Microcephaly, short stature, and impaired glucose metabolism 2 (MSSGM2) is an ultra-rare autosomal recessive syndrome caused by biallelic variants in PPP1R15B, which encodes CReP (constitutive repressor of eIF2-alpha phosphorylation) — the constitutively expressed regulatory subunit that recruits protein phosphatase 1 (PP1/PPP1C) to eIF2-alpha in unstressed cells. The recurrent p.Arg658Cys substitution lies in the PP1-binding site; it reduces PPP1R15B-PPP1C interaction and eIF2-alpha dephosphorylation, so basal phospho-eIF2-alpha rises and cap-dependent translation initiation is chronically attenuated. This is the mechanistic mirror image of Wolcott-Rallison syndrome, where EIF2AK3/PERK loss lowers eIF2-alpha phosphorylation: dysregulation in either direction is deleterious to pancreatic beta cells and other high-secretory tissues. Clinically the two independently reported R658C families share congenital microcephaly with impaired intellectual development and severe short stature, together with skeletal, dental, hair and white-matter involvement. Autoantibody-negative, insulin-treated diabetes attributable to beta-cell apoptosis rather than autoimmunity was reported in the first family, presenting in the second-to-third decade; the siblings in the second family were last assessed at 5 years and 3 years of age — well before that onset window — so the glucose phenotype appears age-dependent and cannot be excluded in young PPP1R15B-positive individuals. A third family with compound heterozygous PPP1R15B variants presented instead with infantile cirrhosis requiring liver transplantation, extending the phenotypic spectrum.
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Conditions with similar clinical presentations that must be differentiated from Microcephaly, Short Stature, and Impaired Glucose Metabolism 2:
name: Microcephaly, Short Stature, and Impaired Glucose Metabolism 2
creation_date: "2026-07-31T19:30:00Z"
category: Mendelian
description: >-
Microcephaly, short stature, and impaired glucose metabolism 2 (MSSGM2) is an
ultra-rare autosomal recessive syndrome caused by biallelic variants in
PPP1R15B, which encodes CReP (constitutive repressor of eIF2-alpha
phosphorylation) — the constitutively expressed regulatory subunit that
recruits protein phosphatase 1 (PP1/PPP1C) to eIF2-alpha in unstressed cells.
The recurrent p.Arg658Cys substitution lies in the PP1-binding site; it
reduces PPP1R15B-PPP1C interaction and eIF2-alpha dephosphorylation, so basal
phospho-eIF2-alpha rises and cap-dependent translation initiation is
chronically attenuated. This is the mechanistic mirror image of
Wolcott-Rallison syndrome, where EIF2AK3/PERK loss lowers eIF2-alpha
phosphorylation: dysregulation in either direction is deleterious to
pancreatic beta cells and other high-secretory tissues. Clinically the two
independently reported R658C families share congenital microcephaly with
impaired intellectual development and severe short stature, together with
skeletal, dental, hair and white-matter involvement. Autoantibody-negative,
insulin-treated diabetes attributable to beta-cell apoptosis rather than
autoimmunity was reported in the first family, presenting in the second-to-third
decade; the siblings in the second family were last assessed at 5 years and 3
years of age — well before that onset window — so the glucose phenotype appears
age-dependent and cannot be excluded in young PPP1R15B-positive individuals. A
third family with compound heterozygous PPP1R15B variants presented instead
with infantile cirrhosis requiring liver transplantation, extending the
phenotypic spectrum.
parents:
- Microcephaly
- Monogenic diabetes
disease_term:
preferred_term: microcephaly, short stature, and impaired glucose metabolism 2
term:
id: MONDO:0014785
label: microcephaly, short stature, and impaired glucose metabolism 2
references:
- reference: PMID:26159176
title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
- reference: PMID:26307080
title: "Homozygous mutation in the eukaryotic translation initiation factor 2alpha phosphatase gene, PPP1R15B, is associated with severe microcephaly, short stature and intellectual disability."
- reference: PMID:27640355
title: "Infantile Cirrhosis, Growth Impairment, and Neurodevelopmental Anomalies Associated with Deficiency of PPP1R15B."
- reference: PMID:38139150
title: "The PPP1R15 Family of eIF2-alpha Phosphatase Targeting Subunits (GADD34 and CReP)."
- reference: PMID:38159565
title: "Recruitment of trimeric eIF2 by phosphatase non-catalytic subunit PPP1R15B."
pathophysiology:
- name: Biallelic PPP1R15B (CReP) Variants Disrupting the PP1-Binding Site
description: >-
Biallelic PPP1R15B variants — recurrently the homozygous missense
c.1972G>A; p.Arg658Cys — alter a conserved residue inside the PPP1C
(protein phosphatase 1) binding domain of CReP. CReP is the constitutively
expressed member of the PPP1R15 family and acts as the non-catalytic
targeting subunit that presents eIF2-alpha to PP1 under basal, unstressed
conditions. Damaging this interface is the initiating molecular lesion of
the syndrome. A second, mechanistically distinct route to the same endpoint
is the homozygous p.Asn423Asp variant adjacent to helix H1 of the
substrate-recruitment module, which impairs capture of the trimeric eIF2
substrate while leaving PP1 binding largely intact; both allele classes
converge on deficient eIF2-alpha dephosphorylation.
role: trigger
biological_scale: MOLECULAR
genes:
- preferred_term: PPP1R15B
term:
id: hgnc:14951
label: PPP1R15B
molecular_functions:
- preferred_term: protein phosphatase 1 binding
term:
id: GO:0008157
label: protein phosphatase 1 binding
modifier: DECREASED
downstream:
- target: Loss of CReP-Directed eIF2-alpha Dephosphorylation
causal_link_type: DIRECT
description: >-
The PP1-binding-site substitution directly reduces PP1 recruitment and
therefore eIF2-alpha dephosphorylation.
evidence:
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "The R658C mutation decreases PP1 binding and eIF2α \ndephosphorylation and results in β-cell apoptosis."
explanation: >-
Directly links the variant to decreased PP1 binding and impaired
eIF2-alpha dephosphorylation, establishing this causal edge.
evidence:
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "The R658C mutation in PPP1R15B affects a conserved amino acid within the domain important for protein phosphatase 1 (PP1) binding."
explanation: >-
Localizes the recurrent disease variant to the conserved PP1-binding
domain of CReP, establishing the initiating molecular lesion.
- reference: PMID:26307080
reference_title: "Homozygous mutation in the eukaryotic translation initiation factor 2alpha phosphatase gene, PPP1R15B, is associated with severe microcephaly, short stature and intellectual disability."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "The p.R658C PPP1R15B mutation is located within the PPP1C binding site."
explanation: Independently confirms the variant maps to the PPP1C binding site.
- reference: PMID:38159565
reference_title: "Recruitment of trimeric eIF2 by phosphatase non-catalytic subunit PPP1R15B."
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "A homozygous N423D variant, adjacent to H1, reducing \nsubstrate binding and dephosphorylation was discovered in a rare syndrome with \nmicrocephaly, developmental delay, and intellectual disability."
explanation: >-
Documents the alternative substrate-recruitment lesion converging on the
same deficient eIF2-alpha dephosphorylation.
- name: Loss of CReP-Directed eIF2-alpha Dephosphorylation
description: >-
Reduced PPP1R15B-PPP1C interaction impairs the holophosphatase that
dephosphorylates eIF2-alpha at Ser51 in unstressed cells. Patient-derived
cells show diminished PPP1R15B-PPP1C complex formation with a consequent
rise in phospho-eIF2-alpha. Patient cells also upregulate PPP1R15B mRNA and
protein, an ineffective compensatory response because the encoded protein
is itself defective.
role: intermediate
biological_scale: MOLECULAR
biological_processes:
- preferred_term: peptidyl-serine dephosphorylation
term:
id: GO:0070262
label: peptidyl-serine dephosphorylation
modifier: DECREASED
downstream:
- target: Chronic Attenuation of Cap-Dependent Translation Initiation
causal_link_type: DIRECT
description: >-
Raised basal phospho-eIF2-alpha is the direct mechanistic cause of reduced
cap-dependent translation initiation.
evidence:
- reference: PMID:26307080
reference_title: "Homozygous mutation in the eukaryotic translation initiation factor 2alpha phosphatase gene, PPP1R15B, is associated with severe microcephaly, short stature and intellectual disability."
supports: SUPPORT
evidence_source: OTHER
snippet: "phosphorylated eIF2α attenuates protein \ntranslation."
explanation: >-
States the canonical mechanism by which increased phospho-eIF2-alpha
attenuates translation, supporting this edge.
evidence:
- reference: PMID:26307080
reference_title: "Homozygous mutation in the eukaryotic translation initiation factor 2alpha phosphatase gene, PPP1R15B, is associated with severe microcephaly, short stature and intellectual disability."
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "We show that patient cells have greatly diminished levels of PPP1R15B-PPP1C interaction, which results in increased eIF2α phosphorylation and resistance to cellular stress."
explanation: >-
Directly demonstrates in patient cells that the variant reduces the
phosphatase complex and raises eIF2-alpha phosphorylation.
- reference: PMID:26307080
reference_title: "Homozygous mutation in the eukaryotic translation initiation factor 2alpha phosphatase gene, PPP1R15B, is associated with severe microcephaly, short stature and intellectual disability."
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "Finally, we find that patient cells have elevated levels of PPP1R15B mRNA and protein, suggesting activation of a compensatory program aimed at restoring cellular homeostasis which is ineffective due to PPP1R15B alteration."
explanation: >-
Documents the ineffective compensatory upregulation of the defective
protein in patient cells.
- reference: PMID:27640355
reference_title: "Infantile Cirrhosis, Growth Impairment, and Neurodevelopmental Anomalies Associated with Deficiency of PPP1R15B."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "identified compound heterozygous mutations \nin PPP1R15B resulting in increased levels of phosphorylated eukaryotic \ntranslation initiation factor 2α."
explanation: >-
A third family with compound heterozygous PPP1R15B variants shows the same
biochemical consequence of raised phospho-eIF2-alpha.
- name: Chronic Attenuation of Cap-Dependent Translation Initiation
description: >-
Phosphorylated eIF2-alpha sequesters eIF2B and blocks regeneration of the
eIF2-GTP/Met-tRNA ternary complex, so a sustained rise in basal
phospho-eIF2-alpha chronically dampens global cap-dependent translation
initiation. Because this is the constitutive (unstressed) arm of the
integrated stress response rather than a transient stress response, the
burden falls on tissues with high protein-synthetic and secretory demand
and on rapidly proliferating progenitors.
role: intermediate
biological_scale: CELLULAR
biological_processes:
- preferred_term: regulation of translational initiation by eIF2 alpha phosphorylation
term:
id: GO:0010998
label: regulation of translational initiation by eIF2 alpha phosphorylation
modifier: INCREASED
- preferred_term: translational initiation
term:
id: GO:0006413
label: translational initiation
modifier: DECREASED
downstream:
- target: Pancreatic Beta-Cell Secretory Failure and Apoptosis
causal_link_type: DIRECT
description: >-
Beta cells are among the tissues most sensitive to translational and
ER-stress imbalance because of their proinsulin biosynthetic load.
evidence:
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "PPP1R15B deficiency sensitizes β-cells to FFA- and ER stress–induced apoptosis and activates the intrinsic pathway of apoptosis via DP5, PUMA, and Bim-S."
explanation: >-
Connects loss of PPP1R15B function to beta-cell apoptosis, supporting
this edge.
- target: Impaired Brain Growth and Neurodevelopment
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
description: >-
Attributed to the translational demands of proliferating neural
progenitors; the intervening steps between reduced translation and reduced
brain growth are not established in human tissue.
evidence:
- reference: PMID:26307080
reference_title: "Homozygous mutation in the eukaryotic translation initiation factor 2alpha phosphatase gene, PPP1R15B, is associated with severe microcephaly, short stature and intellectual disability."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "PPP1R15B now joins the expanding list of translation-associated proteins which when \nmutated cause rare genetic diseases."
explanation: >-
Places the disorder in the class of translation-associated genes whose
disruption causes neurodevelopmental disease, supporting the link from
translational attenuation to impaired brain growth.
- target: Hepatocellular Injury and Infantile Liver Failure
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
description: >-
Reported only in the compound heterozygous family; hepatocytes are another
high-secretory cell type, but the route from raised phospho-eIF2-alpha to
cirrhosis is not established and the allele dependence is unexplained.
evidence:
- reference: PMID:27640355
reference_title: "Infantile Cirrhosis, Growth Impairment, and Neurodevelopmental Anomalies Associated with Deficiency of PPP1R15B."
supports: PARTIAL
evidence_source: HUMAN_CLINICAL
snippet: "identified compound heterozygous mutations \nin PPP1R15B resulting in increased levels of phosphorylated eukaryotic \ntranslation initiation factor 2α."
explanation: >-
Links the same biochemical lesion (raised phospho-eIF2-alpha) to the
family in which liver disease occurred. Marked PARTIAL because the paper
establishes the association, not the intervening mechanism.
- target: Impaired Somatic Growth
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
description: >-
Growth failure is cell-intrinsic rather than endocrine-mediated, but the
steps from reduced translation to reduced stature are not delineated.
evidence:
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "these results are in keeping with bone dysplasia without marked disturbance of calcium metabolism, with severe growth retardation unrelated to pituitary or thyroid dysfunction."
explanation: >-
Excludes endocrine mediation of the growth failure, supporting a
cell-intrinsic translational route for this edge.
evidence:
- reference: PMID:26307080
reference_title: "Homozygous mutation in the eukaryotic translation initiation factor 2alpha phosphatase gene, PPP1R15B, is associated with severe microcephaly, short stature and intellectual disability."
supports: SUPPORT
evidence_source: OTHER
snippet: "phosphorylated eIF2α attenuates protein \ntranslation."
explanation: >-
States the core mechanistic principle that phospho-eIF2-alpha attenuates
translation, linking the phosphatase defect to reduced translation. This
is background exposition in the paper's introduction, not primary data.
- name: Pancreatic Beta-Cell Secretory Failure and Apoptosis
description: >-
Pancreatic beta cells are exquisitely sensitive to translational and
ER-stress imbalance because of their proinsulin biosynthetic load.
PPP1R15B deficiency reduces cellular insulin content, blunts
glucose-stimulated insulin secretion, and sensitizes beta cells to
apoptosis both basally and under ER stress or free-fatty-acid exposure,
acting through the intrinsic (mitochondrial) pathway via the BH3-only
proteins DP5, PUMA and Bim. Important evidence caveat: this node rests on
siRNA knockdown in rat INS-1E and primary rat beta cells, not on the R658C
hypomorph and not on human tissue — no human beta-cell histopathology is
available. The human data are in fact only partly concordant: affected
individuals retain detectable glucagon-stimulated C-peptide and initially
modest insulin requirements, so a secretory defect is better supported than
outright loss of beta-cell mass.
role: intermediate
biological_scale: CELLULAR
cell_types:
- preferred_term: pancreatic beta cell
term:
id: CL:0000169
label: type B pancreatic cell
biological_processes:
- preferred_term: insulin secretion involved in cellular response to glucose stimulus
term:
id: GO:0035773
label: insulin secretion involved in cellular response to glucose stimulus
modifier: DECREASED
- preferred_term: apoptotic process
term:
id: GO:0006915
label: apoptotic process
modifier: INCREASED
downstream:
- target: Impaired Glucose Metabolism and Young-Onset Diabetes
causal_link_type: DIRECT
description: >-
Loss of glucose-stimulated insulin secretion, compounded by beta-cell
apoptosis, produces the clinical diabetes.
evidence:
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "Glucose-stimulated insulin secretion is blunted by PPP1R15B deficiency in β-cells."
explanation: >-
Establishes the secretory failure that directly produces impaired
glucose metabolism.
evidence:
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "PPP1R15B deficiency sensitizes β-cells to FFA- and ER stress–induced apoptosis and activates the intrinsic pathway of apoptosis via DP5, PUMA, and Bim-S."
explanation: >-
Identifies the apoptotic pathway by which PPP1R15B deficiency kills beta
cells.
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "Glucose-stimulated insulin secretion is blunted by PPP1R15B deficiency in β-cells."
explanation: Directly states the secretory phenotype caused by PPP1R15B deficiency.
- name: Impaired Brain Growth and Neurodevelopment
description: >-
Chronically reduced translational output constrains the rapid protein
synthesis required by proliferating neural progenitors during
corticogenesis, yielding severe congenital microcephaly with impaired
intellectual development. Structural neuroimaging in affected individuals
shows white-matter rarefaction, delayed myelination, and hypoplasia of the
brainstem and spinal cord, indicating that both neuron production and
myelination are affected.
role: consequence
biological_scale: TISSUE
cell_types:
- preferred_term: neural progenitor cell
term:
id: CL:0011020
label: neural progenitor cell
biological_processes:
- preferred_term: regulation of translational initiation
term:
id: GO:0006446
label: regulation of translational initiation
modifier: DYSREGULATED
evidence:
- reference: PMID:26307080
reference_title: "Homozygous mutation in the eukaryotic translation initiation factor 2alpha phosphatase gene, PPP1R15B, is associated with severe microcephaly, short stature and intellectual disability."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "hypoplastic brainstem and cord, delayed myelination"
explanation: >-
Documents the neurodevelopmental phenotype including brainstem/cord
hypoplasia and delayed myelination.
- reference: PMID:26307080
reference_title: "Homozygous mutation in the eukaryotic translation initiation factor 2alpha phosphatase gene, PPP1R15B, is associated with severe microcephaly, short stature and intellectual disability."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "the brainstem was small and there was decreased cerebellar volume"
explanation: >-
Neuroimaging evidence that the growth failure of the developing CNS extends
beyond the cortex to brainstem and cerebellum.
- name: Impaired Somatic Growth
description: >-
Growth restriction begins prenatally (small for gestational age) and
continues postnatally to produce severe short stature with low body weight
and BMI. In the index family the growth failure was independent of
pituitary or thyroid dysfunction and was accompanied by a mild bone
dysplasia without disturbed calcium or phosphate metabolism, consistent
with a cell-intrinsic translational constraint on growth rather than an
endocrine axis defect.
role: consequence
biological_scale: ORGANISM
evidence:
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "these results are in keeping with bone dysplasia without marked disturbance of calcium metabolism, with severe growth retardation unrelated to pituitary or thyroid dysfunction."
explanation: >-
Establishes that growth failure is not secondary to pituitary or thyroid
disease, supporting a cell-intrinsic mechanism.
- name: Hepatocellular Injury and Infantile Liver Failure
description: >-
A hepatic arm reported to date only in the compound heterozygous family:
progressive cirrhosis of indeterminate etiology presenting in infancy and
requiring liver transplantation at 7 and 22 months. Hepatocytes are, like
beta cells, a high-secretory cell type plausibly vulnerable to sustained
translational attenuation, but the mechanistic route from raised
phospho-eIF2-alpha to cirrhosis is not established, and why this arm appears
in the compound heterozygous family and not in the two R658C families is
unresolved (see the genotype-phenotype discussion). Curated as a distinct,
weakly connected branch rather than a general feature of the syndrome.
role: consequence
biological_scale: TISSUE
cell_types:
- preferred_term: hepatocyte
term:
id: CL:0000182
label: hepatocyte
evidence:
- reference: PMID:27640355
reference_title: "Infantile Cirrhosis, Growth Impairment, and Neurodevelopmental Anomalies Associated with Deficiency of PPP1R15B."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "developed cirrhosis of indeterminate etiology and required liver"
explanation: >-
Documents the hepatic phenotype that this node represents.
- reference: PMID:27640355
reference_title: "Infantile Cirrhosis, Growth Impairment, and Neurodevelopmental Anomalies Associated with Deficiency of PPP1R15B."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "The first demonstration of PPP1R15B associated with liver disease \nexpands the phenotypic spectrum of PPP1R15B related diseases."
explanation: >-
Establishes hepatic disease as a genuine but spectrum-expanding
manifestation of PPP1R15B deficiency.
- name: Impaired Glucose Metabolism and Young-Onset Diabetes
description: >-
Loss of functional beta-cell mass manifests as insulin-requiring diabetes
presenting in the second-to-third decade, in one sibling with acute
hyperglycemia and ketosis. Residual beta-cell function persists (detectable
glucagon-stimulated C-peptide) and insulin requirements are initially
modest, but the course can become brittle with marked glucose variability
and severe hypoglycemia.
role: consequence
biological_scale: ORGANISM
evidence:
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "diabetes presenting with an acute onset of hyperglycemia and ketosis at age 28 years."
explanation: >-
Documents young-adult-onset diabetes presenting with hyperglycemia and
ketosis in an affected sibling.
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Glucagon-stimulated C-peptide was detectable."
explanation: Indicates retained partial beta-cell function.
mechanistic_hypotheses:
- hypothesis_group_id: bidirectional_eif2a_dysregulation
hypothesis_label: Bidirectional eIF2-alpha dysregulation converges on beta-cell failure
description: >-
MSSGM2 (excess eIF2-alpha phosphorylation from phosphatase-subunit loss)
and Wolcott-Rallison syndrome (deficient eIF2-alpha phosphorylation from
EIF2AK3/PERK loss) are proposed to be mechanistic mirror images: departure
from tightly regulated eIF2-alpha phosphorylation in either direction is
deleterious to beta cells and other secretory tissues, producing
overlapping syndromic diabetes with microcephaly and growth failure. This
framing is well supported for the shared endpoint, but the reason
particular tissues (brain, bone, liver) are selectively vulnerable, and why
hepatic disease dominates in some families, is not established.
status: EMERGING
evidence:
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Our findings support the concept that dysregulated eIF2α phosphorylation, whether decreased by mutation"
explanation: >-
States the bidirectional-dysregulation hypothesis directly, comparing
PPP1R15B and EIF2AK3 disease.
phenotypes:
- category: Neurologic
name: Microcephaly
description: >-
Congenital, severe microcephaly is a cardinal feature, reported in all
affected individuals in both independently ascertained R658C families.
frequency: VERY_FREQUENT
phenotype_term:
preferred_term: Microcephaly
term:
id: HP:0000252
label: Microcephaly
evidence:
- reference: PMID:26307080
reference_title: "Homozygous mutation in the eukaryotic translation initiation factor 2alpha phosphatase gene, PPP1R15B, is associated with severe microcephaly, short stature and intellectual disability."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "we report a consanguineous family with severe microcephaly"
explanation: Reports severe microcephaly in the affected siblings.
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "intellectual disability, and microcephaly"
explanation: Independent family confirming microcephaly as a defining feature.
- category: Growth
name: Short Stature
description: >-
Severe short stature with growth restriction beginning prenatally (small
for gestational age) and persisting into adulthood; the affected sister
measured 139 cm at 31 years of age.
frequency: VERY_FREQUENT
phenotype_term:
preferred_term: Short stature
term:
id: HP:0004322
label: Short stature
evidence:
- reference: PMID:26307080
reference_title: "Homozygous mutation in the eukaryotic translation initiation factor 2alpha phosphatase gene, PPP1R15B, is associated with severe microcephaly, short stature and intellectual disability."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "severe microcephaly, \nshort stature, hypoplastic brainstem and cord"
explanation: Documents short stature in the affected siblings.
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "diabetes of youth with short stature"
explanation: Independent family confirming short stature as a core feature.
- category: Neurologic
name: Intellectual Disability
description: >-
Impaired intellectual development is present in all reported R658C
individuals. In the index patient, mental level at 15 years was comparable
to a 5- to 6-year-old, with a 200-300 word vocabulary and inability to read
or write.
frequency: VERY_FREQUENT
phenotype_term:
preferred_term: Intellectual disability
term:
id: HP:0001249
label: Intellectual disability
evidence:
- reference: PMID:26307080
reference_title: "Homozygous mutation in the eukaryotic translation initiation factor 2alpha phosphatase gene, PPP1R15B, is associated with severe microcephaly, short stature and intellectual disability."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "delayed myelination and \nintellectual disability in two siblings."
explanation: Documents intellectual disability in both affected siblings.
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "At 15 years of age, his mental level was comparable to that of a 5- to 6-year-old child."
explanation: Quantifies the degree of intellectual impairment in the index patient.
- category: Endocrine
name: Young-Onset Diabetes Mellitus
description: >-
Insulin-requiring, autoantibody-negative diabetes presenting in the
second-to-third decade (ages 15 and 28 years in the index family). Onset may
be acute with hyperglycemia and ketosis, and the course can become brittle
with severe hypoglycemia and seizures. No `frequency` is asserted: diabetes
is documented in 2 of the 4 reported R658C individuals, but the two who lack
it were last assessed at 5 and 3 years of age, far below the reported onset
window, so the observed fraction reflects age at ascertainment rather than a
penetrance estimate.
phenotype_term:
preferred_term: Diabetes mellitus
term:
id: HP:0000819
label: Diabetes mellitus
evidence:
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "diabetes presenting with an acute onset of hyperglycemia and ketosis at age 28 years."
explanation: Documents young-adult onset diabetes with ketosis.
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "He was treated with twice-daily insulin injections."
explanation: Indicates insulin dependence.
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Type 1 diabetes–specific autoantibodies (islet cell antibody, GAD, IA2 antibodies) were negative."
explanation: >-
Establishes that the diabetes is autoantibody-negative, supporting a
non-autoimmune, beta-cell-intrinsic mechanism.
- reference: PMID:26307080
reference_title: "Homozygous mutation in the eukaryotic translation initiation factor 2alpha phosphatase gene, PPP1R15B, is associated with severe microcephaly, short stature and intellectual disability."
supports: NO_EVIDENCE
evidence_source: HUMAN_CLINICAL
snippet: "At her last clinical assessment at 5 years and 2 months of age"
explanation: >-
Diabetes is not reported in the second R658C family, but the proband was
last assessed at 5 years 2 months — well before the second-to-third decade
onset window — so this is uninformative about the glucose phenotype rather
than evidence against it.
- category: Neurologic
name: Delayed Myelination
description: >-
Delayed myelination on serial brain MRI in the second R658C family;
myelination progressed between 15 months and later imaging but remained
delayed for age.
phenotype_term:
preferred_term: Delayed myelination
term:
id: HP:0012448
label: Delayed myelination
evidence:
- reference: PMID:26307080
reference_title: "Homozygous mutation in the eukaryotic translation initiation factor 2alpha phosphatase gene, PPP1R15B, is associated with severe microcephaly, short stature and intellectual disability."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "delayed myelination"
explanation: Reports delayed myelination as part of the neuroimaging phenotype.
- category: Neurologic
name: Abnormal Cerebral White Matter Morphology
description: >-
White-matter rarefaction with increased sulcal size and moderate ventricular
enlargement on MRI in the index patient — a structural white-matter
abnormality distinct from the delayed myelination documented in the second
family, so the two are curated separately.
phenotype_term:
preferred_term: Abnormal cerebral white matter morphology
term:
id: HP:0002500
label: Abnormal cerebral white matter morphology
evidence:
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "MRI showed rarefaction of the white matter"
explanation: Documents structural white-matter rarefaction on MRI.
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "showing a moderate white matter rarefaction characterized by increased sulcal size and moderate enlargement of ventricular system."
explanation: Characterizes the white-matter and ventricular changes in detail.
- category: Neurologic
name: Brainstem Hypoplasia
description: >-
Hypoplasia of the brainstem — reported together with a hypoplastic spinal
cord, for which no separate HPO descriptor is bound here — was documented in
the consanguineous family reported by Kernohan and colleagues.
phenotype_term:
preferred_term: Hypoplasia of the brainstem
term:
id: HP:0002365
label: Hypoplasia of the brainstem
evidence:
- reference: PMID:26307080
reference_title: "Homozygous mutation in the eukaryotic translation initiation factor 2alpha phosphatase gene, PPP1R15B, is associated with severe microcephaly, short stature and intellectual disability."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "hypoplastic brainstem and cord"
explanation: Directly documents hypoplastic brainstem and cord.
- category: Skeletal
name: Kyphoscoliosis
description: >-
Kyphoscoliosis with hyperlordosis and mildly abnormal (tall) vertebral
bodies, part of a mild bone dysplasia without disturbed calcium metabolism.
phenotype_term:
preferred_term: Kyphoscoliosis
term:
id: HP:0002751
label: Kyphoscoliosis
evidence:
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "showing kyphoscoliosis with tall vertebral bodies and hyperlordosis."
explanation: Radiographic documentation of kyphoscoliosis and vertebral changes.
- category: Skeletal
name: Pectus Excavatum
description: Chest wall deformity reported in the index patient.
phenotype_term:
preferred_term: Pectus excavatum
term:
id: HP:0000767
label: Pectus excavatum
evidence:
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "He also had kyphoscoliosis, pectus excavatum"
explanation: Documents pectus excavatum in the index patient.
- category: Dental
name: Oligodontia and Dental Hypoplasia
description: >-
Reduced tooth number with dental hypoplasia in the index patient; dental
hypoplasia was also present in his affected sister.
phenotype_term:
preferred_term: Oligodontia
term:
id: HP:0000677
label: Oligodontia
evidence:
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "oligodontia and dental hypoplasia"
explanation: Documents oligodontia and dental hypoplasia.
- category: Integumentary
name: Sparse Hair
description: >-
Sparse hair reported independently in both R658C families — sparse scalp hair
in the index patient, and fine, sparse hair in the second family.
phenotype_term:
preferred_term: Sparse hair
term:
id: HP:0008070
label: Sparse hair
evidence:
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "sparse hair"
explanation: Documents sparse hair in the index patient.
- reference: PMID:26307080
reference_title: "Homozygous mutation in the eukaryotic translation initiation factor 2alpha phosphatase gene, PPP1R15B, is associated with severe microcephaly, short stature and intellectual disability."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Hair was fine and sparse"
explanation: Independent corroboration of sparse hair in the second family.
- category: Other
name: High-Pitched Voice
description: A high-pitched voice was present in both affected siblings.
phenotype_term:
preferred_term: Abnormally high-pitched voice
term:
id: HP:0001620
label: Abnormally high-pitched voice
evidence:
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "and a high-pitched voice."
explanation: Documents high-pitched voice.
- category: Neurologic
name: Sensorineural Hearing Impairment
description: Neurogenic (sensorineural) deafness with 39% hearing loss in the index patient.
phenotype_term:
preferred_term: Sensorineural hearing impairment
term:
id: HP:0000407
label: Sensorineural hearing impairment
evidence:
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "He had neurogenic deafness (hearing loss of 39%)."
explanation: Documents sensorineural hearing loss.
- category: Growth
name: Small for Gestational Age
description: >-
Both siblings in the index family were born small for gestational age,
indicating prenatal onset of the growth restriction.
phenotype_term:
preferred_term: Small for gestational age
term:
id: HP:0001518
label: Small for gestational age
evidence:
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "they were born small for gestational age."
explanation: Establishes prenatal onset of growth restriction.
- category: Endocrine
name: Delayed Puberty
description: >-
Delayed puberty with an undescended right testis requiring surgical
correction in the index patient; pubertal development was ultimately
completed (Tanner stage 5).
phenotype_term:
preferred_term: Delayed puberty
term:
id: HP:0000823
label: Delayed puberty
evidence:
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "He had delayed puberty, with an undescended right testis that was surgically corrected."
explanation: Documents delayed puberty in the index patient.
- category: Endocrine
name: Hypothyroidism
description: >-
Documented in the proband of the second R658C family, who had an elevated TSH
of 9.53 mmol/L in infancy and required thyroid replacement, adequately
controlled by 22 months of age. Notably discordant across families: the index
family's proband had explicitly normal thyroxine, so hypothyroidism is a
variable rather than constant feature of the syndrome.
phenotype_term:
preferred_term: Hypothyroidism
term:
id: HP:0000821
label: Hypothyroidism
evidence:
- reference: PMID:26307080
reference_title: "Homozygous mutation in the eukaryotic translation initiation factor 2alpha phosphatase gene, PPP1R15B, is associated with severe microcephaly, short stature and intellectual disability."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Despite her hypothyroidism being adequately controlled at 22 months of age"
explanation: Directly documents hypothyroidism requiring treatment in the proband.
- reference: PMID:26307080
reference_title: "Homozygous mutation in the eukaryotic translation initiation factor 2alpha phosphatase gene, PPP1R15B, is associated with severe microcephaly, short stature and intellectual disability."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "TSH was increased: 9.53 mmol/l (normal: 0.5–5.5 mmol/l)."
explanation: Provides the biochemical basis for the hypothyroidism diagnosis.
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: REFUTE
evidence_source: HUMAN_CLINICAL
snippet: "but normal levels of calcium, IGF-1, and thyroxine."
explanation: >-
The index family's proband had normal thyroxine, showing hypothyroidism is
not a constant feature across R658C individuals.
- category: Neurologic
name: Cerebellar Hypoplasia
description: >-
Decreased cerebellar volume with a small brainstem on neuroimaging in the
second R658C family, accompanying the ataxic gait and truncal instability.
phenotype_term:
preferred_term: Cerebellar hypoplasia
term:
id: HP:0001321
label: Cerebellar hypoplasia
evidence:
- reference: PMID:26307080
reference_title: "Homozygous mutation in the eukaryotic translation initiation factor 2alpha phosphatase gene, PPP1R15B, is associated with severe microcephaly, short stature and intellectual disability."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "the brainstem was small and there was decreased cerebellar volume"
explanation: Documents decreased cerebellar volume on neuroimaging.
- category: Neurologic
name: Ataxic Gait
description: >-
Wide-based ataxic gait with truncal instability accentuated by turning,
reported as deteriorating, together with kinetic tremor and mild dysmetria —
consistent with the cerebellar hypoplasia.
phenotype_term:
preferred_term: Ataxic gait
term:
id: HP:0002066
label: Gait ataxia
evidence:
- reference: PMID:26307080
reference_title: "Homozygous mutation in the eukaryotic translation initiation factor 2alpha phosphatase gene, PPP1R15B, is associated with severe microcephaly, short stature and intellectual disability."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "wide-based ataxic gait, with truncal instability"
explanation: Documents the ataxic gait and truncal instability.
- category: Neurologic
name: Thin Corpus Callosum
description: Thin corpus callosum on brain MRI in the second R658C family.
phenotype_term:
preferred_term: Thin corpus callosum
term:
id: HP:0033725
label: Thin corpus callosum
evidence:
- reference: PMID:26307080
reference_title: "Homozygous mutation in the eukaryotic translation initiation factor 2alpha phosphatase gene, PPP1R15B, is associated with severe microcephaly, short stature and intellectual disability."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "a thin corpus callosum"
explanation: Documents thin corpus callosum on neuroimaging.
- category: Skeletal
name: Delayed Bone Age
description: >-
Significantly delayed bone age on skeletal survey, consistent with the
generalized growth failure.
phenotype_term:
preferred_term: Delayed skeletal maturation
term:
id: HP:0002750
label: Delayed skeletal maturation
evidence:
- reference: PMID:26307080
reference_title: "Homozygous mutation in the eukaryotic translation initiation factor 2alpha phosphatase gene, PPP1R15B, is associated with severe microcephaly, short stature and intellectual disability."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "A skeletal survey showed significantly delayed bone age"
explanation: Documents delayed skeletal maturation.
- category: Hepatic
name: Infantile Cirrhosis
description: >-
A distinct presentation reported in one sibling pair with compound
heterozygous PPP1R15B variants: cirrhosis of indeterminate etiology in
infancy requiring liver transplantation at 7 and 22 months. This extends the
phenotypic spectrum beyond the R658C microcephaly-diabetes presentation and
was not a feature of the two R658C families.
phenotype_term:
preferred_term: Cirrhosis
term:
id: HP:0001394
label: Cirrhosis
evidence:
- reference: PMID:27640355
reference_title: "Infantile Cirrhosis, Growth Impairment, and Neurodevelopmental Anomalies Associated with Deficiency of PPP1R15B."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "developed cirrhosis of indeterminate etiology and required liver"
explanation: >-
Documents infantile cirrhosis requiring transplantation in a distinct
PPP1R15B family.
- reference: PMID:27640355
reference_title: "Infantile Cirrhosis, Growth Impairment, and Neurodevelopmental Anomalies Associated with Deficiency of PPP1R15B."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "expands the phenotypic spectrum of PPP1R15B related diseases."
explanation: Frames hepatic disease as an expansion of the PPP1R15B spectrum.
genetic:
- name: PPP1R15B
gene_term:
preferred_term: PPP1R15B
term:
id: hgnc:14951
label: PPP1R15B
relationship_type: CAUSATIVE
variants:
- name: "p.Arg658Cys (c.1972G>A)"
description: >-
Recurrent homozygous missense variant in the C-terminal PP1-binding region,
independently reported in two unrelated consanguineous families with the
full microcephaly-short stature-diabetes syndrome. It weakens PPP1R15B-PP1
binding and thereby reduces eIF2-alpha dephosphorylation.
clinical_significance: PATHOGENIC
evidence:
- reference: PMID:26307080
reference_title: "Homozygous mutation in the eukaryotic translation initiation factor 2alpha phosphatase gene, PPP1R15B, is associated with severe microcephaly, short stature and intellectual disability."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "a homozygous missense mutation, c.1972G>A; p.Arg658Cys, in protein phosphatase 1, \nregulatory subunit 15b (PPP1R15B)"
explanation: Specifies the recurrent variant at cDNA and protein level.
- name: p.Asn423Asp
description: >-
Homozygous missense variant adjacent to helix H1 of the substrate-recruitment
module, reported in a rare syndrome with microcephaly, developmental delay and
intellectual disability. Mechanistically distinct from p.Arg658Cys: it reduces
capture of the trimeric eIF2 substrate rather than binding of the PP1 catalytic
subunit, converging on the same biochemical endpoint of deficient eIF2-alpha
dephosphorylation. Diabetes was not established in the primary report, so this
allele is best regarded as an overlapping PPP1R15B-related phenotype.
clinical_significance: PATHOGENIC
evidence:
- reference: PMID:38159565
reference_title: "Recruitment of trimeric eIF2 by phosphatase non-catalytic subunit PPP1R15B."
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "A homozygous N423D variant, adjacent to H1, reducing \nsubstrate binding and dephosphorylation was discovered in a rare syndrome with \nmicrocephaly, developmental delay, and intellectual disability."
explanation: >-
Establishes a second pathogenic allele acting through impaired substrate
recruitment, and the phenotype in which it was found.
evidence:
- reference: PMID:26307080
reference_title: "Homozygous mutation in the eukaryotic translation initiation factor 2alpha phosphatase gene, PPP1R15B, is associated with severe microcephaly, short stature and intellectual disability."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "a homozygous missense mutation, c.1972G>A; p.Arg658Cys, in protein phosphatase 1, \nregulatory subunit 15b (PPP1R15B)"
explanation: Identifies the causal gene and the recurrent variant at cDNA and protein level.
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "we report the first homozygous mutation in the \nPPP1R15B gene"
explanation: >-
First report establishing PPP1R15B as the causal gene for the syndrome.
inheritance:
- name: Autosomal recessive inheritance
description: >-
Both index families were consanguineous with homozygous p.Arg658Cys in
affected siblings; a third family carried compound heterozygous variants.
In the first-reported family the parents had normal fasting glucose,
consistent with recessive inheritance.
inheritance_term:
preferred_term: Autosomal recessive inheritance
term:
id: HP:0000007
label: Autosomal recessive inheritance
evidence:
- reference: PMID:26307080
reference_title: "Homozygous mutation in the eukaryotic translation initiation factor 2alpha phosphatase gene, PPP1R15B, is associated with severe microcephaly, short stature and intellectual disability."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "we report a consanguineous family with severe microcephaly"
explanation: >-
Consanguineous pedigree with a homozygous variant in two affected siblings
supports autosomal recessive inheritance.
diagnosis:
- name: Molecular Confirmation of Biallelic PPP1R15B Variants
description: >-
Diagnosis rests on molecular confirmation, since the clinical triad overlaps
several other ER-stress/translation-associated syndromic diabetes disorders.
Exome sequencing identified the causal variant in both index families, with
confirmation and family segregation by Sanger sequencing or PCR-RFLP
genotyping. In practice a broad exome/genome or a monogenic-diabetes panel
containing PPP1R15B is the appropriate first-line test, with parental
segregation to establish biallelic status.
diagnosis_term:
preferred_term: whole exome sequencing
term:
id: NCIT:C101295
label: Whole Exome Sequencing
evidence:
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "we performed exome sequencing on patient 1’s genomic DNA and identified 18 rare homozygous autosomal variants after filtering"
explanation: Documents exome sequencing as the diagnostic route to the causal variant.
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "We confirmed these variants in patient 1 and genotyped them in patient 2 and in two nonaffected relatives (a grandmother and an aunt) by Sanger sequencing or PCR-RFLP genotyping."
explanation: >-
Documents the orthogonal confirmation and family segregation testing that
establishes biallelic status.
- reference: PMID:26307080
reference_title: "Homozygous mutation in the eukaryotic translation initiation factor 2alpha phosphatase gene, PPP1R15B, is associated with severe microcephaly, short stature and intellectual disability."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Whole-exome sequencing identified a homozygous missense mutation, c.1972G>A; p.Arg658Cys, in protein phosphatase 1, \nregulatory subunit 15b (PPP1R15B)"
explanation: Independent family diagnosed by the same exome-sequencing route.
- name: Distinguishing the Diabetes from Type 1 Diabetes
description: >-
Because the diabetes presents in youth and can debut with hyperglycemia and
ketosis, it is readily mistaken for type 1 diabetes. Pancreatic autoantibody
testing is the discriminator: the index patient was autoantibody-negative
with detectable glucagon-stimulated C-peptide, indicating retained beta-cell
function rather than autoimmune beta-cell destruction.
diagnosis_term:
preferred_term: autoantibody measurement
term:
id: NCIT:C181397
label: Autoantibody Measurement
evidence:
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Type 1 diabetes–specific autoantibodies (islet cell antibody, GAD, IA2 antibodies) were negative."
explanation: >-
Autoantibody negativity is the key laboratory finding separating this
disorder from type 1 diabetes.
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Glucagon-stimulated C-peptide was detectable."
explanation: >-
Retained C-peptide indicates residual beta-cell function, unlike typical
autoimmune type 1 diabetes.
biochemical:
- name: Hyperglycemia and Elevated HbA1c
presence: Elevated
notes: >-
At diabetes diagnosis the index patient had marked hyperglycemia with a
fasting glucose of 13.4 mmol/L and HbA1c 13.0% (119 mmol/mol), reflecting
substantial pre-existing glycemic decompensation at presentation.
evidence:
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Fasting glucose was 13.4 mmol/L and HbA1c was 13.0% (119 mmol/mol)."
explanation: Provides the quantitative glycemic markers at diabetes onset.
- name: Detectable C-Peptide
presence: Detectable
notes: >-
Glucagon-stimulated C-peptide remained detectable, indicating preserved
residual beta-cell function. This distinguishes the disorder from
Wolcott-Rallison syndrome, in which C-peptide is undetectable, and supports
a secretory defect rather than complete beta-cell loss.
evidence:
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Glucagon-stimulated C-peptide was detectable."
explanation: Documents retained endogenous insulin secretory capacity.
- name: Elevated TSH
presence: Elevated
notes: >-
Elevated TSH (9.53, reference 0.5-5.5 mIU/L) in the proband of the second
R658C family, the biochemical basis of the hypothyroidism in that family.
Discordant across families — the index family had normal thyroxine.
reference_ranges:
- lower_bound: 0.5
upper_bound: 5.5
unit: mIU/L
population: pediatric
notes: >-
Interval as reported in the source alongside the patient value. The
source publishes the unit as "mmol/l", which is not a valid unit for
thyrotropin (a molar concentration rather than an activity
concentration) and is almost certainly a typographical error; the
standard unit mIU/L is recorded in this structured field, while the
quoted snippet below preserves the published wording verbatim. The
numeric values are unambiguous as a mild TSH elevation against a normal
interval.
evidence:
- reference: PMID:26307080
reference_title: "Homozygous mutation in the eukaryotic translation initiation factor 2alpha phosphatase gene, PPP1R15B, is associated with severe microcephaly, short stature and intellectual disability."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "TSH was increased: 9.53 mmol/l (normal: 0.5–5.5 mmol/l)."
explanation: >-
Source of both the patient value and the normal interval recorded in
this reference range.
evidence:
- reference: PMID:26307080
reference_title: "Homozygous mutation in the eukaryotic translation initiation factor 2alpha phosphatase gene, PPP1R15B, is associated with severe microcephaly, short stature and intellectual disability."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "TSH was increased: 9.53 mmol/l (normal: 0.5–5.5 mmol/l)."
explanation: Quantifies the thyroid abnormality in the second family.
differential_diagnoses:
- name: Wolcott-Rallison syndrome (EIF2AK3)
description: >-
The most important differential and the mechanistic mirror image: EIF2AK3
/PERK loss lowers eIF2-alpha phosphorylation, whereas PPP1R15B loss raises
it, yet both converge on syndromic diabetes with microcephaly, growth
retardation and skeletal disease. The practical discriminators are onset and
C-peptide — Wolcott-Rallison causes neonatal diabetes with beta-cell loss
and undetectable C-peptide, while PPP1R15B causes later-onset diabetes with
residual C-peptide.
disease_term:
preferred_term: Wolcott-Rallison syndrome
term:
id: MONDO:0009192
label: Wolcott-Rallison syndrome
evidence:
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "In the Wolcott-Rallison syndrome (with decreased eIF2α phosphorylation), neonatal diabetes is due to β-cell loss and C-peptide is undetectable (13), while DNAJC3, IER3IP1, and PPP1R15B mutations (with increased eIF2α phosphorylation) lead to permanent neonatal or young-onset diabetes with residual C-peptide levels"
explanation: >-
Gives the explicit clinical discriminator (C-peptide undetectable vs
residual) between Wolcott-Rallison and PPP1R15B disease.
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Homozygous mutations in EIF2AK3 cause Wolcott-Rallison syndrome, a syndromic form of neonatal diabetes with epiphyseal dysplasia, growth retardation, and variable other manifestations including microcephaly"
explanation: >-
Establishes the overlapping phenotype that makes this the primary
differential.
- name: DNAJC3- and IER3IP1-related syndromic diabetes
description: >-
Both raise eIF2-alpha phosphorylation like PPP1R15B and share beta-cell
dysfunction, microcephaly and intellectual disability, so they are
mechanistically adjacent and clinically overlapping. Distinguished by gene
rather than by phenotype, which is why molecular testing is the diagnostic
core.
evidence:
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "and with syndromes caused by mutations in the ER cochaperone DNAJC3 and in the immediate early response 3 interacting protein 1 (IER3IP1), which both lead to higher levels of ER stress with more eIF2α phosphorylation"
explanation: >-
Names the two mechanistically adjacent disorders sharing raised
eIF2-alpha phosphorylation.
- name: CACH/VWM (vanishing white matter disease, eIF2B)
description: >-
Mutations in eIF2B, the target of phosphorylated eIF2-alpha, cause childhood
ataxia with CNS hypomyelination / vanishing white matter disease. Relevant
here because MSSGM2 also produces white-matter rarefaction, delayed
myelination and ataxia, so the leukoencephalopathy phenotype alone does not
separate them; severe CACH/VWM can likewise be multisystem.
disease_term:
preferred_term: leukoencephalopathy with vanishing white matter
term:
id: MONDO:0800448
label: leukoencephalopathy with vanishing white matter
evidence:
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "It is notable that the mutations affecting the target of phosphorylated eIF2α, the guanine nucleotide exchange factor eIF2B, feature prominent neurodegenerative manifestations known as the CACH (childhood ataxia with central nervous system hypomyelination)/VWM (vanishing white matter disease) syndrome"
explanation: >-
Establishes the eIF2B/CACH-VWM disorders as part of the same pathway and
therefore a differential for the white-matter phenotype.
treatments:
- name: Insulin Therapy
description: >-
Insulin replacement is the mainstay for the diabetes; both affected
siblings in the index family were insulin treated. Initial requirements may
be relatively low (~0.5 units/kg/day), reflecting residual beta-cell
function, but the course may evolve to significant glucose variability with
severe hypoglycemia and seizures, warranting careful titration and glucose
monitoring.
therapeutic_modality: PROTEIN_REPLACEMENT
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: Impaired Glucose Metabolism and Young-Onset Diabetes
treatment_effect: BYPASSES
description: >-
Exogenous insulin replaces the hormone the failing beta-cell mass can no
longer secrete; it does not correct the underlying eIF2-alpha phosphatase
defect.
evidence:
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "He was treated with twice-daily insulin injections."
explanation: >-
Documents insulin replacement as the intervention applied to the
diabetes node.
evidence:
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "He was treated with twice-daily insulin injections."
explanation: Documents insulin therapy as the treatment used for the diabetes.
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "but evolved to significant glucose variability with severe hypoglycemia episodes and seizures."
explanation: >-
Documents the brittle course and hypoglycemia risk that shapes insulin
management.
- name: Genetic Counseling
description: >-
Autosomal recessive inheritance carries a 25% recurrence risk for siblings,
and both index families were consanguineous with two affected siblings each
— the recurrence is documented, not theoretical. Counseling covers
recurrence risk, carrier testing for at-risk relatives, and reproductive
options. Framed as standard practice for a confirmed autosomal recessive
disorder rather than a disease-specific validated protocol.
therapeutic_modality: BEHAVIORAL
treatment_term:
preferred_term: genetic counseling
term:
id: NCIT:C15240
label: Genetic Counseling
evidence:
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: PARTIAL
evidence_source: HUMAN_CLINICAL
snippet: "We studied two siblings with young-onset diabetes, intellectual disability, microcephaly, and short stature who were born to first-cousin consanguineous parents without diabetes"
explanation: >-
Documents consanguinity with unaffected carrier parents and two affected
siblings, the recessive pedigree structure that grounds counseling.
PARTIAL because the paper documents the genetics, not counseling
practice itself.
- name: Liver Transplantation
description: >-
In the hepatic-predominant presentation, progressive infantile cirrhosis
required liver transplantation in both affected siblings, at 7 and 22
months of age.
therapeutic_modality: SURGERY
treatment_term:
preferred_term: Liver Transplantation
term:
id: NCIT:C15271
label: Liver Transplantation
target_mechanisms:
- target: Hepatocellular Injury and Infantile Liver Failure
treatment_effect: BYPASSES
description: >-
Transplantation replaces the failed organ. It does not correct the
underlying eIF2-alpha phosphatase defect, which persists in every other
tissue, so it is organ salvage rather than disease-modifying therapy.
evidence:
- reference: PMID:27640355
reference_title: "Infantile Cirrhosis, Growth Impairment, and Neurodevelopmental Anomalies Associated with Deficiency of PPP1R15B."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "required liver \ntransplantation; S1 at 7 months and S2 at 22 months."
explanation: >-
Documents transplantation as the intervention for the hepatic failure
node.
evidence:
- reference: PMID:27640355
reference_title: "Infantile Cirrhosis, Growth Impairment, and Neurodevelopmental Anomalies Associated with Deficiency of PPP1R15B."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "required liver \ntransplantation; S1 at 7 months and S2 at 22 months."
explanation: Documents liver transplantation in the hepatic presentation.
discussions:
- discussion_id: gap_ppp1r15b_genotype_phenotype_hepatic_vs_neuro
prompt: >-
Why do PPP1R15B variants produce a microcephaly-diabetes phenotype in some
families and a hepatic-predominant infantile cirrhosis phenotype in others?
kind: KNOWLEDGE_GAP
status: OPEN
attaches_to:
- pathophysiology#Loss of CReP-Directed eIF2-alpha Dephosphorylation
- phenotypes#Infantile Cirrhosis
rationale: >-
The two R658C families share a homozygous PP1-binding-site missense variant
and a concordant neurodevelopmental/endocrine phenotype without reported
liver disease, whereas the compound heterozygous family presented with
infantile cirrhosis requiring transplantation. Whether this reflects
allele-specific residual CReP activity, genetic background, or ascertainment
is unresolved, and it directly affects prognostic counseling and
surveillance.
proposed_experiments:
- experiment_id: exp_ppp1r15b_allele_series_residual_activity
name: Allele-series comparison of residual CReP-PP1 activity
description: >-
Quantify PPP1R15B-PPP1C binding, basal phospho-eIF2-alpha, and
translational output across the reported allele series in matched
patient-derived cells to test whether hepatic-predominant alleles retain
different residual activity than R658C.
- experiment_id: exp_ppp1r15b_hepatic_surveillance
name: Systematic hepatic surveillance in R658C individuals
description: >-
Prospectively assess transaminases, synthetic function, and elastography
in molecularly confirmed R658C individuals to test whether subclinical
liver involvement is present but unascertained.
- discussion_id: interp_ppp1r15b_inhibitors_directionally_counterproductive
prompt: >-
Would PPP1R15B/CReP inhibitors (e.g. Raphin1) or other agents that further
raise phospho-eIF2-alpha be expected to worsen MSSGM2?
kind: INTERPRETATION
status: OPEN
attaches_to:
- pathophysiology#Loss of CReP-Directed eIF2-alpha Dephosphorylation
- pathophysiology#Pancreatic Beta-Cell Secretory Failure and Apoptosis
rationale: >-
PPP1R15B/CReP is an active drug target, and selective CReP inhibitors are
being developed to raise phospho-eIF2-alpha therapeutically in other
contexts. In MSSGM2 the defect is already excessive phospho-eIF2-alpha from
deficient CReP function, so pharmacologically inhibiting the same node is
directionally counterproductive rather than therapeutic. The concern is not
purely theoretical: in rodent and human beta cells the eIF2-alpha
phosphatase inhibitor salubrinal exacerbates cell death. This is a
prescribing-relevant caution rather than an established clinical
contraindication, since no such agent has been given to an affected
individual; it is recorded here so the inference is explicit rather than
left for a reader to reconstruct.
proposed_experiments:
- experiment_id: exp_ppp1r15b_inhibitor_directionality
name: Directionality test of CReP inhibition in R658C beta cells
description: >-
Compare apoptosis and glucose-stimulated insulin secretion in
R658C-knockin versus wild-type human beta cells exposed to selective
CReP/PPP1R15B inhibitors, to test whether further raising
phospho-eIF2-alpha worsens the beta-cell phenotype.
evidence:
- reference: PMID:38139150
reference_title: "The PPP1R15 Family of eIF2-alpha Phosphatase Targeting Subunits (GADD34 and CReP)."
supports: SUPPORT
evidence_source: OTHER
snippet: "we will discuss several pharmacological inhibitors of \nGADD34 and/or CReP that show promise as treatments and the controversies as to \ntheir mechanism of action."
explanation: >-
Confirms that pharmacological CReP inhibitors exist and are under active
development, making the directionality caution clinically relevant.
- reference: PMID:26159176
reference_title: "A Missense Mutation in PPP1R15B Causes a Syndrome Including Diabetes, Short Stature, and Microcephaly."
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "salubrinal actually exacerbates cell death through ER stress"
explanation: >-
Shows that pharmacologically raising phospho-eIF2-alpha harms beta cells,
supporting the counterproductive-direction inference.
- discussion_id: gap_ppp1r15b_tissue_selectivity_and_isr_targeting
prompt: >-
Is the disorder's tissue selectivity explained by differential dependence on
constitutive eIF2-alpha dephosphorylation, and can it be pharmacologically
targeted?
kind: KNOWLEDGE_GAP
status: OPEN
attaches_to:
- pathophysiology#Chronic Attenuation of Cap-Dependent Translation Initiation
- pathophysiology#Pancreatic Beta-Cell Secretory Failure and Apoptosis
rationale: >-
CReP is ubiquitously expressed, yet disease burden falls on brain,
pancreatic beta cells, bone, teeth and liver. Establishing which tissues
depend most on basal eIF2-alpha dephosphorylation would clarify why these
organs fail and whether modulating the integrated stress response could be
therapeutic. This matters because the beta-cell phenotype is driven by
apoptosis, which is in principle preventable if intervention precedes
beta-cell loss.
proposed_experiments:
- experiment_id: exp_ppp1r15b_isogenic_tissue_panel
name: Isogenic R658C-knockin human tissue panel
description: >-
Measure basal phospho-eIF2-alpha and translational output across isogenic
R658C-knockin human iPSC-derived neurons, beta cells and hepatocytes to
map differential dependence on constitutive eIF2-alpha dephosphorylation.
- experiment_id: exp_ppp1r15b_isr_modulator_beta_cell_rescue
name: ISR-modulator rescue in R658C beta cells
description: >-
Test whether integrated-stress-response modulators restore
glucose-stimulated insulin secretion and reduce apoptosis in
R658C-knockin human beta cells.
notes: >-
No GeneReviews chapter exists for PPP1R15B-related disease as of this curation
(a PubMed search for "PPP1R15B GeneReviews" returned no results), so the
GeneReviews phenotype-baseline step was not applicable. The disorder is
ultra-rare: MSSGM2 is defined by two independently reported consanguineous
families homozygous for the same p.Arg658Cys variant, plus one compound
heterozygous family with a hepatic-predominant presentation. Population
prevalence is therefore not estimable and no prevalence records are asserted;
frequency values are given only for the cardinal features present in all
reported R658C individuals. MSSGM1 (MONDO:0000208, TRMT10A) is a distinct
genetic entity with a deliberately similar clinical label and is not merged
here.
Hypothyroidism is discordant across families and is curated as such rather
than as a constant feature: the proband of the second R658C family had an
elevated TSH requiring replacement, whereas the index family's proband had
explicitly normal thyroxine. Hepatic fibrosis/cirrhosis is review-aggregated
for the R658C phenotype, so the Infantile Cirrhosis phenotype here is scoped
strictly to the compound heterozygous family in which it was primarily
reported, and should be widened only if primary R658C evidence emerges.
Frequency discipline. `frequency:` is asserted only for microcephaly, short
stature and intellectual disability — features documented in all four reported
R658C individuals. It is deliberately omitted for diabetes, which is present
in 2 of 4 but whose two negatives were assessed at 5 and 3 years of age,
far below the second-to-third-decade onset window, making the observed
fraction a statement about ascertainment age rather than penetrance.
Deep-research provenance and a caution. This entry was curated with a falcon
(Edison) deep-research run, retained at
research/Microcephaly_Short_Stature_and_Impaired_Glucose_Metabolism_2-deep-research-falcon.md.
Its substantive findings were independently verified against cached primary
abstracts before use, and one error was caught in the process: the report
cites the Abdulkarim 2015 paper as PMID:26310607, which is incorrect — the
correct identifier is PMID:26159176 (verified via the cached record and the
paper's DOI 10.2337/db15-0477). The report's genuine added value was
surfacing the p.Asn423Asp substrate-recruitment allele (PMID:38159565),
which is curated above.
Question: You are an expert researcher providing comprehensive, well-cited information.
Provide detailed information focusing on: 1. Key concepts and definitions with current understanding 2. Recent developments and latest research (prioritize 2023-2024 sources) 3. Current applications and real-world implementations 4. Expert opinions and analysis from authoritative sources 5. Relevant statistics and data from recent studies
Format as a comprehensive research report with proper citations. Include URLs and publication dates where available. Always prioritize recent, authoritative sources and provide specific citations for all major claims.
Please provide a comprehensive research report on Microcephaly, Short Stature, and Impaired Glucose Metabolism 2 covering all of the disease characteristics listed below. This report will be used to populate a disease knowledge base entry. Be thorough and cite primary literature (PMID preferred) for all claims.
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This report will be used to populate a disease knowledge base entry with: - Pathophysiology descriptions with causal chains - Gene/protein annotations (HGNC, GO terms) - Phenotype associations (HP terms) with frequencies - Cell type involvement (CL terms) - Anatomical locations (UBERON terms) - Chemical entities (CHEBI terms) - Treatment annotations (NCIT terms) - Evidence items with PMIDs and exact abstract quotes - Epidemiology, prognosis, diagnostic, and prevention information - Animal model descriptions with phenotype recapitulation details
MSSGM2 is an ultra-rare autosomal-recessive neurodevelopmental–endocrine disorder caused by biallelic pathogenic variants in PPP1R15B, encoding the constitutive repressor of eIF2α phosphorylation (CReP). The best-established phenotype combines congenital or early growth failure and microcephaly, intellectual disability, and later autoimmune-negative diabetes. The foundational evidence is a 2015 report of two affected siblings homozygous for p.Arg658Cys; a 2024 structural study described a homozygous p.Asn423Asp variant with an overlapping growth and neurodevelopmental phenotype but without established diabetes in the available report. The evidence base remains too small for reliable prevalence, penetrance, survival, or phenotype-frequency estimates. (abdulkarim2015amissensemutation pages 1-2, fatalska2024recruitmentoftrimeric pages 10-12, fatalska2024recruitmentoftrimeric pages 8-10)
| Domain | Summary | Key details / ontology hints | Evidence |
|---|---|---|---|
| Disease definition | Microcephaly, short stature, and impaired glucose metabolism 2 (MSSGM2) is an ultra-rare Mendelian multisystem disorder linked to biallelic PPP1R15B dysfunction, with neurodevelopmental abnormalities and diabetes or impaired glucose metabolism as major manifestations. | Mendelian disorder; syndrome-level, disease-aggregated knowledge derived from published case reports and reviews. | (abdulkarim2015amissensemutation pages 1-2, stone2021monogenicandsyndromic pages 6-8, gobble2025neonatalandsyndromic pages 7-8) |
| Causal gene / protein | Causal gene: PPP1R15B; protein: protein phosphatase 1 regulatory subunit 15B / CReP, a regulatory subunit of an eIF2α phosphatase complex. | Pathway anchor: eIF2α dephosphorylation / integrated stress response (ISR). | (abdulkarim2015amissensemutation pages 1-2, fatalska2024recruitmentoftrimeric pages 10-12, hicks2023theppp1r15family pages 7-9, gobble2025neonatalandsyndromic pages 7-8) |
| Inheritance | Autosomal recessive. | Reported affected individuals carried homozygous missense variants; one index family was consanguineous. | (abdulkarim2015amissensemutation pages 4-7, abdulkarim2015amissensemutation pages 3-4, gobble2025neonatalandsyndromic pages 7-8) |
| Established variants | Best-established disease variant: p.Arg658Cys (R658C) in PPP1R15B. A later p.Asn423Asp (N423D) homozygous variant was reported with overlapping neurodevelopmental/growth features and impaired substrate recruitment; diabetes status was not established in the extracted evidence. | R658C impairs PP1 binding; N423D impairs eIF2 recruitment while preserving PP1 binding. Variant-class evidence is strongest for homozygous missense change(s); avoid overcalling broader allelic series from current sparse literature. | (abdulkarim2015amissensemutation pages 1-2, fatalska2024recruitmentoftrimeric pages 10-12, fatalska2024recruitmentoftrimeric pages 8-10, fatalska2024recruitmentoftrimeric pages 3-5) |
| Core phenotype | Core syndrome comprises microcephaly, short stature/growth retardation, intellectual disability/developmental delay, and impaired glucose metabolism/diabetes. Additional reported findings include sensorineural deafness, delayed puberty, kyphoscoliosis, pectus excavatum, dental anomalies/oligodontia, sparse hair, hepatic fibrosis/cirrhosis, and hypothyroidism. | HPO suggestions: Microcephaly HP:0000252; Short stature HP:0004322; Intellectual disability HP:0001249; Diabetes mellitus HP:0000819; Sensorineural hearing impairment HP:0000407; Kyphoscoliosis HP:0002751; Pectus excavatum HP:0000767; Oligodontia HP:0000677. | (abdulkarim2015amissensemutation pages 4-7, abdulkarim2015amissensemutation pages 3-4, stone2021monogenicandsyndromic pages 6-8, gobble2025neonatalandsyndromic pages 7-8) |
| Diabetes course | Diabetes has been reported from adolescence to adulthood in the primary family, with insulin dependence, negative type 1 diabetes autoantibodies, residual C-peptide, moderate insulin requirements, and ketosis in at least one patient. Reviews describe the glucose phenotype as late-onset relative to the congenital growth/neurodevelopmental features. | Reported ages at onset in extracted evidence: 15 years and 28 years. Insulin requirement examples: ~0.5 and ~0.7 U/kg/day. | (abdulkarim2015amissensemutation pages 4-7, abdulkarim2015amissensemutation pages 3-4, abdulkarim2015amissensemutation pages 9-11, stone2021monogenicandsyndromic pages 6-8) |
| Key mechanism | PPP1R15B/CReP normally helps PP1 dephosphorylate eIF2α-Ser51. Disease variants impair PP1 binding and/or eIF2 substrate recruitment, causing persistently increased eIF2α phosphorylation, dysregulated ISR/ER-stress signaling, impaired translation/secretory homeostasis, β-cell dysfunction, and apoptosis. | Cell/process hints: pancreatic beta cell (CL:0000169); endoplasmic reticulum stress GO:0034976; response to unfolded protein GO:0006986; regulation of translation GO:0006417; apoptotic process GO:0006915. | (abdulkarim2015amissensemutation pages 1-2, abdulkarim2015amissensemutation pages 9-11, abdulkarim2015amissensemutation pages 7-9, fatalska2024recruitmentoftrimeric pages 10-12, hicks2023theppp1r15family pages 7-9, fatalska2024recruitmentoftrimeric pages 3-5) |
| Diagnosis | Diagnosis is based on syndromic clinical recognition plus molecular confirmation of biallelic PPP1R15B variants, typically by exome sequencing with segregation confirmation. Supportive evaluations include diabetes phenotyping, neurodevelopmental assessment, hearing testing, and imaging/skeletal/endocrine workup as clinically indicated. | In the index report, exome sequencing, segregation filtering, and confirmatory Sanger/PCR-RFLP genotyping were used. Differential considerations include other ER-stress/monogenic diabetes syndromes such as Wolcott-Rallison syndrome. | (abdulkarim2015amissensemutation pages 4-7, abdulkarim2015amissensemutation pages 1-2, hicks2023theppp1r15family pages 7-9) |
| Treatment | No disease-specific approved therapy or disease-targeted clinical trial was identified in the available evidence. Current care is supportive and phenotype-directed: insulin for diabetes, endocrine management, developmental/educational support, audiology, orthopedic care, dental care, and surveillance for liver/thyroid/puberty complications. | NCIT-style intervention hints: Insulin Therapy; Genetic Counseling; Physical Therapy; Occupational Therapy; Hearing Aid. These are management extrapolations, not validated disease-specific protocols. | (abdulkarim2015amissensemutation pages 9-11, gobble2025neonatalandsyndromic pages 7-8) |
| Epidemiology | Extremely rare; available evidence supports only a very small number of reported individuals worldwide. No robust prevalence, incidence, carrier-frequency, or sex-ratio estimates were identified in the extracted sources. | Human evidence base includes the original two siblings plus later review-level mention of additional patients/affected siblings and one N423D patient with overlapping phenotype. | (stone2021monogenicandsyndromic pages 6-8, fatalska2024recruitmentoftrimeric pages 8-10, vaneynde2022theroleof pages 6-7, abdulkarim2015amissensemutation pages 4-7) |
| Evidence limitations | Knowledge remains constrained by very small sample size, incomplete longitudinal follow-up, review-level aggregation of some later cases, uncertain phenotype frequencies, and lack of disease-specific natural-history studies, treatment trials, or omics datasets. Some later features (e.g., hepatic fibrosis, hypothyroidism) are review-reported and not fully resolvable to individual primary cases from the extracted evidence. | Use cautious wording for penetrance, prognosis, and variant spectrum; avoid unsupported identifiers or precise epidemiologic estimates. | (stone2021monogenicandsyndromic pages 6-8, gobble2025neonatalandsyndromic pages 7-8, vaneynde2022theroleof pages 6-7, abdulkarim2015amissensemutation pages 4-7) |
Table: This table condenses the most reliable current knowledge on PPP1R15B-related MSSGM2 for disease knowledge-base use. It highlights established facts, likely clinical annotations, and major evidence gaps from the small published case literature.
This is aggregated disease-level knowledge derived principally from published families, not an EHR-derived cohort. The original article appeared in Diabetes 64(11), November 2015, DOI 10.2337/db15-0477, PMID 26310607. Its abstract states: “Here, we report the first homozygous mutation in the PPP1R15B gene … in two siblings affected by a novel syndrome of diabetes of youth with short stature, intellectual disability, and microcephaly.” (abdulkarim2015amissensemutation pages 1-2)
The disease is caused by germline biallelic PPP1R15B dysfunction. The original family had first-cousin parents and homozygous p.Arg658Cys in both affected siblings, establishing autosomal-recessive transmission. Consanguinity is therefore a reproductive risk factor—not a biological cause beyond increasing the probability that both parents carry the same rare allele. (abdulkarim2015amissensemutation pages 3-4, abdulkarim2015amissensemutation pages 4-7)
No validated susceptibility loci, modifier genes, protective alleles, founder effect, germline mosaicism, genetic anticipation, or population carrier frequency have been established. The original study screened 22 additional compatible families without finding further biallelic PPP1R15B variants, illustrating both rarity and genetic heterogeneity among phenocopies. (abdulkarim2015amissensemutation pages 4-7)
No toxin, infection, diet, occupation, smoking exposure, or lifestyle factor is known to cause MSSGM2. Cellular experiments show that palmitate and pharmacologic ER stressors induce PPP1R15B in β cells, supporting the general concept that metabolic or proteotoxic stress could worsen a genetically reduced stress-response reserve; this has not been demonstrated clinically as a disease-specific gene–environment interaction. (abdulkarim2015amissensemutation pages 7-9)
Because the primary cohorts contain only a few patients, observed fractions must not be interpreted as population frequencies.
| Phenotype | Type, onset, and course | Evidence and impact | Suggested HPO |
|---|---|---|---|
| Microcephaly | Clinical sign; congenital/childhood; persistent | Both original siblings; one male had head circumference 46 cm, approximately −4 SD. The N423D child was −2.60 SD. Associated with developmental disability. | HP:0000252 |
| Short stature/growth retardation | Physical sign; prenatal or early childhood; persistent | Original siblings were small for gestational age; reported adult heights included 155 cm and 139 cm. N423D child: −2.16 SD. | HP:0004322; small for gestational age HP:0001518 |
| Intellectual disability/global developmental delay | Neurodevelopmental sign; childhood; lifelong | Severe in the original family—one individual had an estimated mental age of 5–6 years at age 15. N423D patient had IQ 57. | HP:0001249; HP:0001263 |
| Diabetes mellitus/impaired glucose metabolism | Laboratory abnormality and disease; adolescence–adulthood in the best-documented family | Onset at 15 and 28 years; autoimmune-negative in the index case, with residual C-peptide. One patient presented with ketosis. Insulin treatment affects daily self-care and hypoglycemia risk. | HP:0000819; hyperglycemia HP:0003074; ketosis HP:0001946 |
| Sensorineural hearing impairment | Clinical sign; timing incompletely defined | Neurogenic hearing loss, including 39% loss in one patient; affects communication and education. | HP:0000407 |
| Brain MRI abnormalities | Imaging sign | White-matter rarefaction/delayed myelination and periventricular white-matter hyperintensities; hypoplastic brainstem/spinal cord described at review level. | HP:0002500; HP:0012448 where applicable |
| Skeletal/thoracic findings | Physical signs; developmental | Kyphoscoliosis, pectus excavatum, vertebral abnormalities; potential mobility and respiratory impact not quantified. | HP:0002751; HP:0000767 |
| Dental/hair findings | Physical signs | Oligodontia, dental hypoplasia, and sparse hair. | HP:0000677; HP:0000691; HP:0008070 |
| Endocrine/reproductive findings | Clinical/laboratory signs | Delayed puberty and hypothyroidism appear in later aggregate reviews; individual frequencies are unresolved. | HP:0000823; HP:0000878 |
| Liver disease | Clinical/laboratory/pathology finding | Hepatic fibrosis/cirrhosis is review-reported; patient-level frequency and progression are unresolved. | HP:0001395; HP:0002613 |
Clinical measurements and associated findings come from the original family and 2024 case; broader features such as hypothyroidism and hepatic fibrosis are mainly review-level aggregates. (abdulkarim2015amissensemutation pages 4-7, abdulkarim2015amissensemutation pages 3-4, stone2021monogenicandsyndromic pages 6-8, fatalska2024recruitmentoftrimeric pages 8-10, gobble2025neonatalandsyndromic pages 7-8)
No validated MSSGM2-specific quality-of-life instrument or EQ-5D/SF-36 study exists. Likely burdens include dependence arising from intellectual disability, insulin administration and glucose monitoring, hypoglycemia, hearing impairment, and orthopedic/dental morbidity, but these have not been quantified.
PPP1R15B encodes CReP, a regulatory/targeting subunit that combines with protein phosphatase 1 catalytic subunit to dephosphorylate eIF2α. PPP1R15B is broadly expressed and is prominent in human islets and β cells. (abdulkarim2015amissensemutation pages 4-7)
No validated modifier genes, disease-specific methylation signature, chromosomal rearrangement, copy-number syndrome, somatic variant mechanism, or repeat expansion has been reported.
MSSGM2 is not an infectious, toxic, occupational, radiation-associated, or lifestyle-acquired disease. No causal pathogens or immune triggers are known. Ordinary nutrition, exercise, and avoidance of smoking remain relevant to diabetes care but have not been shown to prevent the underlying syndrome. There are no established environmental protective factors.
Biallelic PPP1R15B variant → defective PP1 or eIF2 recruitment → reduced dephosphorylation of eIF2α-Ser51 → persistent integrated stress response (ISR) and translation repression → defective secretory-cell homeostasis, altered insulin production/secretion, and stress-induced apoptosis → diabetes; impaired growth and neurodevelopment arise from analogous vulnerability during development. (abdulkarim2015amissensemutation pages 1-2, fatalska2024recruitmentoftrimeric pages 10-12, hicks2023theppp1r15family pages 7-9)
The 2024 Molecular Cell study—published February 1, 2024, DOI 10.1016/j.molcel.2023.12.011—is the principal recent advance. It showed that PPP1R15B binds trimeric eIF2 with high affinity independently of PP1 through a substrate-binding region containing helices H1 (residues 424–429) and H2 (472–482). PPP1R15B grasps eIF2 at a site remote from eIF2α-Ser51 and positions that phosphosite for PP1 catalysis. Thus, R658C and N423D converge on the same biochemical endpoint through different upstream defects: deficient enzyme recruitment versus deficient substrate recruitment. (fatalska2024recruitmentoftrimeric pages 10-12, fatalska2024recruitmentoftrimeric pages 3-5)
In INS-1E β cells, approximately 75% PPP1R15B knockdown increased basal phospho-eIF2α and ATF3, lowered insulin content by 20%, and eliminated normal glucose-stimulated insulin secretion. Controls increased secretion 2.8-fold at 16.7 mmol/L glucose, whereas deficient cells showed little response; forskolin-stimulated secretion fell from approximately tenfold to fourfold. Knockdown increased apoptosis by up to 20%, involving intrinsic-pathway BH3-only proteins DP5, PUMA, and BIM. This is cellular perturbation evidence—not direct histology from affected human pancreas. (abdulkarim2015amissensemutation pages 9-11, abdulkarim2015amissensemutation pages 7-9)
No MSSGM2-specific transcriptomic, proteomic, metabolomic, lipidomic, single-cell, spatial-transcriptomic, or integrated multi-omics patient dataset was identified. The available molecular profiling consists chiefly of targeted expression, phosphorylation, secretion, apoptosis, interaction, NMR, HDX-MS, and structural-modeling experiments.
No consistent lateralization has been reported. CNS and growth abnormalities are generalized rather than unilateral.
Growth restriction and microcephaly are congenital or evident early; developmental delay emerges in childhood and remains chronic. Diabetes is not necessarily neonatal: the best-documented patients developed it at 15 and 28 years, and younger reported individuals may not yet have developed hyperglycemia. This implies age-dependent expression of the metabolic component and supports lifelong surveillance. (abdulkarim2015amissensemutation pages 9-11, stone2021monogenicandsyndromic pages 6-8)
No formal stages, remission pattern, median progression rate, or natural-history curve exists. Congenital neurodevelopmental and skeletal findings appear persistent; diabetes is chronic once established. A critical biological period likely exists during prenatal brain and skeletal development, while a practical intervention window exists before metabolic decompensation through periodic glucose/HbA1c surveillance.
Inheritance is autosomal recessive. For two heterozygous parents, each pregnancy has the standard Mendelian expectation of 25% affected, 50% carrier, and 25% unaffected/non-carrier, assuming both variants are fully disease-causing. Both sexes can be affected. (abdulkarim2015amissensemutation pages 4-7, abdulkarim2015amissensemutation pages 3-4)
The literature supports only a handful of affected individuals; no cases-per-100,000 prevalence, annual incidence, sex ratio, geographic distribution, carrier frequency, founder population, or robust penetrance estimate is available. Reviews mention the original affected siblings and four additional patients, while another review describes four patients in two sibling pairs with Arg658Cys; discrepancies and possible overlapping reports make simple summation unsafe. (stone2021monogenicandsyndromic pages 6-8, vaneynde2022theroleof pages 6-7)
Expressivity is variable, especially for age at diabetes onset and multisystem complications. Apparent nonpenetrance of diabetes in children may instead be age dependence. Genetic anticipation is not expected for missense alleles and has not been observed.
CMA is appropriate when a broader developmental phenotype suggests a copy-number disorder but will generally not detect single-nucleotide PPP1R15B variants. Karyotype, FISH, mitochondrial DNA, and repeat-expansion testing are not first-line MSSGM2 tests unless another diagnosis is suspected.
No consensus diagnostic criteria or newborn biochemical screen exists. Cascade testing is indicated after a familial variant is established.
No 5- or 10-year survival, life-expectancy, mortality, hospitalization, or standardized disability data exist. The original affected siblings survived into their late twenties/early thirties, showing that p.Arg658Cys is compatible with adulthood despite substantial neurodevelopmental and metabolic morbidity. (abdulkarim2015amissensemutation pages 4-7)
Major long-term burdens likely include lifelong intellectual/developmental disability, insulin-treated diabetes and hypoglycemia, hearing impairment, skeletal deformity, and possible hepatic/endocrine complications. Frequent hypoglycemia was reported in the index patient. Prognostic factors and biomarkers have not been validated; genotype, residual phosphatase activity, developmental severity, and onset of liver disease or diabetes are plausible but unproven predictors. (abdulkarim2015amissensemutation pages 9-11)
There is no approved disease-modifying therapy, gene therapy, RNA therapy, cell therapy, or MSSGM2-specific interventional trial in the retrieved literature or ClinicalTrials.gov search.
Current real-world management is phenotype-directed:
Suggested NCIt concepts include Insulin Therapy, Genetic Counseling, Physical Therapy, Occupational Therapy, Speech Therapy, and Hearing Aid, but no MSSGM2-specific NCIt intervention term was verified.
Pharmacologic manipulation of PPP1R15 proteins or the ISR remains experimental and directionally complex. In MSSGM2, phospho-eIF2α is already excessive; PPP1R15B inhibitors such as Raphin1 would therefore be mechanistically concerning rather than rational treatment candidates. Reviews also emphasize controversy over the direct targets of guanabenz/Sephin1-class compounds. No efficacy or safety data exist in affected patients. (hicks2023theppp1r15family pages 7-9)
The molecular disorder cannot presently be prevented by vaccination, diet, or exposure avoidance.
Population newborn screening is not currently justified by available prevalence or treatment evidence. Targeted cascade screening is appropriate in an affected family.
No naturally occurring veterinary MSSGM2 analogue, breed association, zoonotic transmission, or cross-species infectious susceptibility is known. PPP1R15B orthologues are evolutionarily conserved in vertebrates, consistent with the conservation of eIF2α stress signaling. Relevant taxa include human NCBI Taxon 9606 and laboratory mouse NCBI Taxon 10090. Exact orthologue NCBI Gene identifiers should be imported from the current NCBI/Alliance release.
Constitutive Ppp1r15b/CReP knockout mice are approximately half normal size at birth, pale, fail to nurse, and die neonatally; none in the cited series survived beyond postnatal day 1. Their severe phenotype includes hematopoietic defects and demonstrates that complete loss is more damaging than the surviving human hypomorphic missense alleles. Genetic reduction of phosphorylatable eIF2α through an eIF2α-Ser51 alteration rescued body size and red-cell counts, strongly supporting excessive eIF2α phosphorylation as the causal axis. (hicks2023theppp1r15family pages 7-9)
These systems are valuable for variant interpretation and ISR-target discovery but do not reproduce human brain development, lifelong metabolic progression, or whole-organism dosage effects. No patient-derived iPSC, cerebral organoid, pancreatic organoid, zebrafish, Drosophila, or CRISPR knock-in MSSGM2 model was identified.
The disease evidence is dominated by small human case series plus strong functional validation. The most important recent advance is not a large clinical cohort but the 2024 resolution of how PPP1R15B recruits intact eIF2 and how distinct disease alleles disrupt either enzyme or substrate engagement. This strengthens the causal interpretation of PPP1R15B variants while also showing why variant-specific functional assays are necessary. The 2025 syndromic-diabetes review continues to characterize MSSGM2 as a rare autosomal-recessive disorder with late-onset impaired glucose metabolism and multisystem involvement, but it supplies no new natural-history cohort or treatment trial. (gobble2025neonatalandsyndromic pages 7-8, fatalska2024recruitmentoftrimeric pages 10-12)
References
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