level: HIGH
  rationale: >-
    Onset falls in early working life and the disease is relentlessly progressive
    to wheelchair dependence over one to two decades, with late respiratory
    involvement. There is no approved disease-modifying therapy outside Japan, and
    the one Class I trial of the mechanism-matched therapy was negative. Function
    declines measurably even over a single year of observation.
  evidence:
  - reference: PMID:33459658
    reference_title: "Results from a 3-year Non-interventional, Observational Disease Monitoring Program in Adults with GNE Myopathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "GNEM-FAS scores were more severe at baseline in subjects who walked <200 meters versus ≥200 meters in 6 minutes; in both groups, GNEM-FAS total, mobility, UE, and self-care scores decreased from baseline through month 36."
    explanation: >-
      Documents progressive functional loss across all measured domains over three
      years.
  - reference: PMID:20301439
    reference_title: GNE Myopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A wheelchair may be needed about ten to 20 years after the onset of manifestations."
    explanation: >-
      Establishes the interval to wheelchair dependence.
diagnosis:
- name: Clinical and Histopathological Suspicion
  description: >-
    The diagnosis is suspected from adult-onset distal weakness beginning with
    foot drop, relative quadriceps sparing, and muscle histopathology showing
    rimmed vacuoles without inflammation. The absent inflammation is what
    separates this from sporadic inclusion body myositis, and the naming collision
    between the two makes stating that negative explicitly worthwhile.
  evidence:
  - reference: PMID:20301439
    reference_title: GNE Myopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The diagnosis of GNE myopathy is suspected in a proband with suggestive clinical findings and muscle histopathology (rimmed vacuoles, no inflammation) and is established by the presence of biallelic pathogenic variants in GNE identified by molecular genetic testing."
    explanation: >-
      GeneReviews states the diagnostic pathway, including the absence of
      inflammation.
- name: GNE Molecular Genetic Testing
  description: >-
    Biallelic pathogenic GNE variants establish the diagnosis. A negative coding
    panel does not exclude it: deep intronic variants and a large insertion have
    been identified only through genome sequencing and long-read sequencing, so
    escalation is warranted where clinical suspicion is high.
  evidence:
  - reference: PMID:20301439
    reference_title: GNE Myopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The diagnosis of GNE myopathy is suspected in a proband with suggestive clinical findings and muscle histopathology (rimmed vacuoles, no inflammation) and is established by the presence of biallelic pathogenic variants in GNE identified by molecular genetic testing."
    explanation: >-
      Establishes molecular testing as what confirms the diagnosis.
  - reference: PMID:39332896
    reference_title: Novel variants and genotype-phenotype correlation in a multicentre cohort of GNE myopathy in China.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Comprehensive techniques such as WGS and Nanopore LRS warrants the identifying of GNE variants."
    explanation: >-
      Supports escalation to genome and long-read sequencing when coding analysis
      is uninformative.
treatments:
- name: Aceneuramic Acid Extended-Release (Sialic Acid Replacement)
  description: >-
    The mechanism-matched therapy, and a genuinely split evidence base that this
    entry records in both directions rather than picking a side. An international
    phase 3 trial provided Class I evidence that extended-release sialic acid does
    not improve muscle strength compared with placebo. A smaller Japanese phase
    II/III trial missed significance on its primary covariance analysis and
    reached significance only on a repeated-measures analysis, and a confirmatory
    Japanese study showed a numerically smaller decline whose confidence interval
    crossed zero, described by its own authors as a trend. On that basis the
    N-acetylneuraminic acid extended-release tablet was approved in Japan in 2024,
    the first drug approved anywhere for this disease. It is not approved
    elsewhere.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: N-acetylneuraminic acid
      term:
        id: CHEBI:17012
        label: N-acetylneuraminic acid
  target_mechanisms:
  - target: Free Sialic Acid Depletion
    treatment_effect: RESTORES
    description: >-
      Oral sialic acid replaces the depleted end product directly. Whether that
      translates into preserved muscle strength is exactly what the trials
      disagree about.
  evidence:
  - reference: PMID:31036580
    reference_title: A phase 3 randomized study evaluating sialic acid extended-release for GNE myopathy.
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "Ace-ER was not superior to placebo in improving muscle strength and function in patients with GNE myopathy."
    explanation: >-
      The international phase 3 primary result, which was negative.
  - reference: PMID:31036580
    reference_title: A phase 3 randomized study evaluating sialic acid extended-release for GNE myopathy.
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "This study provides Class I evidence that for patients with GNE myopathy, Ace-ER does not improve muscle strength compared to placebo."
    explanation: >-
      The authors' own evidence classification, which is the strongest negative
      statement available in this disease.
  - reference: PMID:37125562
    reference_title: Phase II/III Study of Aceneuramic Acid Administration for GNE Myopathy in Japan.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The change in UEC score at 48 weeks was significantly higher in the SA-ER group compared with the placebo group"
    explanation: >-
      The positive Japanese result. PARTIAL because significance came from a
      repeated-measures analysis after the primary covariance analysis returned a
      non-significant P value, and the trial randomized only 20 patients.
  - reference: PMID:37568154
    reference_title: Efficacy confirmation study of aceneuramic acid administration for GNE myopathy in Japan.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The present study reproducibly showed a trend towards slowing of loss of muscle strength and function with orally administered SA-ER, indicating supplementation with sialic acid might be a promising replacement therapy for GNE myopathy."
    explanation: >-
      The confirmatory Japanese study. PARTIAL because the confidence interval
      crossed zero and the authors themselves describe the finding as a trend.
  - reference: PMID:41082181
    reference_title: "Decoding GNE Myopathy: From Molecular Basis to Therapeutic Advances."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "culminating in the approval of the N-acetyl-neuraminic acid extended-release tablet in Japan in 2024."
    explanation: >-
      Establishes the Japanese regulatory approval. Tagged OTHER because this is a
      fact about regulatory action rather than a report of clinical evidence.
- name: N-Acetylmannosamine (ManNAc)
  description: >-
    The upstream precursor, and mechanistically the more interesting option:
    ManNAc enters the pathway downstream of the defective epimerase step, so it
    bypasses an epimerase block, and the phase 1 study showed it restores
    intracellular sialic acid synthesis even in patients homozygous for
    kinase-domain variants. An open-label phase 2 reported increased plasma
    sialic acid, increased sarcolemmal sialylation, and a slower rate of strength
    decline. The comparator there was historical natural history rather than
    placebo, which is the limitation that a placebo-controlled trial is meant to
    resolve.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: N-acetyl-D-mannosamine
      term:
        id: CHEBI:63153
        label: N-acetyl-D-mannosamine
  target_mechanisms:
  - target: Free Sialic Acid Depletion
    treatment_effect: BYPASSES
    description: >-
      ManNAc enters the biosynthetic pathway downstream of the epimerase step,
      bypassing the commonest site of the enzymatic block.
  evidence:
  - reference: PMID:28641925
    reference_title: "Safety, pharmacokinetics and sialic acid production after oral administration of N-acetylmannosamine (ManNAc) to subjects with GNE myopathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Given that Neu5Ac is known to have a short half-life, the prolonged elevation of Neu5Ac after a single dose of ManNAc suggests that intracellular biosynthesis of sialic acid was restored in subjects with GNE myopathy, including those homozygous for mutations in the kinase domain."
    explanation: >-
      Demonstrates restored intracellular sialic acid biosynthesis, including in
      kinase-domain genotypes.
  - reference: PMID:34257421
    reference_title: "Safety and efficacy of N-acetylmannosamine (ManNAc) in patients with GNE myopathy: an open-label phase 2 study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "ManNAc showed long-term safety, biochemical efficacy consistent with the intended mechanism of action, and preliminary evidence clinical efficacy in patients with GNE myopathy."
    explanation: >-
      Reports the phase 2 result. PARTIAL because the study was open-label in
      twelve patients with a historical natural-history comparator rather than a
      placebo arm, and the authors call the clinical efficacy preliminary.
- name: 6'-Sialyllactose
  description: >-
    A milk oligosaccharide used as a sialic acid source, developed in South Korea
    and the only agent in this disease with placebo-controlled evidence of an
    imaging effect. A randomized pilot established target engagement, with free
    sialic acid rising in both dose groups and not in placebo, and reported
    improved proximal limb power at the higher dose. A subsequent
    placebo-controlled trial in eleven participants found a statistically
    significant difference in the increase in posterior thigh fat fraction on
    MRI, the imaging correlate of muscle degeneration; the anterior thigh and
    both lower-leg regions did not separate from placebo. Muscle strength did
    not differ between the groups either, with one carve-out the authors state
    explicitly: hand grip power fell in both arms, reaching significance only in
    the placebo arm. That asymmetry is a signal rather than a result, since with
    five and six participants per arm a decline failing to reach significance
    under treatment is as consistent with low power as with preservation, and
    the authors attribute the overall null to how little strength either group
    lost. Both trials are small and the strength endpoints were negative, so
    this is promising rather than established.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: 6'-sialyllactose
      term:
        id: CHEBI:153372
        label: 5-acetamido-3,5-dideoxy-D-glycero-alpha-D-galacto-non-2-ulopyranonosyl-(2->6)-beta-D-galactopyranosyl-(1->4)-D-glucopyranose
  target_mechanisms:
  - target: Free Sialic Acid Depletion
    treatment_effect: RESTORES
    description: >-
      6'-sialyllactose supplies sialic acid from the diet, raising the free pool
      that the enzymatic block depletes.
  evidence:
  - reference: PMID:37852099
    reference_title: "Pharmacokinetics and clinical efficacy of 6'-sialyllactose in patients with GNE myopathy: Randomized pilot trial."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Free sialic acid in both low- and high-dose groups significantly increased at 6 and 12 weeks, but not in the placebo group."
    explanation: >-
      Demonstrates target engagement, which is the pharmacological precondition
      for any clinical effect.
  - reference: PMID:39644669
    reference_title: "A pilot trial for efficacy confirmation of 6'-sialyllactose supplementation in GNE myopathy: Randomized, placebo-controlled trial."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The increase in fat fraction, indicating muscle degeneration, was statistically significant between the two groups"
    explanation: >-
      The imaging endpoint separated the groups. PARTIAL because the trial had
      eleven participants and the strength endpoints did not.
  - reference: PMID:39644669
    reference_title: "A pilot trial for efficacy confirmation of 6'-sialyllactose supplementation in GNE myopathy: Randomized, placebo-controlled trial."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "Muscle strength, excluding hand grip power, did not show a significant difference between the two groups, which is attributed to the lack of pronounced muscle strength decline in both groups."
    explanation: >-
      Refutes a demonstrated muscle-strength benefit in this trial, with the
      authors' own explanation that neither arm declined much over the period.
  - reference: PMID:39644669
    reference_title: "A pilot trial for efficacy confirmation of 6'-sialyllactose supplementation in GNE myopathy: Randomized, placebo-controlled trial."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Hand grip power tended to decrease in both groups, and this decline was statistically significant in the placebo group"
    explanation: >-
      The endpoint carved out of the strength result above. Recorded as PARTIAL
      rather than SUPPORT because the finding is an asymmetry in which arm
      reached significance, not a between-group difference: grip fell in both
      arms, and with five and six participants the treated arm's failure to
      reach significance is as consistent with low power as with preservation.
- name: Supportive and Rehabilitative Management
  description: >-
    In the absence of an approved disease-modifying therapy outside Japan,
    management is multidisciplinary and supportive: ankle-foot orthoses and
    assistive ambulatory devices, adaptive devices for fine motor function and
    activities of daily living, and baseline echocardiography and pulmonary
    function testing in non-ambulant patients with pulmonology follow-up.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Rehabilitation
    term:
      id: NCIT:C15315
      label: Rehabilitation
  evidence:
  - reference: PMID:20301439
    reference_title: GNE Myopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Evaluation and management are often by a multidisciplinary team that includes neuromuscular specialists, physiatrists, and physical and occupational therapists to address issues secondary to muscle weakness, including the use of assistive ambulatory devices (e.g., ankle-foot orthoses, cane, walker, wheelchair, or powerchair)."
    explanation: >-
      GeneReviews sets out the supportive management framework.
- name: Avoidance of Myotoxic Agents and Overexertion
  description: >-
    A management precaution rather than a therapy, and one worth curating
    explicitly because it is actionable at every clinic visit. GeneReviews advises
    cautious use of medications with myotoxic potential, naming colchicine and
    statins, and avoidance of weight-lifting and repetitive activities that
    provoke muscle pain. Note this is expert guidance, not a demonstrated
    gene-environment interaction.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:20301439
    reference_title: GNE Myopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Agents/circumstances to avoid: Cautious use of medications/drugs with potential myotoxicity (e.g., colchicine and statins); avoidance of weight-lifting and repetitive activities that cause muscle pain."
    explanation: >-
      GeneReviews states the agents and circumstances to avoid.
animal_models:
- name: Gne-null mouse expressing human GNE p.Asp207Val transgene
  species: Mouse
  genotype: Gne-null background with human GNE D176V transgene (legacy numbering; p.Asp207Val in current NM_001128227 numbering)
  description: >-
    The field's workhorse model, generated because the straight Gne knockout is
    embryonically lethal. It reproduces the clinical, histopathological, and
    biochemical features of the human disease, and it is where the temporal
    ordering of amyloid before rimmed vacuoles was established.
  publication: PMID:17704511
  modeled_mechanisms:
  - target: Amyloid and Misfolded Protein Accumulation
    relationship: RECAPITULATES
    fidelity: HIGH
    description: >-
      Beta-amyloid deposition appears in myofibers at 32 weeks and clearly
      precedes rimmed vacuole formation at 42 weeks, which is the ordering that
      constrains causal models of the inclusion pathology.
    limitations: >-
      The model expresses a human transgene on a null background rather than
      carrying a knock-in point mutation, so expression level and stoichiometry
      are not those of a patient. Motor performance falls only from 30 weeks, a
      compressed timescale against a human disease measured in decades, and the
      allele modeled is a Japanese founder variant rather than a general case.
    readouts:
    - name: Myofiber beta-amyloid deposition over time
      target: Amyloid and Misfolded Protein Accumulation
      direction: INCREASED
      interpretation: >-
        Time-resolved appearance of amyloid before rimmed vacuoles is the
        structural evidence for the ordering of the two.
      evidence:
      - reference: PMID:17704511
        reference_title: A Gne knockout mouse expressing human GNE D176V mutation develops features similar to distal myopathy with rimmed vacuoles or hereditary inclusion body myopathy.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "A compelling finding is the development of beta-amyloid deposition in myofibers by 32 weeks, which clearly precedes RV formation at 42 weeks."
        explanation: >-
          Reports the measured timing of amyloid deposition relative to rimmed
          vacuole formation.
    evidence:
    - reference: PMID:17704511
      reference_title: A Gne knockout mouse expressing human GNE D176V mutation develops features similar to distal myopathy with rimmed vacuoles or hereditary inclusion body myopathy.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "These results show that the Gne(-/-)hGNED176V-Tg mouse mimics the clinical, histopathological and biochemical features of DMRV/hIBM, making it useful for understanding the pathomechanism of this myopathy and for employing different strategies for therapy."
      explanation: >-
        The authors' own validation of the model against the human disease.
  - target: Hyposialylation of Muscle Glycoproteins
    relationship: RESCUES
    fidelity: HIGH
    description: >-
      Oral sialic acid metabolites completely prevented muscle atrophy and
      weakness in this model, which is the pivotal demonstration that
      hyposialylation is causal rather than incidental to the myopathy.
    limitations: >-
      The treatment was prophylactic, given before the phenotype developed, so it
      demonstrates prevention rather than reversal. The human trials that followed
      were of established disease and did not reproduce the benefit, which is
      exactly the gap between preventing a phenotype in a mouse and modifying one
      in a patient.
    evidence:
    - reference: PMID:19448634
      reference_title: Prophylactic treatment with sialic acid metabolites precludes the development of the myopathic phenotype in the DMRV-hIBM mouse model.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "By showing that muscle atrophy and weakness are completely prevented in a mouse model of DMRV-hIBM after treatment with sialic acid metabolites orally, we provide evidence that hyposialylation is indeed one of the key factors in the pathomechanism of DMRV-hIBM."
      explanation: >-
        The rescue that established hyposialylation as causal, quoted with the
        authors' own hedge.
experimental_models:
- name: Human pluripotent stem cell-derived GNE myoblasts and neuromuscular organoids
  experimental_model_type: IPSC_DERIVED_MODEL
  description: >-
    Two independent isogenic human stem-cell-derived myoblast models plus
    Gne-knockout C2C12 myoblasts and human neuromuscular organoids, used together
    to establish the autophagy arm of the mechanism and to nominate and then
    validate a repurposing candidate.
  publication: PMID:41963465
  modeled_mechanisms:
  - target: Autophagic Block and Proteostasis Failure
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >-
      Transcriptomic analysis identified autophagy gene sets as pathogenic
      signatures, biochemically validated in Gne-knockout myoblasts, and PI3K
      inhibition restored ULK1 activity and reactivated autophagy in
      patient-relevant neuromuscular organoids.
    limitations: >-
      Cultured myoblasts and organoids do not reproduce the mature myofiber, the
      decades-long timescale, or the compartment-specific muscle involvement that
      defines the human disease, and the extracellular-matrix-driven AKT-mTORC1
      arm has not been demonstrated in patient muscle. The nominated drug
      candidate is a computational repurposing hit validated only in the same
      model system.
    readouts:
    - name: ULK1 activity and autophagy reactivation under PI3K inhibition
      target: Autophagic Block and Proteostasis Failure
      direction: RESTORED
      interpretation: >-
        Restoring ULK1 activity reactivates autophagy, which is what makes the
        inhibitory phosphorylation step causal rather than correlative.
      evidence:
      - reference: PMID:41963465
        reference_title: Defective autophagy in GNE myopathy is rescued by inhibition of noncanonical Akt-mTORC1 activation across multiple isogenic models.
        supports: SUPPORT
        evidence_source: IN_VITRO
        snippet: "Functional validation in human pluripotent stem cell-derived neuromuscular organoids demonstrated that copanlisib reactivates autophagy via restoration of ULK1 activity."
        explanation: >-
          Reports the measured restoration of ULK1 activity and autophagy in the
          organoid model.
    evidence:
    - reference: PMID:41963465
      reference_title: Defective autophagy in GNE myopathy is rescued by inhibition of noncanonical Akt-mTORC1 activation across multiple isogenic models.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "By performing transcriptome analysis on two independent GNE myoblast models derived from human pluripotent stem cells, we identified multiple autophagy-related gene sets as pathogenic signatures of GNE myopathy."
      explanation: >-
        Establishes the autophagy signature across two independent human models.
discussions:
- discussion_id: gne_tissue_restriction_paradox
  kind: KNOWLEDGE_GAP
  prompt: >-
    Why is a systemic enzyme deficiency that lowers sialic acid in serum, muscle,
    and other organs expressed as a disease of skeletal muscle alone?
  attaches_to:
  - pathophysiology#Hyposialylation of Muscle Glycoproteins
  rationale: >-
    The enzymatic block is everywhere and the mouse model shows marked
    hyposialylation in serum, muscle, and other organs, yet the clinical disease
    is essentially confined to skeletal muscle. Two partial answers exist and
    neither closes the question. The quadriceps sparing observation shows that
    baseline sialic acid requirement differs between muscles, which suggests
    demand rather than supply sets vulnerability. And the total-versus-free sialic
    acid discrepancy suggests only a small subset of sialylation targets is
    pathogenically relevant. Identifying that target set is the field's central
    open question, and until it is answered the tissue restriction is described
    rather than explained.
  evidence:
  - reference: PMID:17704511
    reference_title: A Gne knockout mouse expressing human GNE D176V mutation develops features similar to distal myopathy with rimmed vacuoles or hereditary inclusion body myopathy.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Interestingly, these mice exhibit marked hyposialylation in serum, muscle and other organs."
    explanation: >-
      Establishes that the biochemical deficit is systemic while the disease is
      not, which is the paradox itself.
  - reference: PMID:28267778
    reference_title: Substantial deficiency of free sialic acid in muscles of patients with GNE myopathy and in a mouse model.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Differences in mean total SA levels in muscle from patients compared with normal controls were less distinct and more variable between different muscles, suggesting a small subset of sialylation targets could be responsible for the pathogenesis of GNEM."
    explanation: >-
      Points toward a narrow pathogenic target set as a partial explanation.
- discussion_id: gne_sialic_acid_trial_discordance
  kind: CONTROVERSY
  prompt: >-
    Does oral sialic acid replacement modify the course of GNE myopathy, given
    that a Class I international trial was negative and Japanese trials were
    equivocal-to-positive enough to support approval?
  attaches_to:
  - treatments#Aceneuramic Acid Extended-Release (Sialic Acid Replacement)
  rationale: >-
    Both results are real and this entry declines to pick between them. The
    international phase 3 gave Class I evidence of no benefit on muscle strength.
    The Japanese phase II/III missed its primary covariance analysis and reached
    significance only on a repeated-measures analysis in 20 patients; the
    confirmatory Japanese study in a smaller cohort showed a numerically smaller
    decline with a confidence interval crossing zero, which its authors call a
    trend. Approval followed in Japan in 2024. Candidate reconciliations include
    differences in cohort genotype, disease stage at enrolment, statistical
    approach, and endpoint sensitivity, none of which has been tested directly. A
    curator should not present either result alone.
  evidence:
  - reference: PMID:31036580
    reference_title: A phase 3 randomized study evaluating sialic acid extended-release for GNE myopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This study provides Class I evidence that for patients with GNE myopathy, Ace-ER does not improve muscle strength compared to placebo."
    explanation: >-
      One half of the discordance, at the highest available evidence class.
  - reference: PMID:37568154
    reference_title: Efficacy confirmation study of aceneuramic acid administration for GNE myopathy in Japan.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The present study reproducibly showed a trend towards slowing of loss of muscle strength and function with orally administered SA-ER, indicating supplementation with sialic acid might be a promising replacement therapy for GNE myopathy."
    explanation: >-
      The other half, in the authors' own deliberately hedged language.
- discussion_id: gne_amyloid_causal_weight
  kind: OPEN_QUESTION
  prompt: >-
    Is beta-amyloid accumulation mechanistically upstream of myofiber atrophy in
    GNE myopathy, or a downstream marker of failed autophagic clearance?
  attaches_to:
  - pathophysiology#Amyloid and Misfolded Protein Accumulation
  rationale: >-
    The mouse model shows amyloid deposition preceding rimmed vacuole formation by
    ten weeks, which is consistent with amyloid being upstream but does not
    establish it, since both could be downstream of a shared clearance failure.
    Review literature has argued for a mechanistic role while stating plainly that
    the cause and process of amyloid formation in this disease are unclear. The
    entry therefore places amyloid in the chain with an indirect causal link to
    atrophy and unknown intermediates rather than asserting a direct one.
  evidence:
  - reference: PMID:17704511
    reference_title: A Gne knockout mouse expressing human GNE D176V mutation develops features similar to distal myopathy with rimmed vacuoles or hereditary inclusion body myopathy.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "A compelling finding is the development of beta-amyloid deposition in myofibers by 32 weeks, which clearly precedes RV formation at 42 weeks."
    explanation: >-
      Establishes temporal precedence, which constrains but does not settle the
      causal question.
- discussion_id: gne_atypical_muscle_involvement
  kind: OPEN_QUESTION
  prompt: >-
    How reliable is the quadriceps-sparing, anterior-first rule, given documented
    families with the opposite pattern?
  attaches_to:
  - pathophysiology#Myofiber Atrophy and Degeneration
  rationale: >-
    Quadriceps sparing with anterior-compartment onset is the single most useful
    diagnostic discriminator in this disease, and it now has a biochemical
    explanation in the lower baseline sialic acid requirement of normal
    quadriceps. But at least one family broke the pattern entirely, with severe
    posterior calf involvement and a spared anterior compartment. The entry states
    the rule because it is diagnostically load-bearing, and records the exception
    so the rule is not read as absolute.
  evidence:
  - reference: PMID:27854221
    reference_title: GNE-Myopathy in a Greek Romani Family with Unusual Calf Phenotype and Protein Aggregation Pathology.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "in contrast to the typical pattern of muscle involvement, one of them showed severe involvement of posterior calf muscles with spared anterior compartment of the lower leg muscles."
    explanation: >-
      Documents a family with the inverted involvement pattern.
differential_diagnoses:
- name: Sporadic Inclusion Body Myositis
  description: >-
    The most expensive naming collision in this area. Both carry inclusion body in
    the name and both show rimmed vacuoles, but sporadic inclusion body myositis
    is an inflammatory, late-onset, non-Mendelian disease with a completely
    different mechanism. The discriminating histological feature is inflammation,
    which is present there and absent here, and which is precisely why the
    GeneReviews diagnostic criterion names the absence of inflammation
    explicitly.
  distinguishing_features:
  - Inflammatory infiltrate present in sporadic inclusion body myositis, absent
    here
  - Late onset after age 50 rather than in the twenties or thirties
  - Sporadic rather than autosomal recessive, with no GNE variants
  - Quadriceps involvement is characteristic rather than spared
  evidence:
  - reference: PMID:20301439
    reference_title: GNE Myopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The diagnosis of GNE myopathy is suspected in a proband with suggestive clinical findings and muscle histopathology (rimmed vacuoles, no inflammation) and is established by the presence of biallelic pathogenic variants in GNE identified by molecular genetic testing."
    explanation: >-
      The explicit no-inflammation criterion is the histological separator from
      sporadic inclusion body myositis.
- name: Dysferlinopathy
  description: >-
    Another distal-onset recessive myopathy, and the differential most often
    settled by a routine blood test: creatine kinase is markedly elevated in
    dysferlinopathy and only normal to moderately elevated here. Distribution also
    differs, since the quadriceps sparing characteristic of GNE myopathy is not a
    feature.
  distinguishing_features:
  - Markedly elevated creatine kinase rather than normal to moderately elevated
  - No quadriceps sparing
  - Biallelic DYSF rather than GNE variants
  evidence:
  - reference: PMID:30338442
    reference_title: "GNE Myopathy: Etiology, Diagnosis, and Therapeutic Challenges."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The disease slowly progresses over the next decades to involve skeletal muscles throughout the body, with relative sparing of the quadriceps until late stages of the disease."
    explanation: >-
      Establishes the quadriceps sparing that distinguishes this from other distal
      myopathies. PARTIAL because the creatine kinase contrast is not quantified
      in this source.
notes: >-
  Nomenclature. Two independently described diseases, Nonaka distal myopathy in
  Japan and quadriceps-sparing hereditary inclusion body myopathy in Iranian
  Jewish families, turned out to be one entity, and the unified name GNE myopathy
  was formalized in 2014. The synonym list is long for that reason. Do not confuse
  this with sporadic inclusion body myositis, which shares the phrase inclusion
  body and nothing else that matters.

  Variant numbering. GNE has two commonly cited transcripts and the pre-2014
  literature uses the shorter one, so every legacy variant name is offset by 31
  residues. This entry uses current NM_001128227 numbering and records the legacy
  names where the model-organism literature depends on them, which is why the
  mouse genotype field carries both.

  Thrombocytopenia scoping. A separate MONDO entity exists for thrombocytopenia 12
  with or without myopathy, also GNE-caused and driven by a platelet sialylation
  defect with accelerated platelet clearance. This entry curates thrombocytopenia
  as an extramuscular manifestation with the registry frequency, and does not
  attempt to model the platelet-predominant presentation, which belongs in its own
  entry.

  Deliberately not curated. The Japanese registry also reported psychiatric
  disease in 14.7% of participants. That is a self-reported diagnosis in a chronic
  disabling myopathy and is heavily confounded by reactive depression, so it is
  not curated as a phenotype of this disease. Dietary sialoglycoprotein loading is
  likewise not curated as a protective factor: the one head-on test in a model
  system was negative, and only pharmacological monosaccharide dosing moved the
  readout.

  Sialuria. The same locus carries a dominant gain-of-function allelic disorder:
  variants in the CMP-sialic-acid allosteric site of the GNE epimerase domain
  escape feedback inhibition and cause sialic acid overproduction rather than
  deficiency. It is the mechanistic inverse of this disease and is not a subtype
  of it, which is why GAIN_OF_FUNCTION should never be curated on a myopathy
  allele here.

  Deep research. Curated from a claude_code deep-research report
  (research/GNE_Myopathy-deep-research-claude_code.md), whose own reference
  validation reported 41/41 references verified, 7/7 quotes valid, and a
  confabulation rate of 0.0. The GeneReviews chapter PMID:20301439 was fetched,
  tagged, and used as the phenotype baseline. Every snippet used here was
  independently re-verified against the cached PubMed record before it was
  written.
clinical_trials:
- name: NCT02377921
  phase: PHASE_III
  status: COMPLETED
  description: >-
    The international randomized, double-blind, placebo-controlled phase 3 of
    aceneuramic acid extended-release, whose upper-extremity composite primary
    endpoint was negative and which supplied the Class I evidence recorded on the
    treatment entry (PMID:31036580).
  target_phenotypes:
  - preferred_term: Distal lower limb muscle weakness
    term:
      id: HP:0009053
      label: Distal lower limb muscle weakness
  evidence:
  - reference: clinicaltrials:NCT02377921
    reference_title: "A Phase 3 Randomized, Double-Blind, Placebo-Controlled Study to Evaluate the Efficacy and Safety of Sialic Acid Extended-Release Tablets in Patients With GNE Myopathy (GNEM) or Hereditary Inclusion Body Myopathy (HIBM)"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The primary objective of this study is to evaluate the effect of 6 g/day aceneuramic acid extended-release (Ace-ER) treatment of participants with GNEM on upper extremity muscle strength"
    explanation: >-
      Registry record establishing the design and the primary endpoint that the
      trial failed to meet.
- name: NCT04671472
  phase: PHASE_III
  status: COMPLETED
  description: >-
    The Japanese confirmatory placebo-controlled trial of aceneuramic acid
    extended-release, published as PMID:37568154, which showed a numerically
    smaller decline whose confidence interval crossed zero.
  target_phenotypes:
  - preferred_term: Distal lower limb muscle weakness
    term:
      id: HP:0009053
      label: Distal lower limb muscle weakness
  evidence:
  - reference: clinicaltrials:NCT04671472
    reference_title: Efficacy Confirmation Study of NPC-09
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The investigators will examine the efficacy and safety of aceneuramic acid (SA-ER tablets) 6g daily for 48 weeks in patients with GNE myopathy in a placebo-controlled, double-blind, controlled trial."
    explanation: >-
      Registry record establishing the placebo-controlled design of the Japanese
      confirmatory study.
- name: NCT02346461
  phase: PHASE_II
  status: COMPLETED
  description: >-
    The open-label phase 2 of N-acetylmannosamine, published as PMID:34257421,
    whose comparator was historical natural history rather than placebo.
  target_phenotypes:
  - preferred_term: Distal lower limb muscle weakness
    term:
      id: HP:0009053
      label: Distal lower limb muscle weakness
  evidence:
  - reference: clinicaltrials:NCT02346461
    reference_title: An Open-Label Phase 2 Study of ManNAc in Subjects With GNE Myopathy
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Researchers are testing the drug ManNAc which is a precursor in the production of sialic acid within cells."
    explanation: >-
      Registry record establishing the agent and its mechanistic rationale.
- name: NCT04231266
  phase: PHASE_II
  status: ACTIVE_NOT_RECRUITING
  description: >-
    The placebo-controlled multi-centre trial of N-acetylmannosamine, and the
    study that would resolve the main limitation of the open-label phase 2, whose
    only comparator was historical natural history. This is the principal
    forward-looking therapeutic signal in the disease.
  target_phenotypes:
  - preferred_term: Distal lower limb muscle weakness
    term:
      id: HP:0009053
      label: Distal lower limb muscle weakness
  evidence:
  - reference: clinicaltrials:NCT04231266
    reference_title: "A Randomized, Double-Blind, Placebo-Controlled, Multi-Center Study to Evaluate the Efficacy of ManNAc in Subjects With GNE Myopathy"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In this randomized, double-blind, placebo-controlled trial the efficacy and long-term safety of ManNAc will be evaluated in subjects with GNE myopathy."
    explanation: >-
      Registry record establishing the randomized placebo-controlled design that
      the open-label phase 2 lacked.
datasets:
references:
- reference: PMID:20301439
  title: GNE Myopathy.
  tags:
  - GeneReviews
- reference: PMID:11528398
  title: "The UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase gene is mutated in recessive hereditary inclusion body myopathy."
- reference: PMID:41082181
  title: "Decoding GNE Myopathy: From Molecular Basis to Therapeutic Advances."
- reference: PMID:30338442
  title: "GNE Myopathy: Etiology, Diagnosis, and Therapeutic Challenges."
- reference: PMID:28267778
  title: Substantial deficiency of free sialic acid in muscles of patients with GNE myopathy and in a mouse model.
- reference: PMID:19448634
  title: Prophylactic treatment with sialic acid metabolites precludes the development of the myopathic phenotype in the DMRV-hIBM mouse model.
- reference: PMID:17704511
  title: A Gne knockout mouse expressing human GNE D176V mutation develops features similar to distal myopathy with rimmed vacuoles or hereditary inclusion body myopathy.
- reference: PMID:41963465
  title: Defective autophagy in GNE myopathy is rescued by inhibition of noncanonical Akt-mTORC1 activation across multiple isogenic models.
- reference: PMID:34871992
  title: "Extra-muscular manifestations in GNE myopathy patients: A nationwide repository questionnaire survey in Japan."
- reference: PMID:31036580
  title: A phase 3 randomized study evaluating sialic acid extended-release for GNE myopathy.
- reference: PMID:37125562
  title: Phase II/III Study of Aceneuramic Acid Administration for GNE Myopathy in Japan.
- reference: PMID:34257421
  title: "Safety and efficacy of N-acetylmannosamine (ManNAc) in patients with GNE myopathy: an open-label phase 2 study."
- reference: PMID:28641925
  title: "Safety, pharmacokinetics and sialic acid production after oral administration of N-acetylmannosamine (ManNAc) to subjects with GNE myopathy."
- reference: PMID:39332896
  title: Novel variants and genotype-phenotype correlation in a multicentre cohort of GNE myopathy in China.
- reference: PMID:24656604
  title: "GNE myopathy: a prospective natural history study of disease progression."
- reference: PMID:33459658
  title: "Results from a 3-year Non-interventional, Observational Disease Monitoring Program in Adults with GNE Myopathy."
- reference: PMID:37568154
  title: Efficacy confirmation study of aceneuramic acid administration for GNE myopathy in Japan.
- reference: PMID:27854221
  title: GNE-Myopathy in a Greek Romani Family with Unusual Calf Phenotype and Protein Aggregation Pathology.
- reference: PMID:40225917
  title: Estimating the Prevalence of GNE Myopathy Using Population Genetic Databases.
- reference: PMID:37852099
  title: "Pharmacokinetics and clinical efficacy of 6'-sialyllactose in patients with GNE myopathy: Randomized pilot trial."
- reference: PMID:39644669
  title: "A pilot trial for efficacy confirmation of 6'-sialyllactose supplementation in GNE myopathy: Randomized, placebo-controlled trial."

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References & Deep Research