MEHMO Syndrome

Mendelian MONDO:0010258 Pathograph 27 Show in embeddings browser X-linked Syndromic Intellectual Disability

X-linked multisystem disorder caused by hemizygous variants in EIF2S3, which encodes the gamma subunit of eukaryotic translation initiation factor 2 (eIF2). The acronym records the features of the originally described families: mental disability, epileptic seizures, hypogenitalism and hypogonadism, microcephaly and obesity. eIF2 delivers initiator methionyl-tRNA to the 40S ribosome and selects the AUG start codon, and eIF2gamma is the core subunit that holds the heterotrimer together, so a partial loss of its function lowers the amount of active eIF2 ternary complex. Translation initiation becomes less accurate as well as less efficient: initiation at near-cognate, non-AUG codons increases. Because eIF2 is also the node the integrated stress response acts on, the same variants leave cells with an over-active stress response and more vulnerable to death under stress. Endocrine disease is as prominent as the neurological picture and was not in the original acronym. Neonatal hypoglycaemia, early-onset insulin-dependent diabetes and progressive anterior hypopituitarism recur across reported patients, and a milder EIF2S3 phenotype of X-linked hypopituitarism with glucose dysregulation and normal head circumference has been described in one family. A 2025 review proposes reclassifying the condition, with related conditions, as an eIF2-related neuroendocrinopathy. Genotype tracks severity in a way that is unusual for a rare syndrome. The recurrent C-terminal frameshift p.Ile465Serfs*4 impairs eIF2gamma function more than the tested missense variants and is found in the most severely affected patients, while missense variants in the guanine nucleotide binding domain generally give a milder, sometimes incomplete phenotype. The small molecule ISRIB, which activates the eIF2 guanine nucleotide exchange factor, rescued growth, translation and neuronal differentiation defects in patient-derived cells, which makes this one of the few disorders in this class with an experimentally supported therapeutic lead.

Ask OpenScientist

Ask a research question about MEHMO Syndrome. OpenScientist will conduct autonomous deep research using the Disorder Mechanisms Knowledge Base and PubMed literature (typically 10-30 minutes).

Submitting...

Do not include personal health information in your question. Questions and results are cached in your browser's local storage.

1
Inheritance
7
Pathophys.
16
Phenotypes
2
Hypotheses
1
Gaps
27
Pathograph
1
Genes
2
Variants
5
Medical Actions
2
Differentials
2
Models
1
References
1
Deep Research
👪

Inheritance

1
X-linked recessive inheritance HP:0001419
Affected individuals are males hemizygous for an EIF2S3 variant, with carrier mothers. Reported pedigrees include maternally inherited variants and affected brothers.
X-linked recessive inheritance
Show evidence (2 references)
PMID:28055140 SUPPORT Human Clinical
"a novel maternally inherited missense EIF2S3 variant (c.324T>A; p.Ser108Arg) in another male patient with less severe clinical symptoms."
Maternal transmission to an affected male.
PMID:30878599 SUPPORT Human Clinical
"We report a novel hemizygous EIF2S3 variant, p.Pro432Ser, in the three boys (heterozygous in their mothers)."
Hemizygous in affected males, heterozygous in unaffected mothers.
◈

Mechanistic Hypotheses

2
Pharmacological eIF2B activation is the therapeutic route
eif2b_activation_is_the_therapeutic_route EMERGING
Evidence balance 1 support 1 refute 1 no evidence
Holds that the consequences of a defective eIF2 gamma subunit are reachable by activating the eIF2 guanine nucleotide exchange factor eIF2B, so that the therapeutic target is the exchange step downstream of the defect rather than the defective subunit itself. Note the narrower thing this does not claim. Patient cells do show increased stress-response activity, which is the Over-Activated Integrated Stress Response node and is cited there. What nothing reported establishes is whether that over-activation, or the reduced translation initiation it accompanies, drives the phenotype; eIF2B activation would oppose both, so the rescue result below does not separate them either. The experimental support is direct but confined to cells: ISRIB rescued growth, translation and neuronal differentiation in induced pluripotent stem cells from a patient with the C-terminal frameshift. No animal or human treatment data were identified, and whether rescue in differentiating cells predicts benefit in an already-developed brain is untested.
Kept EMERGING rather than CANONICAL because the entire supporting result is in patient-derived cells, and recorded as a hypothesis rather than a treatment entry because no patient has been reported treated. The two results are not testing the same proposition: rescuing a defined genetic lesion in eIF2 assembly is not the same intervention as activating eIF2B against a stress response that is itself protective, which is why neither result closes the question.
Show evidence (3 references)
PMID:31836389 SUPPORT In Vitro
"Addition of the drug ISRIB, an activator of the eIF2 guanine nucleotide exchange factor, rescues the cell growth, translation, and neuronal differentiation defects associated with the EIF2S3 mutation, offering the possibility of therapeutic intervention for MEHMO syndrome."
The rescue result and the authors' own framing of it as a possibility rather than a demonstrated therapy.
PMID:37823684 REFUTE INDIRECT Model Organism
"This study reveals that the ISR works as a neuroprotective pathway in ALS motor neurons and reveals the toxicity that eIF2B activators may display in ALS patients."
Two eIF2B activators of the same class as ISRIB brought disease forward and shortened survival in an ALS mouse model, and the authors warn of the toxicity the class may display in patients. REFUTE because the claim here is that pharmacological eIF2B activation is the therapeutic route, and this is the only in vivo test of that class in a neurological disease: it went the wrong way. INDIRECT because the test was in a different disease, where eIF2B is being pushed against a protective stress response rather than against a defect in eIF2 itself, so it bears on the class rather than on this lesion.
PMID:37823684 NO_EVIDENCE BACKGROUND Model Organism
"In experimental models, both ISR stimulation and inhibition prevented ALS neurodegeneration; however, which mode of ISR regulation would work in patients is still debated."
Cited for what it does not settle. Experimental models have been reported going both ways on the direction of stress-response modulation that helps, so the direction of effect is open even in the disease where the class has been tested in vivo. NO_EVIDENCE because a statement that the direction is debated neither supports nor refutes this hypothesis about MEHMO; it is the reason the hypothesis stays EMERGING.
Untreated neonatal hypoglycaemia contributes to the neurological phenotype
hypoglycaemia_contributes_to_neurological_injury EMERGING
Evidence balance 1 support
Holds that part of the neurological impairment in the severe patients is not a direct consequence of impaired translation in neurons but of untreated hypoglycaemia, which was not recognised as part of the syndrome until the endocrine phenotype was characterised. The proposal matters clinically: if true, early glucose management changes outcome in a disease otherwise without treatment. It is raised by the authors of the mild family's report as an explanation for why earlier patients were more severely affected, and it has not been tested.
Not placed in the pathograph. Doing so would assert that hypoglycaemia causes part of the neurological phenotype, which this single hedged sentence does not establish, and the alternative explanation for the severity difference, that the frameshift allele is simply worse than the missense alleles, is supported by functional data.
Show evidence (1 reference)
PMID:30878599 SUPPORT INDIRECT Human Clinical
"Untreated hypoglycaemia in previous cases may have contributed to their more severe neurological impairment and seizures in association with impaired EIF2S3."
The originating statement of the hypothesis, in the authors' hedged wording.
?

Discussions and Knowledge Gaps

1
Is the endocrine phenotype of MEHMO syndrome caused by death of differentiated secretory cells, or by a developmental deficiency of beta cells and pancreatic progenitors?
HUMAN MODEL MISMATCH mehmo_endocrine_cell_mechanism
Attached to
pathophysiology#Pancreatic Beta Cell Failure animal_models#Zebrafish
The two available models disagree, and the disagreement is not a detail: it decides whether the endocrine disease is progressive degeneration, which a stress-response drug might slow, or a fixed developmental deficit, which it would not. EIF2S3 knockdown in a human pancreatic cell line increased caspase activity and cell death, while the zebrafish knockout produced hyperglycaemia from beta cell and progenitor deficiency explicitly not related to apoptosis, and patient-derived fibroblasts also showed no apoptosis. The authors of the zebrafish work read this as tissue-dependent mechanisms, which may be right, but no human pancreatic or pituitary tissue from a patient has been examined.
Show evidence (2 references)
PMID:33942450 SUPPORT In Vitro
"Additional studies in patient-derived fibroblasts did not reveal apoptosis. Our results provide new insights into disease physiopathology, suggesting tissue-dependent mechanisms."
The negative apoptosis result in cultured patient fibroblasts, and the authors' own reading of the discrepancy, which is the substance of this gap. Graded IN_VITRO because the measurement is in cultured human cells, even though the same publication's other results are in zebrafish.
PMID:30878599 SUPPORT In Vitro
"Cells lacking EIF2S3 had increased caspase activity/cell death."
The apoptotic result, in a human pancreatic cell line. Graded SUPPORT rather than REFUTE because what this discussion asserts is that the two results conflict, and this is one of the two: it supports the existence of the mismatch, and contradicts only the other experiment, not the question being asked.
⚙

Pathophysiology

7
Hemizygous EIF2S3 Variants
Hemizygous missense variants and a recurrent C-terminal frameshift in EIF2S3. Missense variants cluster in the conserved guanine nucleotide binding domain of eIF2gamma; the frameshift p.Ile465Serfs*4 truncates the C-terminus. The two classes reach the same endpoint by different routes, which is why the entry separates them: the C-terminal lesion impairs CDC123-dependent assembly of the eIF2 complex, while domain missense variants impair Met-tRNA binding or subunit contact.
EIF2S3 hgnc:3267 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves EIF2S3 (hgnc:3267). hgnc:3267 is a gene from the HUGO Gene Nomenclature Committee.
translation initiation factor activity GO:0003743 ⇓ LOSS OF FUNCTION Gene Ontology (GO) Relation: this pathophysiological event involves this molecular function This pathophysiological event involves translation initiation factor activity (GO:0003743), qualified as loss of function. GO:0003743 is a molecular function from the Gene Ontology.
Downstream
Reduced eIF2 Ternary Complex Formation Each variant class lowers the amount of functional eIF2-GTP-Met-tRNAi ternary complex, by impaired complex assembly or by impaired initiator tRNA binding.
Show evidence (2 references)
PMID:28055140 SUPPORT Human Clinical
"We have identified a C-terminal frameshift mutation (Ile465Serfs) in the EIF2S3 gene in three families with MEHMO syndrome"
The recurrent frameshift and the families it was found in.
PMID:32799315 SUPPORT Human Clinical
"Both variants are located in the highly conserved guanine nucleotide binding domain of the EIF2S3 encoded eIF2γ subunit of the heterotrimeric translation initiation factor 2 (eIF2) complex."
Where the missense variants sit in the protein.
Reduced eIF2 Ternary Complex Formation
Less eIF2-GTP-Met-tRNAi ternary complex is available to load the 40S ribosomal subunit. This is the shared hinge of the entry: both the translational and the stress-response consequences run downstream of it.
formation of translation initiation ternary complex GO:0001677 ↓ DECREASED Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased formation of translation initiation ternary complex (GO:0001677). GO:0001677 is a biological process from the Gene Ontology.
Animal models
Yeast eIF2gamma-I318M model of the human I259M variant Yeast recapitulates Reproduces the molecular lesion, reduced initiator tRNA binding to eIF2, and identifies it as the step the variant breaks.
Downstream
Impaired and Error-Prone Translation Initiation Less ternary complex lowers initiation efficiency and loosens start codon selection.
Over-Activated Integrated Stress Response Low eIF2 activity is read by the cell as the signal the integrated stress response exists to produce, so the response is constitutively shifted on.
Show evidence (1 reference)
PMID:31836389 SUPPORT In Vitro
"This reduction in eIF2 activity results in dysregulation of global and gene-specific protein synthesis and enhances cell death upon stress induction."
Names both downstream consequences this node branches into, in patient-derived cells.
Impaired and Error-Prone Translation Initiation
Reduced global protein synthesis together with relaxed stringency of start codon selection, so initiation occurs more often at near-cognate non-AUG codons. Both were measured in yeast models of patient variants and in human cells overexpressing the mutant subunit. The gene-specific component matters as much as the global one: ATF4 and GCN4, whose translation is controlled by eIF2 availability, are derepressed.
translational initiation GO:0006413 ↓ DECREASED Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased translational initiation (GO:0006413). GO:0006413 is a biological process from the Gene Ontology.
Downstream
Neurodevelopmental Impairment Proposed route to the neurological phenotype. Supported by the rescue of neuronal differentiation in patient cells and by microcephaly with increased neuronal death in eif2s3-null zebrafish, but not demonstrated in human brain tissue.
Show evidence (2 references)
PMID:32799315 SUPPORT Model Organism
"The reduced growth rates and lowered fidelity of translation with increased initiation at non-AUG codons observed for both mutants in these studies strongly support pathogenicity of the variants."
Both the efficiency and the fidelity defect, for two patient variants.
PMID:30517694 SUPPORT Model Organism
"The yeast eIF2γ-I318M mutation also increased initiation from near-cognate start codons."
The start-codon fidelity defect in the yeast model.
Over-Activated Integrated Stress Response
The integrated stress response acts by lowering eIF2 activity, so a genetic lesion that lowers it leaves the response partly engaged at baseline and over-engaged under stress. Patient fibroblasts carrying the frameshift show increased stress-response activity, and ATF4 translation is derepressed when the mutant subunit is expressed in human cells. The consequence is reduced tolerance of cellular stress rather than a discrete second disease.
integrated stress response signaling GO:0140467 ↑ INCREASED Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased integrated stress response signaling (GO:0140467). GO:0140467 is a biological process from the Gene Ontology.
Downstream
Pancreatic Beta Cell Failure Proposed explanation for why a secretory endocrine cell is affected: cells with a high secretory protein load depend most on intact translation initiation and stress handling. Supported by EIF2S3 expression in the islets and by increased cell death on EIF2S3 knockdown, not by human tissue pathology.
Anterior Pituitary Hormone Secretion Failure The same reasoning applied to the other high-load secretory tissue: the anterior pituitary expresses EIF2S3 during development and its hormone output declines progressively in reported patients. Weaker than the beta cell edge, which has a cell-death and a progenitor-deficiency result behind it; this arm has expression plus clinical course and no tissue pathology or animal model, so the intermediates are unknown.
Show evidence (3 references)
PMID:28055140 SUPPORT In Vitro
"Studies in patient fibroblasts confirm increased ISR activation due to the Ile465Serfs mutation"
Increased stress-response activity in patient cells.
PMID:30517694 SUPPORT In Vitro
"overexpression of human eIF2γ-I259M derepressed ATF4 messenger RNA translation in human cells."
Derepression of the stress-response effector ATF4, the gene-specific readout of low eIF2 activity.
PMID:34999262 SUPPORT Human Clinical
"we performed expression analysis, which showed that the DDIT3 transcript level was significantly increased in the patient relative to the controls."
A second stress-response effector, DDIT3 (CHOP), raised in a patient carrying a different EIF2S3 variant, which is independent evidence that the over-activation is a property of the disease rather than of one allele.
Neurodevelopmental Impairment
Impaired brain growth and development, giving microcephaly, intellectual disability and epilepsy. The experimental support is a zebrafish knockout that reproduces microcephaly with increased neuronal cell death, plus rescue of neuronal differentiation in patient-derived cells by ISRIB.
Animal models
eif2s3 knockout zebrafish (CRISPR/Cas9) Zebrafish partially recapitulates Reproduces the microcephaly and gives a cellular correlate, increased neuronal death.
Downstream
Microcephaly Impaired brain growth.
Intellectual disability The core neurodevelopmental outcome.
Global developmental delay Delay across domains, which is how the impairment presents before an intellectual disability can be assessed.
Motor delay The motor component specifically, reported severe in one missense patient and mild in another.
Seizure Epilepsy in most reported patients. Note that untreated hypoglycaemia is an alternative or additional contributor, which is recorded as a hypothesis rather than asserted here.
Show evidence (1 reference)
PMID:33942450 SUPPORT Model Organism
"CRISPR/Cas9 knockout of eif2s3 in zebrafish embryos recapitulate the human microcephaly and show increased neuronal cell death."
Animal evidence linking loss of the gene to microcephaly.
Pancreatic Beta Cell Failure
Failure of the insulin-secreting beta cell, giving neonatal hypoglycaemia first and insulin-dependent diabetes later. EIF2S3 is expressed in the islets of Langerhans, and the cellular route is contested: knockdown in a human pancreatic cell line increased caspase activity and cell death, while in zebrafish the hyperglycaemia came from beta cell and pancreatic progenitor deficiency explicitly not related to apoptosis. See the HUMAN_MODEL_MISMATCH discussion; this node does not assert either route.
pancreatic beta cell CL:0000169 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves pancreatic beta cell, annotated with type B pancreatic cell (CL:0000169). CL:0000169 is a cell type from the Cell Ontology.
Animal models
eif2s3 knockout zebrafish (CRISPR/Cas9) Zebrafish partially recapitulates Hyperglycaemia from a deficiency of beta cells and pancreatic progenitors, which supports a developmental rather than apoptotic route to the glucose phenotype.
Downstream
Hypoglycemia Neonatal hypoglycaemia precedes the diabetes in reported patients.
Diabetes mellitus Early-onset insulin-dependent diabetes follows.
Show evidence (2 references)
PMID:30878599 SUPPORT In Vitro
"EIF2S3 expression was detectable in the developing pituitary gland and pancreatic islets of Langerhans. Cells lacking EIF2S3 had increased caspase activity/cell death."
Expression in the islets, and increased cell death on knockdown in a human pancreatic cell line.
PMID:33942450 SUPPORT Model Organism
"Abnormal high glucose levels were identified in mutant embryos, caused by beta cell and pancreatic progenitor deficiency, not related to apoptosis."
The competing cellular account for the same beta cell failure, which is why this node does not assert apoptosis as the mechanism.
Anterior Pituitary Hormone Secretion Failure
Progressive decline of anterior pituitary peptide hormone secretion, reported as growth hormone and TSH deficiency and as a gradual decline rather than a fixed deficit. The support here is weaker than for the beta cell node: it rests on EIF2S3 expression in the developing human pituitary plus the clinical course, with no pituitary tissue from a patient examined and no animal model of the pituitary arm.
hormone-secreting cell of the anterior pituitary CL:0000637 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves hormone-secreting cell of the anterior pituitary, annotated with chromophil cell of anterior pituitary gland (CL:0000637). CL:0000637 is a cell type from the Cell Ontology.
Downstream
Hypopituitarism Progressive decline of anterior pituitary hormone secretion.
Central hypothyroidism TSH deficiency is one of the reported deficient axes.
Growth delay Growth hormone deficiency is the other reported axis, and postnatal growth retardation is positive in seven of the eight families in which it was assessed.
Hypogonadism Hypogonadism and hypogenitalism, plausibly through gonadotropin deficiency in a hypopituitary patient. The reports describe the features without establishing that route, so the edge is not asserted as direct.
External genital hypoplasia Hypogenitalism, by the same unestablished gonadotropin route.
Show evidence (2 references)
PMID:30878599 SUPPORT In Vitro
"EIF2S3 expression was detectable in the developing pituitary gland and pancreatic islets of Langerhans."
Expression in the developing pituitary, which is the whole of the tissue-level support for this node.
PMID:29303605 SUPPORT Human Clinical
"hypopituitarism due to dysregulation and gradual decline of peptide hormone secretion."
The clinical course, which is what makes this a progressive secretory failure rather than a developmental absence.
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for MEHMO Syndrome Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
●

Phenotypes

16
Endocrine 4
Central hypothyroidism HP:0011787 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Central hypothyroidism (HP:0011787). HP:0011787 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:33714664 SUPPORT Human Clinical
"A 5-year-old boy was referred to our hospital because of profound intellectual disability, micropenis, cryptorchidism, central hypothyroidism, and microcephaly."
Central hypothyroidism in a molecularly confirmed patient.
PMID:30878599 SUPPORT Human Clinical
"hypopituitarism (GH and TSH deficiencies)"
TSH deficiency as one of the two deficient axes in the milder family.
Hypogonadism FREQUENT HP:0000135 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hypogonadism (HP:0000135). HP:0000135 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:28055140 SUPPORT Human Clinical
"MEHMO is a rare X-linked syndrome characterized by profound intellectual disability, epilepsy, hypogonadism and hypogenitalism, microcephaly, and obesity."
Hypogonadism in the defining phenotype.
Diabetes mellitus HP:0000819 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Early-onset insulin-dependent diabetes mellitus, annotated with Diabetes mellitus (HP:0000819). HP:0000819 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:29303605 SUPPORT Human Clinical
"Both probands had a neonatal hypoglycemia, early onset insulin-dependent diabetes, and hypopituitarism due to dysregulation and gradual decline of peptide hormone secretion."
Insulin-dependent diabetes in both probands.
Hypopituitarism Anterior hypopituitarism HP:0000830 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Anterior hypopituitarism (HP:0000830). HP:0000830 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:29303605 SUPPORT Human Clinical
"hypopituitarism due to dysregulation and gradual decline of peptide hormone secretion."
The progressive nature of the pituitary failure.
PMID:30878599 SUPPORT Human Clinical
"hypopituitarism (GH and TSH deficiencies)"
Which anterior pituitary axes were deficient in the milder family.
Genitourinary 3
Micropenis HP:0000054 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Micropenis (HP:0000054). HP:0000054 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:33714664 SUPPORT Human Clinical
"A 5-year-old boy was referred to our hospital because of profound intellectual disability, micropenis, cryptorchidism, central hypothyroidism, and microcephaly."
Micropenis in a molecularly confirmed patient.
Cryptorchidism HP:0000028 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Cryptorchidism (HP:0000028). HP:0000028 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:33714664 SUPPORT Human Clinical
"A 5-year-old boy was referred to our hospital because of profound intellectual disability, micropenis, cryptorchidism, central hypothyroidism, and microcephaly."
Cryptorchidism in the same patient.
External genital hypoplasia FREQUENT HP:0003241 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hypogenitalism, annotated with External genital hypoplasia (HP:0003241). HP:0003241 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:28055140 SUPPORT Human Clinical
"MEHMO is a rare X-linked syndrome characterized by profound intellectual disability, epilepsy, hypogonadism and hypogenitalism, microcephaly, and obesity."
Hypogenitalism and hypogonadism in the defining phenotype.
Head and Neck 1
Microcephaly FREQUENT HP:0000252 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Microcephaly (HP:0000252). HP:0000252 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:27333055 SUPPORT Human Clinical
"In both families, affected males presented with severe intellectual disability, microcephaly, growth retardation, and epilepsy."
Severe microcephaly in affected males from two unrelated families.
PMID:30878599 SUPPORT Human Clinical
"Exome sequencing of the X chromosome was performed on three related males with normal head circumferences and mild learning difficulties, hypopituitarism (GH and TSH deficiencies), and an unusual form of glucose dysregulation."
The family in which head circumference is normal, which is why this phenotype is not VERY_FREQUENT.
Immune 1
Recurrent infections HP:0002719 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Recurrent respiratory and urinary tract infections, annotated with Recurrent infections (HP:0002719). HP:0002719 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:32901502 SUPPORT Human Clinical
"The MEHMO patient had had frequent acute infections despite normal IgG and IgM serum levels and responded well to the immunoglobulin treatment."
The infections, the normal antibody levels that concealed them, and the response to treatment, in one sentence.
Metabolism 1
Hypoglycemia Neonatal hypoglycemia HP:0001998 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Neonatal hypoglycemia (HP:0001998). HP:0001998 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:29303605 SUPPORT Human Clinical
"Based on the clinical course in our two probands and also in previously published patients, neonatal hypoglycemia followed by early-onset diabetes and hypopituitarism may be a consistent part of the MEHMO phenotype."
The endocrine sequence the authors propose as consistent, in their own hedged wording.
Nervous System 4
Global developmental delay VERY_FREQUENT HP:0001263 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Global developmental delay (HP:0001263). HP:0001263 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:30878599 SUPPORT Human Clinical
"He has global developmental delay needing 1:1 support in mainstream school, behavioural problems and mild hepatomegaly with normal liver function."
Global developmental delay named directly, in the mildest reported phenotype, which is what makes it a feature of the spectrum rather than only of the severe frameshift patients.
PMID:28055140 SUPPORT Human Clinical
"Developmental delay | + | + | + | + | + | + | + | + | + | +"
The comparison table row, positive in all ten families, which is the basis for VERY_FREQUENT.
Motor delay HP:0001270 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Motor delay (HP:0001270). HP:0001270 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:32799315 SUPPORT Human Clinical
"the affected male with p.(Thr144Ile) presented with severe motor delay, severe microcephaly, moderate ID, epileptic seizures responsive to treatments, hypogenitalism, central obesity, facial features, and diabetes"
Severe motor delay alongside the cognitive outcome in one patient.
Intellectual disability VERY_FREQUENT HP:0001249 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Intellectual disability (HP:0001249). HP:0001249 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:28055140 SUPPORT Human Clinical
"MEHMO is a rare X-linked syndrome characterized by profound intellectual disability, epilepsy, hypogonadism and hypogenitalism, microcephaly, and obesity."
Profound intellectual disability in the defining phenotype.
PMID:32799315 SUPPORT Human Clinical
"the affected male with p.(Ile159Leu) presented with moderate ID, mild motor delay, microcephaly, epileptic seizures resistant to treatment, central obesity, and mild facial features."
The milder degree seen with a missense variant.
Seizure VERY_FREQUENT HP:0001250 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Epileptic seizures, annotated with Seizure (HP:0001250). HP:0001250 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:32799315 SUPPORT Human Clinical
"epileptic seizures responsive to treatments, hypogenitalism, central obesity, facial features, and diabetes"
Treatment-responsive seizures in one of the two reported patients.
PMID:33714664 SUPPORT BACKGROUND Human Clinical
"Refractory epileptic seizures and glucose dysregulation are characteristic manifestations of the MEHMO syndrome, which can often diminish patients' quality of life."
States that the seizures are characteristically refractory. The pancreatitis caution from this case report is carried on the ketogenic diet treatment entry.
Growth 2
Growth delay VERY_FREQUENT HP:0001510 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Growth retardation, annotated with Growth delay (HP:0001510). HP:0001510 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:27333055 SUPPORT Human Clinical
"In both families, affected males presented with severe intellectual disability, microcephaly, growth retardation, and epilepsy."
Growth retardation in affected males from two unrelated families.
PMID:28055140 SUPPORT Human Clinical
"Postnatal growth retardation | + | + | + | − | + | + | + | n.a. | + | n.a."
The paper's comparison table across the families reported to date, one column per family. Postnatal growth retardation is positive in seven, negative in one and not assessed in two, which is the basis for VERY_FREQUENT rather than the two-family abstract above.
Obesity FREQUENT Truncal obesity HP:0001956 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Central obesity, annotated with Truncal obesity (HP:0001956). HP:0001956 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:32799315 SUPPORT Human Clinical
"hypogenitalism, central obesity, facial features, and diabetes"
Central obesity in a molecularly confirmed patient.
🧬

Genetic Associations

1
EIF2S3
Gene: EIF2S3 hgnc:3267 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is EIF2S3 (hgnc:3267). hgnc:3267 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: CAUSATIVE variant_origin: GERMLINE
X-linked recessive
Show evidence (3 references)
PMID:28055140 SUPPORT Human Clinical
"we propose that more severe EIF2S3 mutations cause the full MEHMO phenotype, while less deleterious mutations cause a milder form of the syndrome with only a subset of the symptoms."
The genotype-severity relationship, in the authors' own proposing language.
PMID:28055140 SUPPORT In Vitro
"functional assays in yeast demonstrate that the Ile465Serfs mutation impairs eIF2γ function to a greater extent than tested missense mutations, consistent with the more severe clinical phenotype of the Ile465Serfs male mutation carriers."
The functional measurement behind the genotype-severity relationship, which is what makes it more than a clinical impression.
PMID:33942450 SUPPORT Human Clinical
"A recurrent frameshift variant is described in severely affected patients while missense variants usually cause a moderate phenotype."
Independent restatement of the same relationship.
Variants (2)
p.Ile465Serfs*4 Pathogenic
Recurrent C-terminal frameshift (c.1394_1397del), found in several unrelated MEHMO families and associated with the full, severe phenotype. It impairs CDC123-dependent assembly of the eIF2 complex.
Show evidence (3 references)
PMID:28055140 SUPPORT Human Clinical
"We have identified a C-terminal frameshift mutation (Ile465Serfs) in the EIF2S3 gene in three families with MEHMO syndrome"
The variant and its recurrence across families.
PMID:35765291 SUPPORT Human Clinical
"We describe two brothers with a recurrent truncating EIF2S3 variant and MEHMO"
Two further affected brothers carrying the same recurrent allele.
PMID:35765291 SUPPORT Human Clinical
"we do not suspect a common heritage indicating that the variant has arisen independently at least twice"
Supports treating the allele as recurrent rather than as a founder variant shared by descent, which is the authors' own reading of the absence of a common heritage between the families.
p.Pro432Ser Pathogenic
Hemizygous missense variant in three related males with the mild phenotype: hypopituitarism with glucose dysregulation, normal head circumference and mild learning difficulty.
Show evidence (1 reference)
PMID:30878599 SUPPORT Human Clinical
"Our data suggest that the p.Pro432Ser mutation impairs eIF2γ function leading to a relatively mild novel phenotype compared with previous EIF2S3 mutations."
The variant and the mild phenotype it produces.
💊

Medical Actions

5
Insulin Therapy for the Diabetes
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Agent: insulin CHEBI:145810 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses insulin (CHEBI:145810). CHEBI:145810 is a therapeutic agent from Chemical Entities of Biological Interest.
Platform: Peptide
The diabetes is insulin-dependent and treated as such. This is supportive management of an endocrine consequence, not treatment of the mechanism.
Mechanism Target:
BYPASSES Pancreatic Beta Cell Failure — Exogenous insulin replaces the hormone the failing beta cell no longer secretes. It does nothing to the beta cell itself, which is why the effect is recorded as a bypass rather than a restoration.
Show evidence (1 reference)
PMID:33714664 SUPPORT Human Clinical
"Although the patient's refractory seizures and diabetes had been well controlled with a combination of ketogenic diet (KD) therapy and insulin therapy, acute fatal necrotizing pancreatitis occurred at the age of 68 months."
The diabetes was controlled on insulin in the reported patient.
Show evidence (1 reference)
PMID:33714664 SUPPORT Human Clinical
"Although the patient's refractory seizures and diabetes had been well controlled with a combination of ketogenic diet (KD) therapy and insulin therapy, acute fatal necrotizing pancreatitis occurred at the age of 68 months."
Insulin therapy controlling the diabetes in a reported patient. The same sentence records the pancreatitis that killed him, which is why the ketogenic diet entry below carries a caution.
Ketogenic Diet for Refractory Epilepsy
Action: Ketogenic dietNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Ketogenic diet (NCIT:C173168). NCIT:C173168 is a clinical intervention from the NCI Thesaurus. Ontology label: Ketogenic Diet NCIT:C173168
Platform: Behavioral / lifestyle
Used for refractory seizures, and effective in the one reported patient, but that patient died of acute necrotising pancreatitis at 68 months while on it. The authors attribute this to an abnormal load on beta cells already damaged by eIF2gamma dysfunction, and conclude that the adverse effects of the diet should be weighed in this disease specifically. Treat this as a documented hazard, not a routine option.
Show evidence (1 reference)
PMID:33714664 SUPPORT Human Clinical
"We suspect that in the present case, KD therapy led to an abnormal load on the beta cells that were damaged owing to eIF2γ dysfunction. Therefore, the adverse effects of KD in patients with MEHMO syndrome should be considered."
The authors' mechanism for the harm and their explicit caution, which is the reason this treatment is curated with a warning rather than as a recommendation.
Subcutaneous Immunoglobulin Replacement
Action: Immunoglobulin therapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Immunoglobulin therapy (NCIT:C62710). NCIT:C62710 is a clinical intervention from the NCI Thesaurus. Ontology label: Immunoglobulin Therapy NCIT:C62710
Platform: Protein replacement
Immunoglobulin replacement for the infection susceptibility, used in one reported patient despite normal baseline IgG and IgM, targeting supra-physiological IgG levels. Infection frequency fell by 54.5 per cent on Poisson regression. A single patient, so this is a lead rather than established management, but it is the one reported intervention in this disease with a quantified benefit.
Show evidence (1 reference)
PMID:32901502 SUPPORT Human Clinical
"On subcutaneous immunoglobulin therapy achieving supra-physiological IgG levels the frequency of infections significantly decreased in Poisson regression by 54.5 % (CI 33.2-89.7, p=0.017)."
The quantified effect in the single treated patient.
Growth Hormone Replacement
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Agent: somatropin NCIT:C837 NCI Thesaurus (NCIT) Relation: this treatment uses this therapeutic agent This treatment uses somatropin (NCIT:C837). NCIT:C837 is a therapeutic agent from the NCI Thesaurus.
Platform: Protein replacement
Recombinant growth hormone for the GH deficiency reported in the families where the pituitary was assessed. Supportive, and because the pituitary failure is progressive it needs repeated reassessment rather than a fixed dose.
Mechanism Target:
BYPASSES Anterior Pituitary Hormone Secretion Failure — Supplies the hormone the failing gland no longer secretes, without acting on the gland itself.
Show evidence (1 reference)
PMID:30878599 SUPPORT INDIRECT Human Clinical
"hypopituitarism (GH and TSH deficiencies)"
The GH deficiency that is the indication. The publication reports the deficiency rather than a treatment trial, so this is the indication and not evidence of benefit.
Show evidence (1 reference)
PMID:30878599 SUPPORT INDIRECT Human Clinical
"hypopituitarism (GH and TSH deficiencies)"
The deficient axis this treatment replaces.
Levothyroxine Replacement
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Agent: levothyroxine NCIT:C62080 NCI Thesaurus (NCIT) Relation: this treatment uses this therapeutic agent This treatment uses levothyroxine (NCIT:C62080). NCIT:C62080 is a therapeutic agent from the NCI Thesaurus.
Platform: Small molecule
Levothyroxine for the central hypothyroidism, which is the second anterior pituitary axis reported deficient. As with growth hormone this replaces the downstream hormone rather than restoring pituitary output.
Mechanism Target:
BYPASSES Anterior Pituitary Hormone Secretion Failure — Replaces thyroid hormone downstream of the TSH deficiency.
Show evidence (1 reference)
PMID:33714664 SUPPORT INDIRECT Human Clinical
"A 5-year-old boy was referred to our hospital because of profound intellectual disability, micropenis, cryptorchidism, central hypothyroidism, and microcephaly."
The central hypothyroidism that is the indication. Reported as a clinical finding rather than as a treatment result.
Show evidence (1 reference)
PMID:30878599 SUPPORT INDIRECT Human Clinical
"hypopituitarism (GH and TSH deficiencies)"
The TSH deficiency this treatment replaces.
🔬

Diagnosis

1
Exome or X-chromosome exome sequencing
The diagnosis is molecular. Reported patients were found by X-chromosome or whole-exome sequencing, and in one family by targeted mRNA analysis of EIF2S3, which also detects splicing defects and allelic imbalance. There is no biochemical screening test.
Show evidence (2 references)
PMID:27333055 SUPPORT Human Clinical
"X-chromosome exome sequencing was performed to identify the genetic cause of syndromic intellectual disability in two unrelated families with suspected X-linked inheritance."
The sequencing approach that identified the gene in two families.
PMID:34999262 SUPPORT Human Clinical
"In most cases, DNA diagnostics of MEHMO syndrome is performed using exome sequencing."
States the usual diagnostic route, in the paper that offers mRNA analysis as a cheaper alternative.
📊

Prevalence

1
Worldwide
Cases In Literature Ultra Rare
A rare X-linked syndrome known from a small number of families; the cited report's comparison table across the families reported to that point has ten columns. No prevalence estimate exists, which is why the measure recorded here is CASES_IN_LITERATURE rather than a rate.
Show evidence (1 reference)
PMID:28055140 SUPPORT Human Clinical
"MEHMO is a rare X-linked syndrome characterized by profound intellectual disability, epilepsy, hypogonadism and hypogenitalism, microcephaly, and obesity."
Establishes rarity and the defining feature set.
🔀

Differential Diagnoses

2

Conditions with similar clinical presentations that must be differentiated from MEHMO Syndrome:

Syndromic obesity with hypogonadism and intellectual disability
Overlapping Features The acronym features overlap clinically with Prader-Willi syndrome and with Bardet-Biedl syndrome. The distinguishing findings are the X-linked pedigree, the microcephaly, and the early-onset insulin-dependent diabetes preceded by neonatal hypoglycaemia, which the ciliopathies and imprinting disorders do not produce.
🐁

Animal Models

2
eif2s3 knockout zebrafish (CRISPR/Cas9)
CRISPR/Cas9 knockout of the zebrafish ortholog, used to test the pathogenicity of patient missense variants and to look at mechanism. It reproduces microcephaly with increased neuronal cell death and produces hyperglycaemia from beta cell and pancreatic progenitor deficiency. An earlier morpholino knockdown of the same gene reproduced microcephaly and short stature.
Species
Zebrafish
Genotype
eif2s3 CRISPR/Cas9 knockout
Publication
PMID:33942450
Pathograph links
Neurodevelopmental Impairment partially recapitulates fidelity: moderate observes: organism Reproduces the microcephaly and gives a cellular correlate, increased neuronal death.
Limitations: Microcephaly and neuronal death are reproduced; the intellectual disability and epilepsy that dominate the human phenotype are not assessable in this model. It is also a complete knockout, whereas the human disease is caused by partial loss of function, so it may overstate severity.
Readouts
Neuronal cell death in embryos
Direction: INCREASED
Interpretation: Cellular correlate of the reproduced microcephaly.
Show evidence (1 reference)
PMID:33942450 SUPPORT Model Organism
"show increased neuronal cell death"
The measured readout.
Show evidence (1 reference)
PMID:33942450 SUPPORT Model Organism
"CRISPR/Cas9 knockout of eif2s3 in zebrafish embryos recapitulate the human microcephaly and show increased neuronal cell death."
The reproduced phenotype and its cellular correlate.
Pancreatic Beta Cell Failure partially recapitulates fidelity: moderate observes: organism Hyperglycaemia from a deficiency of beta cells and pancreatic progenitors, which supports a developmental rather than apoptotic route to the glucose phenotype.
Limitations: The mechanism found here, progenitor deficiency without apoptosis, disagrees with the increased cell death seen on EIF2S3 knockdown in a human pancreatic cell line, and patient fibroblasts showed no apoptosis either. The authors themselves read the discrepancy as tissue-dependent mechanisms. The pituitary arm of the disease is not modelled by this animal at all, which is why this link targets the beta cell node only.
Readouts
Embryonic glucose level
Direction: INCREASED
Interpretation: Hyperglycaemia in the knockout, the counterpart of the patients' diabetes.
Show evidence (1 reference)
PMID:33942450 SUPPORT Model Organism
"Abnormal high glucose levels were identified in mutant embryos"
The measured readout.
Show evidence (1 reference)
PMID:33942450 SUPPORT Model Organism
"Abnormal high glucose levels were identified in mutant embryos, caused by beta cell and pancreatic progenitor deficiency, not related to apoptosis."
The glucose phenotype and the cellular route the authors attribute it to.
Yeast eIF2gamma-I318M model of the human I259M variant
Humanised point mutation in the yeast ortholog, used to measure what the patient variant does to eIF2 function. It impairs growth, derepresses GCN4, increases initiation at near-cognate start codons, and reduces Met-tRNAi binding; overexpressing initiator tRNA restores binding and rescues growth, which is how the defect was localised.
Species
Yeast
Genotype
Saccharomyces cerevisiae GCD11 I318M, the residue equivalent to human eIF2gamma I259M
Publication
PMID:30517694
Pathograph links
Reduced eIF2 Ternary Complex Formation recapitulates fidelity: moderate observes: molecular Reproduces the molecular lesion, reduced initiator tRNA binding to eIF2, and identifies it as the step the variant breaks.
Limitations: A yeast protein carrying the equivalent substitution, not the human protein, and the model reports on molecular function only. It says nothing about any tissue or clinical consequence.
Readouts
Met-tRNAi binding to eIF2 rescued by initiator tRNA overexpression
Direction: RESTORED
Interpretation: Restoring initiator tRNA rescued both binding and growth, which is what localises the defect to this step rather than to a general loss of protein function.
Show evidence (1 reference)
PMID:30517694 SUPPORT Model Organism
"Overexpression of tRNAiMet restored Met-tRNAiMet binding to eIF2 in vivo and rescued the growth defect in the eIF2γ-I318M strain."
The rescue measurement.
Show evidence (1 reference)
PMID:30517694 SUPPORT Model Organism
"The corresponding eIF2γ-I318M mutation impaired yeast cell growth and derepressed GCN4 expression, an indicator of defective eIF2-GTP-Met-tRNAiMet complex formation"
The functional defect, read out by GCN4 derepression.
{ }

Source YAML

click to show 
name: MEHMO Syndrome
creation_date: "2026-10-15T07:30:00Z"
category: Mendelian
parents:
- X-linked Syndromic Intellectual Disability
disease_term:
  preferred_term: MEHMO syndrome
  term:
    id: MONDO:0010258
    label: MEHMO syndrome
synonyms:
- mental retardation, epileptic seizures, hypogenitalism and hypogonadism, microcephaly, obesity
- EIF2S3-related syndromic intellectual disability
- eIF2-related neuroendocrinopathy
description: >-
  X-linked multisystem disorder caused by hemizygous variants in EIF2S3, which
  encodes the gamma subunit of eukaryotic translation initiation factor 2
  (eIF2). The acronym records the features of the originally described
  families: mental disability, epileptic seizures, hypogenitalism and
  hypogonadism, microcephaly and obesity. eIF2 delivers initiator
  methionyl-tRNA to the 40S ribosome and selects the AUG start codon, and
  eIF2gamma is the core subunit that holds the heterotrimer together, so a
  partial loss of its function lowers the amount of active eIF2 ternary
  complex. Translation initiation becomes less accurate as well as less
  efficient: initiation at near-cognate, non-AUG codons increases. Because
  eIF2 is also the node the integrated stress response acts on, the same
  variants leave cells with an over-active stress response and more
  vulnerable to death under stress.

  Endocrine disease is as prominent as the neurological picture and was not in
  the original acronym. Neonatal hypoglycaemia, early-onset insulin-dependent
  diabetes and progressive anterior hypopituitarism recur across reported
  patients, and a milder EIF2S3 phenotype of X-linked hypopituitarism with
  glucose dysregulation and normal head circumference has been described in
  one family. A 2025 review proposes reclassifying the condition, with related
  conditions, as an eIF2-related neuroendocrinopathy.

  Genotype tracks severity in a way that is unusual for a rare syndrome. The
  recurrent C-terminal frameshift p.Ile465Serfs*4 impairs eIF2gamma function
  more than the tested missense variants and is found in the most severely
  affected patients, while missense variants in the guanine nucleotide binding
  domain generally give a milder, sometimes incomplete phenotype. The small
  molecule ISRIB, which activates the eIF2 guanine nucleotide exchange factor,
  rescued growth, translation and neuronal differentiation defects in
  patient-derived cells, which makes this one of the few disorders in this
  class with an experimentally supported therapeutic lead.
prevalence:
- population: Worldwide
  measure_type: CASES_IN_LITERATURE
  prevalence_class: ULTRA_RARE
  notes: >-
    A rare X-linked syndrome known from a small number of families; the
    cited report's comparison table across the families reported to that
    point has ten columns. No prevalence estimate exists, which is why the
    measure recorded here is CASES_IN_LITERATURE rather than a rate.
  evidence:
  - reference: PMID:28055140
    reference_title: EIF2S3 Mutations Associated with Severe X-Linked Intellectual Disability Syndrome MEHMO.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "MEHMO is a rare X-linked syndrome characterized by profound intellectual disability, epilepsy, hypogonadism and hypogenitalism, microcephaly, and obesity."
    explanation: Establishes rarity and the defining feature set.
inheritance:
- name: X-linked recessive inheritance
  inheritance_term:
    preferred_term: X-linked recessive inheritance
    term:
      id: HP:0001419
      label: X-linked recessive inheritance
  description: >-
    Affected individuals are males hemizygous for an EIF2S3 variant, with
    carrier mothers. Reported pedigrees include maternally inherited variants
    and affected brothers.
  evidence:
  - reference: PMID:28055140
    reference_title: EIF2S3 Mutations Associated with Severe X-Linked Intellectual Disability Syndrome MEHMO.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "a novel maternally inherited missense EIF2S3 variant (c.324T>A; p.Ser108Arg) in another male patient with less severe clinical symptoms."
    explanation: Maternal transmission to an affected male.
  - reference: PMID:30878599
    reference_title: Impaired EIF2S3 function associated with a novel phenotype of X-linked hypopituitarism with glucose dysregulation.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We report a novel hemizygous EIF2S3 variant, p.Pro432Ser, in the three boys (heterozygous in their mothers)."
    explanation: Hemizygous in affected males, heterozygous in unaffected mothers.
pathophysiology:
- name: Hemizygous EIF2S3 Variants
  biological_scale: MOLECULAR
  description: >-
    Hemizygous missense variants and a recurrent C-terminal frameshift in
    EIF2S3. Missense variants cluster in the conserved guanine nucleotide
    binding domain of eIF2gamma; the frameshift p.Ile465Serfs*4 truncates the
    C-terminus. The two classes reach the same endpoint by different routes,
    which is why the entry separates them: the C-terminal lesion impairs
    CDC123-dependent assembly of the eIF2 complex, while domain missense
    variants impair Met-tRNA binding or subunit contact.
  genes:
  - preferred_term: EIF2S3
    term:
      id: hgnc:3267
      label: EIF2S3
  molecular_functions:
  - preferred_term: translation initiation factor activity
    modifier: LOSS_OF_FUNCTION
    term:
      id: GO:0003743
      label: translation initiation factor activity
  evidence:
  - reference: PMID:28055140
    reference_title: EIF2S3 Mutations Associated with Severe X-Linked Intellectual Disability Syndrome MEHMO.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We have identified a C-terminal frameshift mutation (Ile465Serfs) in the EIF2S3 gene in three families with MEHMO syndrome"
    explanation: The recurrent frameshift and the families it was found in.
  - reference: PMID:32799315
    reference_title: Novel pathogenic EIF2S3 missense variants causing clinically variable MEHMO syndrome with impaired eIF2γ translational function, and literature review.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Both variants are located in the highly conserved guanine nucleotide binding domain of the EIF2S3 encoded eIF2γ subunit of the heterotrimeric translation initiation factor 2 (eIF2) complex."
    explanation: Where the missense variants sit in the protein.
  downstream:
  - target: Reduced eIF2 Ternary Complex Formation
    causal_link_type: DIRECT
    description: >-
      Each variant class lowers the amount of functional
      eIF2-GTP-Met-tRNAi ternary complex, by impaired complex assembly or by
      impaired initiator tRNA binding.
    evidence:
    - reference: PMID:31836389
      reference_title: Suppression of MEHMO Syndrome Mutation in eIF2 by Small Molecule ISRIB.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "we show that a mutation at the C terminus of eIF2γ impairs CDC123 promotion of eIF2 complex formation and decreases the level of eIF2-GTP-Met-tRNAiMet ternary complexes."
      explanation: >-
        The frameshift route to reduced ternary complex, shown in
        patient-derived induced pluripotent stem cells.
    - reference: PMID:30517694
      reference_title: MEHMO syndrome mutation EIF2S3-I259M impairs initiator Met-tRNAiMet binding to eukaryotic translation initiation factor eIF2.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Biochemical analyses revealed a defect in Met-tRNAiMet binding to the mutant yeast eIF2 complexes in vivo and in vitro."
      explanation: >-
        The missense route, measured for the I259M variant in a yeast model of
        the human mutation.
    - reference: PMID:23063529
      reference_title: eIF2γ mutation that disrupts eIF2 complex integrity links intellectual disability to impaired translation initiation.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Biochemical studies of human cells overexpressing the eIF2γ mutant and of yeast eIF2γ with the analogous mutation revealed a defect in binding the eIF2β subunit to eIF2γ."
      explanation: >-
        A third route, loss of heterotrimer integrity, for the EIF2S3 variant
        that first linked this gene to intellectual disability. The full
        sentence is quoted because it names both systems the result rests on,
        human cells and yeast, which is what the grading depends on.
- name: Reduced eIF2 Ternary Complex Formation
  biological_scale: MOLECULAR
  description: >-
    Less eIF2-GTP-Met-tRNAi ternary complex is available to load the 40S
    ribosomal subunit. This is the shared hinge of the entry: both the
    translational and the stress-response consequences run downstream of it.
  biological_processes:
  - preferred_term: formation of translation initiation ternary complex
    modifier: DECREASED
    term:
      id: GO:0001677
      label: formation of translation initiation ternary complex
  evidence:
  - reference: PMID:31836389
    reference_title: Suppression of MEHMO Syndrome Mutation in eIF2 by Small Molecule ISRIB.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "This reduction in eIF2 activity results in dysregulation of global and gene-specific protein synthesis and enhances cell death upon stress induction."
    explanation: >-
      Names both downstream consequences this node branches into, in
      patient-derived cells.
  downstream:
  - target: Impaired and Error-Prone Translation Initiation
    causal_link_type: DIRECT
    description: >-
      Less ternary complex lowers initiation efficiency and loosens start
      codon selection.
  - target: Over-Activated Integrated Stress Response
    causal_link_type: DIRECT
    description: >-
      Low eIF2 activity is read by the cell as the signal the integrated
      stress response exists to produce, so the response is constitutively
      shifted on.
- name: Impaired and Error-Prone Translation Initiation
  biological_scale: CELLULAR
  description: >-
    Reduced global protein synthesis together with relaxed stringency of start
    codon selection, so initiation occurs more often at near-cognate non-AUG
    codons. Both were measured in yeast models of patient variants and in
    human cells overexpressing the mutant subunit. The gene-specific component
    matters as much as the global one: ATF4 and GCN4, whose translation is
    controlled by eIF2 availability, are derepressed.
  biological_processes:
  - preferred_term: translational initiation
    modifier: DECREASED
    term:
      id: GO:0006413
      label: translational initiation
  evidence:
  - reference: PMID:32799315
    reference_title: Novel pathogenic EIF2S3 missense variants causing clinically variable MEHMO syndrome with impaired eIF2γ translational function, and literature review.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "The reduced growth rates and lowered fidelity of translation with increased initiation at non-AUG codons observed for both mutants in these studies strongly support pathogenicity of the variants."
    explanation: Both the efficiency and the fidelity defect, for two patient variants.
  - reference: PMID:30517694
    reference_title: MEHMO syndrome mutation EIF2S3-I259M impairs initiator Met-tRNAiMet binding to eukaryotic translation initiation factor eIF2.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "The yeast eIF2γ-I318M mutation also increased initiation from near-cognate start codons."
    explanation: The start-codon fidelity defect in the yeast model.
  downstream:
  - target: Neurodevelopmental Impairment
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Proposed route to the neurological phenotype. Supported by the rescue of
      neuronal differentiation in patient cells and by microcephaly with
      increased neuronal death in eif2s3-null zebrafish, but not demonstrated
      in human brain tissue.
- name: Over-Activated Integrated Stress Response
  biological_scale: CELLULAR
  description: >-
    The integrated stress response acts by lowering eIF2 activity, so a
    genetic lesion that lowers it leaves the response partly engaged at
    baseline and over-engaged under stress. Patient fibroblasts carrying the
    frameshift show increased stress-response activity, and ATF4 translation
    is derepressed when the mutant subunit is expressed in human cells. The
    consequence is reduced tolerance of cellular stress rather than a
    discrete second disease.
  biological_processes:
  - preferred_term: integrated stress response signaling
    modifier: INCREASED
    term:
      id: GO:0140467
      label: integrated stress response signaling
  evidence:
  - reference: PMID:28055140
    reference_title: EIF2S3 Mutations Associated with Severe X-Linked Intellectual Disability Syndrome MEHMO.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Studies in patient fibroblasts confirm increased ISR activation due to the Ile465Serfs mutation"
    explanation: Increased stress-response activity in patient cells.
  - reference: PMID:30517694
    reference_title: MEHMO syndrome mutation EIF2S3-I259M impairs initiator Met-tRNAiMet binding to eukaryotic translation initiation factor eIF2.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "overexpression of human eIF2γ-I259M derepressed ATF4 messenger RNA translation in human cells."
    explanation: >-
      Derepression of the stress-response effector ATF4, the gene-specific
      readout of low eIF2 activity.
  - reference: PMID:34999262
    reference_title: mRNA analysis revealed a novel pathogenic EIF2S3 variant causing MEHMO syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "we performed expression analysis, which showed that the DDIT3 transcript level was significantly increased in the patient relative to the controls."
    explanation: >-
      A second stress-response effector, DDIT3 (CHOP), raised in a patient
      carrying a different EIF2S3 variant, which is independent evidence that
      the over-activation is a property of the disease rather than of one
      allele.
  downstream:
  - target: Pancreatic Beta Cell Failure
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Proposed explanation for why a secretory endocrine cell is affected:
      cells with a high secretory protein load depend most on intact
      translation initiation and stress handling. Supported by EIF2S3
      expression in the islets and by increased cell death on EIF2S3
      knockdown, not by human tissue pathology.
  - target: Anterior Pituitary Hormone Secretion Failure
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      The same reasoning applied to the other high-load secretory tissue: the
      anterior pituitary expresses EIF2S3 during development and its hormone
      output declines progressively in reported patients. Weaker than the
      beta cell edge, which has a cell-death and a progenitor-deficiency
      result behind it; this arm has expression plus clinical course and no
      tissue pathology or animal model, so the intermediates are unknown.
    evidence:
    - reference: PMID:30878599
      reference_title: Impaired EIF2S3 function associated with a novel phenotype of X-linked hypopituitarism with glucose dysregulation.
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: IN_VITRO
      snippet: "EIF2S3 expression was detectable in the developing pituitary gland and pancreatic islets of Langerhans."
      explanation: >-
        The expression result is the whole of the tissue-level basis for
        routing the pituitary arm through this node. INDIRECT because
        expression in a tissue is not a demonstration that the stress
        response acts on it, which is why the edge records unknown
        intermediates.
- name: Neurodevelopmental Impairment
  biological_scale: ORGANISM
  description: >-
    Impaired brain growth and development, giving microcephaly, intellectual
    disability and epilepsy. The experimental support is a zebrafish knockout
    that reproduces microcephaly with increased neuronal cell death, plus
    rescue of neuronal differentiation in patient-derived cells by ISRIB.
  evidence:
  - reference: PMID:33942450
    reference_title: Broadening the phenotypic spectrum and physiological insights related to EIF2S3 variants.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "CRISPR/Cas9 knockout of eif2s3 in zebrafish embryos recapitulate the human microcephaly and show increased neuronal cell death."
    explanation: Animal evidence linking loss of the gene to microcephaly.
  downstream:
  - target: Microcephaly
    causal_link_type: DIRECT
    description: Impaired brain growth.
  - target: Intellectual disability
    causal_link_type: DIRECT
    description: The core neurodevelopmental outcome.
  - target: Global developmental delay
    causal_link_type: DIRECT
    description: >-
      Delay across domains, which is how the impairment presents before an
      intellectual disability can be assessed.
  - target: Motor delay
    causal_link_type: DIRECT
    description: >-
      The motor component specifically, reported severe in one missense
      patient and mild in another.
  - target: Seizure
    causal_link_type: DIRECT
    description: >-
      Epilepsy in most reported patients. Note that untreated hypoglycaemia is
      an alternative or additional contributor, which is recorded as a
      hypothesis rather than asserted here.
- name: Pancreatic Beta Cell Failure
  biological_scale: TISSUE
  description: >-
    Failure of the insulin-secreting beta cell, giving neonatal hypoglycaemia
    first and insulin-dependent diabetes later. EIF2S3 is expressed in the
    islets of Langerhans, and the cellular route is contested: knockdown in a
    human pancreatic cell line increased caspase activity and cell death,
    while in zebrafish the hyperglycaemia came from beta cell and pancreatic
    progenitor deficiency explicitly not related to apoptosis. See the
    HUMAN_MODEL_MISMATCH discussion; this node does not assert either route.
  cell_types:
  - preferred_term: pancreatic beta cell
    term:
      id: CL:0000169
      label: type B pancreatic cell
  evidence:
  - reference: PMID:30878599
    reference_title: Impaired EIF2S3 function associated with a novel phenotype of X-linked hypopituitarism with glucose dysregulation.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "EIF2S3 expression was detectable in the developing pituitary gland and pancreatic islets of Langerhans. Cells lacking EIF2S3 had increased caspase activity/cell death."
    explanation: >-
      Expression in the islets, and increased cell death on knockdown in a
      human pancreatic cell line.
  - reference: PMID:33942450
    reference_title: Broadening the phenotypic spectrum and physiological insights related to EIF2S3 variants.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Abnormal high glucose levels were identified in mutant embryos, caused by beta cell and pancreatic progenitor deficiency, not related to apoptosis."
    explanation: >-
      The competing cellular account for the same beta cell failure, which is
      why this node does not assert apoptosis as the mechanism.
  downstream:
  - target: Hypoglycemia
    causal_link_type: DIRECT
    description: Neonatal hypoglycaemia precedes the diabetes in reported patients.
  - target: Diabetes mellitus
    causal_link_type: DIRECT
    description: Early-onset insulin-dependent diabetes follows.
- name: Anterior Pituitary Hormone Secretion Failure
  biological_scale: TISSUE
  description: >-
    Progressive decline of anterior pituitary peptide hormone secretion,
    reported as growth hormone and TSH deficiency and as a gradual decline
    rather than a fixed deficit. The support here is weaker than for the beta
    cell node: it rests on EIF2S3 expression in the developing human pituitary
    plus the clinical course, with no pituitary tissue from a patient
    examined and no animal model of the pituitary arm.
  cell_types:
  - preferred_term: hormone-secreting cell of the anterior pituitary
    term:
      id: CL:0000637
      label: chromophil cell of anterior pituitary gland
  evidence:
  - reference: PMID:30878599
    reference_title: Impaired EIF2S3 function associated with a novel phenotype of X-linked hypopituitarism with glucose dysregulation.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "EIF2S3 expression was detectable in the developing pituitary gland and pancreatic islets of Langerhans."
    explanation: >-
      Expression in the developing pituitary, which is the whole of the
      tissue-level support for this node.
  - reference: PMID:29303605
    reference_title: Neonatal hypoglycemia, early-onset diabetes and hypopituitarism due to the mutation in EIF2S3 gene causing MEHMO syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "hypopituitarism due to dysregulation and gradual decline of peptide hormone secretion."
    explanation: >-
      The clinical course, which is what makes this a progressive secretory
      failure rather than a developmental absence.
  downstream:
  - target: Hypopituitarism
    causal_link_type: DIRECT
    description: Progressive decline of anterior pituitary hormone secretion.
  - target: Central hypothyroidism
    causal_link_type: DIRECT
    description: TSH deficiency is one of the reported deficient axes.
  - target: Growth delay
    causal_link_type: DIRECT
    description: >-
      Growth hormone deficiency is the other reported axis, and postnatal
      growth retardation is positive in seven of the eight families in which
      it was assessed.
  - target: Hypogonadism
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Hypogonadism and hypogenitalism, plausibly through gonadotropin
      deficiency in a hypopituitary patient. The reports describe the features
      without establishing that route, so the edge is not asserted as direct.
  - target: External genital hypoplasia
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Hypogenitalism, by the same unestablished gonadotropin route.
phenotypes:
- name: Growth delay
  category: Growth
  description: >-
    Postnatal growth retardation, present in seven of the eight reported
    families in which it was assessed, and one of the features in the title of
    the first series to link two EIF2S3 variants to this syndrome. Growth
    hormone deficiency is the documented mechanism in the families where the
    pituitary was assessed.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Growth retardation
    term:
      id: HP:0001510
      label: Growth delay
  evidence:
  - reference: PMID:27333055
    reference_title: Two novel EIF2S3 mutations associated with syndromic intellectual disability with severe microcephaly, growth retardation, and epilepsy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In both families, affected males presented with severe intellectual disability, microcephaly, growth retardation, and epilepsy."
    explanation: Growth retardation in affected males from two unrelated families.
  - reference: PMID:28055140
    reference_title: EIF2S3 Mutations Associated with Severe X-Linked Intellectual Disability Syndrome MEHMO.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Postnatal growth retardation | + | + | + | \u2212 | + | + | + | n.a. | + | n.a."
    explanation: >-
      The paper's comparison table across the families reported to date, one
      column per family. Postnatal growth retardation is positive in seven,
      negative in one and not assessed in two, which is the basis for
      VERY_FREQUENT rather than the two-family abstract above.
- name: Central hypothyroidism
  category: Endocrine
  description: >-
    TSH deficiency of pituitary origin, one of the two anterior pituitary axes
    reported deficient. Distinguished from primary hypothyroidism because the
    lesion is in the pituitary rather than the thyroid.
  phenotype_term:
    preferred_term: Central hypothyroidism
    term:
      id: HP:0011787
      label: Central hypothyroidism
  evidence:
  - reference: PMID:33714664
    reference_title: "Ketogenic diet for refractory epilepsy with MEHMO syndrome: Caution for acute necrotizing pancreatitis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A 5-year-old boy was referred to our hospital because of profound intellectual disability, micropenis, cryptorchidism, central hypothyroidism, and microcephaly."
    explanation: Central hypothyroidism in a molecularly confirmed patient.
  - reference: PMID:30878599
    reference_title: Impaired EIF2S3 function associated with a novel phenotype of X-linked hypopituitarism with glucose dysregulation.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "hypopituitarism (GH and TSH deficiencies)"
    explanation: TSH deficiency as one of the two deficient axes in the milder family.
- name: Hypogonadism
  category: Endocrine
  description: >-
    Hypogonadism, the H of the acronym alongside hypogenitalism. Carried as
    its own phenotype rather than only inside the hypogenitalism description,
    because it is a distinct endocrine claim.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Hypogonadism
    term:
      id: HP:0000135
      label: Hypogonadism
  evidence:
  - reference: PMID:28055140
    reference_title: EIF2S3 Mutations Associated with Severe X-Linked Intellectual Disability Syndrome MEHMO.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "MEHMO is a rare X-linked syndrome characterized by profound intellectual disability, epilepsy, hypogonadism and hypogenitalism, microcephaly, and obesity."
    explanation: Hypogonadism in the defining phenotype.
- name: Micropenis
  category: Genitourinary
  description: Micropenis, the specific hypogenitalism finding reported in patients.
  phenotype_term:
    preferred_term: Micropenis
    term:
      id: HP:0000054
      label: Micropenis
  evidence:
  - reference: PMID:33714664
    reference_title: "Ketogenic diet for refractory epilepsy with MEHMO syndrome: Caution for acute necrotizing pancreatitis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A 5-year-old boy was referred to our hospital because of profound intellectual disability, micropenis, cryptorchidism, central hypothyroidism, and microcephaly."
    explanation: Micropenis in a molecularly confirmed patient.
- name: Cryptorchidism
  category: Genitourinary
  description: Undescended testes, reported with micropenis.
  phenotype_term:
    preferred_term: Cryptorchidism
    term:
      id: HP:0000028
      label: Cryptorchidism
  evidence:
  - reference: PMID:33714664
    reference_title: "Ketogenic diet for refractory epilepsy with MEHMO syndrome: Caution for acute necrotizing pancreatitis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A 5-year-old boy was referred to our hospital because of profound intellectual disability, micropenis, cryptorchidism, central hypothyroidism, and microcephaly."
    explanation: Cryptorchidism in the same patient.
- name: Global developmental delay
  category: Neurological
  description: >-
    Developmental delay across domains, reported directly in the mild
    hypopituitarism family and positive in every family of the comparison
    table. Carried separately from Motor delay, which is bound to the
    motor-specific term because that is what its own source reports.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
  evidence:
  - reference: PMID:30878599
    reference_title: Impaired EIF2S3 function associated with a novel phenotype of X-linked hypopituitarism with glucose dysregulation.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "He has global developmental delay needing 1:1 support in mainstream school, behavioural problems and mild hepatomegaly with normal liver function."
    explanation: >-
      Global developmental delay named directly, in the mildest reported
      phenotype, which is what makes it a feature of the spectrum rather than
      only of the severe frameshift patients.
  - reference: PMID:28055140
    reference_title: EIF2S3 Mutations Associated with Severe X-Linked Intellectual Disability Syndrome MEHMO.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Developmental delay | + | + | + | + | + | + | + | + | + | +"
    explanation: >-
      The comparison table row, positive in all ten families, which is the
      basis for VERY_FREQUENT.
- name: Motor delay
  category: Neurological
  description: >-
    Motor delay, severe in one missense patient and mild in another. Bound to
    the motor-delay term rather than to global developmental delay because
    that is what the quoted source reports; no frequency is asserted, since
    the evidence is two patients.
  phenotype_term:
    preferred_term: Motor delay
    term:
      id: HP:0001270
      label: Motor delay
  evidence:
  - reference: PMID:32799315
    reference_title: Novel pathogenic EIF2S3 missense variants causing clinically variable MEHMO syndrome with impaired eIF2γ translational function, and literature review.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the affected male with p.(Thr144Ile) presented with severe motor delay, severe microcephaly, moderate ID, epileptic seizures responsive to treatments, hypogenitalism, central obesity, facial features, and diabetes"
    explanation: Severe motor delay alongside the cognitive outcome in one patient.
- name: Intellectual disability
  category: Neurological
  description: >-
    Profound in patients with the recurrent C-terminal frameshift; moderate,
    or in the mildest reported family only learning difficulty, with missense
    variants.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Intellectual disability
    term:
      id: HP:0001249
      label: Intellectual disability
  evidence:
  - reference: PMID:28055140
    reference_title: EIF2S3 Mutations Associated with Severe X-Linked Intellectual Disability Syndrome MEHMO.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "MEHMO is a rare X-linked syndrome characterized by profound intellectual disability, epilepsy, hypogonadism and hypogenitalism, microcephaly, and obesity."
    explanation: Profound intellectual disability in the defining phenotype.
  - reference: PMID:32799315
    reference_title: Novel pathogenic EIF2S3 missense variants causing clinically variable MEHMO syndrome with impaired eIF2γ translational function, and literature review.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the affected male with p.(Ile159Leu) presented with moderate ID, mild motor delay, microcephaly, epileptic seizures resistant to treatment, central obesity, and mild facial features."
    explanation: The milder degree seen with a missense variant.
- name: Seizure
  category: Neurological
  description: >-
    Epileptic seizures, treatment-responsive in some patients and refractory
    in others. One refractory patient was treated with a ketogenic diet and
    developed acute necrotising pancreatitis, which is a reason for caution
    with that option in this disease.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Epileptic seizures
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:32799315
    reference_title: Novel pathogenic EIF2S3 missense variants causing clinically variable MEHMO syndrome with impaired eIF2γ translational function, and literature review.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "epileptic seizures responsive to treatments, hypogenitalism, central obesity, facial features, and diabetes"
    explanation: Treatment-responsive seizures in one of the two reported patients.
  - reference: PMID:33714664
    reference_title: "Ketogenic diet for refractory epilepsy with MEHMO syndrome: Caution for acute necrotizing pancreatitis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Refractory epileptic seizures and glucose dysregulation are characteristic manifestations of the MEHMO syndrome, which can often diminish patients' quality of life."
    quote_role: BACKGROUND
    explanation: >-
      States that the seizures are characteristically refractory. The
      pancreatitis caution from this case report is carried on the ketogenic
      diet treatment entry.
- name: Microcephaly
  category: Neurological
  description: >-
    Microcephaly, severe in the patients with the frameshift variant. Head
    circumference is normal in the mild hypopituitarism-predominant family,
    which is one of the features that distinguishes that phenotype.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Microcephaly
    term:
      id: HP:0000252
      label: Microcephaly
  evidence:
  - reference: PMID:27333055
    reference_title: Two novel EIF2S3 mutations associated with syndromic intellectual disability with severe microcephaly, growth retardation, and epilepsy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In both families, affected males presented with severe intellectual disability, microcephaly, growth retardation, and epilepsy."
    explanation: Severe microcephaly in affected males from two unrelated families.
  - reference: PMID:30878599
    reference_title: Impaired EIF2S3 function associated with a novel phenotype of X-linked hypopituitarism with glucose dysregulation.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Exome sequencing of the X chromosome was performed on three related males with normal head circumferences and mild learning difficulties, hypopituitarism (GH and TSH deficiencies), and an unusual form of glucose dysregulation."
    explanation: >-
      The family in which head circumference is normal, which is why this
      phenotype is not VERY_FREQUENT.
- name: Obesity
  category: Metabolic
  description: >-
    Obesity, frequently described as central or truncal, and one of the
    original acronym features.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Central obesity
    term:
      id: HP:0001956
      label: Truncal obesity
  evidence:
  - reference: PMID:32799315
    reference_title: Novel pathogenic EIF2S3 missense variants causing clinically variable MEHMO syndrome with impaired eIF2γ translational function, and literature review.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "hypogenitalism, central obesity, facial features, and diabetes"
    explanation: Central obesity in a molecularly confirmed patient.
- name: External genital hypoplasia
  category: Endocrine
  description: >-
    Hypogenitalism and hypogonadism, in the acronym and reported across
    patients.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Hypogenitalism
    term:
      id: HP:0003241
      label: External genital hypoplasia
  evidence:
  - reference: PMID:28055140
    reference_title: EIF2S3 Mutations Associated with Severe X-Linked Intellectual Disability Syndrome MEHMO.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "MEHMO is a rare X-linked syndrome characterized by profound intellectual disability, epilepsy, hypogonadism and hypogenitalism, microcephaly, and obesity."
    explanation: Hypogenitalism and hypogonadism in the defining phenotype.
- name: Recurrent infections
  category: Immunological
  description: >-
    Frequent respiratory and urinary tract infections despite normal serum IgG
    and IgM, reported in one patient with the frameshift variant and
    attributed by the authors to the protein synthesis defect. A functional
    susceptibility rather than a measurable antibody deficiency, which is why
    it was missed by the usual screening tests.
  phenotype_term:
    preferred_term: Recurrent respiratory and urinary tract infections
    term:
      id: HP:0002719
      label: Recurrent infections
  evidence:
  - reference: PMID:32901502
    reference_title: Immunologic phenotype of a child with the MEHMO syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The MEHMO patient had had frequent acute infections despite normal IgG and IgM serum levels and responded well to the immunoglobulin treatment."
    explanation: >-
      The infections, the normal antibody levels that concealed them, and the
      response to treatment, in one sentence.
- name: Hypoglycemia
  category: Endocrine
  description: >-
    Neonatal hypoglycaemia, which precedes the diabetes and is proposed as a
    consistent part of the phenotype. Untreated, it may contribute to the
    neurological impairment.
  phenotype_term:
    preferred_term: Neonatal hypoglycemia
    term:
      id: HP:0001998
      label: Neonatal hypoglycemia
  evidence:
  - reference: PMID:29303605
    reference_title: Neonatal hypoglycemia, early-onset diabetes and hypopituitarism due to the mutation in EIF2S3 gene causing MEHMO syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Based on the clinical course in our two probands and also in previously published patients, neonatal hypoglycemia followed by early-onset diabetes and hypopituitarism may be a consistent part of the MEHMO phenotype."
    explanation: >-
      The endocrine sequence the authors propose as consistent, in their own
      hedged wording.
- name: Diabetes mellitus
  category: Endocrine
  description: >-
    Early-onset insulin-dependent diabetes, following the neonatal
    hypoglycaemia. In the milder family the glucose abnormality was described
    as an unusual form of dysregulation rather than frank diabetes.
  phenotype_term:
    preferred_term: Early-onset insulin-dependent diabetes mellitus
    term:
      id: HP:0000819
      label: Diabetes mellitus
  evidence:
  - reference: PMID:29303605
    reference_title: Neonatal hypoglycemia, early-onset diabetes and hypopituitarism due to the mutation in EIF2S3 gene causing MEHMO syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Both probands had a neonatal hypoglycemia, early onset insulin-dependent diabetes, and hypopituitarism due to dysregulation and gradual decline of peptide hormone secretion."
    explanation: Insulin-dependent diabetes in both probands.
- name: Hypopituitarism
  category: Endocrine
  description: >-
    Anterior hypopituitarism from a progressive decline in peptide hormone
    secretion, with growth hormone and TSH deficiency reported. It is the
    dominant feature of the milder EIF2S3 phenotype.
  phenotype_term:
    preferred_term: Anterior hypopituitarism
    term:
      id: HP:0000830
      label: Anterior hypopituitarism
  evidence:
  - reference: PMID:29303605
    reference_title: Neonatal hypoglycemia, early-onset diabetes and hypopituitarism due to the mutation in EIF2S3 gene causing MEHMO syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "hypopituitarism due to dysregulation and gradual decline of peptide hormone secretion."
    explanation: The progressive nature of the pituitary failure.
  - reference: PMID:30878599
    reference_title: Impaired EIF2S3 function associated with a novel phenotype of X-linked hypopituitarism with glucose dysregulation.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "hypopituitarism (GH and TSH deficiencies)"
    explanation: Which anterior pituitary axes were deficient in the milder family.
genetic:
- name: EIF2S3
  gene_term:
    preferred_term: EIF2S3
    term:
      id: hgnc:3267
      label: EIF2S3
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  notes: >-
    EIF2S3 at Xp22 encodes eIF2gamma, the core subunit of the heterotrimeric
    translation initiation factor eIF2. Genotype tracks severity more closely
    here than in most rare syndromes: the recurrent C-terminal frameshift
    p.Ile465Serfs*4 impairs eIF2gamma function more than the tested missense
    variants and is found in the most severely affected patients, while
    missense variants in the guanine nucleotide binding domain give a milder
    or incomplete phenotype, down to a family with hypopituitarism, glucose
    dysregulation, normal head circumference and only mild learning
    difficulty. Reported variants include p.Ser108Arg, p.Thr144Ile,
    p.Met145Val, p.Ile159Leu, p.Ile259Met, p.Pro432Ser and the Ile465Serfs
    frameshift. A de novo variant has been reported, so an affected male
    without a carrier mother does not exclude the diagnosis.
  inheritance:
  - name: X-linked recessive
    inheritance_term:
      preferred_term: X-linked recessive inheritance
      term:
        id: HP:0001419
        label: X-linked recessive inheritance
  evidence:
  - reference: PMID:28055140
    reference_title: EIF2S3 Mutations Associated with Severe X-Linked Intellectual Disability Syndrome MEHMO.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "we propose that more severe EIF2S3 mutations cause the full MEHMO phenotype, while less deleterious mutations cause a milder form of the syndrome with only a subset of the symptoms."
    explanation: >-
      The genotype-severity relationship, in the authors' own proposing
      language.
  - reference: PMID:28055140
    reference_title: EIF2S3 Mutations Associated with Severe X-Linked Intellectual Disability Syndrome MEHMO.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "functional assays in yeast demonstrate that the Ile465Serfs mutation impairs eIF2γ function to a greater extent than tested missense mutations, consistent with the more severe clinical phenotype of the Ile465Serfs male mutation carriers."
    explanation: >-
      The functional measurement behind the genotype-severity relationship,
      which is what makes it more than a clinical impression.
  - reference: PMID:33942450
    reference_title: Broadening the phenotypic spectrum and physiological insights related to EIF2S3 variants.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A recurrent frameshift variant is described in severely affected patients while missense variants usually cause a moderate phenotype."
    explanation: Independent restatement of the same relationship.
  variants:
  - name: p.Ile465Serfs*4
    description: >-
      Recurrent C-terminal frameshift (c.1394_1397del), found in several
      unrelated MEHMO families and associated with the full, severe phenotype.
      It impairs CDC123-dependent assembly of the eIF2 complex.
    clinical_significance: PATHOGENIC
    evidence:
    - reference: PMID:28055140
      reference_title: EIF2S3 Mutations Associated with Severe X-Linked Intellectual Disability Syndrome MEHMO.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "We have identified a C-terminal frameshift mutation (Ile465Serfs) in the EIF2S3 gene in three families with MEHMO syndrome"
      explanation: The variant and its recurrence across families.
    - reference: PMID:35765291
      reference_title: Expanding the phenotype of the recurrent truncating eIF2γ pathogenic variant p.(Ile465Serfs*4) identified in two brothers with MEHMO syndrome.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "We describe two brothers with a recurrent truncating EIF2S3 variant and MEHMO"
      explanation: Two further affected brothers carrying the same recurrent allele.
    - reference: PMID:35765291
      reference_title: Expanding the phenotype of the recurrent truncating eIF2γ pathogenic variant p.(Ile465Serfs*4) identified in two brothers with MEHMO syndrome.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "we do not suspect a common heritage indicating that the variant has arisen independently at least twice"
      explanation: >-
        Supports treating the allele as recurrent rather than as a founder
        variant shared by descent, which is the authors' own reading of the
        absence of a common heritage between the families.
  - name: p.Pro432Ser
    description: >-
      Hemizygous missense variant in three related males with the mild
      phenotype: hypopituitarism with glucose dysregulation, normal head
      circumference and mild learning difficulty.
    clinical_significance: PATHOGENIC
    evidence:
    - reference: PMID:30878599
      reference_title: Impaired EIF2S3 function associated with a novel phenotype of X-linked hypopituitarism with glucose dysregulation.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Our data suggest that the p.Pro432Ser mutation impairs eIF2γ function leading to a relatively mild novel phenotype compared with previous EIF2S3 mutations."
      explanation: The variant and the mild phenotype it produces.
treatments:
- name: Insulin Therapy for the Diabetes
  description: >-
    The diabetes is insulin-dependent and treated as such. This is supportive
    management of an endocrine consequence, not treatment of the mechanism.
  therapeutic_modality: PEPTIDE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: insulin
      term:
        id: CHEBI:145810
        label: insulin
  target_mechanisms:
  - target: Pancreatic Beta Cell Failure
    treatment_effect: BYPASSES
    description: >-
      Exogenous insulin replaces the hormone the failing beta cell no longer
      secretes. It does nothing to the beta cell itself, which is why the
      effect is recorded as a bypass rather than a restoration.
    evidence:
    - reference: PMID:33714664
      reference_title: "Ketogenic diet for refractory epilepsy with MEHMO syndrome: Caution for acute necrotizing pancreatitis."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Although the patient's refractory seizures and diabetes had been well controlled with a combination of ketogenic diet (KD) therapy and insulin therapy, acute fatal necrotizing pancreatitis occurred at the age of 68 months."
      explanation: The diabetes was controlled on insulin in the reported patient.
  evidence:
  - reference: PMID:33714664
    reference_title: "Ketogenic diet for refractory epilepsy with MEHMO syndrome: Caution for acute necrotizing pancreatitis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Although the patient's refractory seizures and diabetes had been well controlled with a combination of ketogenic diet (KD) therapy and insulin therapy, acute fatal necrotizing pancreatitis occurred at the age of 68 months."
    explanation: >-
      Insulin therapy controlling the diabetes in a reported patient. The same
      sentence records the pancreatitis that killed him, which is why the
      ketogenic diet entry below carries a caution.
- name: Ketogenic Diet for Refractory Epilepsy
  description: >-
    Used for refractory seizures, and effective in the one reported patient,
    but that patient died of acute necrotising pancreatitis at 68 months while
    on it. The authors attribute this to an abnormal load on beta cells
    already damaged by eIF2gamma dysfunction, and conclude that the adverse
    effects of the diet should be weighed in this disease specifically. Treat
    this as a documented hazard, not a routine option.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Ketogenic diet
    term:
      id: NCIT:C173168
      label: Ketogenic Diet
  evidence:
  - reference: PMID:33714664
    reference_title: "Ketogenic diet for refractory epilepsy with MEHMO syndrome: Caution for acute necrotizing pancreatitis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We suspect that in the present case, KD therapy led to an abnormal load on the beta cells that were damaged owing to eIF2γ dysfunction. Therefore, the adverse effects of KD in patients with MEHMO syndrome should be considered."
    explanation: >-
      The authors' mechanism for the harm and their explicit caution, which is
      the reason this treatment is curated with a warning rather than as a
      recommendation.
- name: Subcutaneous Immunoglobulin Replacement
  description: >-
    Immunoglobulin replacement for the infection susceptibility, used in one
    reported patient despite normal baseline IgG and IgM, targeting
    supra-physiological IgG levels. Infection frequency fell by 54.5 per cent
    on Poisson regression. A single patient, so this is a lead rather than
    established management, but it is the one reported intervention in this
    disease with a quantified benefit.
  therapeutic_modality: PROTEIN_REPLACEMENT
  treatment_term:
    preferred_term: Immunoglobulin therapy
    term:
      id: NCIT:C62710
      label: Immunoglobulin Therapy
  evidence:
  - reference: PMID:32901502
    reference_title: Immunologic phenotype of a child with the MEHMO syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "On subcutaneous immunoglobulin therapy achieving supra-physiological IgG levels the frequency of infections significantly decreased in Poisson regression by 54.5 % (CI 33.2-89.7, p=0.017)."
    explanation: The quantified effect in the single treated patient.
- name: Growth Hormone Replacement
  description: >-
    Recombinant growth hormone for the GH deficiency reported in the families
    where the pituitary was assessed. Supportive, and because the pituitary
    failure is progressive it needs repeated reassessment rather than a fixed
    dose.
  therapeutic_modality: PROTEIN_REPLACEMENT
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: somatropin
      term:
        id: NCIT:C837
        label: Somatropin
  target_mechanisms:
  - target: Anterior Pituitary Hormone Secretion Failure
    treatment_effect: BYPASSES
    description: >-
      Supplies the hormone the failing gland no longer secretes, without
      acting on the gland itself.
    evidence:
    - reference: PMID:30878599
      reference_title: Impaired EIF2S3 function associated with a novel phenotype of X-linked hypopituitarism with glucose dysregulation.
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: HUMAN_CLINICAL
      snippet: "hypopituitarism (GH and TSH deficiencies)"
      explanation: >-
        The GH deficiency that is the indication. The publication reports the
        deficiency rather than a treatment trial, so this is the indication
        and not evidence of benefit.
  evidence:
  - reference: PMID:30878599
    reference_title: Impaired EIF2S3 function associated with a novel phenotype of X-linked hypopituitarism with glucose dysregulation.
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: "hypopituitarism (GH and TSH deficiencies)"
    explanation: The deficient axis this treatment replaces.
- name: Levothyroxine Replacement
  description: >-
    Levothyroxine for the central hypothyroidism, which is the second
    anterior pituitary axis reported deficient. As with growth hormone this
    replaces the downstream hormone rather than restoring pituitary output.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: levothyroxine
      term:
        id: NCIT:C62080
        label: Levothyroxine
  target_mechanisms:
  - target: Anterior Pituitary Hormone Secretion Failure
    treatment_effect: BYPASSES
    description: >-
      Replaces thyroid hormone downstream of the TSH deficiency.
    evidence:
    - reference: PMID:33714664
      reference_title: "Ketogenic diet for refractory epilepsy with MEHMO syndrome: Caution for acute necrotizing pancreatitis."
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: HUMAN_CLINICAL
      snippet: "A 5-year-old boy was referred to our hospital because of profound intellectual disability, micropenis, cryptorchidism, central hypothyroidism, and microcephaly."
      explanation: >-
        The central hypothyroidism that is the indication. Reported as a
        clinical finding rather than as a treatment result.
  evidence:
  - reference: PMID:30878599
    reference_title: Impaired EIF2S3 function associated with a novel phenotype of X-linked hypopituitarism with glucose dysregulation.
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: "hypopituitarism (GH and TSH deficiencies)"
    explanation: The TSH deficiency this treatment replaces.
diagnosis:
- name: Exome or X-chromosome exome sequencing
  description: >-
    The diagnosis is molecular. Reported patients were found by X-chromosome
    or whole-exome sequencing, and in one family by targeted mRNA analysis of
    EIF2S3, which also detects splicing defects and allelic imbalance. There
    is no biochemical screening test.
  evidence:
  - reference: PMID:27333055
    reference_title: Two novel EIF2S3 mutations associated with syndromic intellectual disability with severe microcephaly, growth retardation, and epilepsy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "X-chromosome exome sequencing was performed to identify the genetic cause of syndromic intellectual disability in two unrelated families with suspected X-linked inheritance."
    explanation: The sequencing approach that identified the gene in two families.
  - reference: PMID:34999262
    reference_title: mRNA analysis revealed a novel pathogenic EIF2S3 variant causing MEHMO syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In most cases, DNA diagnostics of MEHMO syndrome is performed using exome sequencing."
    explanation: >-
      States the usual diagnostic route, in the paper that offers mRNA
      analysis as a cheaper alternative.
mechanistic_hypotheses:
- hypothesis_group_id: eif2b_activation_is_the_therapeutic_route
  hypothesis_label: Pharmacological eIF2B activation is the therapeutic route
  status: EMERGING
  description: >-
    Holds that the consequences of a defective eIF2 gamma subunit are
    reachable by activating the eIF2 guanine nucleotide exchange factor eIF2B,
    so that the therapeutic target is the exchange step downstream of the
    defect rather than the defective subunit itself. Note the narrower thing
    this does not claim. Patient cells do show increased stress-response
    activity, which is the Over-Activated Integrated Stress Response node and
    is cited there. What nothing reported establishes is whether that
    over-activation, or the reduced translation initiation it accompanies,
    drives the phenotype; eIF2B activation would oppose both, so the rescue
    result below does not separate them either. The experimental support is
    direct but confined
    to cells: ISRIB rescued growth, translation and neuronal differentiation
    in induced pluripotent stem cells from a patient with the C-terminal
    frameshift. No animal or human treatment data were identified, and whether
    rescue in differentiating cells predicts benefit in an already-developed
    brain is untested.
  evidence:
  - reference: PMID:31836389
    reference_title: Suppression of MEHMO Syndrome Mutation in eIF2 by Small Molecule ISRIB.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Addition of the drug ISRIB, an activator of the eIF2 guanine nucleotide exchange factor, rescues the cell growth, translation, and neuronal differentiation defects associated with the EIF2S3 mutation, offering the possibility of therapeutic intervention for MEHMO syndrome."
    explanation: >-
      The rescue result and the authors' own framing of it as a possibility
      rather than a demonstrated therapy.
  - reference: PMID:37823684
    reference_title: Pharmacological inhibition of the integrated stress response accelerates disease progression in an amyotrophic lateral sclerosis mouse model.
    supports: REFUTE
    directness: INDIRECT
    evidence_source: MODEL_ORGANISM
    snippet: "This study reveals that the ISR works as a neuroprotective pathway in ALS motor neurons and reveals the toxicity that eIF2B activators may display in ALS patients."
    explanation: >-
      Two eIF2B activators of the same class as ISRIB brought disease forward
      and shortened survival in an ALS mouse model, and the authors warn of
      the toxicity the class may display in patients. REFUTE because the claim
      here is that pharmacological eIF2B activation is the therapeutic route,
      and this is the only in vivo test of that class in a neurological
      disease: it went the wrong way. INDIRECT because the test was in a
      different disease, where eIF2B is being pushed against a protective
      stress response rather than against a defect in eIF2 itself, so it bears
      on the class rather than on this lesion.
  - reference: PMID:37823684
    reference_title: Pharmacological inhibition of the integrated stress response accelerates disease progression in an amyotrophic lateral sclerosis mouse model.
    supports: NO_EVIDENCE
    quote_role: BACKGROUND
    evidence_source: MODEL_ORGANISM
    snippet: "In experimental models, both ISR stimulation and inhibition prevented ALS neurodegeneration; however, which mode of ISR regulation would work in patients is still debated."
    explanation: >-
      Cited for what it does not settle. Experimental models have been
      reported going both ways on the direction of stress-response modulation
      that helps, so the direction of effect is open even in the disease where
      the class has been tested in vivo. NO_EVIDENCE because a statement that
      the direction is debated neither supports nor refutes this hypothesis
      about MEHMO; it is the reason the hypothesis stays EMERGING.
  notes: >-
    Kept EMERGING rather than CANONICAL because the entire supporting result
    is in patient-derived cells, and recorded as a hypothesis rather than a
    treatment entry because no patient has been reported treated. The two
    results are not testing the same proposition: rescuing a defined genetic
    lesion in eIF2 assembly is not the same intervention as activating eIF2B
    against a stress response that is itself protective, which is why neither
    result closes the question.
- hypothesis_group_id: hypoglycaemia_contributes_to_neurological_injury
  hypothesis_label: Untreated neonatal hypoglycaemia contributes to the neurological phenotype
  status: EMERGING
  description: >-
    Holds that part of the neurological impairment in the severe patients is
    not a direct consequence of impaired translation in neurons but of
    untreated hypoglycaemia, which was not recognised as part of the syndrome
    until the endocrine phenotype was characterised. The proposal matters
    clinically: if true, early glucose management changes outcome in a disease
    otherwise without treatment. It is raised by the authors of the mild
    family's report as an explanation for why earlier patients were more
    severely affected, and it has not been tested.
  evidence:
  - reference: PMID:30878599
    reference_title: Impaired EIF2S3 function associated with a novel phenotype of X-linked hypopituitarism with glucose dysregulation.
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: "Untreated hypoglycaemia in previous cases may have contributed to their more severe neurological impairment and seizures in association with impaired EIF2S3."
    explanation: >-
      The originating statement of the hypothesis, in the authors' hedged
      wording.
  notes: >-
    Not placed in the pathograph. Doing so would assert that hypoglycaemia
    causes part of the neurological phenotype, which this single hedged
    sentence does not establish, and the alternative explanation for the
    severity difference, that the frameshift allele is simply worse than the
    missense alleles, is supported by functional data.
animal_models:
- name: eif2s3 knockout zebrafish (CRISPR/Cas9)
  species: Zebrafish
  genotype: eif2s3 CRISPR/Cas9 knockout
  publication: PMID:33942450
  description: >-
    CRISPR/Cas9 knockout of the zebrafish ortholog, used to test the
    pathogenicity of patient missense variants and to look at mechanism. It
    reproduces microcephaly with increased neuronal cell death and produces
    hyperglycaemia from beta cell and pancreatic progenitor deficiency. An
    earlier morpholino knockdown of the same gene reproduced microcephaly and
    short stature.
  modeled_mechanisms:
  - target: Neurodevelopmental Impairment
    relationship: PARTIALLY_RECAPITULATES
    fidelity: MODERATE
    model_scale: ORGANISM
    description: >-
      Reproduces the microcephaly and gives a cellular correlate, increased
      neuronal death.
    limitations: >-
      Microcephaly and neuronal death are reproduced; the intellectual
      disability and epilepsy that dominate the human phenotype are not
      assessable in this model. It is also a complete knockout, whereas the
      human disease is caused by partial loss of function, so it may
      overstate severity.
    evidence:
    - reference: PMID:33942450
      reference_title: Broadening the phenotypic spectrum and physiological insights related to EIF2S3 variants.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "CRISPR/Cas9 knockout of eif2s3 in zebrafish embryos recapitulate the human microcephaly and show increased neuronal cell death."
      explanation: The reproduced phenotype and its cellular correlate.
    readouts:
    - name: Neuronal cell death in embryos
      target: Neurodevelopmental Impairment
      direction: INCREASED
      interpretation: Cellular correlate of the reproduced microcephaly.
      evidence:
      - reference: PMID:33942450
        reference_title: Broadening the phenotypic spectrum and physiological insights related to EIF2S3 variants.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "show increased neuronal cell death"
        explanation: The measured readout.
  - target: Pancreatic Beta Cell Failure
    relationship: PARTIALLY_RECAPITULATES
    fidelity: MODERATE
    model_scale: ORGANISM
    description: >-
      Hyperglycaemia from a deficiency of beta cells and pancreatic
      progenitors, which supports a developmental rather than apoptotic route
      to the glucose phenotype.
    limitations: >-
      The mechanism found here, progenitor deficiency without apoptosis,
      disagrees with the increased cell death seen on EIF2S3 knockdown in a
      human pancreatic cell line, and patient fibroblasts showed no apoptosis
      either. The authors themselves read the discrepancy as tissue-dependent
      mechanisms. The pituitary arm of the disease is not modelled by this
      animal at all, which is why this link targets the beta cell node only.
    evidence:
    - reference: PMID:33942450
      reference_title: Broadening the phenotypic spectrum and physiological insights related to EIF2S3 variants.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Abnormal high glucose levels were identified in mutant embryos, caused by beta cell and pancreatic progenitor deficiency, not related to apoptosis."
      explanation: The glucose phenotype and the cellular route the authors attribute it to.
    readouts:
    - name: Embryonic glucose level
      target: Pancreatic Beta Cell Failure
      direction: INCREASED
      interpretation: Hyperglycaemia in the knockout, the counterpart of the patients' diabetes.
      evidence:
      - reference: PMID:33942450
        reference_title: Broadening the phenotypic spectrum and physiological insights related to EIF2S3 variants.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "Abnormal high glucose levels were identified in mutant embryos"
        explanation: The measured readout.
- name: Yeast eIF2gamma-I318M model of the human I259M variant
  species: Yeast
  genotype: Saccharomyces cerevisiae GCD11 I318M, the residue equivalent to human eIF2gamma I259M
  publication: PMID:30517694
  description: >-
    Humanised point mutation in the yeast ortholog, used to measure what the
    patient variant does to eIF2 function. It impairs growth, derepresses
    GCN4, increases initiation at near-cognate start codons, and reduces
    Met-tRNAi binding; overexpressing initiator tRNA restores binding and
    rescues growth, which is how the defect was localised.
  modeled_mechanisms:
  - target: Reduced eIF2 Ternary Complex Formation
    relationship: RECAPITULATES
    fidelity: MODERATE
    model_scale: MOLECULAR
    description: >-
      Reproduces the molecular lesion, reduced initiator tRNA binding to
      eIF2, and identifies it as the step the variant breaks.
    limitations: >-
      A yeast protein carrying the equivalent substitution, not the human
      protein, and the model reports on molecular function only. It says
      nothing about any tissue or clinical consequence.
    evidence:
    - reference: PMID:30517694
      reference_title: MEHMO syndrome mutation EIF2S3-I259M impairs initiator Met-tRNAiMet binding to eukaryotic translation initiation factor eIF2.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "The corresponding eIF2γ-I318M mutation impaired yeast cell growth and derepressed GCN4 expression, an indicator of defective eIF2-GTP-Met-tRNAiMet complex formation"
      explanation: The functional defect, read out by GCN4 derepression.
    readouts:
    - name: Met-tRNAi binding to eIF2 rescued by initiator tRNA overexpression
      target: Reduced eIF2 Ternary Complex Formation
      direction: RESTORED
      interpretation: >-
        Restoring initiator tRNA rescued both binding and growth, which is
        what localises the defect to this step rather than to a general loss
        of protein function.
      evidence:
      - reference: PMID:30517694
        reference_title: MEHMO syndrome mutation EIF2S3-I259M impairs initiator Met-tRNAiMet binding to eukaryotic translation initiation factor eIF2.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "Overexpression of tRNAiMet restored Met-tRNAiMet binding to eIF2 in vivo and rescued the growth defect in the eIF2γ-I318M strain."
        explanation: The rescue measurement.
differential_diagnoses:
- name: Other eIF2-related and integrated stress response disorders
  description: >-
    A 2025 review proposes grouping MEHMO syndrome with other conditions
    affecting eIF2 and its regulation as eIF2-related neuroendocrinopathies.
    dismech has no such grouping yet; the proposal is recorded here rather
    than acted on.
  evidence:
  - reference: PMID:41207135
    reference_title: "MEHMO syndrome: Review and proposed classification as an eIF2-related neuroendocrinopathy."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: "reports of additional cases suggest a consideration for a re-definition of the acronym and a re-classification of the condition along with others as eIF2-related neuroendocrinopathies."
    explanation: The proposed reclassification, as a proposal.
- name: Syndromic obesity with hypogonadism and intellectual disability
  description: >-
    The acronym features overlap clinically with Prader-Willi syndrome and
    with Bardet-Biedl syndrome. The distinguishing findings are the X-linked
    pedigree, the microcephaly, and the early-onset insulin-dependent diabetes
    preceded by neonatal hypoglycaemia, which the ciliopathies and
    imprinting disorders do not produce.
discussions:
- discussion_id: mehmo_endocrine_cell_mechanism
  kind: HUMAN_MODEL_MISMATCH
  prompt: >-
    Is the endocrine phenotype of MEHMO syndrome caused by death of
    differentiated secretory cells, or by a developmental deficiency of beta
    cells and pancreatic progenitors?
  rationale: >-
    The two available models disagree, and the disagreement is not a detail:
    it decides whether the endocrine disease is progressive degeneration,
    which a stress-response drug might slow, or a fixed developmental
    deficit, which it would not. EIF2S3 knockdown in a human pancreatic cell
    line increased caspase activity and cell death, while the zebrafish
    knockout produced hyperglycaemia from beta cell and progenitor deficiency
    explicitly not related to apoptosis, and patient-derived fibroblasts also
    showed no apoptosis. The authors of the zebrafish work read this as
    tissue-dependent mechanisms, which may be right, but no human pancreatic
    or pituitary tissue from a patient has been examined.
  attaches_to:
  - pathophysiology#Pancreatic Beta Cell Failure
  - animal_models#Zebrafish
  evidence:
  - reference: PMID:33942450
    reference_title: Broadening the phenotypic spectrum and physiological insights related to EIF2S3 variants.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Additional studies in patient-derived fibroblasts did not reveal apoptosis. Our results provide new insights into disease physiopathology, suggesting tissue-dependent mechanisms."
    explanation: >-
      The negative apoptosis result in cultured patient fibroblasts, and the
      authors' own reading of the discrepancy, which is the substance of this
      gap. Graded IN_VITRO because the measurement is in cultured human cells,
      even though the same publication's other results are in zebrafish.
  - reference: PMID:30878599
    reference_title: Impaired EIF2S3 function associated with a novel phenotype of X-linked hypopituitarism with glucose dysregulation.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Cells lacking EIF2S3 had increased caspase activity/cell death."
    explanation: >-
      The apoptotic result, in a human pancreatic cell line. Graded SUPPORT
      rather than REFUTE because what this discussion asserts is that the two
      results conflict, and this is one of the two: it supports the existence
      of the mismatch, and contradicts only the other experiment, not the
      question being asked.
references:
- reference: PMID:41207135
  title: "MEHMO syndrome: Review and proposed classification as an eIF2-related neuroendocrinopathy."
notes: >-
  Lump/split decision: DISEASE. One gene, one molecular lesion class, and one
  conserved chain from reduced eIF2 ternary complex formation to the
  neurological and endocrine phenotypes. MONDO records no descendants for
  MONDO:0010258 and no causal gene other than EIF2S3.

  The milder EIF2S3 phenotype of X-linked hypopituitarism with glucose
  dysregulation and normal head circumference is curated inside this entry
  rather than as a separate disease or a has_subtypes row. It is the same gene
  acting through the same mechanism with less functional loss, and the authors
  who described it present it as an expansion of the EIF2S3 phenotypic range
  rather than a distinct entity. A has_subtypes row was considered and not
  taken because the published variant-to-severity relationship is a gradient
  rather than two groups, and no MONDO term exists for the mild phenotype.

  Two things are deliberately not asserted. ISRIB is recorded as a
  mechanistic hypothesis, not a treatment, because no patient has been
  reported treated with it. And untreated neonatal hypoglycaemia as a cause of
  part of the neurological phenotype is a hypothesis rather than a pathograph
  edge, on one hedged sentence.

  No GeneReviews chapter exists; a PubMed genereviews[book] title search for
  MEHMO and EIF2S3 returned nothing.
📚

References & Deep Research

References

1
PMID:41207135
MEHMO syndrome: Review and proposed classification as an eIF2-related neuroendocrinopathy.
No top-level findings curated for this source.

Deep Research

1

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

Evaluations and curation notes (1)

Create: MEHMO Syndrome · 2026-10-15T07:32:55Z · View source

Created kb/disorders/MEHMO_Syndrome.yaml for MONDO:0010258, the X-linked EIF2S3 neuroendocrine disorder. Deep research: one OpenScientist run (research/MEHMO_Syndrome-deep-research-openscientist.md). Its validation blocks reported 22/22 references resolved and 29/29 terms resolved, with two labels mismatched, one of them HP:0000055 reported as 'Hypogonadism / micropenis' when HPO calls it Abnormal female external genitalia morphology. That term is not bound in this entry; HP:0003241 is used for hypogenitalism instead. just preflight-dr returned WARN on two counts, both dispositioned by reading the report: DDIT3 at 8 mentions is this disease's own integrated-stress-response effector (CHOP) rather than a second disease entity, and the OMIM number the report cites, 300161, is the EIF2S3 gene record, with the disease number 300148 also present in the report and matching MONDO's xref. Three citations were taken from the report after reading each abstract, and all three changed the entry: PMID:32901502 added an immunologic phenotype (frequent infections despite normal IgG and IgM) and the one reported intervention with a quantified benefit, immunoglobulin replacement cutting infection frequency by 54.5 per cent; PMID:34999262 added a second stress-response effector raised in a patient with a different variant, which makes the ISR over-activation a property of the disease rather than of one allele; and PMID:37823684 added the counterweight to the ISRIB hypothesis, two eIF2B activators of the same class accelerating disease in an ALS mouse model. Scope decisions. The milder EIF2S3 phenotype of X-linked hypopituitarism with glucose dysregulation and normal head circumference is curated inside this entry rather than as a separate disease or a has_subtypes row, because it is the same gene acting through the same mechanism with less functional loss, the published variant-to-severity relationship is a gradient rather than two groups, and no MONDO term exists for it. The reasoning is recorded in the entry's notes. Deliberately not asserted. ISRIB is a mechanistic hypothesis, not a treatment entry, because no patient has been reported treated, and the ALS result above is why that distinction is worth keeping. Untreated neonatal hypoglycaemia as a cause of part of the neurological phenotype is a second EMERGING hypothesis rather than a pathograph edge, resting on one hedged sentence. A HUMAN_MODEL_MISMATCH discussion records the live disagreement about the endocrine cell mechanism: EIF2S3 knockdown in a human pancreatic line increased cell death, while the zebrafish knockout produced hyperglycaemia from progenitor deficiency explicitly not related to apoptosis, and patient fibroblasts showed no apoptosis either. One near-miss worth recording, of exactly the class CLAUDE.md warns about. NCIT:C15742 was written from memory as 'Hormone Replacement Therapy'; the OAK lookup returned Postremission Therapy. The correct term, NCIT:C15599, was read from the ontology and bound instead. Nothing else in the entry was written from memory. Validation: just validate, just validate-disorders (52/52 snippets, 53 titles, 0 issues), check-entity-refs, check-causal-targets, check-duplicate-keys, check-coarse-phenotypes, check-qualifier-terms, check-granularity, check-genereviews (NO_CHAPTER, which the entry's notes record).

OpenScientist ▸
MEHMO Syndrome: A Comprehensive Disease Characterization Report
openscientist-autonomous 16 citations 2026-10-15T07:10:24.692929

MEHMO Syndrome: A Comprehensive Disease Characterization Report

Disease: MEHMO Syndrome · MONDO: MONDO:0010258 · OMIM: #300148 · Category: Mendelian (X-linked)

Summary

MEHMO syndrome is a rare, X-linked recessive, multisystem neuroendocrine disorder caused by hemizygous loss-of-function or hypomorphic variants in EIF2S3 (Xp22.11), the gene encoding the γ subunit of eukaryotic translation initiation factor 2 (eIF2γ). The acronym MEHMO denotes its five cardinal features: Mental retardation (intellectual disability), Epileptic seizures, Hypogonadism/Hypogenitalism, Microcephaly, and Obesity. Because eIF2γ is the core GTPase scaffold of the eIF2 heterotrimer that delivers initiator methionyl-tRNA (Met-tRNAi) to the ribosome, MEHMO is now best understood as a prototypical eIF2-related neuroendocrinopathy — a disorder of translation initiation and the integrated stress response (ISR).

The mechanistic core is well established. Pathogenic EIF2S3 variants reduce the abundance or function of the eIF2·GTP·Met-tRNAi ternary complex, either by impairing Met-tRNAi binding directly (e.g., p.Ile259Met) or by disrupting CDC123-promoted assembly of the eIF2 heterotrimer (e.g., the recurrent C-terminal frameshift p.Ile465Serfs4). The resulting deficit in translation initiation chronically derepresses the ISR (elevated ATF4/GCN4 and DDIT3/CHOP), injuring translation-dependent, secretory, and rapidly dividing tissues — most prominently the developing brain and the endocrine pancreas/pituitary. This produces the characteristic endocrine trajectory of neonatal hypoglycemia → early-onset insulin-dependent diabetes → hypopituitarism*, alongside the neurodevelopmental and growth phenotypes. Severity tracks tightly with residual eIF2γ function: truncating variants cause severe, full MEHMO, while hypomorphic missense variants produce milder, clinically variable partial phenotypes.

Management is currently supportive (anticonvulsants, hormone replacement, nutritional support, immunoglobulin for recurrent infections), but the molecular understanding has generated rational experimental therapeutics. ISRIB, a small-molecule activator of eIF2B, restored eIF2 function in patient-derived iPSCs, and initiator tRNA augmentation rescued the defect in yeast — though ISR modulation carries context-dependent risks that temper enthusiasm. This report synthesizes 7 confirmed findings across 22 reviewed papers into a full characterization spanning disease definition, etiology, phenotype, genetics, mechanism, anatomy, temporal course, epidemiology, diagnostics, prognosis, treatment, prevention, cross-species biology, and model organisms.

1. Disease Information

Overview. MEHMO syndrome is a rare X-linked recessive syndromic intellectual disability disorder with a distinctive endocrine and metabolic component. It is defined clinically by its acronymic cardinal features and molecularly by variants in EIF2S3. Recent reviews propose reclassifying MEHMO, together with related conditions, under the umbrella of eIF2-related neuroendocrinopathies, reflecting the shared translation-initiation pathology (PMID: 41207135): "reports of additional cases suggest a consideration for a re-definition of the acronym and a re-classification of the condition along with others as eIF2-related neuroendocrinopathies."

Key identifiers.

Resource Identifier
OMIM #300148 (MEHMO syndrome)
MONDO MONDO:0010258
Gene (OMIM) EIF2S3, 300161
Cytogenetic locus Xp22.11
Inheritance X-linked recessive

Synonyms / alternative names. Mental retardation–epileptic seizures–hypogonadism/hypogenitalism–microcephaly–obesity syndrome; MEHMO syndrome; EIF2S3-related X-linked intellectual disability; proposed broader term "eIF2-related neuroendocrinopathy."

Information source type. The knowledge base here is derived from aggregated disease-level resources (OMIM, review articles) combined with individual-patient case reports and small family series, which dominate the literature given the rarity of the condition.

2. Etiology

Primary cause — genetic. MEHMO is a monogenic Mendelian disorder caused by hemizygous pathogenic variants in EIF2S3 (PMID: 28055140): "We have identified a C-terminal frameshift mutation (Ile465Serfs) in the EIF2S3 gene in three families with MEHMO syndrome and a novel maternally inherited missense EIF2S3 variant (c.324T>A; p.Ser108Arg) in another male patient with less severe clinical symptoms." There is no environmental or infectious cause; the disease is fully explained by the genetic lesion.

Genetic risk factors. The causal variants are the risk factors. There is a clear genotype–severity correlation: the recurrent truncating p.Ile465Serfs*4 produces the severe, complete MEHMO phenotype, whereas hypomorphic missense variants (p.Ser108Arg, p.Thr144Ile, p.Met145Val, p.Ile159Leu, p.Ile259Met) produce milder and more variable phenotypes.

Modifier genes. No distinct modifier genes have been formally identified. However, functionally related genes in the same pathway (CDC123, which promotes eIF2 assembly; EIF2B subunits; and initiator tRNA abundance) are mechanistic modulators — tRNAiMet overexpression rescues the defect experimentally.

Environmental risk / protective factors. Not applicable as causes. One important iatrogenic/environmental interaction is documented: a ketogenic diet, used for refractory epilepsy, preceded fatal acute necrotizing pancreatitis in a MEHMO patient (PMID: 33714664) — an acquired dietary exposure interacting with the underlying metabolic vulnerability.

Gene–environment interactions. The ketogenic-diet/pancreatitis event is the principal documented gene–environment interaction: the EIF2S3-driven pancreatic vulnerability appears to sensitize patients to high-fat dietary stress.

3. Phenotypes

The cardinal (acronym) features plus the broader clinical spectrum, with suggested HPO terms and typical characteristics:

Phenotype HPO term Type Onset Frequency / Notes
Intellectual disability HP:0001249 Clinical/behavioral Infancy Core; often profound in severe cases
Epileptic seizures HP:0001250 Clinical sign Infancy/childhood Core; may be refractory
Hypogonadism / micropenis HP:0000055 Physical Congenital Core
Hypogenitalism / cryptorchidism HP:0000028 Physical Congenital Core
Microcephaly HP:0000252 Physical Congenital/postnatal Core; can be severe
Obesity HP:0001513 Physical Childhood Core (variable)
Neonatal hypoglycemia HP:0001998 Lab abnormality Neonatal Early endocrine sign
Insulin-dependent diabetes HP:0100651 Lab/clinical Infancy/childhood Follows hypoglycemia
Hypopituitarism HP:0040075 Lab/clinical Childhood Progressive hormone decline
Central hypothyroidism HP:0011787 Lab abnormality Childhood Part of pituitary involvement
Hypertrichosis HP:0000998 Physical Childhood Reported in multiple cases
Developmental/motor delay HP:0001270 Clinical Infancy Common
Recurrent infections HP:0002719 Clinical Variable Immunologic component documented
Facial dysmorphism — Physical Congenital Reported

Severity and progression. Phenotype severity is variable and genotype-dependent (PMID: 32799315): "underscoring clinically variable expressivity of MEHMO." The endocrine phenotype is progressive/evolving (hypoglycemia evolving into diabetes and hypopituitarism), whereas structural features (microcephaly, hypogenitalism) are congenital and stable. Seizures may be episodic and refractory.

Quality of life. Profound intellectual disability, epilepsy, and multi-hormone deficiency impose severe impairment on daily functioning and lifelong dependence on caregiving; no disease-specific QOL instrument has been applied, so this is a qualitative assessment.

4. Genetic / Molecular Information

Causal gene. EIF2S3 (HGNC-approved symbol EIF2S3; OMIM 300161) at Xp22.11, encoding eIF2γ (UniProt P41091), the largest and core GTPase subunit of the heterotrimeric eIF2 complex.

Pathogenic variants (representative).

Variant (protein) cDNA Type Phenotype Reference
p.Ile465Serfs*4 — C-terminal frameshift (truncating) Severe, full MEHMO PMID: 28055140, PMID: 35765291
p.Ser108Arg c.324T>A Missense Milder PMID: 28055140
p.Ile259Met — Missense Milder; impairs Met-tRNAi binding PMID: 30517694
p.Thr144Ile, p.Met145Val, p.Ile159Leu — Missense Clinically variable PMID: 32799315
(c.820C>G) c.820C>G Missense (novel) Profound ID, microcephaly, hypoglycemia PMID: 34999262

Variant classification. Reported variants are classified pathogenic/likely pathogenic under ACMG/AMP criteria, supported by segregation, functional assays (yeast, patient fibroblasts/iPSCs), and absence/rarity in population databases (gnomAD). As an X-linked gene intolerant to loss-of-function, these variants are extremely rare in the general population.

Functional consequences. Variants act as partial loss-of-function / hypomorphic alleles — reducing eIF2γ function rather than abolishing it (complete loss would be embryonic-lethal, consistent with eIF2γ's essentiality). Truncating variants disrupt the C-terminal CDC123-interacting region; missense variants perturb the GTP-binding/switch and tRNA-binding surfaces.

Origin. Germline, X-linked. Variants are typically maternally inherited (carrier mothers) or arise de novo.

Epigenetic modifier — X-inactivation. Skewed X-chromosome inactivation modulates carrier-female expression (usually asymptomatic/mild). No disease-specific DNA-methylation signature has been described.

Chromosomal abnormalities. None; MEHMO is a single-gene disorder without large-scale cytogenetic rearrangements.

5. Environmental Information

MEHMO is a Mendelian disorder with no environmental, lifestyle, or infectious cause. The only environmentally relevant factor is iatrogenic: a ketogenic diet used to control refractory seizures was temporally associated with fatal acute necrotizing pancreatitis (PMID: 33714664), indicating a dietary exposure that interacts dangerously with the disease's intrinsic pancreatic vulnerability. Recurrent infections reflect an intrinsic immunologic phenotype rather than a primary infectious etiology.

6. Mechanism / Pathophysiology

Ordered causal chain

  1. Hemizygous EIF2S3 variant (truncating or hypomorphic missense) → leads to structurally/functionally impaired eIF2γ protein.
  2. Impaired eIF2γ → results in reduced Met-tRNAi binding (e.g., p.Ile259Met) and/or defective CDC123-promoted assembly of the eIF2 heterotrimer (e.g., p.Ile465Serfs4). (These are the two demonstrated biochemical branches.)*
  3. Either branch → decreases the active eIF2·GTP·Met-tRNAi ternary complex available for 43S preinitiation complex formation.
  4. Reduced ternary complex → lowers cap-dependent translation initiation and permits aberrant initiation at near-cognate (non-AUG) start codons.
  5. The same deficit → derepresses/activates the integrated stress response (ISR) — upregulating ATF4 (yeast GCN4) and downstream DDIT3/CHOP (demonstrated: elevated DDIT3 transcript in patient cells).
  6. Chronic ISR activation + reduced translational capacity → injures translation-dependent, secretory, and proliferative tissues, branching to:
  7. 6a. Developing brain → increased neuronal cell death → microcephaly, intellectual disability, epilepsy (zebrafish: increased neuronal cell death).
  8. 6b. Endocrine pancreas → β-cell / pancreatic-progenitor deficiency → neonatal hypoglycemia then insulin-dependent diabetes (zebrafish: hyperglycemia from β-cell/progenitor deficiency, not apoptosis).
  9. 6c. Pituitary → impaired peptide-hormone secretion / gradual decline → hypopituitarism, central hypothyroidism, hypogonadism.
  10. These tissue failures → produce the integrated clinical MEHMO phenotype; severity scales with residual eIF2γ function.

Detail by category

Molecular pathway. The eIF2 ternary-complex / ISR axis is the central pathway. eIF2 is the GTPase that delivers Met-tRNAi to the 40S ribosome; its activity is recycled by the GEF eIF2B. ISR signaling phosphorylates eIF2α, converting eIF2 from substrate to inhibitor of eIF2B. In MEHMO, the lesion is in eIF2γ itself, lowering functional ternary complex and mimicking a chronically "stressed" translational state.

Biochemical defect. (PMID: 30517694): "we propose that the I259M mutation impairs Met-tRNAiMet binding, causing altered control of protein synthesis that underlies MEHMO syndrome" — and tRNAiMet overexpression rescues the yeast defect. For the C-terminal variant (PMID: 31836389): "a mutation at the C terminus of eIF2γ impairs CDC123 promotion of eIF2 complex formation and decreases the level of eIF2-GTP-Met-tRNA."

Protein dysfunction / structure. eIF2γ (P41091) contains a G-domain with switch 1/switch 2 regions and domains II/III that form the Met-tRNAi binding site; conformational changes couple GTP/GDP state to tRNA affinity and start-codon fidelity (PMID: 18000047): "how the two-switch regions involved in formation of the tRNA-binding site on subunit gamma exchange conformational information with alpha and beta." MEHMO missense variants localize to the "highly conserved guanine nucleotide binding domain" (PMID: 32799315), while the C-terminal truncation disrupts the Cdc123-interacting domain 3 (PMID: 37507029).

Cellular processes. Dysregulated translation initiation, ISR/CHOP-mediated stress, and increased neuronal cell death (GO:0006417 regulation of translation; GO:0140467 integrated stress response signaling; GO:0006915 apoptotic process — though zebrafish β-cell loss was not apoptotic).

Metabolic changes. Glucose homeostasis is centrally disrupted (hypoglycemia → hyperglycemia/diabetes), reflecting pancreatic endocrine failure rather than a primary enzymopathy.

Immune involvement. An intrinsic immunologic phenotype produces recurrent infections responsive to immunoglobulin, despite grossly normal baseline immunoglobulin levels.

Suggested ontology terms. GO:0006413 (translational initiation), GO:0140467 (integrated stress response signaling), GO:0043022 (ribosome binding); CL:0000169 (type B pancreatic/β cell), CL:0000540 (neuron), CL:0000659 (pituitary hormone-secreting cell); CHEBI:15996 (GTP), CHEBI:17659 (GDP).

7. Anatomical Structures Affected

  • Primary organs: Brain (UBERON:0000955), pancreas — endocrine islets (UBERON:0000006), pituitary gland (UBERON:0000007).
  • Secondary / systems: Endocrine system (thyroid axis, gonadal axis), reproductive organs (external genitalia — micropenis, cryptorchid testes), immune system.
  • Body systems: Nervous, endocrine, reproductive, metabolic, and immune.
  • Tissue / cell level: Nervous tissue (neurons, CL:0000540), pancreatic β cells and progenitors (CL:0000169), pituitary hormone-secreting cells (CL:0000659).
  • Subcellular level: Cytoplasmic translation machinery — the eIF2 ternary complex and 43S preinitiation complex (GO:0005850 eukaryotic translation initiation factor 2 complex; GO:0005829 cytosol).
  • Localization / lateralization: Bilateral, symmetric central nervous system and systemic involvement; no lateralization.

8. Temporal Development

  • Onset: Congenital/neonatal. Structural features (microcephaly, hypogenitalism) present at birth; neonatal hypoglycemia is an early sign.
  • Onset pattern: Chronic with an evolving endocrine course.
  • Progression: The endocrine phenotype is progressive — neonatal hypoglycemia evolves into early-onset insulin-dependent diabetes, with gradual decline of pituitary peptide-hormone secretion producing hypopituitarism (PMID: 29303605): "neonatal hypoglycemia followed by early-onset diabetes and hypopituitarism may be a consistent part of the MEHMO phenotype."
  • Course: Chronic, lifelong; severe cases carry high early-childhood mortality.
  • Critical period / window: The perinatal/early-childhood window — when the brain and endocrine pancreas are developing — is the period of greatest vulnerability and the plausible window for mechanism-based intervention.

9. Inheritance and Population

  • Inheritance: X-linked recessive (PMID: 33714664): "caused by a hemizygous variant in the EIF2S3 gene on chromosome Xp22." Affected individuals are males; carrier females are usually asymptomatic or mildly affected depending on X-inactivation skewing.
  • Penetrance / expressivity: High penetrance in hemizygous males but variable expressivity, strongly governed by the specific variant (genotype–phenotype correlation).
  • Epidemiology: Ultra-rare; prevalence not formally established (fewer than ~a few dozen families reported worldwide). Exact incidence/prevalence per 100,000 is not available.
  • Sex ratio: Strongly male-predominant due to X-linked recessive inheritance.
  • Founder effects / consanguinity: No established founder mutation; the p.Ile465Serfs*4 is recurrent across unrelated families, suggesting a mutational hotspot rather than a founder haplotype.
  • Carrier frequency / geographic distribution: Not defined given rarity; cases reported across multiple populations.

10. Diagnostics

Genetic testing (definitive). Diagnosis rests on identifying a pathogenic EIF2S3 variant. Exome sequencing is the usual route (PMID: 34999262): "In most cases, DNA diagnostics of MEHMO syndrome is performed using exome sequencing." mRNA/RNA analysis of EIF2S3 is a cost-effective complement that detects coding variants, splicing defects, and allelic imbalance, and in one study revealed the novel c.820C>G variant. Targeted single-gene testing and X-linked intellectual disability gene panels including EIF2S3 are also appropriate; WGS is useful when exome is negative.

Functional confirmation. Pathogenicity is supported by functional assays — yeast complementation, patient-fibroblast/iPSC ternary-complex and ISR readouts, and a molecular biomarker: elevated DDIT3/CHOP transcript in patient cells (PMID: 34999262).

Laboratory / clinical workup. Glucose monitoring (neonatal hypoglycemia; later hyperglycemia/diabetes), pituitary hormone panel (TSH/free T4 for central hypothyroidism, gonadotropins, growth hormone axis), and immunologic evaluation. Brain imaging documents microcephaly; EEG characterizes seizures.

Differential diagnosis. Other X-linked intellectual disability syndromes, syndromic congenital hypopituitarism, neonatal/infancy-onset diabetes syndromes, and other eIF2-pathway neuroendocrinopathies. The combination of the acronymic features plus the hypoglycemia→diabetes→hypopituitarism trajectory and an EIF2S3 variant is distinguishing.

Screening. Cascade carrier testing of at-risk female relatives once a familial variant is identified; prenatal/preimplantation testing is feasible in known families. No population newborn screen exists.

11. Outcome / Prognosis

Prognosis is guarded, particularly for the severe truncating genotype. Reported complications include refractory epilepsy, insulin-dependent diabetes, multi-hormone pituitary failure, recurrent infections, and — in one case on a ketogenic diet — fatal acute necrotizing pancreatitis (PMID: 33714664). Severe cases carry substantial early-childhood mortality; milder missense genotypes survive longer with variable disability. Formal survival rates, life expectancy, and mortality statistics are not available given the rarity and heterogeneity of cases.

Morbidity is dominated by profound intellectual disability, epilepsy, and endocrine failure, producing lifelong functional dependence. Prognostic factor: residual eIF2γ function (and hence variant type) is the strongest predictor of severity — truncating p.Ile465Serfs*4 predicts the full severe phenotype, missense variants predict milder courses.

12. Treatment

There is no disease-modifying therapy; management is supportive and multidisciplinary.

Domain Intervention Evidence / Notes
Epilepsy Anticonvulsants; ketogenic diet with caution Ketogenic diet controlled seizures/diabetes but preceded fatal pancreatitis (PMID: 33714664)
Diabetes Insulin Standard for insulin-dependent diabetes
Hypopituitarism Hormone replacement (thyroid, GH, sex steroids as indicated) Supportive
Recurrent infections Subcutaneous immunoglobulin Reduced infection frequency 54.5% (CI 33.2–89.7, p=0.017, Poisson) (PMID: 32901502)
Nutrition / growth Supportive feeding, metabolic monitoring Hypoglycemia management

Quantitative immunoglobulin evidence (PMID: 32901502): "On subcutaneous immunoglobulin therapy achieving supra-physiological IgG levels the frequency of infections significantly decreased in Poisson regression by 54.5 % (CI 33.2-89.7, p=0.017)."

Experimental / mechanism-based therapeutics. - ISRIB (small-molecule eIF2B activator) restored eIF2 function and ternary complex in patient-derived iPSCs carrying the C-terminal variant (PMID: 31836389). Its mechanism (PMID: 25875391): "ISRIB, a potent drug-like small molecule, renders cells insensitive to eIF2α phosphorylation and enhances cognitive function in rodents." Structurally, it "acts as a molecular staple, pinning together tetrameric subcomplexes of eIF2B" (PMID: 31550413). - Initiator tRNAiMet augmentation rescued the yeast growth defect (PMID: 30517694), a conceptual therapeutic avenue. - Caveat: ISR modulation is context-dependent and potentially harmful — in an SOD1 ALS mouse model, pharmacological ISR inhibition accelerated motor-neuron loss (PMID: 37823684): "ISR stimulation and inhibition prevented ALS neurodegeneration; however, which mode of ISR regulation would work in patients is still debated." This mandates caution before clinical translation to MEHMO.

Suggested NCIT terms: Insulin therapy, Immunoglobulin therapy, Anticonvulsant agent, Hormone replacement therapy.

13. Prevention

Primary prevention of the underlying genetic disorder is not possible, but reproductive and secondary measures apply: - Genetic counseling for families with an identified EIF2S3 variant (X-linked recessive recurrence risks). - Carrier / cascade testing of at-risk female relatives. - Prenatal diagnosis and preimplantation genetic testing for known familial variants. - Tertiary prevention of complications: vigilant glucose monitoring to prevent hypoglycemic brain injury, hormone replacement to prevent sequelae of pituitary failure, immunoglobulin to reduce infection burden, and avoidance/careful use of ketogenic diet given pancreatitis risk.

14. Other Species / Natural Disease

No naturally occurring MEHMO-equivalent disease has been described in companion animals or wildlife. The gene is deeply conserved: EIF2S3 orthologs exist across eukaryotes (human EIF2S3; mouse Eif2s3x/Eif2s3y; zebrafish eif2s3; yeast ortholog GCD11), and archaeal aIF2γ structures have informed the human mechanism. The eIF2 translation-initiation machinery is among the most evolutionarily conserved cellular systems, so disease mechanisms are experimentally transferable across species (yeast complementation, zebrafish models). No zoonotic or cross-species transmission applies (non-infectious genetic disease). NCBI Taxonomy: Homo sapiens (9606); models include Danio rerio (7955) and Saccharomyces cerevisiae (4932).

15. Model Organisms

Model Type Key findings Reference
Yeast (S. cerevisiae, GCD11) Cellular/genetic eIF2γ-I318M (human I259M) impairs Met-tRNAi binding, derepresses GCN4, increases non-AUG initiation; tRNAiMet overexpression rescues growth PMID: 30517694
Zebrafish (eif2s3 CRISPR KO) Vertebrate in vivo Recapitulates microcephaly with increased neuronal cell death; hyperglycemia from β-cell/pancreatic-progenitor deficiency (not apoptosis) PMID: 33942450
Patient fibroblasts / iPSCs In vitro human Demonstrate impaired eIF2 function, reduced ternary complex, elevated DDIT3/CHOP; ISRIB rescues PMID: 31836389, PMID: 34999262

Phenotype recapitulation. The zebrafish model captures two core MEHMO features — microcephaly (via neuronal cell death) and glucose dysregulation (via β-cell/progenitor deficiency) (PMID: 33942450): "Abnormal high glucose levels were identified in mutant embryos, caused by beta cell and pancreatic progenitor deficiency, not related to apoptosis." Limitations: no single model reproduces the full multisystem syndrome (hypogonadism, obesity, hypopituitarism, intellectual disability are not all captured), and the essentiality of eIF2γ constrains complete-knockout modeling. Resources: ZFIN (zebrafish), SGD (yeast), Cellosaurus (patient iPSC/fibroblast lines).

Mechanistic Model / Interpretation

   EIF2S3 variant (Xp22.11)
   |-- truncating p.Ile465Serfs*4 --> disrupts CDC123-binding (domain 3)
   |                                   `-> defective eIF2 heterotrimer ASSEMBLY
   `-- missense (e.g., p.Ile259Met) --> perturbs G-domain switch / tRNA site
                        `-> impaired Met-tRNAi BINDING
        |
        v
      v  eIF2.GTP.Met-tRNAi  TERNARY COMPLEX
        |
  +-------------+-------------+
  v                           v
  v cap-dependent initiation   chronic ISR activation
  + aberrant non-AUG start     (^ ATF4/GCN4, ^ DDIT3/CHOP)
  |                           |
  +-------------+-------------+
        v
Injury to translation-dependent tissues
  |-> BRAIN: neuronal death -> microcephaly, ID, epilepsy
  |-> PANCREAS: beta-cell/progenitor loss -> hypoglycemia -> diabetes
  `-> PITUITARY: v hormone secretion -> hypopituitarism
        |
        v
  Integrated MEHMO phenotype
   (severity proportional to residual eIF2-gamma function)

The model is internally coherent and bridges biochemistry (yeast, iPSC), structure (eIF2γ switch/tRNA surfaces, Cdc123 crystal structure), and in-vivo phenotype (zebrafish). The two upstream biochemical branches (assembly defect vs. tRNA-binding defect) converge on a single downstream node — reduced ternary complex / heightened ISR — which then fans out to the affected tissues. This convergence explains why phenotypically similar disease arises from mechanistically distinct variant classes, and why severity tracks with residual function rather than variant location alone.

Evidence Base

PMID Role Contribution
28055140 Supports Establishes EIF2S3 as causal gene; p.Ile465Serfs*4 + p.Ser108Arg; genotype–severity
41207135 Supports Reclassification as eIF2-related neuroendocrinopathy
30517694 Supports Core defect: I259M impairs Met-tRNAi binding; tRNAiMet rescue
31836389 Supports C-terminal variant impairs CDC123 assembly; ISRIB rescue in iPSCs
37507029 Supports Crystal structure of human Cdc123–eIF2γ; MEHMO mutations affect assembly
29303605 Supports Endocrine trajectory: hypoglycemia → diabetes → hypopituitarism
33942450 Supports Zebrafish model: microcephaly + β-cell deficiency hyperglycemia
33714664 Supports/Caveat Confirms acronym & X-linkage; ketogenic diet → fatal pancreatitis
32799315 Supports Novel missense variants; variable expressivity; conserved G-domain
34999262 Supports mRNA diagnostics; novel c.820C>G; elevated DDIT3 biomarker
32901502 Supports Quantitative immunoglobulin benefit (54.5% infection reduction)
35765291 Supports Recurrent p.Ile465Serfs*4 in two brothers; phenotype expansion
18000047 Supports eIF2γ switch regions form tRNA-binding site (structural basis)
25875391 Supports ISRIB mechanism: eIF2B activation restores translation
31550413 Supports ISRIB "molecular staple" structure on eIF2B
29489452 Supports ISRIB rescues eIF2B mutant complexes (VWMD) — proof of concept
37823684 Challenges/Caveat ISR inhibition harmful in ALS model — context-dependence caveat
23291527, 30988256, 17825838 Supports Archaeal aIF2γ structures: tRNA binding, switch 3, GTP/GDP states
21854064 Context eIF2γ phosphosites in switch/nucleotide-binding domains
30954456 Context Brain–pituitary–pancreas link in MEHMO

Limitations and Knowledge Gaps

  • Epidemiology undefined. No reliable prevalence, incidence, survival, or life-expectancy figures exist; the evidence base is small case reports/series, limiting generalizability.
  • Genotype–phenotype resolution. While truncating-vs-missense severity correlation is clear, the quantitative relationship between specific residual eIF2γ activity and individual phenotype features (e.g., which patients develop obesity vs. diabetes) is not fully mapped.
  • Modifier genes and X-inactivation. The contribution of X-inactivation skewing and genetic modifiers to variable expressivity is inferred but not systematically studied.
  • No complete animal model. No single model recapitulates the full multisystem syndrome; eIF2γ essentiality complicates knockout approaches.
  • Therapeutics unproven in patients. ISRIB and tRNAiMet augmentation are in-vitro/model-stage only; the ALS data show ISR modulation can be harmful, so human efficacy and safety are unknown.
  • Mechanistic inference. The brain/pituitary/pancreas tissue-injury steps are partly inferred from a single zebrafish model and clinical correlation rather than directly demonstrated human tissue mechanism.

Proposed Follow-up Experiments / Actions

  1. Establish an international MEHMO patient registry to generate prevalence, natural-history, mortality, and genotype–phenotype data with adequate power.
  2. Systematic variant functional calibration: quantify residual ternary-complex formation / ISR activation for each reported EIF2S3 variant in a uniform iPSC or cell-free assay and correlate with clinical severity scores.
  3. Patient-iPSC–derived organoids (brain, pancreatic islet, pituitary) to directly test the inferred tissue-injury branches of the causal chain and the ISR/CHOP axis in human cells.
  4. Preclinical ISRIB (and tRNAiMet augmentation) efficacy/safety studies in the zebrafish eif2s3 model and patient-derived systems, explicitly testing for the context-dependent harms flagged by the ALS data before any clinical consideration.
  5. Biomarker validation: assess DDIT3/CHOP and ISR-target transcripts as diagnostic/therapeutic-response biomarkers across a patient cohort.
  6. Dietary-risk study: characterize pancreatic vulnerability mechanistically to define whether ketogenic diet is contraindicated in MEHMO and identify safer anticonvulsant strategies.
  7. X-inactivation and carrier-female phenotyping to clarify modifier effects and improve genetic counseling.

Report compiled from 7 confirmed findings across 22 reviewed papers over 5 investigation iterations. Evidence types span human clinical case reports, yeast and zebrafish model organisms, patient-derived in-vitro systems, and structural/computational studies.

Artifacts

Reference Validation

Checked with linkml-reference-validator 0.3.0.

Outcome Count
References checked 22
Resolved 22
Unresolved (possible confabulation) 0
Unverifiable 0
References weighed for topical relevance 22
On topic 11
Off topic 0

All extracted references resolved successfully.

Term Validation

Checked with linkml-term-validator 0.4.5, through the ols: adapter.

Outcome Count
Terms checked 29
Resolved 29
Unresolved (possible confabulation) 0
Obsolete 0
Unverifiable 0
Terms whose name was checked 23
Terms named correctly 13
Terms named as a different term 2
Terms whose name is worth a second look 8

Terms the report names something else

These identifiers resolve, so nothing about them looks wrong, and the ontology calls them something unrelated to what the report calls them. That usually means the identifier is not the one the sentence needs:

  • HP:0000055 (1 mention) - the report calls it "Hypogonadism / micropenis"; HP calls it Abnormal female external genitalia morphology
  • UBERON:0000955 (1 mention) - the report calls it "Primary organs: Brain"; UBERON calls it brain**

Terms whose name is worth a second look

The report's name for these is recognisably related to the term's own name without being one of them. A loose paraphrase reads the same way as a citation of the wrong sibling term - and so does a related synonym, which the ontology records precisely because it names something adjacent rather than the same thing - so these are listed rather than judged:

  • MONDO:0010258 (2 mentions) - the report calls it "MONDO"; MONDO calls it MEHMO syndrome
  • HP:0001250 (1 mention) - the report calls it "Epileptic seizures"; HP calls it Seizure, and lists "Epileptic seizure" among its other names
  • HP:0000028 (1 mention) - the report calls it "Hypogenitalism / cryptorchidism"; HP calls it Cryptorchidism
  • HP:0100651 (1 mention) - the report calls it "Insulin-dependent diabetes"; HP calls it Type I diabetes mellitus, and lists "Insulin-dependent diabetes mellitus" among its other names
  • HP:0001270 (1 mention) - the report calls it "Developmental/motor delay"; HP calls it Motor delay, and lists "Motor developmental delay" among its other names
  • CL:0000169 (2 mentions) - the report calls it "type B pancreatic/β cell"; CL calls it type B pancreatic cell
  • CL:0000659 (2 mentions) - the report calls it "pituitary hormone-secreting cell"; CL calls it eggshell secreting cell
  • CHEBI:17659 (1 mention) - the report calls it "GDP"; CHEBI calls it UDP