Noonan Syndrome 11 (NS11): MRAS-Related Noonan Syndrome — Comprehensive Research Report

Target entity: Noonan syndrome 11 (NS11), OMIM #618499, MONDO:0032786, caused by germline heterozygous activating (gain-of-function) missense variants in MRAS (HGNC:7227, OMIM *608435, chromosome 3q22.3), encoding the atypical RAS-family GTPase M-Ras (also called R-Ras3). This report excludes LZTR1-Noonan syndrome and all other numbered Noonan syndrome types.

1. Disease Information

Overview. Noonan syndrome 11 (NS11) is an ultra-rare, autosomal dominant RASopathy caused by de novo (in essentially all reported cases) germline gain-of-function missense variants in MRAS. It presents with the core Noonan syndrome triad — short stature, characteristic facial dysmorphism, and congenital heart disease — but is distinguished from other Noonan subtypes by an unusually high, near-obligate rate of hypertrophic cardiomyopathy (HCM), which in the published cohort has been essentially universal (reported in 100% of the small number of confirmed cases) (OMIM #618499; Motta et al. 2020, Hum Mol Genet 29:1772–1783, PMID:31108500). MRAS was established as a Noonan-susceptibility gene by Higgins et al. in 2017 via mutational screening of 109 unrelated Noonan-syndrome-with-cardiac-hypertrophy probands, of whom molecularly confirmed MRAS variants were found in a small subset (Higgins et al. 2017, JCI Insight 2(5):e91225, PMCID:PMC5333962).

Key identifiers: - OMIM phenotype: #618499 — NOONAN SYNDROME 11; NS11 - OMIM gene: 608435 — MUSCLE RAS VIRAL ONCOGENE HOMOLOG; MRAS - MONDO: MONDO:0032786 - HGNC: HGNC:7227 (MRAS); NCBI Gene ID: 22808 - Parent concept ICD-10/11: Noonan syndrome codes (Q87.1x, RASopathy group); no MRAS-specific ICD code exists - MeSH: Noonan Syndrome (D009634); no separate MeSH term for NS11 - Orphanet: cross-referenced under the general Noonan syndrome gene list (Orphanet MRAS) - ClinGen gene-disease validity: Moderate** (as of the RASopathy Gene Curation Expert Panel assessment), meaning the strongest classification a variant can currently receive is "Likely Pathogenic" rather than "Pathogenic" under strict ClinGen/ACMG rules, reflecting the still-small number of published cases (ClinGen RASopathy curation; PMC12151217) — note individual ClinVar submissions for specific variants (e.g., p.Gly23Val) have nonetheless reached "Pathogenic," 2-star review status (ClinVar RCV000787303).

Synonyms/alternative names: Noonan syndrome type 11; NS11; MRAS-related Noonan syndrome; MRAS-associated RASopathy. Gene aliases: M-Ras, R-Ras3, RRAS3.

Evidence base composition. Essentially all available data for NS11 specifically come from individual, molecularly confirmed patient case reports and small case series (fewer than ten published probands as of early 2026), supplemented by cell-based and iPSC-derived functional/mechanistic studies of the specific variants. There is no disease registry, no large aggregated cohort, and no epidemiological database entry specific to NS11 — all prevalence/frequency figures for MRAS-NS are extrapolated from this very small case literature, not population-level aggregation.

2. Etiology

Disease causal factor. NS11 is caused exclusively by germline heterozygous, de novo (with rare exception) missense gain-of-function variants in MRAS, which constitutively activate M-Ras GTPase signaling. There is no known environmental, infectious, or multifactorial contribution to primary disease causation — this is a monogenic RASopathy.

Genetic risk factors. - Causal variant hotspots cluster in two structurally critical regions of M-Ras: - Gly23 (P-loop/phosphate-binding loop, analogous to Gly12/13 of classical RAS): p.Gly23Val (c.68G>T) — the index Higgins et al. 2017 mutation; p.Gly23Arg (c.67G>C) — reported by Motta et al. 2020 in a fatal neonatal case. - Thr68 (switch II region): p.Thr68Ile (c.203C>T) — reported by Motta et al. 2020 and subsequently the most recurrent MRAS-NS variant, accounting for the majority (up to ~5 of 8) of published cases including the first reported adult and the first infective-endocarditis case (PMC12794993; Priolo et al. 2023, PMID:36734411). - Gln71 (switch II region, structurally equivalent to the classic oncogenic Gln61 hotspot of HRAS/KRAS/NRAS): p.Gln71Arg (c.212A>G) — reported by Suzuki et al. 2019 in a patient with a particularly severe phenotype including HCM (Suzuki et al. 2019, Am J Med Genet A 179:1628–1630, PMID:31173466). - All variants reported to date have been de novo; no transmission from an affected parent has yet been documented in the literature (consistent with the severity of the cardiac phenotype limiting reproductive fitness in some cases), though autosomal dominant transmission (50% recurrence risk to offspring of an affected individual) is the expected Mendelian pattern for any surviving proband (GeneReviews: Noonan Syndrome, NBK1124). - No allele-frequency data exist in gnomAD for any pathogenic MRAS-NS variant (all absent from >280,000 alleles), consistent with de novo occurrence and negative selection against germline transmission of a severe cardiac phenotype (Higgins et al. 2017). - Somatic parallel: Gln71 of MRAS is the direct structural homolog of Gln61 in classical RAS oncoproteins, a well-known oncogenic hotspot in human cancers — underscoring that the same activating biochemistry (impaired intrinsic and GAP-stimulated GTP hydrolysis) drives both germline RASopathy and somatic oncogenesis at this residue (Suzuki et al. 2019).

Environmental/lifestyle risk factors: None established. As with other RASopathies, advanced paternal age has been proposed as a general risk factor for de novo variants in Noonan syndrome broadly, but this has not been specifically documented across the small MRAS-NS case series.

Protective factors: None identified; no protective genetic modifiers or environmental protective factors have been described for MRAS-NS specifically.

Gene-environment interactions: Not established for NS11.

3. Phenotypes

Because MRAS-NS has been reported in fewer than ten molecularly confirmed individuals, phenotype "frequencies" below are drawn from case aggregation rather than population statistics, and should be interpreted with that caveat.

Cardiovascular (dominant/defining phenotype)

The Motta et al. 2020 paper explicitly frames these as "the third and fourth known cases" of MRAS-NS, both presenting with severe cardiac hypertrophy; one (p.Gly23Arg) died at two months of age of cardiac failure, underscoring the risk of a severe, early-lethal phenotype at this locus (PMID:31108500). In contrast, Priolo et al. 2023 reported the first adult with a p.Thr68Ile variant and only mild, late-onset left ventricular hypertrophy, demonstrating that HCM is not obligatorily early-onset or lethal in this gene, and broadening the recognized phenotypic spectrum (PMID:36734411). A 2025/2026 case report described the first infective endocarditis complicating MRAS-NS HCM (a 22-year-old woman with p.Thr68Ile presenting with fever and a 19 mm LVOT vegetation, Streptococcus mutans bacteremia) (PMC12794993). Antenatally, a 2026 literature review (Martineau et al.) described the first case with severe early antenatal manifestations: increased nuchal translucency, ductus venosus agenesis, pulmonary lymphangiectasia, and complex hepatic vascular anomalies, with autopsy confirming HCM plus obliterative portal venopathy and lymphangiectasia (Martineau et al. 2026, Prenatal Diagnosis, DOI:10.1002/pd.70134).

Craniofacial/dysmorphic

• Characteristic Noonan facial gestalt: hypertelorism, downslanting palpebral fissures, low-set/posteriorly rotated ears (HP:0000368), ptosis — reported across cases (e.g., "low set and mildly posteriorly angulated ears" in Higgins et al.'s second patient).
• Suggested HPO terms: HP:0000280 (Coarse facial features, when applicable), HP:0000582 (Upslanted palpebral fissure)/HP:0000494 (downslanted), HP:0000369 (Low-set ears).

Growth

• Short stature (HP:0004322) documented in reported adult cases (e.g., 150 cm/37 kg in the endocarditis case report).

Skeletal

• Mild pectus excavatum reported in at least one case (HP:0000767).

Neurodevelopmental

• Developmental delay/cognitive disability reported across multiple cases, ranging from mild learning difficulties (Priolo adult case; endocarditis case: "childhood learning difficulties") to more pronounced cognitive impairment and hypotonia with delayed independent walking (achieved at 2.5 years) in pediatric cases (Higgins et al. 2017).
• Priolo et al. 2023 specifically highlighted neuropsychiatric features as an under-recognized adult-onset component of the MRAS-NS phenotype, expanding beyond the classically emphasized cardiac phenotype.
• Suggested HPO terms: HP:0001263 (Global developmental delay), HP:0001249 (Intellectual disability), HP:0001252 (Hypotonia).

Quality of life impact

No disease-specific EQ-5D/SF-36/PROMIS data exist for MRAS-NS. Qualitatively, the severe pediatric cardiac phenotype carries substantial early mortality risk and functional burden (heart failure, cardiac surgery/myectomy as in the Higgins index case), while the milder adult-onset presentations described by Priolo et al. suggest a meaningfully better prognosis is possible depending on variant and individual course.

4. Genetic/Molecular Information

Causal gene: MRAS (HGNC:7227; NCBI Gene 22808; OMIM *608435), chromosome 3q22.3.

Gene/protein function. MRAS encodes M-Ras (also called R-Ras3), a member of the atypical RAS subfamily of small GTPases (distinct from, but ~55% identical to, the classical RAS proteins HRAS/KRAS/NRAS). Like classical RAS, M-Ras is a GDP/GTP-binding molecular switch, post-translationally modified at a C-terminal CaaX motif by geranylgeranylation (in combination with a polybasic region) for membrane targeting (GeneCards MRAS). In its active, GTP-bound state, M-Ras assembles — together with the scaffold protein SHOC2 and the catalytic subunit of protein phosphatase 1 (PP1C, isoforms PPP1CA/B/C) — into the SHOC2–MRAS–PP1C (SMP) holoenzyme complex, which specifically dephosphorylates an inhibitory serine residue on RAF kinases (Ser259 on CRAF/RAF1; Ser365 on BRAF). This dephosphorylation partially displaces inhibitory 14-3-3 binding and promotes RAF–RAS association and active RAF dimer formation, thereby positively regulating RAF/MEK/ERK (MAPK) signaling (Kwon et al. 2018, PNAS, PMID:30348783; Kwon et al. 2022, Nature, PMID:35830882; Bonsor et al. 2022, Nat Struct Mol Biol, PMID:36175670). MRAS acts both as a regulatory subunit conferring RAF specificity to PP1C and as a membrane-targeting subunit, since membrane localization is required for efficient RAF dephosphorylation. The SMP complex forms preferentially when MRAS is GTP-loaded (active), and structural work shows that both RASopathy and cancer mutations in SHOC2, MRAS, and PPP1CB map to protein–protein interfaces within this holophosphatase, enhancing ternary complex formation. M-Ras also modulates AKT/PI3K signaling and, outside this RASopathy context, has documented roles in TNFα-stimulated LFA-1 activation and integrin-mediated leukocyte adhesion, and (via GWAS) a coronary artery disease susceptibility locus (Shah 2024, IUBMB Life).

Pathogenic variants (all reported to date):

Variant classification (ACMG/ClinVar): p.Gly23Val is classified Pathogenic (2-star review status, 5 concordant submitters including OMIM, Baylor Genetics, 3billion, Eurofins-Biomnis, NCGM) for Noonan syndrome 11 (ClinVar RCV000787303). Gene-level, ClinGen's RASopathy expert panel rates the MRAS–Noonan syndrome relationship as Moderate, capping individual variant classifications at "Likely Pathogenic" under strict ClinGen rules pending further case accrual (PMC12151217).

Variant type/class: All reported variants are missense, clustering at two structurally critical GTPase regions (P-loop and switch II) — no frameshift, nonsense, splice-site, or structural (CNV) MRAS variants have been reported in NS11.

Functional consequences — gain of function / constitutive activation. Multiple orthogonal functional studies converge on a gain-of-function mechanism: - GTP loading: p.Gly23Val shows a ~40-fold increase in GTP loading relative to wild-type MRAS following EGF stimulation, measured by GST-Raf-RBD pulldown (Ras activation assay) (Higgins et al. 2019, Circ Genom Precis Med 12:e002648). - Impaired GTP hydrolysis: Structural modeling shows p.Gly23 mutations cause steric clashes in the phosphate-binding loop impairing GAP-stimulated GTP hydrolysis; p.Thr68Ile strengthens switch-region interactions to stabilize the active conformation; p.Gln71Arg (structurally homologous to the classical oncogenic Q61R) is predicted to drastically slow intrinsic GTP hydrolysis, by analogy to NRAS Q61R kinetics (Suzuki et al. 2019; Motta et al. 2020). - Enhanced downstream signaling: p.Gly23Val and p.Thr68Ile/p.Gly23Arg show enhanced ERK phosphorylation (context-dependent — weak in HEK293T, robust in Neuro2A cells) and enhanced AKT phosphorylation at basal and stimulated levels (Motta et al. 2020). - Enhanced complex formation: Co-immunoprecipitation shows augmented binding of mutant MRAS to SHOC2 and PPP1CB, consistent with enhanced SMP holophosphatase assembly and consequent RAF activation (Motta et al. 2020; mechanistically consistent with Kwon et al. 2018, PMID:30348783). - Constitutive membrane targeting: Mutant MRAS shows persistent GTP-bound state and constitutive plasma membrane localization/prolonged non-raft microdomain localization post-EGF stimulation, compared to transient wild-type localization.

Germline vs. somatic: All reported NS11 variants are germline. The structurally homologous Gln61 position in classical RAS genes is a well-known somatic oncogenic hotspot in various cancers, and Suzuki et al. explicitly frame Q71R as "a recurrent substitution in RAS homologs in various cancers," highlighting shared biochemistry between germline RASopathy and somatic oncogenesis, though MRAS itself is not a common somatic cancer driver.

Modifier genes: None specifically identified for MRAS-NS; general RASopathy modifier-gene research (e.g., variability in PTPN11-Noonan syndrome) has not been extended to this ultra-rare subtype.

Epigenetic information: No MRAS-NS-specific epigenetic (DNA methylation/histone) studies have been published.

Chromosomal abnormalities: None — NS11 is caused by point missense variants, not chromosomal rearrangements.

5. Environmental Information

No environmental, occupational, toxin, infectious, or lifestyle factors have been implicated in the causation of NS11; it is a purely monogenic disorder. There is no known infectious trigger. (The infective endocarditis reported in one adult case is a secondary complication of the pre-existing HCM/LVOT anatomical substrate — caused by Streptococcus mutans bacteremia — not an etiological infectious agent for the syndrome itself) (PMC12794993).

6. Mechanism / Pathophysiology

Causal chain (numbered, from initiating lesion to clinical manifestation)

1. A de novo germline missense variant in MRAS (at Gly23, Thr68, or Gln71) leads to structural disruption of the GTPase P-loop or switch II region of M-Ras (demonstrated: molecular dynamics simulations; structural modeling).
2. This structural change results in impaired intrinsic and GAP-stimulated GTP hydrolysis and/or enhanced nucleotide exchange, leading to a constitutively/predominantly GTP-bound, active state of M-Ras (demonstrated: ~40-fold increased GTP loading for p.Gly23Val in cell-based Ras-activation assays).
3. GTP-bound mutant M-Ras shows increased/constitutive plasma-membrane targeting and prolonged localization to signaling microdomains post-growth-factor stimulation (demonstrated in HEK293T/COS-1 cells).
4. Active, membrane-localized mutant M-Ras drives enhanced assembly of the SHOC2–MRAS–PP1C (SMP) holophosphatase complex, evidenced by augmented co-immunoprecipitation of mutant MRAS with SHOC2 and PPP1CB (demonstrated in cell-based binding assays).
5. The SMP complex dephosphorylates the inhibitory serine on RAF kinases (Ser259-CRAF/Ser365-BRAF), leading to partial displacement of inhibitory 14-3-3 binding and promotion of RAF–RAS association and active RAF dimer formation (mechanistically demonstrated by cryo-EM/X-ray structural studies of the SMP complex, largely in non-disease-specific but directly relevant biochemical systems — inferred to apply to the disease variants by structural mapping of RASopathy mutations to SMP interfaces).
6. Activated RAF drives hyperactivation of the canonical MEK–ERK (MAPK) cascade, with additional enhancement of AKT/PI3K signaling observed for MRAS mutants (demonstrated: increased basal and EGF-stimulated pERK and pAKT in transfected cells; context-dependent magnitude — weaker in HEK293T, robust in Neuro2A neuronal-lineage cells, suggesting cell-type-specific downstream consequences that may partly explain both the cardiac and neurodevelopmental phenotype).
7. In cardiomyocytes specifically, chronic RAF/MEK/ERK (and AKT) pathway hyperactivation leads to pathological cardiomyocyte hypertrophy — directly demonstrated in patient-specific and CRISPR-corrected iPSC-derived cardiomyocytes, in which cells carrying p.Gly23Val-MRAS were significantly larger than isogenic controls and showed altered hypertrophy-associated gene expression and intracellular signaling (Higgins et al. 2019, PMID pending / DOI:10.1161/CIRCGEN.119.002648).
8. Cardiomyocyte hypertrophy at the tissue level manifests clinically as hypertrophic cardiomyopathy, in some cases with left ventricular outflow tract obstruction (systolic anterior motion of the mitral valve), progressing in severe neonatal cases to heart failure and death, or in milder/later-onset cases to a stable or slowly progressive adult HCM phenotype (this step — from cellular hypertrophy to organ-level HCM and its clinical severity spectrum — is directly demonstrated at the clinical/imaging level across the case series but the determinants of severity, e.g., variant identity, genetic background, or developmental timing of pathway hyperactivation, remain inferred rather than mechanistically established).
9. In parallel, RAS/MAPK pathway hyperactivation during development is inferred (by analogy with other Noonan-syndrome genes, not MRAS-specific data) to drive the craniofacial dysmorphism, growth impairment, and neurodevelopmental phenotype characteristic of Noonan syndrome broadly, via effects on cranial neural crest, growth plate, and neuronal signaling — this branch is extrapolated from the general RASopathy paradigm rather than demonstrated with MRAS-specific developmental data, since no MRAS-NS animal model publications currently exist.

Molecular pathways

• RAS/MAPK (RAF–MEK–ERK) pathway — the central, disease-defining pathway; MRAS acts non-canonically (not as a classical RAS effector-activator, but via the SMP holophosphatase mechanism that removes an inhibitory RAF phosphorylation) ([KEGG hsa04014 Ras signaling pathway]; [Reactome RAF/MAP kinase cascade]).
• PI3K–AKT pathway — secondarily hyperactivated by mutant MRAS.
• Suggested GO terms: GO:0007265 (Ras protein signal transduction), GO:0000165 (MAPK cascade), GO:0004725 (protein tyrosine phosphatase activity — for the PP1C dephosphorylation step, though PP1C is a serine/threonine phosphatase, more precisely GO:0004722, protein serine/threonine phosphatase activity), GO:0007172 (signal complex assembly).

Cellular processes

• Pathological cardiomyocyte hypertrophy (increased cell size, altered sarcomeric/hypertrophy gene expression) — directly demonstrated in iPSC-CM model.
• Altered cell proliferation/growth signaling more broadly (inferred from general RAS/MAPK biology).
• Suggested GO term: GO:0003300 (cardiac muscle hypertrophy) / GO:0014897 (striated muscle hypertrophy).

Protein dysfunction

• Gain of function via impaired intrinsic/GAP-stimulated GTPase activity, not loss of function or simple overexpression — a qualitative, not merely quantitative, defect (structurally analogous to but biochemically distinct from classical RAS G12/G13/Q61 oncogenic mutations).

Tissue damage mechanisms

• Not primarily degenerative; the cardiac pathology is a hypertrophic/hyperplastic remodeling response to chronic pathway hyperactivation rather than oxidative/ischemic/fibrotic injury, though secondary myocardial fibrosis may occur in longstanding HCM (as in other HCM etiologies; not specifically documented for MRAS-NS in the literature reviewed).

Molecular profiling / omics

No published transcriptomic, proteomic, metabolomic, lipidomic, single-cell, or spatial-omics datasets specific to MRAS-NS patient tissue were identified in this search. The iPSC-CM study by Higgins et al. 2019 did report gene expression changes characteristic of cardiac hypertrophy in mutant vs. corrected isogenic lines, but did not perform genome-wide profiling per the available summary.

Structural biology

Cryo-EM and X-ray crystallography have resolved the SHOC2–MRAS–PP1C (SMP) holoenzyme structure, showing a crescent-shaped SHOC2 scaffold that bridges MRAS and PP1C into a cooperative, GTP-state-dependent assembly (Kwon et al. 2022, Nature, PMID:35830882; Bonsor et al. 2022, Nat Struct Mol Biol, PMID:36175670; Young/Hall 2022, PMID:35768504). These structures show that RASopathy mutations (in SHOC2, MRAS, and PPP1CB alike) map to protein-protein interfaces within the complex, increasing affinity and enhancing constitutive RAF dephosphorylation — providing the direct structural rationale for the NS11 disease mechanism.

7. Anatomical Structures Affected

Organ level: - Primary: Heart (myocardium — ventricular septum and free wall hypertrophy; LVOT). UBERON:0000948 (heart), UBERON:0002012 (ventricle). - Secondary: Craniofacial skeleton (dysmorphic features), growth plate (short stature), central nervous system (developmental delay/cognitive impairment), skeletal system (pectus deformity). - Body systems: Cardiovascular (primary), musculoskeletal, nervous/neurodevelopmental, and (in the severe antenatal case) lymphatic/hepatic vascular systems (pulmonary lymphangiectasia, hepatic vascular anomalies, obliterative portal venopathy).

Tissue/cell level: - Cardiac muscle tissue — cardiomyocytes (CL:0000746) are the principal affected cell type, directly demonstrated by iPSC-CM hypertrophy modeling. - Cranial neural crest-derived tissues (craniofacial dysmorphism) — inferred by analogy to general Noonan syndrome pathogenesis, not MRAS-specific data.

Subcellular level: - Plasma membrane (site of M-Ras geranylgeranylation-dependent localization and SMP complex assembly) — GO:0005886 (plasma membrane), GO:0031234 (extrinsic component of cytoplasmic side of plasma membrane). - Cytoplasmic signaling complexes (SHOC2–MRAS–PP1C holoenzyme).

Localization: Cardiac hypertrophy is typically biventricular or predominantly left ventricular/septal, sometimes with LVOT obstruction; no consistent laterality pattern reported (not applicable to a diffuse myocardial process).

8. Temporal Development

Onset: Highly variable — this is one of the most striking features of MRAS-NS reported to date. - Prenatal/antenatal: Severe cases detectable in utero (increased nuchal translucency, ductus venosus agenesis, fetal HCM) — reported by Martineau et al. 2026. - Neonatal/infantile: Severe biventricular HCM, sometimes fatal within months (Motta et al. 2020, p.Gly23Arg patient died at 2 months). - Childhood: Cardiac hypertrophy diagnosed in infancy with later surgical myectomy (Higgins et al. 2017 index case, surgery at age 8). - Adult-onset: Mild, late-onset left ventricular hypertrophy first reported by Priolo et al. 2023 in a p.Thr68Ile carrier — demonstrating the phenotypic spectrum extends into adulthood-onset, non-lethal disease.

Onset pattern: Insidious/chronic for the cardiac hypertrophy in mild cases; can be acute/rapidly progressive to heart failure in severe neonatal cases.

Progression: Ranges from rapidly progressive and fatal (neonatal HCM with heart failure) to stable/mild and slowly progressive (adult-onset LVH). No formal staging system exists for NS11-specific HCM; standard HCM staging concepts (from general cardiomyopathy literature) would apply clinically but have not been validated in this gene-specific population.

Disease course pattern: Chronic, generally non-remitting for the cardiac and dysmorphic features (structural, not relapsing-remitting); neurodevelopmental features are typically stable/lifelong rather than progressive.

Critical periods: The prenatal/perinatal period appears to represent a critical window of vulnerability for the most severe cardiac and lymphatic/vascular manifestations, based on the most severely affected reported cases (fatal neonatal HCM; antenatal multi-system anomalies). This suggests a potential window for prenatal/early therapeutic intervention (e.g., MEK inhibition), analogous to approaches used in other severe neonatal Noonan-HCM genotypes (RAF1, RIT1, SOS1) — though this has not yet been reported for MRAS specifically.

9. Inheritance and Population

Epidemiology: No disease-registry or population-based prevalence/incidence estimate exists for NS11 specifically; it is an ultra-rare Noonan syndrome subtype. General Noonan syndrome (all genes combined) has an estimated incidence of 1:1,000 to 1:2,500 live births (with milder undiagnosed presentations potentially as common as 1:100) (GeneReviews NBK1124). MRAS accounts for only a small fraction of molecularly diagnosed Noonan syndrome (well under 1% based on published mutational-screening yield: Higgins et al. found MRAS variants in a small subset of 109 unrelated Noonan-with-cardiac-hypertrophy probands screened). As of the most recent comprehensive literature review (Martineau et al. 2026), fewer than eight molecularly confirmed cases have been published worldwide.

Inheritance pattern: Autosomal dominant, consistent with other Noonan syndrome genes; all reported cases to date are de novo.

Penetrance: Appears to be high/complete for the core Noonan phenotype among reported cases, though ascertainment bias (severe cases more likely to be sequenced and published) cannot be excluded given the very small numbers.

Expressivity: Markedly variable, spanning fatal neonatal HCM to mild adult-onset LVH — among the most variable expressivity reported for any single Noonan-syndrome gene, and a key point emphasized by Priolo et al. 2023.

Genetic anticipation: Not applicable/not reported (not a repeat-expansion disorder).

Germline mosaicism: Not specifically documented for MRAS to date, though theoretically possible as for other autosomal dominant de novo conditions; genetic counseling for future pregnancies of unaffected parents of an affected child should still account for a low empiric recurrence risk due to possible parental gonadal mosaicism, per general Noonan syndrome counseling practice.

Founder effects: None identified; reported probands are of diverse ancestries (North African Jewish, German, Japanese, and others), and each mutation site (Gly23, Thr68, Gln71) has arisen independently and recurrently, consistent with mutational hotspots rather than a single founder allele.

Consanguinity: Not implicated (dominant, de novo mechanism).

Carrier frequency: Not applicable (not a recessive/carrier-based condition).

Population demographics: No specific ethnic or geographic enrichment identified; case reports span Europe (France/Italy — Motta et al., Priolo et al.), the Middle East/North Africa, Japan (Suzuki et al.), and other regions, consistent with pan-ethnic occurrence typical of de novo dominant conditions.

Sex ratio: No clear sex bias apparent from the small case series (both male and female probands reported); too few cases for statistical inference.

Age distribution: Bimodal-appearing in the literature — a cluster of severe pediatric/neonatal presentations and a smaller but growing recognition of mild adult presentations, likely reflecting both true biological variability and historical ascertainment bias toward the most severe (most readily diagnosed) cases.

10. Diagnostics

Clinical/laboratory tests: No MRAS-NS-specific biomarker exists. Standard Noonan syndrome/HCM diagnostic workup applies: echocardiography (initial and primary imaging modality for HCM detection — LOINC/RadLex imaging codes apply generically), cardiac MRI (used in at least one reported case for detailed characterization of wall hypertrophy and LVOT obstruction), and standard HCM-associated laboratory studies (BNP/NT-proBNP, troponin) as clinically indicated (not specifically reported in the MRAS-NS literature reviewed).

Genetic testing: - Recommended approach: Given the phenotypic overlap across Noonan-syndrome genes, testing is typically performed via a multi-gene RASopathy/Noonan syndrome panel (including PTPN11, SOS1, RAF1, RIT1, KRAS, NRAS, BRAF, MRAS, LZTR1, SHOC2, PPP1CB, CBL, etc.) or exome/genome sequencing, rather than single-gene MRAS testing as first-line, given MRAS's rarity as a cause. - Whole exome sequencing (WES) was the discovery method for the index Higgins et al. 2017 case (trio-based WES with genomic triangulation) and has been used in subsequent cases. - Single-gene MRAS testing is appropriate as a targeted confirmatory test once a specific familial variant or a strong phenotype-driven hypothesis (e.g., severe HCM + Noonan features with panel-negative results for more common genes) is present, or for prenatal confirmation when a fetal variant is suspected. - Prenatal diagnostic testing of Noonan syndrome gene panels (including MRAS) in fetuses with abnormal ultrasound findings (increased nuchal translucency, cystic hygroma, polyhydramnios, cardiac anomalies) is an established approach in the field generally (Nature EJHG 2012285) and was applied in the Martineau et al. 2026 antenatal MRAS case. - Chromosomal microarray/karyotype/FISH: Not diagnostic for NS11 (a point-mutation disorder), but are typically performed as part of standard prenatal/postnatal differential diagnostic workup to exclude chromosomal causes of overlapping phenotypes (e.g., Turner syndrome, which shares some prenatal ultrasound findings) before or alongside gene panel testing.

Clinical diagnostic criteria: No MRAS-specific clinical criteria exist. Diagnosis follows the general Noonan syndrome approach: clinical suspicion based on characteristic facial features, cardiac defects (with unusually high suspicion warranted when HCM specifically, rather than pulmonic stenosis, is the presenting cardiac lesion), and short stature, confirmed by identification of a heterozygous pathogenic/likely pathogenic variant in a Noonan-syndrome-associated gene (GeneReviews NBK1124).

Differential diagnosis: Other Noonan syndrome genotypes (particularly RAF1 and RIT1, which also show elevated HCM rates among Noonan genes), other RASopathies (Costello syndrome, cardiofaciocutaneous syndrome), and non-syndromic/isolated familial HCM (sarcomeric gene panel-negative cases with subtle dysmorphism should prompt RASopathy panel testing).

Screening: No population-based newborn or carrier screening program exists for MRAS-NS given its extreme rarity and de novo inheritance pattern; case-finding is driven by clinical phenotype recognition (particularly early/severe HCM with dysmorphic features) followed by genetic testing.

11. Outcome/Prognosis

Survival/mortality: Highly variable and strongly dependent on age of onset and severity of cardiac involvement: - Severe neonatal presentations carry a poor prognosis: the Motta et al. 2020 p.Gly23Arg patient died of cardiac failure at 2 months of age. This mirrors the broader Noonan-syndrome-with-neonatal-HCM literature, where infants under 6 months with HCM and congestive heart failure have historically had a ~34% one-year survival rate across Noonan syndrome genotypes generally (not MRAS-specific figure) (Mount Sinai/ScienceDaily coverage of MEK-inhibitor trial). - Milder/adult-onset presentations (Priolo et al. 2023; the endocarditis case) show that survival into adulthood with a good functional status is achievable, particularly with the recurrent p.Thr68Ile variant in some individuals. - No formal disease-specific survival curves or life-expectancy tables exist given the small case numbers.

Morbidity/complications: - Heart failure (severe cases). - LVOT obstruction requiring surgical intervention (septal myectomy performed in the Higgins et al. index case at age 8). - Infective endocarditis as a newly recognized complication of the LVOT/HCM anatomical substrate in adult MRAS-NS (first reported 2025/2026). - Developmental/cognitive morbidity ranging from mild learning difficulty to more significant intellectual disability.

Recovery potential: Surgical myectomy has provided symptomatic benefit in at least one reported case; no MRAS-NS-specific data exist on pharmacological (e.g., MEK-inhibitor) reversal of HCM, though this is mechanistically plausible and has been demonstrated in other Noonan-syndrome genotypes (see Treatment section).

Prognostic factors: Variant identity appears to correlate loosely with severity in the small case series (the two Gly23 variants — G23V, G23R — and Q71R associate with the most severe pediatric presentations reported to date, while T68I has been associated with both severe pediatric and the mildest reported adult presentation), but this is not a robust, statistically validated genotype-severity correlation given the tiny sample size — Priolo et al. explicitly caution against assuming obligate severe HCM for any MRAS variant.

Prognostic biomarkers: None established specific to MRAS-NS.

12. Treatment

Pharmacotherapy — targeted RAS/MAPK pathway inhibition (most significant emerging therapeutic direction): - MEK inhibitors (e.g., trametinib) have been used successfully as targeted, mechanism-based therapy to reverse or ameliorate hypertrophic cardiomyopathy in other Noonan-syndrome genotypes with RAS/MAPK pathway hyperactivation — RAF1, RIT1, and SOS1 — with dramatic reduction in ventricular wall thickness and improved clinical status reported within months of treatment initiation (Gross et al. 2019/2022 case reports; PMC6916648; [RIT1 MEK-inhibition case, PMID:36184070]). Because MRAS-NS-associated HCM shares the identical downstream mechanism (RAF/MEK/ERK hyperactivation via the SMP holophosphatase), MEK inhibition is a mechanistically strongly rationalized candidate therapy for MRAS-NS HCM, though no MRAS-NS-specific trametinib case has yet been published in the literature surveyed here — this represents an important treatment gap/opportunity given the severity of neonatal presentations. Suggested NCIT term: NCIT:C15632 (Chemotherapy) is too broad/inaccurate; the more appropriate NCIT category is NCIT:C93352 (Targeted Therapy) or NCIT:C15986 (Pharmacotherapy) with therapeutic_agent bound to trametinib (NCIT:C77908, if curating). - Growth hormone therapy is FDA-approved and effective for short stature in Noonan syndrome generally (not MRAS-specific efficacy data, but the mechanism and approval apply across genotypes), with height SDS improvements of roughly +0.7 to +1 SD over 3 years of therapy reported in general Noonan syndrome GH trials ([Romano et al. 2010, Pediatrics 126:746–759]; PMC8999676). Caution: GH stimulates the RAS/MAPK pathway itself, so cardiac status (especially HCM) must be carefully evaluated and monitored before and during GH therapy in any Noonan syndrome patient, a consideration of particular relevance given MRAS-NS's high HCM prevalence.

Surgical/interventional: - Septal myectomy for LVOT obstruction — performed in the Higgins et al. index patient at age 8, with the paper describing this as part of her clinical course before her Noonan diagnosis was established. Suggested NCIT term: NCIT:C15329 (Surgical Procedure), or more specifically a cardiac procedure term.

Supportive/anti-infective: - Endocarditis prophylaxis/treatment: The 2025/2026 endocarditis case was managed per 2023 European Society of Cardiology guidelines with intravenous gentamicin plus ceftriaxone, with fever resolution within 5 days (PMC12794993) — underscoring that patients with MRAS-NS HCM/LVOT pathology may warrant standard endocarditis-prophylaxis consideration for high-risk procedures, per general cardiology guidelines for structural heart disease. - Standard heart-failure supportive management for severe neonatal presentations (not itemized in detail in the case reports reviewed).

Rehabilitative/supportive care: - Developmental/early intervention services, physical/occupational therapy as clinically indicated for hypotonia and developmental delay (general Noonan syndrome management guideline, not MRAS-specific) — see [Romano et al. 2010 Noonan syndrome management guidelines, Pediatrics].

Experimental/investigational: - No MRAS-NS-specific clinical trials (NCT-registered) were identified. Broader Noonan-syndrome/RASopathy MEK-inhibitor and other targeted-therapy trials (e.g., trametinib compassionate-use/case-series programs for neonatal Noonan-HCM) are ongoing and would plausibly be applicable to MRAS-NS on a compassionate or off-label basis given shared pathway biology. - A related preclinical direction: mavacamten (a cardiac myosin inhibitor, FDA-approved for sarcomeric HCM) has shown benefit in improving myocardial energy balance in a preclinical RASopathy-associated HCM model (Pediatric Research, 2026), suggesting another potential pharmacologic avenue for RASopathy-HCM including MRAS-NS, though again without MRAS-specific data yet.

Treatment strategy/algorithm: No MRAS-NS-specific treatment algorithm exists. Clinically, management should follow (a) general Noonan syndrome multidisciplinary surveillance guidelines (cardiology, growth, development, ophthalmology, audiology), (b) standard pediatric/adult HCM management principles (including consideration of implantable defibrillator risk-stratification in severe cases, though not specifically discussed in the MRAS literature reviewed), and (c) growing consideration of early mechanism-targeted MEK inhibition for severe neonatal HCM, extrapolating from the RAF1/RIT1/SOS1 precedent.

13. Prevention

Primary prevention: Not applicable in the traditional sense — NS11 arises from de novo germline mutation and cannot currently be prevented; there are no known modifiable risk-factor exposures.

Secondary prevention/early detection: - Prenatal ultrasound screening for the characteristic (though nonspecific) Noonan syndrome antenatal findings (increased nuchal translucency, cystic hygroma, polyhydramnios, pleural/pericardial effusion, and especially fetal cardiac hypertrophy) can prompt prenatal Noonan-syndrome gene panel testing (including MRAS) via chorionic villus sampling or amniocentesis, as was done in the Martineau et al. 2026 antenatal case. - Once a proband is diagnosed, early and vigilant cardiac surveillance (echocardiography starting in infancy, given the very high HCM prevalence in this specific genotype) is the key secondary-prevention strategy to detect and manage HCM before decompensation.

Genetic counseling: Essential for families of an affected individual — counseling should convey the (a) predominantly de novo occurrence, (b) 50% recurrence risk to future offspring of an affected individual should they reproduce, (c) low but non-zero empiric recurrence risk for parents of an affected child due to possible (undocumented but theoretically possible) germline mosaicism, and (d) markedly variable expressivity (from fatal neonatal HCM to mild adult-onset disease), meaning a specific variant's severity cannot be reliably predicted in a new case, per current evidence (Priolo et al. 2023 explicitly caution against assuming HCM is an "obligatory, early-onset and severe complication").

Screening/risk stratification: Given the small case numbers, no formal MRAS-specific risk-stratification tool exists; standard HCM risk-stratification approaches (family history, wall thickness, LVOT gradient, arrhythmia risk factors) would be applied clinically by extension from general HCM/Noonan syndrome cardiology practice.

Public health/behavioral/prophylactic interventions: Not applicable to this monogenic disorder beyond the endocarditis-prophylaxis consideration noted under Treatment.

14. Other Species / Natural Disease

No naturally occurring MRAS-associated Noonan-syndrome-like disease has been reported in non-human species in the literature surveyed. The orthologous gene is well conserved (mouse Mras, MGI:1100856, "muscle and microspikes RAS"; rat Mras, UniProt P97538). No veterinary case reports, OMIA entries, or comparative pathology studies specific to spontaneous MRAS-driven cardiomyopathy in companion animals or wildlife were identified.

Taxonomy/comparative biology: MRAS orthologs are broadly conserved across vertebrates (human MRAS NCBI Gene 22808; mouse Mras MGI:1100856; rat Mras UniProt P97538/Gene), consistent with its fundamental role in RAS/MAPK signaling; the conservation of the specific mutated residues (Gly23, Thr68, Gln71 all noted as "highly conserved from zebrafish to humans" in the primary literature) supports functional conservation and the biological plausibility of cross-species modeling.

15. Model Organisms

This is a notable evidence gap for NS11 specifically:

• No germline MRAS-NS mouse, zebrafish, or other whole-organism knock-in model was identified in the literature reviewed for this report. This contrasts with several other Noonan-syndrome genes (e.g., LZTR1, PTPN11, RAF1), for which dedicated mouse models exist (e.g., a 2026 JCI Insight paper on "Dysregulation of RAS proteostasis by autosomal-dominant LZTR1 mutation induces Noonan syndrome–like phenotypes in mice" demonstrates this modeling approach has been applied to other Noonan genes but evidently not yet published for MRAS).
• An existing Mras-knockout mouse exists but has been studied in the context of coronary artery disease/atherosclerosis (showing a B-cell phenotype and reduced macrophage infiltration in atherosclerotic plaques) rather than as a Noonan-syndrome or cardiac-hypertrophy disease model — this is a loss-of-function model relevant to a distinct MRAS biology (GWAS-identified coronary artery disease association) and does not recapitulate the gain-of-function NS11 mechanism (Shah 2024, IUBMB Life).
• Cellular/iPSC models are the primary experimental system used to date:
• Patient-derived and CRISPR/Cas9-corrected isogenic iPSC-derived cardiomyocytes (iPSC-CMs) carrying p.Gly23Val-MRAS: mutant/patient-derived iPSC-CMs were significantly larger than corrected isogenic controls, with altered gene expression and signaling consistent with cardiac hypertrophy — providing direct, tissue-relevant (though in vitro) recapitulation of the cardiac phenotype and representing the strongest available functional disease model (Higgins et al. 2019, Circ Genom Precis Med, DOI:10.1161/CIRCGEN.119.002648).
• Heterologous overexpression systems (HEK293T, COS-1, Neuro2A cells) transiently expressing tagged wild-type or mutant MRAS constructs have been used across all the primary genetic/functional papers (Higgins 2017, Motta 2020, Suzuki 2019) to establish GTP-loading, ERK/AKT signaling, and SHOC2/PPP1CB binding phenotypes.
• Zebrafish RASopathy models exist as a general platform (e.g., FRET-based "Teen" ERK biosensor zebrafish models used to study RASopathy-associated ERK dynamics and MEK-inhibitor rescue; PMC11005195), and zebrafish/frog systems are recognized as valuable for RASopathy research generally (PMID:32506834), but no MRAS-specific zebrafish knock-in model was found in this search.

Model limitations: The absence of an in vivo (whole-organism) MRAS-NS model is a significant gap limiting understanding of the developmental origins of the extracardiac phenotype (craniofacial dysmorphism, growth, neurodevelopment) and precluding preclinical in vivo testing of MEK-inhibitor or other targeted therapies specifically for this genotype — an important direction for future research given the mechanistic rationale for such therapy.

Summary of Key Ontology Term Suggestions for KB Curation

• Gene: hgnc:7227 (MRAS)
• MONDO: MONDO:0032786 (Noonan syndrome 11)
• Key HP terms: HP:0001639 (Hypertrophic cardiomyopathy), HP:0001692 (Left ventricular outflow tract obstruction), HP:0004322 (Short stature), HP:0001263 (Global developmental delay), HP:0001249 (Intellectual disability), HP:0000369 (Low-set ears), HP:0001252 (Hypotonia)
• Key GO terms (biological process): GO:0007265 (Ras protein signal transduction), GO:0000165 (MAPK cascade), GO:0003300/GO:0014897 (cardiac/striated muscle hypertrophy)
• Key CL terms: CL:0000746 (cardiomyocyte)
• Key UBERON terms: UBERON:0000948 (heart), UBERON:0002012 (ventricle)
• CHEBI/NCIT for treatment: trametinib (MEK inhibitor, targeted therapy), NCIT:C15329 (Surgical Procedure, for myectomy)
• Functional impact category: GAIN_OF_FUNCTION (constitutive/hyperactive GTPase signaling — not simply increased pathway flux, given evidence of qualitatively altered nucleotide cycling and complex assembly)

Sources

• OMIM #618499 — Noonan Syndrome 11 (NS11)
• OMIM *608435 — MRAS (Muscle RAS Viral Oncogene Homolog)
• Higgins EM et al. 2017. "Elucidation of MRAS-mediated Noonan syndrome with cardiac hypertrophy." JCI Insight 2(5):e91225. (PMCID: PMC5333962)
• Higgins EM et al. 2019. "MRAS Variants Cause Cardiomyocyte Hypertrophy in Patient-Specific iPSC-Derived Cardiomyocytes." Circ Genom Precis Med 12:e002648.
• Motta M et al. 2020. "Activating MRAS mutations cause Noonan syndrome associated with hypertrophic cardiomyopathy." Hum Mol Genet 29(11):1772–1783. PMID:31108500.
• Suzuki H et al. 2019. "Severe Noonan syndrome phenotype associated with a germline Q71R MRAS variant." Am J Med Genet A 179:1628–1630. PMID:31173466.
• Priolo M et al. 2023. "Natural history of MRAS-related Noonan syndrome: Evidence of mild adult-onset left ventricular hypertrophy and neuropsychiatric features." Am J Med Genet C Semin Med Genet. PMID:36734411.
• Martineau et al. 2026. "Hypertrophic Cardiomyopathy as a Key Feature of MRAS-Related Noonan Syndrome: New Case and Comprehensive Literature Review." Prenatal Diagnosis. DOI:10.1002/pd.70134.
• Novel characterization of MRAS mutation-associated Noonan syndrome: infective endocarditis case report. PMC12794993.
• Kwon JJ et al. 2018. "SHOC2-MRAS-PP1 complex positively regulates RAF activity and contributes to Noonan syndrome pathogenesis." PNAS. PMID:30348783.
• Kwon JJ et al. 2022. "Structure of the MRAS–SHOC2–PP1C phosphatase complex." Nature. PMID:35830882.
• Bonsor DA et al. 2022. "Structure of the SHOC2–MRAS–PP1C complex provides insights into RAF activation and Noonan syndrome." Nat Struct Mol Biol. PMID:36175670.
• ClinVar RCV000787303 — MRAS c.68G>T (p.Gly23Val)
• ClinGen RASopathy gene curation — MRAS (HGNC:7227)
• GeneReviews — Noonan Syndrome (NBK1124)
• Gross AM et al. and related case reports — MEK-inhibition (trametinib) in Noonan-syndrome hypertrophic cardiomyopathy (RAF1, RIT1, SOS1). PMC6916648.
• GeneCards — MRAS
• Shah et al. 2024. "MRAS in coronary artery disease—Uncharted territory." IUBMB Life.

Reference Validation

Checked with linkml-reference-validator 0.2.1.

All extracted references resolved successfully.

Term Validation

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

Terms the report names something else

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

• HP:0001692 (2 mentions) - the report calls it "Variable", "Left ventricular outflow tract obstruction"; HP calls it Atrial arrhythmia
• UBERON:0002012 (2 mentions) - the report calls it "ventricle"; UBERON calls it pulmonary artery

Obsolete terms

These terms are real but deprecated. Citing one is not a fabrication; it does mean the report is naming something the ontology has retired:

• HP:0000368 (obsolete Low-set, posteriorly rotated ears) (1 mention) - replaced by HP:0000358

Terms whose name is worth a second look

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

• HP:0000280 (1 mention) - the report calls it "Coarse facial features, when applicable"; HP calls it Coarse facial features
• HP:0000494 (1 mention) - the report calls it "downslanted"; HP calls it Downslanted palpebral fissures
• GO:0014897 (2 mentions) - the report calls it "cardiac/striated muscle hypertrophy"; GO calls it striated muscle hypertrophy
• CL:0000746 (2 mentions) - the report calls it "cardiomyocytes", "Cardiac muscle tissue — cardiomyocytes", "cardiomyocyte"; CL calls it cardiac muscle cell**, and lists "cardiac muscle fiber" among its other names
• NCIT:C15329 (2 mentions) - the report calls it "Surgical Procedure, for myectomy"; NCIT calls it Surgical Procedure

Terms named inconsistently

The report gives these identifiers more than one name of its own:

• HP:0001692 - called "Variable", "Left ventricular outflow tract obstruction"
• CL:0000746 - called "cardiomyocytes", "Cardiac muscle tissue — **cardiomyocytes", "cardiomyocyte"

Prefixes with no resolver

Terms carrying these prefixes were not checked either way, because no configured ontology covers them. An unrecognised prefix may name an ontology this run could not reach as easily as one that does not exist, so nothing here is evidence of fabrication: MGI.

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.

Disease Characteristics Research Template

Target Disease

• Disease Name: Noonan Syndrome 11 NS11 the MRAS-related form of Noonan syndrome OMIM 618499 MONDO:0032786 caused by germline activating missense variants in the MRAS gene encoding the RAS-family GTPase M-Ras. NOT LZTR1-related Noonan syndrome and NOT any other numbered Noonan syndrome type.
• MONDO ID: (if available)
• Category: Genetic

Research Objectives

Please provide a comprehensive research report on Noonan Syndrome 11 NS11 the MRAS-related form of Noonan syndrome OMIM 618499 MONDO:0032786 caused by germline activating missense variants in the MRAS gene encoding the RAS-family GTPase M-Ras. NOT LZTR1-related Noonan syndrome and NOT any other numbered Noonan syndrome type. 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.

For each section, suggested databases/resources are listed. These are the first places you should search for information on each topic.

1. Disease Information

Search first: OMIM, Orphanet, ICD-10/ICD-11, MeSH, PubMed

• What is the disease? Provide a concise overview.
• What are the key identifiers? (OMIM, Orphanet, ICD-10/ICD-11, MeSH, Mondo)
• What are the common synonyms and alternative names?
• Is the information derived from individual patients (e.g., EHR) or aggregated disease-level resources?

2. Etiology

• Disease Causal Factors: What are the primary causes? (genetic, environmental, infectious, mechanistic)
• Risk Factors:

  Search first: PubMed, Cochrane Library, UpToDate, clinical guidelines, ClinVar, ClinGen, GWAS Catalog, PheGenI, CTD, CDC, WHO, epidemiological databases

• Genetic risk factors (causal variants, susceptibility loci, modifier genes)
• Environmental risk factors (toxins, lifestyle, occupational exposures, age, sex, family history)
• Protective Factors:

  Search first: PubMed, Cochrane Library, clinical trial databases, GWAS Catalog, gnomAD, WHO, CDC, nutrition databases

• Genetic protective factors (protective variants, modifier alleles)
• Environmental protective factors (diet, lifestyle, exposures that reduce risk)
• Gene-Environment Interactions: How do genetic and environmental factors interact to influence disease?

  Search first: CTD, PubMed, PheGenI, GxE databases

3. Phenotypes

Search first: HPO (Human Phenotype Ontology), OMIM, Orphanet, PubMed, clinicaltrials.gov, MedDRA, SNOMED CT, DECIPHER, LOINC

For each phenotype, provide: - Phenotype type: symptoms, clinical signs, physical manifestations, behavioral changes, or laboratory abnormalities

For symptoms/signs: HPO, OMIM, Orphanet, PubMed For behavioral changes: HPO, DSM, RDoC (Research Domain Criteria), PubMed For laboratory abnormalities: LOINC, SNOMED CT, LabTests Online, PubMed - Phenotype characteristics: Search first: OMIM, Orphanet, HPO, PubMed - Age of symptom onset (neonatal, childhood, adult-onset, late-onset) - Symptom severity (mild, moderate, severe, variable) - Symptom progression (stable, progressive, episodic, fluctuating) - Frequency among affected individuals (percentage or qualitative) - Quality of life impact: Effects on daily functioning and well-being (per-phenotype when possible) Search first: EQ-5D database, SF-36, WHO QOL databases, PubMed - Suggest HPO (Human Phenotype Ontology) terms for each phenotype

4. Genetic/Molecular Information

• Causal Genes: Gene mutations or chromosomal abnormalities responsible for disease (gene symbols, OMIM IDs)

  Search first: OMIM, ClinVar, HGMD, Ensembl, NCBI Gene

• Pathogenic Variants:
• Affected genes (gene symbols, HGNC IDs) > Search first: OMIM, NCBI Gene, Ensembl, HGNC, UniProt, GeneCards
• Variant classification (pathogenic, likely pathogenic, VUS per ACMG/AMP guidelines) > Search first: ClinVar, ClinGen, ACMG/AMP guidelines, VarSome
• Variant type/class (missense, frameshift, nonsense, splice-site, structural)
• Allele frequency in population databases > Search first: gnomAD, 1000 Genomes, ExAC, TOPMed, dbSNP
• Somatic vs germline origin > Search first: COSMIC (somatic), ClinVar, ICGC, TCGA
• Functional consequences (loss of function, gain of function, dominant negative)
• Modifier Genes: Genes that modify disease severity or expression
• Epigenetic Information: DNA methylation, histone modifications, chromatin changes affecting disease

  Search first: ENCODE, Roadmap Epigenomics, MethBase, DiseaseMeth

• Chromosomal Abnormalities: Large-scale genetic changes (aneuploidy, translocations, inversions)

  Search first: DECIPHER, ClinVar, ECARUCA, UCSC Genome Browser

5. Environmental Information

• Environmental Factors: Non-genetic contributing factors (toxins, radiation, pollution, occupational exposure)

  Search first: CTD (Comparative Toxicogenomics Database), TOXNET, PubMed, EPA databases

• Lifestyle Factors: Behavioral factors (smoking, diet, exercise, alcohol consumption)

  Search first: CDC databases, WHO, PubMed, NHANES

• Infectious Agents: If applicable, pathogens causing or triggering disease (bacteria, viruses, fungi, parasites)

  Search first: NCBI Taxonomy, ViPR, BV-BRC, MicrobeDB, GIDEON

6. Mechanism / Pathophysiology

• Molecular Pathways: Specific signaling cascades or biochemical pathways involved (Wnt, MAPK, mTOR, PI3K-AKT, etc.)

  Search first: KEGG, Reactome, WikiPathways, PathBank, BioCyc

• Cellular Processes: Cell-level mechanisms (apoptosis, autophagy, cell cycle dysregulation, inflammation, etc.)

  Search first: Gene Ontology (GO), Reactome, KEGG, PubMed

• Protein Dysfunction: How protein structure or function is altered (misfolding, aggregation, loss of function, gain of function)

  Search first: UniProt, PDB (Protein Data Bank), InterPro, Pfam, AlphaFold

• Metabolic Changes: Alterations in metabolic processes (energy metabolism, lipid metabolism, amino acid metabolism)

  Search first: KEGG, BioCyc, HMDB (Human Metabolome Database), BRENDA

• Immune System Involvement: Role of immune response (autoimmunity, immunodeficiency, chronic inflammation)

  Search first: ImmPort, Immunome Database, IEDB, Gene Ontology

• Tissue Damage Mechanisms: How tissues/ are injured (oxidative stress, ischemia, fibrosis, necrosis)

  Search first: PubMed, Gene Ontology, Reactome

• Biochemical Abnormalities: Specific molecular defects (enzyme deficiencies, receptor dysfunction, ion channel defects)

  Search first: BRENDA, UniProt, KEGG, OMIM, PubMed

• Epigenetic Changes: DNA methylation, histone modifications affecting gene expression in disease

  Search first: ENCODE, Roadmap Epigenomics, MethBase, DiseaseMeth

• Molecular Profiling (if available):
• Transcriptomics/gene expression changes > Search first: GEO (Gene Expression Omnibus), ArrayExpress, GTEx, Human Cell Atlas, SRA
• Proteomics findings > Search first: PRIDE, ProteomeXchange, Human Protein Atlas, STRING, BioGRID
• Metabolomics signatures > Search first: MetaboLights, Metabolomics Workbench, HMDB, METLIN
• Lipidomics alterations > Search first: LIPID MAPS, SwissLipids, LipidHome, Metabolomics Workbench
• Genomic structural features > Search first: UCSC Genome Browser, Ensembl, NCBI, dbVar, DGV
• Advanced Technologies (if applicable):
• Single-cell analysis findings (cell-type specific mechanisms, cellular heterogeneity) > Search first: Human Cell Atlas, Single Cell Portal, GEO, CELLxGENE
• Spatial transcriptomics findings > Search first: GEO, Spatial Research, Vizgen, 10x Genomics data
• Multi-omics integration results > Search first: TCGA, ICGC, cBioPortal, LinkedOmics, PubMed
• Functional genomics screens (CRISPR, RNAi) > Search first: DepMap, GenomeRNAi, PubMed, BioGRID ORCS

For each mechanism, describe: - The causal chain from initial trigger to clinical manifestation - Which mechanisms are upstream vs downstream - What cell types and biological processes are involved - Suggest GO terms for biological processes and CL terms for cell types

7. Anatomical Structures Affected

• Organ Level:
• Primary organs directly affected
• Secondary organ involvement (complications, secondary effects)
• Body systems involved (cardiovascular, nervous, digestive, respiratory, endocrine, etc.)

  Search first: Uberon, FMA (Foundational Model of Anatomy), OMIM, HPO, ICD-11, MeSH, SNOMED CT

• Tissue and Cell Level:
• Specific tissue types affected (epithelial, connective, muscle, nervous)
• Specific cell populations targeted (with Cell Ontology terms)

  Search first: Uberon, Human Protein Atlas, Cell Ontology, Human Cell Atlas, CellMarker, PanglaoDB

• Subcellular Level:
• Cellular compartments involved (mitochondria, nucleus, ER, lysosomes) (with GO Cellular Component terms)

  Search first: Gene Ontology (Cellular Component), UniProt, Human Protein Atlas

• Localization:
• Specific anatomical sites (with UBERON terms) > Search first: FMA, Uberon, NeuroNames (for brain), SNOMED CT
• Lateralization (unilateral, bilateral, asymmetric) > Search first: HPO, clinical literature, imaging databases

8. Temporal Development

• Onset:
• Typical age of onset (congenital, pediatric, adult, geriatric)
• Onset pattern (acute, subacute, chronic, insidious)

  Search first: OMIM, Orphanet, HPO, PubMed

• Progression:
• Disease stages (early, intermediate, advanced, end-stage) > Search first: Cancer Staging Manual (AJCC), WHO classifications, PubMed
• Progression rate (rapid, slow, variable)
• Disease course pattern (episodic, relapsing-remitting, progressive, stable)
• Disease duration (self-limited, chronic lifelong)

  Search first: Disease registries, longitudinal cohort databases, natural history studies, PubMed, Orphanet, OMIM

• Patterns:
• Remission patterns (spontaneous, treatment-induced) > Search first: Clinical trial databases, disease registries, PubMed
• Critical periods (time windows of vulnerability or opportunity for intervention) > Search first: PubMed, developmental biology databases, clinical guidelines

9. Inheritance and Population

• Epidemiology:
• Prevalence (cases per 100,000 at given time)
• Incidence (new cases per 100,000 per year)

  Search first: Orphanet, CDC, WHO, GBD (Global Burden of Disease), national registries, SEER, disease registries

• For Genetic Etiology:
• Inheritance pattern (AD, AR, X-linked, mitochondrial, multifactorial, polygenic) > Search first: OMIM, Orphanet, ClinVar, GTR (Genetic Testing Registry)
• Penetrance (complete, incomplete, age-dependent) > Search first: ClinVar, OMIM, PubMed, ClinGen
• Expressivity (variable, consistent) > Search first: OMIM, ClinVar, PubMed
• Genetic anticipation (increasing severity in successive generations) > Search first: OMIM, PubMed (especially for repeat expansion disorders)
• Germline mosaicism > Search first: ClinVar, OMIM, genetic counseling literature, PubMed
• Founder effects (population-specific mutations) > Search first: gnomAD, population genetics databases, PubMed
• Consanguinity role > Search first: OMIM, population studies, genetic counseling resources
• Carrier frequency > Search first: gnomAD, carrier screening databases, GeneReviews, GTR
• Population Demographics:
• Affected populations (ethnic or demographic groups with higher prevalence) > Search first: gnomAD, 1000 Genomes, PAGE Study, PubMed, population registries
• Geographic distribution (endemic areas, regional variation) > Search first: WHO, CDC, GBD, Orphanet, geographic epidemiology databases
• Geographic distribution of specific variants
• Sex ratio (male:female) > Search first: Disease registries, OMIM, PubMed, epidemiological databases
• Age distribution of affected individuals > Search first: CDC, disease registries, SEER, Orphanet

10. Diagnostics

• Clinical Tests:
• Laboratory tests (blood, urine, tissue chemistry, specific enzyme assays) > Search first: LOINC, LabTests Online, PubMed
• Biomarkers (proteins, metabolites, genetic markers, circulating biomarkers) > Search first: FDA Biomarker List, BEST (Biomarkers, EndpointS, and other Tools), PubMed
• Imaging studies (X-ray, CT, MRI, PET, ultrasound) > Search first: RadLex, DICOM, Radiopaedia, imaging databases
• Functional tests (pulmonary function, cardiac stress tests) > Search first: LOINC, clinical guidelines, PubMed
• Electrophysiology (EEG, EMG, ECG, nerve conduction studies) > Search first: LOINC, clinical neurophysiology databases, PubMed
• Biopsy findings (histopathology, immunohistochemistry) > Search first: SNOMED CT, College of American Pathologists resources, PubMed
• Pathology findings (microscopic examination) > Search first: SNOMED CT, Digital Pathology databases, PubMed
• Genetic Testing:

  Search first: GTR (Genetic Testing Registry), GeneReviews, ClinGen

• Overview of recommended genetic testing approach
• Whole genome sequencing (WGS) utility > Search first: GTR, ClinVar, GEL (Genomics England), gnomAD
• Whole exome sequencing (WES) utility > Search first: GTR, ClinVar, OMIM, GeneMatcher
• Gene panels (which panels, which genes) > Search first: GTR, ClinVar, laboratory-specific databases
• Single gene testing > Search first: GTR, ClinVar, OMIM, GeneReviews
• Chromosomal microarray (CMA) > Search first: DECIPHER, ClinVar, dbVar, ECARUCA
• Karyotyping > Search first: Chromosome Abnormality Database, ClinVar, cytogenetics resources
• FISH > Search first: ClinVar, cytogenetics databases, PubMed
• Mitochondrial DNA testing > Search first: MITOMAP, MSeqDR, ClinVar, GTR
• Repeat expansion testing > Search first: GTR, ClinVar, repeat expansion databases, PubMed
• Omics-Based Diagnostics (if applicable):
• RNA sequencing / transcriptomics > Search first: GEO, ArrayExpress, GTEx, RNA-seq databases
• Proteomics > Search first: PRIDE, ProteomeXchange, FDA Biomarker database
• Metabolomics > Search first: MetaboLights, Metabolomics Workbench, HMDB
• Epigenomics > Search first: GEO, ENCODE, Roadmap Epigenomics, MethBase
• Liquid biopsy > Search first: COSMIC, ClinVar, liquid biopsy databases, PubMed
• Clinical Criteria:
• Standardized diagnostic criteria (DSM, ICD, society guidelines) > Search first: DSM-5, ICD-11, clinical society guidelines, UpToDate
• Differential diagnosis (other conditions to rule out, with distinguishing features) > Search first: DynaMed, UpToDate, clinical decision support systems
• Screening:
• Screening methods for asymptomatic individuals (newborn screening, carrier screening, cascade screening) > Search first: ACMG recommendations, CDC newborn screening, GTR

11. Outcome/Prognosis

• Survival and Mortality:
• Survival rate (5-year, 10-year, overall) > Search first: SEER, cancer registries, disease-specific registries, PubMed
• Life expectancy (with and without treatment if applicable) > Search first: Orphanet, disease registries, actuarial databases, PubMed
• Mortality rate > Search first: CDC, WHO, GBD, national mortality databases
• Disease-specific mortality (deaths directly attributable to disease) > Search first: Disease registries, CDC Wonder, GBD, PubMed
• Morbidity and Function:
• Morbidity (disease-related disability and health impacts) > Search first: GBD, WHO, disability databases, PubMed
• Disability outcomes (long-term functional impairments) > Search first: ICF (International Classification of Functioning), disability registries
• Quality of life measures (EQ-5D, SF-36, PROMIS, disease-specific tools) > Search first: EQ-5D database, SF-36, PROMIS, PubMed
• Disease Course:
• Complications (secondary problems: infections, organ failure, etc.) > Search first: ICD codes, disease registries, clinical databases, PubMed
• Recovery potential (likelihood and extent of recovery, with vs without treatment) > Search first: Natural history studies, rehabilitation databases, PubMed
• Prediction:
• Prognostic factors (age, disease severity, biomarkers, treatment response) > Search first: Prognostic models databases, clinical calculators, PubMed
• Prognostic biomarkers (molecular markers predicting disease course) > Search first: FDA Biomarker database, PubMed, cancer prognostic databases

12. Treatment

• Pharmacotherapy:
• Pharmacological treatments (drug names, drug classes, mechanisms of action) > Search first: DrugBank, RxNorm, ATC classification, DailyMed, FDA databases
• Pharmacogenomics (how genetic variants affect drug metabolism, efficacy, toxicity) > Search first: PharmGKB, CPIC (Clinical Pharmacogenetics), FDA Table of PGx Biomarkers
• Advanced Therapeutics:
• Gene therapy (viral vectors, CRISPR, gene replacement, gene editing) > Search first: ClinicalTrials.gov, FDA gene therapy database, ASGCT resources
• Cell therapy (stem cell transplant, CAR-T, cellular therapeutics) > Search first: ClinicalTrials.gov, FDA cell therapy database, FACT standards
• RNA-based therapies (ASOs, siRNA, mRNA therapies) > Search first: ClinicalTrials.gov, FDA approvals, PubMed
• Targeted therapies (treatments directed at specific molecular targets) > Search first: My Cancer Genome, OncoKB, ClinicalTrials.gov, FDA approvals
• Immunotherapies (checkpoint inhibitors, monoclonal antibodies) > Search first: Cancer Immunotherapy Database, FDA approvals, ClinicalTrials.gov
• Surgical and Interventional:
• Surgical interventions (types of surgery, timing, outcomes) > Search first: CPT codes, surgical registries, clinical guidelines, PubMed
• Supportive and Rehabilitative:
• Supportive care (symptom management, pain control, nutrition) > Search first: Clinical guidelines, Cochrane Library, PubMed
• Rehabilitation (physical therapy, occupational therapy, speech therapy) > Search first: Rehabilitation medicine databases, clinical guidelines, PubMed
• Experimental:
• Experimental treatments in clinical trials (with NCT identifiers if available) > Search first: ClinicalTrials.gov, EU Clinical Trials Register, WHO ICTRP
• Treatment Outcomes:
• Treatment response rates > Search first: Clinical trial databases, FDA reviews, systematic reviews, PubMed
• Side effects and adverse events > Search first: FDA Adverse Event Reporting System (FAERS), MedWatch, PubMed
• Treatment Strategy:
• Treatment algorithms (clinical pathways, decision trees) > Search first: Clinical practice guidelines, NCCN Guidelines, UpToDate
• Combination therapies > Search first: ClinicalTrials.gov, treatment guidelines, PubMed
• Personalized medicine approaches (genotype-guided treatment) > Search first: My Cancer Genome, CIViC, PharmGKB, precision medicine databases

For each treatment, suggest NCIT (NCI Thesaurus) clinical-intervention terms where applicable.

13. Prevention

• Prevention Levels:
• Primary prevention (preventing disease occurrence: vaccination, risk factor modification) > Search first: CDC, WHO, USPSTF recommendations, Cochrane Library
• Secondary prevention (early detection and treatment: screening programs, early intervention) > Search first: USPSTF, CDC screening guidelines, WHO
• Tertiary prevention (preventing complications in those with disease) > Search first: Clinical guidelines, disease management protocols, PubMed
• Immunization: Vaccine strategies (if applicable)

  Search first: CDC vaccine schedules, WHO immunization, FDA vaccine database

• Screening and Early Detection:
• Screening programs (population-based: newborn screening, cancer screening) > Search first: CDC screening programs, USPSTF, cancer screening databases
• Genetic screening (carrier screening, preimplantation genetic diagnosis, prenatal testing) > Search first: ACMG recommendations, ACOG guidelines, GTR
• Risk stratification (identifying high-risk individuals for targeted prevention) > Search first: Risk prediction models, clinical calculators, PubMed
• Behavioral Interventions: Lifestyle modifications to reduce risk

  Search first: CDC, WHO, behavioral intervention databases, Cochrane Library

• Counseling: Genetic counseling (risk assessment, family planning guidance)

  Search first: NSGC resources, ACMG guidelines, GeneReviews

• Public Health:
• Public health interventions (sanitation, vector control, health education) > Search first: CDC, WHO, public health databases, PubMed
• Environmental interventions (reducing environmental risk factors) > Search first: EPA databases, WHO environmental health, PubMed
• Prophylaxis: Preventive medications or procedures

  Search first: Clinical guidelines, FDA approvals, PubMed

14. Other Species / Natural Disease

• Taxonomy: Species affected (with NCBI Taxon identifiers)

  Search first: NCBI Taxonomy

• Breed: Specific breeds affected (with VBO identifiers if applicable)

  Search first: VBO (Vertebrate Breed Ontology)

• Gene: Orthologous genes in other species (with NCBI Gene IDs)

  Search first: NCBI Gene

• Natural Disease:
• Naturally occurring disease in other species (companion animals, wildlife) > Search first: OMIA (Online Mendelian Inheritance in Animals), VetCompass, PubMed
• Veterinary relevance and importance in animal health > Search first: OMIA, veterinary databases, PubMed
• Comparative Biology:
• Comparative pathology (similarities and differences across species) > Search first: OMIA, comparative pathology databases, PubMed
• Evolutionary conservation of disease mechanisms > Search first: HomoloGene, OrthoMCL, Alliance of Genome Resources
• Transmission (if applicable):
• Zoonotic potential > Search first: CDC zoonotic diseases, WHO zoonoses, GIDEON
• Cross-species susceptibility > Search first: NCBI Taxonomy, veterinary databases, PubMed

15. Model Organisms

• Model Types:
• Model organism type (mammalian, invertebrate, cellular, in vitro) > Search first: Alliance of Genome Resources, model organism databases
• Specific model systems (mouse, rat, zebrafish, Drosophila, C. elegans, yeast, cell lines, organoids, iPSCs) > Search first: MGI, RGD, ZFIN, FlyBase, WormBase, SGD, ATCC, Cellosaurus
• Induced models (drug treatment, surgical intervention, environmental manipulation) > Search first: MGI, model organism databases, PubMed
• Genetic Models:
• Types available (knockout, knock-in, transgenic, conditional, humanized) > Search first: MGI, IMPC, KOMP, EuMMCR, IMSR
• Model Characteristics:
• Phenotype recapitulation (how well model reproduces human disease features) > Search first: Model organism databases, comparative studies, PubMed
• Model limitations (aspects of human disease not captured) > Search first: Model organism databases, PubMed, review articles
• Applications:
• Research applications (what aspects of disease can be studied) > Search first: Model organism databases, PubMed
• Resources:
• Model databases > Search first: MGI, RGD, ZFIN, FlyBase, WormBase, IMSR, EMMA, MMRRC

Citation Requirements

• Cite primary literature (PMID preferred) for all mechanistic and clinical claims
• Prioritize recent reviews and landmark papers
• Include direct quotes from abstracts where possible to support key statements
• Distinguish evidence source types: human clinical, model organism, in vitro, computational

Output Format

Structure your response as a comprehensive narrative organized by the sections above. For each section, provide: - Factual content with specific details (numbers, percentages, gene names, variant nomenclature) - Ontology term suggestions (HPO, GO, CL, UBERON, CHEBI, NCIT, MONDO) where applicable - Evidence citations with PMIDs - Direct quotes from abstracts to support key claims - Clear indication when information is not available or not applicable for this disease

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

Noonan syndrome 11 (MRAS-related): disease-characteristics report

Scope and evidence standard

This report concerns only Noonan syndrome 11 (NS11) caused by germline activating MRAS variants. It does not describe LZTR1-related Noonan syndrome or any other numbered Noonan syndrome. NS11 is exceptionally rare; consequently, the evidence base consists primarily of a few human cases, cell-functional studies, and structural/biochemical work. Statements labeled “general Noonan/RASopathy care” are clinical extrapolations, not MRAS-specific outcome evidence.

Table: This table summarizes the compact, MRAS-specific evidence base for Noonan syndrome 11, emphasizing what is directly established versus what remains uncertain. It is useful for separating firm gene/mechanism/phenotype findings from gaps in prevalence and treatment data.

1. Disease information

Definition. NS11 is a congenital, lifelong RASopathy caused by heterozygous activating missense variants in MRAS, encoding the small RAS-family GTPase M-Ras. It combines a Noonan-pattern developmental phenotype—characteristic craniofacial appearance, growth impairment, skeletal findings and neurodevelopmental delay—with particularly prominent congenital or early-childhood cardiac hypertrophy/hypertrophic cardiomyopathy (HCM). Open Targets links MONDO:0032786 specifically to MRAS (ENSG00000158186), supported by the primary MRAS literature (including PMID 28289718). (OpenTargets Search: Noonan syndrome 11-MRAS)

Identifiers and names.

• OMIM: 618499, Noonan syndrome 11.
• MONDO: MONDO:0032786, Noonan syndrome 11.
• Causal-gene identity: MRAS; Open Targets approved name “muscle RAS oncogene homolog.” (OpenTargets Search: Noonan syndrome 11-MRAS)
• Common synonyms: MRAS-related Noonan syndrome; MRAS-mediated Noonan syndrome; Noonan syndrome associated with MRAS; NS11.
• Orphanet/MeSH/ICD: no retrieved subtype-specific Orphanet, MeSH, ICD-10 or ICD-11 code was established. Coding generally falls under broader Noonan-syndrome/congenital-malformation categories; such codes do not uniquely identify MRAS-NS11.

The evidence combines individual-level case reports/series with aggregated disease resources. It is not derived from an EHR-scale cohort or population registry.

2. Etiology, risk and protective factors

The primary and sufficient cause is a germline heterozygous activating MRAS missense variant. The initially reported affected individuals carried de novo p.Gly23Val or p.Thr68Ile substitutions; later mechanistic literature recognizes p.Gln71Arg as another NS-associated constitutively active allele. (higgins2017elucidationofmrasmediated pages 1-2, bonsor2024rasandshoc2 pages 6-8)

The first p.Gly23Val case was identified through trio whole-exome sequencing (WES), and the variant was absent from more than 280,000 gnomAD alleles. Screening 109 unrelated genotype-negative patients with suspected RASopathy and cardiac hypertrophy identified the second de novo variant, p.Thr68Ile—approximately 0.9% of that highly selected cohort, not a population prevalence estimate. (higgins2017elucidationofmrasmediated pages 2-4, higgins2017elucidationofmrasmediated pages 9-11, higgins2017elucidationofmrasmediated pages 6-8)

Risk factors. The relevant risk is genetic: a pathogenic MRAS allele in the germline. Most directly documented cases were de novo, so absence of family history does not materially reduce risk in a clinically suggestive child. If an affected person transmits the allele, the expected Mendelian recurrence risk is 50% per pregnancy, although MRAS-specific penetrance cannot yet be quantified. Parental germline mosaicism remains theoretically possible but has not been quantified.

Environmental, lifestyle, infectious and gene–environment factors. No evidence establishes toxins, diet, smoking, occupation, infection, parental age or other environmental exposures as causes or modifiers of NS11. There are likewise no validated genetic or environmental protective factors. These are evidence gaps, not evidence of absolute absence.

3. Phenotypes

MRAS-specific human observations

The directly documented phenotype is dominated by early cardiac disease. One female with p.Gly23Val had biventricular/left-ventricular hypertrophy beginning in infancy, biventricular outflow obstruction and surgical myectomy at age eight. She also had short stature, a long/dysmorphic face, low-set posteriorly rotated ears, global developmental delay and cognitive disability. (higgins2017elucidationofmrasmediated pages 2-4)

The p.Thr68Ile-positive female had cardiac hypertrophy, pulmonary-valve stenosis and an atrial septal defect, with ptosis, low-set posteriorly angulated ears, pectus excavatum, redundant palmar soft tissue/wrinkling, joint hypermobility and hypotonia. Development was delayed: independent walking at 2.5 years, sign language at 15 months, spoken words at four years and special-education support by kindergarten. (higgins2017elucidationofmrasmediated pages 8-9, higgins2017elucidationofmrasmediated pages 11-12)

Suggested phenotype annotations include:

Because the published denominator is extremely small, percentages should not be calculated as stable NS11 frequencies. The strongest qualitative association is cardiac hypertrophy/HCM, while developmental, facial, growth and skeletal findings show variable expression. Disease-specific EQ-5D, SF-36, PROMIS or caregiver-burden data do not exist. Nevertheless, obstructive HCM, surgery, developmental delay and special-education needs plainly create substantial functional burden at the individual level. (higgins2017elucidationofmrasmediated pages 8-9, higgins2017elucidationofmrasmediated pages 2-4)

4. Genetic and molecular information

Gene. MRAS is the sole established causal gene for NS11. Open Targets identifies only MRAS as an associated target for MONDO:0032786. (OpenTargets Search: Noonan syndrome 11-MRAS)

Variant class and origin. Established disease alleles are germline, heterozygous missense variants with gain-of-function effects—not truncating loss-of-function alleles, chromosomal rearrangements or somatic-only mutations. Directly reported variants include:

• p.Gly23Val, reported as c.68G>T in detailed text; de novo and absent from >280,000 population alleles. The retrieved source contained one inconsistent predicted cDNA notation, so clinical reporting should use the transcript-specific laboratory HGVS record rather than infer it from the protein change. (higgins2017elucidationofmrasmediated pages 1-2, higgins2017elucidationofmrasmediated pages 2-4)
• c.203C>T (p.Thr68Ile); de novo. (higgins2017elucidationofmrasmediated pages 8-9, higgins2017elucidationofmrasmediated pages 11-12)
• p.Gln71Arg (Q71R); recognized in later structural/mechanistic studies as a constitutively active NS allele. (bonsor2024rasandshoc2 pages 6-8)

ClinVar classifications should be checked against the current transcript and submission date during implementation. Functional evidence strongly supports pathogenic/gain-of-function interpretation for these recurrent mechanistically coherent alleles, but this report should not substitute for current laboratory ACMG/AMP adjudication.

Modifiers, epigenetics and chromosome abnormalities. No validated modifier gene, MRAS-NS11 episignature, disease-specific methylation profile or recurrent large chromosomal abnormality has been established. No founder allele, anticipation or carrier-frequency estimate is available.

5. Environmental information

NS11 is not an infectious, toxic or lifestyle-mediated disease. No causal pathogen, occupational exposure, pollutant, radiation exposure, diet, alcohol or smoking association is known. Routine healthy lifestyle measures remain relevant to general cardiovascular health but do not prevent the germline disorder.

6. Mechanism and pathophysiology

Upstream causal chain

1. A germline activating substitution changes MRAS nucleotide-state regulation and/or effector interactions.
2. G23V, T68I and Q71R favor the constitutively active, GTP-bound state. Wild-type MRAS shares about 50% sequence identity with canonical RAS proteins but normally binds/activates RAF less efficiently; the disease alleles overcome normal control. (bonsor2024rasandshoc2 pages 6-8)
3. GTP-bound MRAS assembles the SHOC2–MRAS–PP1C holophosphatase at the plasma membrane. SHOC2 acts as scaffold and PP1C as catalytic phosphatase.
4. The complex dephosphorylates RAF’s conserved inhibitory CR2 site—classically CRAF Ser259/BRAF Ser365—releasing 14-3-3-mediated inhibition and facilitating RAF activation/dimerization.
5. RAF activates MEK and ERK, changing developmental gene expression, cell proliferation, differentiation and growth.
6. Dysregulated signaling in developing myocardium and other embryonic tissues produces HCM/structural heart disease, dysmorphism, impaired linear growth and neurodevelopmental abnormalities.

Cell experiments showed p.Gly23Val produced approximately fourfold greater GTP loading at five minutes and 40-fold greater loading at 30 minutes after EGF stimulation than wild-type MRAS, with increased ERK phosphorylation and serum-response-element transcription. (higgins2017elucidationofmrasmediated pages 1-2, higgins2017elucidationofmrasmediated pages 8-9, higgins2017elucidationofmrasmediated pages 9-11)

Young et al. summarized the biochemical result directly: germline MRAS/SHOC2/PPP1CB mutations enhance ternary-complex formation, which “specifically dephosphorylates an inhibitory site on RAF kinases, activating downstream signaling.” Their experiments further distinguish G23V, which can promote direct RAF binding and holophosphatase assembly, from T68I, which preferentially enhances SHOC2–PP1 interaction/RAF-phosphatase function. (young2018shoc2–mras–pp1complexpositively pages 5-6)

The 2024 structural review concludes that G23V, T68I and Q71R place MRAS in a constitutively active GTP-bound state, with Q71R adding contacts to SHOC2; measured complex affinities are in the low-nanomolar range. (bonsor2024rasandshoc2 pages 6-8, bonsor2024rasandshoc2 pages 19-20)

Suggested GO annotations: small GTPase-mediated signal transduction (GO:0007264); Ras protein signal transduction (GO:0007265); MAPK cascade (GO:0000165); positive regulation of ERK1/2 cascade (GO:0070374); protein dephosphorylation (GO:0006470); regulation of protein serine/threonine phosphatase activity; heart development (GO:0007507); cardiac muscle-cell development and proliferation.

Likely relevant cell types: cardiomyocyte (CL:0000746), cardiac fibroblast (CL:0000746-adjacent ontology mapping should be verified), endocardial/endothelial cells, neural progenitors and growth-plate chondrocytes. Direct NS11 single-cell evidence is absent; these are mechanistically plausible annotation targets, not demonstrated cell-selective lesions.

Subcellular components: plasma membrane (GO:0005886), cytosol (GO:0005829), protein-containing complex (GO:0032991), SHOC2–MRAS–PP1C complex where a dedicated ontology term is unavailable.

No NS11-specific metabolic, immune, inflammatory, oxidative-stress, transcriptomic, proteomic, metabolomic, lipidomic, single-cell, spatial-transcriptomic or multi-omic signature has been established. The available molecular profiling consists principally of targeted signaling assays and protein structures.

7. Anatomical structures affected

The heart is the best-supported primary organ, involving ventricular myocardium and potentially pulmonary valve/septa/outflow tracts. Suggested annotations are heart (UBERON:0000948), myocardium (UBERON:0002349), cardiac ventricle (UBERON:0002082), interventricular/atrial septal structures, pulmonary valve and ventricular outflow tract.

Secondary systems include craniofacial structures, skeleton/chest wall, joints, central nervous system/neurodevelopment and the somatic growth axis. No consistent lateralization is described. At subcellular level, disease originates in membrane-associated RAS signaling rather than a primary mitochondrial, lysosomal or endoplasmic-reticulum disorder.

8. Temporal development and natural history

Onset is prenatal/congenital or early pediatric, even if molecular diagnosis occurs later. Cardiac hypertrophy may be recognized in infancy and can progress to obstruction requiring childhood intervention. Developmental delay becomes apparent as milestones are missed; short stature emerges over childhood. (higgins2017elucidationofmrasmediated pages 8-9, higgins2017elucidationofmrasmediated pages 2-4)

NS11 is lifelong. There is no validated staging system, remission pattern, median progression rate or MRAS-specific longitudinal cohort. Critical windows include prenatal cardiac development, infancy for detection of HCM/feeding and developmental difficulties, early childhood for intervention, and later childhood/adulthood for arrhythmia, obstruction and heart-failure surveillance.

9. Inheritance and population

Inheritance is autosomal dominant, with most published cases arising de novo. Expressivity is variable, but penetrance cannot be estimated. Genetic anticipation is not expected for a missense RASopathy and has not been reported. Germline mosaicism, founder effects, consanguinity effects and geographic clustering have not been demonstrated.

There is no reliable NS11-specific prevalence, incidence, sex ratio, age distribution or ancestry enrichment. Both initially described patients were female and of European descent, but that observation is far too small and ascertainment-biased to infer demographic risk. (higgins2017elucidationofmrasmediated pages 9-11)

General Noonan/RASopathy prevalence estimates must not be assigned to NS11. The 109-person selected screening cohort yielded one additional MRAS case, but it consisted specifically of genotype-negative RASopathy patients with cardiac hypertrophy and therefore cannot estimate prevalence. (higgins2017elucidationofmrasmediated pages 6-8)

10. Diagnostics

Clinical evaluation

Suspect NS11 when a child has Noonan-pattern dysmorphism and developmental/growth abnormalities together with early or severe HCM, particularly after common RASopathy genes are negative. Baseline evaluation should include physical/dysmorphology examination, three-generation pedigree, growth parameters, developmental assessment, ECG and echocardiography. Cardiac MRI/Holter monitoring is selected according to HCM severity, rhythm symptoms and image quality.

Molecular confirmation

Preferred testing is a comprehensive RASopathy panel including MRAS, or an HCM/congenital-heart-disease panel that includes MRAS when syndromic features are present. Trio WES is useful when panel testing is negative and proved diagnostic in the discovery case. Genome sequencing can detect coding variants plus classes missed by exome/panel testing, but no recurrent NS11 structural variant is known. Sanger/orthogonal confirmation and parental testing establish de novo status. (higgins2017elucidationofmrasmediated pages 1-2, higgins2017elucidationofmrasmediated pages 2-4)

CMA, karyotype and FISH are not confirmatory for an MRAS missense disorder, but CMA may be appropriate when developmental anomalies suggest a copy-number differential. Mitochondrial, repeat-expansion and liquid-biopsy testing are not indicated for NS11 itself. There is no validated serum, enzyme, metabolomic or epigenomic diagnostic biomarker beyond the molecular variant.

Differential diagnosis

Differentials include other molecular RASopathies—especially RIT1-, RAF1-, PTPN11-, SOS1-, KRAS-, SHOC2- and PPP1CB-related disease—and nonsyndromic sarcomeric HCM. NS11 is distinguished by a pathogenic activating MRAS allele, not phenotype alone. LZTR1-related Noonan syndrome is explicitly a different disease mechanism and must not be labeled NS11.

No newborn population screen exists. Cascade testing is appropriate after a familial pathogenic variant is identified; testing apparently unaffected parents also informs recurrence counseling.

11. Outcome and prognosis

No MRAS-specific five- or ten-year survival, life expectancy, mortality rate or validated prognostic model exists. Prognosis is likely driven chiefly by HCM severity, ventricular obstruction, arrhythmia and heart failure, but this is reasoned from the observed phenotype and broader HCM/RASopathy practice, not an NS11 survival cohort.

Documented morbidity includes childhood myectomy, developmental disability, special-education need, hypotonia and short stature. (higgins2017elucidationofmrasmediated pages 8-9, higgins2017elucidationofmrasmediated pages 2-4) No MRAS-specific tumor-risk estimate or evidence-based cancer-surveillance protocol has been established. Likewise, no disease-specific patient-reported outcome data exist.

12. Treatment

There is no approved MRAS-specific disease-modifying therapy. Management is multidisciplinary and phenotype-directed.

Cardiac treatment

General RASopathy/HCM practice uses non-vasodilating beta-blockers for symptoms/obstruction; disopyramide may be added for left-ventricular outflow-tract obstruction. Severe symptomatic obstruction refractory to medication may require septal myectomy; advanced heart failure or refractory arrhythmia may warrant transplantation. These are general recommendations, although childhood myectomy has been used in an MRAS case. (higgins2017elucidationofmrasmediated pages 2-4, faienza2024cardiacphenotypeand pages 7-8)

Suggested NCIt intervention mappings include echocardiography (C16525), electrocardiography, beta-adrenergic blocker therapy, antiarrhythmic therapy, septal myectomy/cardiac surgery and heart transplantation; exact current NCIt codes should be verified during database ingestion.

Developmental and supportive care

Early developmental evaluation, physical/occupational/speech therapy, individualized education, nutritional/feeding support and hearing/vision assessment should follow general Noonan care. Orthopedic, endocrine/growth, renal and hemostatic evaluations should be driven by examination and standard Noonan guidance. Evidence for these measures is not MRAS-specific.

Targeted/experimental therapy

MEK inhibition is biologically rational because the causal pathway culminates in RAF–MEK–ERK hyperactivation, but efficacy and long-term safety in MRAS-NS11 are unproven. NCT06555237 (MEKinRAS) is a recruiting phase 2 randomized trial begun August 1, 2024, targeting 40 patients aged 0–18 years with genetically confirmed RASopathy and echocardiographic HCM. It compares trametinib 0.025 mg/kg orally once daily plus beta-blocker/disopyramide against standard therapy, measuring echocardiographic hypertrophy, NT-proBNP and high-sensitivity troponin I through 12 months. The Warsaw registry does not explicitly document an MRAS subgroup or MRAS-positive enrollment. (NCT06555237 chunk 1)

There is no established MRAS-directed gene therapy, CRISPR therapy, ASO, siRNA, cell therapy or immunotherapy. Structural studies identify the SHOC2–MRAS–PP1C interface as a potential drug target, but this remains preclinical and is largely being developed in oncology. (bonsor2024rasandshoc2 pages 6-8)

13. Prevention

Primary prevention by diet, vaccination or environmental modification is impossible because NS11 is germline genetic. Reproductive options after identification of a familial pathogenic variant include genetic counseling, prenatal diagnosis and preimplantation genetic testing. For a proven heterozygous affected parent, the theoretical recurrence probability is 50% per conception; after an apparently de novo case, recurrence is low but not zero because of possible parental germline mosaicism.

Secondary prevention consists of early molecular diagnosis and cardiac/developmental surveillance. Tertiary prevention includes prompt management of HCM/outflow obstruction, arrhythmias, developmental needs and other detected complications. There is no NS11-specific prophylactic medication or public-health screening program.

14. Other species and natural disease

MRAS signaling is evolutionarily conserved, and orthologs exist in standard vertebrate model species. However, no well-established naturally occurring veterinary disorder equivalent to human MRAS-NS11, breed association, zoonotic potential or cross-species transmission was identified. NS11 is not transmissible.

15. Model organisms and experimental systems

The strongest models are in vitro biochemical and cellular systems, not a validated whole-animal NS11 model. HEK293T/17 and related transfected-cell assays demonstrated enhanced GTP loading, ERK phosphorylation and transcriptional signaling by mutant MRAS. (higgins2017elucidationofmrasmediated pages 8-9, higgins2017elucidationofmrasmediated pages 9-11)

Purified-protein, crystallographic and cryo-EM studies define the SHOC2–MRAS–PP1C complex and effects of G23V, T68I and Q71R. These models provide high mechanistic resolution but cannot reproduce organism-level cardiomyopathy, development, penetrance or treatment toxicity. (bonsor2024rasandshoc2 pages 6-8, young2018shoc2–mras–pp1complexpositively pages 5-6)

No retrieved evidence established a knock-in mouse, rat, zebrafish, Drosophila, organoid or patient-derived iPSC model that comprehensively recapitulates MRAS-NS11. Such models—especially heterozygous variant-specific cardiomyocyte/iPSC and mouse or zebrafish knock-ins—remain important priorities for natural-history and therapeutic studies.

Key evidence limitations and interpretation

1. Very small patient numbers: apparent phenotype frequencies are unstable and should remain qualitative.
2. Ascertainment bias: discovery focused on genotype-negative patients with cardiac hypertrophy, enriching the apparent HCM association.
3. Mechanistic strength exceeds clinical depth: biochemical causality is strong, but longitudinal prognosis, penetrance and treatment response remain poorly defined.
4. No 2023–2024 MRAS-specific clinical cohort was retrieved: recent work chiefly refines protein structure and therapeutic hypotheses rather than expanding natural history.
5. General Noonan recommendations are not genotype-specific evidence: cardiac and multidisciplinary care should be individualized, especially because severe HCM appears prominent in NS11.

Principal publications and URLs

• Higgins EM et al. “Elucidation of MRAS-mediated Noonan syndrome with cardiac hypertrophy.” JCI Insight. Published March 2017. PMID 28289718. DOI/URL: https://doi.org/10.1172/jci.insight.91225. The report identified de novo MRAS variants and concluded that mutant MRAS enhanced RAS/MAPK signaling. (higgins2017elucidationofmrasmediated pages 1-2, higgins2017elucidationofmrasmediated pages 2-4)
• Young LC et al. “SHOC2–MRAS–PP1 complex positively regulates RAF activity and contributes to Noonan syndrome pathogenesis.” PNAS. Published October 2018. PMID 30348783. DOI/URL: https://doi.org/10.1073/pnas.1720352115. Abstract-level conclusion: the variants enhance a ternary complex that dephosphorylates inhibitory RAF and activates downstream signaling. (young2018shoc2–mras–pp1complexpositively pages 5-6)
• Motta M et al. “Activating MRAS mutations cause Noonan syndrome associated with hypertrophic cardiomyopathy.” Human Molecular Genetics. Published online 2019; volume publication July 2020. DOI/URL: https://doi.org/10.1093/hmg/ddz108; literature databases associated with the MRAS–NS11 record include PMID 31108500. This is the key expanded human-genetic study, although complete patient-level tables were not retrievable in the present evidence set. (OpenTargets Search: Noonan syndrome 11-MRAS)
• Bonsor DA, Simanshu DK. “RAS and SHOC2 Roles in RAF Activation and Therapeutic Considerations.” Annual Review of Cancer Biology. Published June 2024. DOI/URL: https://doi.org/10.1146/annurev-cancerbio-062822-030450. This recent authoritative structural review identifies G23V, T68I and Q71R as constitutively active MRAS alleles. (bonsor2024rasandshoc2 pages 6-8)
• Faienza MF et al. “Cardiac Phenotype and Gene Mutations in RASopathies.” Genes. Published August 2024. DOI/URL: https://doi.org/10.3390/genes15081015. Its treatment discussion is RASopathy-wide rather than MRAS-specific. (faienza2024cardiacphenotypeand pages 7-8)
• ClinicalTrials.gov. MEKinRAS, NCT06555237. Registered/started 2024: https://clinicaltrials.gov/study/NCT06555237. It is potentially relevant to NS11-associated HCM but is not an MRAS-specific trial. (NCT06555237 chunk 1)

References

1. (OpenTargets Search: Noonan syndrome 11-MRAS): Open Targets Query (Noonan syndrome 11-MRAS, 3 results). Buniello, A. et al. (2025). Open Targets Platform: facilitating therapeutic hypotheses building in drug discovery. Nucleic Acids Research.

2. (higgins2017elucidationofmrasmediated pages 1-2): Erin M. Higgins, J. Martijn Bos, Heather Mason-Suares, David J. Tester, Jaeger P. Ackerman, Calum A. MacRae, Katia Sol-Church, Karen W. Gripp, Raul Urrutia, and Michael J. Ackerman. Elucidation of mras-mediated noonan syndrome with cardiac hypertrophy. JCI Insight, Mar 2017. URL: https://doi.org/10.1172/jci.insight.91225, doi:10.1172/jci.insight.91225. This article has 111 citations and is from a domain leading peer-reviewed journal.

3. (bonsor2024rasandshoc2 pages 6-8): Daniel A. Bonsor and Dhirendra K. Simanshu. Ras and shoc2 roles in raf activation and therapeutic considerations. Jun 2024. URL: https://doi.org/10.1146/annurev-cancerbio-062822-030450, doi:10.1146/annurev-cancerbio-062822-030450. This article has 16 citations and is from a peer-reviewed journal.

4. (young2018shoc2–mras–pp1complexpositively pages 5-6): Lucy C. Young, Nicole Hartig, Isabel Boned del Río, Sibel Sari, Benjamin Ringham-Terry, Joshua R. Wainwright, Greg G. Jones, Frank McCormick, and Pablo Rodriguez-Viciana. Shoc2–mras–pp1 complex positively regulates raf activity and contributes to noonan syndrome pathogenesis. Proceedings of the National Academy of Sciences, 115:E10576-E10585, Oct 2018. URL: https://doi.org/10.1073/pnas.1720352115, doi:10.1073/pnas.1720352115. This article has 106 citations and is from a highest quality peer-reviewed journal.

5. (higgins2017elucidationofmrasmediated pages 8-9): Erin M. Higgins, J. Martijn Bos, Heather Mason-Suares, David J. Tester, Jaeger P. Ackerman, Calum A. MacRae, Katia Sol-Church, Karen W. Gripp, Raul Urrutia, and Michael J. Ackerman. Elucidation of mras-mediated noonan syndrome with cardiac hypertrophy. JCI Insight, Mar 2017. URL: https://doi.org/10.1172/jci.insight.91225, doi:10.1172/jci.insight.91225. This article has 111 citations and is from a domain leading peer-reviewed journal.

6. (higgins2017elucidationofmrasmediated pages 9-11): Erin M. Higgins, J. Martijn Bos, Heather Mason-Suares, David J. Tester, Jaeger P. Ackerman, Calum A. MacRae, Katia Sol-Church, Karen W. Gripp, Raul Urrutia, and Michael J. Ackerman. Elucidation of mras-mediated noonan syndrome with cardiac hypertrophy. JCI Insight, Mar 2017. URL: https://doi.org/10.1172/jci.insight.91225, doi:10.1172/jci.insight.91225. This article has 111 citations and is from a domain leading peer-reviewed journal.

7. (higgins2017elucidationofmrasmediated pages 2-4): Erin M. Higgins, J. Martijn Bos, Heather Mason-Suares, David J. Tester, Jaeger P. Ackerman, Calum A. MacRae, Katia Sol-Church, Karen W. Gripp, Raul Urrutia, and Michael J. Ackerman. Elucidation of mras-mediated noonan syndrome with cardiac hypertrophy. JCI Insight, Mar 2017. URL: https://doi.org/10.1172/jci.insight.91225, doi:10.1172/jci.insight.91225. This article has 111 citations and is from a domain leading peer-reviewed journal.

8. (higgins2017elucidationofmrasmediated pages 11-12): Erin M. Higgins, J. Martijn Bos, Heather Mason-Suares, David J. Tester, Jaeger P. Ackerman, Calum A. MacRae, Katia Sol-Church, Karen W. Gripp, Raul Urrutia, and Michael J. Ackerman. Elucidation of mras-mediated noonan syndrome with cardiac hypertrophy. JCI Insight, Mar 2017. URL: https://doi.org/10.1172/jci.insight.91225, doi:10.1172/jci.insight.91225. This article has 111 citations and is from a domain leading peer-reviewed journal.

9. (higgins2017elucidationofmrasmediated pages 6-8): Erin M. Higgins, J. Martijn Bos, Heather Mason-Suares, David J. Tester, Jaeger P. Ackerman, Calum A. MacRae, Katia Sol-Church, Karen W. Gripp, Raul Urrutia, and Michael J. Ackerman. Elucidation of mras-mediated noonan syndrome with cardiac hypertrophy. JCI Insight, Mar 2017. URL: https://doi.org/10.1172/jci.insight.91225, doi:10.1172/jci.insight.91225. This article has 111 citations and is from a domain leading peer-reviewed journal.

10. (faienza2024cardiacphenotypeand pages 7-8): Maria Felicia Faienza, Giovanni Meliota, Donatella Mentino, Romina Ficarella, Mattia Gentile, Ugo Vairo, and Gabriele D’amato. Cardiac phenotype and gene mutations in rasopathies. Genes, 15:1015, Aug 2024. URL: https://doi.org/10.3390/genes15081015, doi:10.3390/genes15081015. This article has 16 citations.

11. (NCT06555237 chunk 1): MEK Inhibitors for the Treatment of Hypertrophic Cardiomyopathy in Patients With RASopathies. Medical University of Warsaw. 2024. ClinicalTrials.gov Identifier: NCT06555237

12. (bonsor2024rasandshoc2 pages 19-20): Daniel A. Bonsor and Dhirendra K. Simanshu. Ras and shoc2 roles in raf activation and therapeutic considerations. Jun 2024. URL: https://doi.org/10.1146/annurev-cancerbio-062822-030450, doi:10.1146/annurev-cancerbio-062822-030450. This article has 16 citations and is from a peer-reviewed journal.

Artifacts

• Edison artifact artifact-00

Reference Validation

Checked with linkml-reference-validator 0.2.1.

All extracted references resolved successfully.

Term Validation

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

Terms the report names something else

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

• HP:0001642 (1 mention) - the report calls it "Congenital structural cardiac sign"; HP calls it Pulmonic stenosis
• HP:0001631 (1 mention) - the report calls it "Congenital structural cardiac sign"; HP calls it Atrial septal defect
• HP:0004322 (1 mention) - the report calls it "Growth manifestation, childhood"; HP calls it Short stature
• HP:0001252 (1 mention) - the report calls it "Neuromuscular sign, infancy/childhood"; HP calls it Hypotonia
• HP:0000767 (1 mention) - the report calls it "Skeletal manifestation"; HP calls it Pectus excavatum
• HP:0001382 (1 mention) - the report calls it "Musculoskeletal sign"; HP calls it Joint hypermobility

Terms whose name is worth a second look

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

• HP:0001263 (1 mention) - the report calls it "Neurodevelopmental sign, early childhood"; HP calls it Global developmental delay, and lists "Developmental delay in early childhood" among its other names

Key Findings

Finding 1 — Activating MRAS missense variants cause NS11 with hypertrophic cardiomyopathy

NS11 was established as a distinct RASopathy through two landmark reports. Higgins et al. (2017) identified a de novo MRAS variant (p.Gly23Val) by whole-exome trio sequencing in a 15-year-old female with Noonan syndrome and cardiac hypertrophy, after screening a cohort of 109 unrelated NS-phenotype patients. Motta et al. (2020) then reported two further unrelated patients with de novo MRAS variants — c.203C>T (p.Thr68Ile) and c.67G>C (p.Gly23Arg) — both with HCM; one died neonatally of cardiac failure. Functional assays in both studies demonstrated high-level M-Ras activation resulting from impaired GTPase activity, establishing a gain-of-function mechanism.

"Targeted sequencing revealed de novo MRAS variants, c.203C > T (p.Thr68Ile) and c.67G > C (p.Gly23Arg) as causative events" — PMID: 31108500

"Functional analyses documented high level of activation of MRAS mutants due to impaired GTPase activity" — PMID: 31108500

This finding anchors the disease definition: NS11 (OMIM #618499) is caused by activating variants in MRAS (3q22.3, HGNC:7227), and is genetically and clinically distinct from LZTR1-related and all other numbered Noonan syndrome subtypes.

Finding 2 — Mechanism: mutant M-Ras enhances the SHOC2–PP1c holoenzyme, boosting RAF/MEK/ERK and PI3K-AKT signaling

The core molecular mechanism connecting M-Ras to disease was defined by Rodriguez-Viciana et al. (2006), who showed that Shoc2/Sur-8 together with the catalytic subunit of protein phosphatase 1 (PP1c) form a highly specific M-Ras effector complex that stimulates RAF by dephosphorylating the inhibitory Ser259 (S259) site on RAF proteins. Motta et al. (2020) demonstrated that NS-causing M-Ras mutants exhibit constitutive plasma-membrane targeting, prolonged non-raft localization, enhanced binding to PPP1CB and SHOC2, and variably increased MAPK and PI3K–AKT activation — showing that the disease mutants amplify precisely this effector interaction.

"M-Ras targets Shoc2-PP1c to stimulate Raf activity by dephosphorylating the S259 inhibitory site of Raf proteins" — PMID: 16630891

"enhanced binding to PPP1CB and SHOC2 protein, and variably increased MAPK and PI3K-AKT activation" — PMID: 31108500

This places NS11 firmly within the SHOC2–PPP1CB–RAF signaling module, the same axis mutated in SHOC2-related Noonan-like syndrome with loose anagen hair (NS/LAH) and PPP1CB-related Noonan-like syndrome — a striking example of pathway-level convergence.

Finding 3 — MEK inhibition (trametinib) is an emerging targeted therapy for NS-associated HCM

Because NS11 pathology is driven by RAS–MAPK hyperactivation, pharmacologic MEK1/2 inhibition is a rational targeted therapy. A growing body of case reports documents off-label trametinib reversing or attenuating severe NS-associated HCM and lymphatic disease across multiple RASopathy genotypes (RIT1, RAF1, PTPN11), and a clinical trial is now registered (NCT06555237). Chaput & Andelfinger (2024) reviewed the repurposing of trametinib and mTOR inhibitors for RASopathy HCM. In parallel, rigosertib (a dual RAS/MAPK + PI3K/AKT inhibitor) reversed HCM in RAF1-NS models.

"repurposing of medications inhibiting the RAS/MAPK on a compassionate use basis has emerged as a promising concept to improve the outcome of these patients" — PMID: 38432396

While direct trametinib data specifically in MRAS-mutant patients are not yet published, the shared downstream mechanism (MEK/ERK hyperactivation) makes this the most promising disease-modifying strategy for NS11's lethal cardiac phenotype.

Finding 4 — Variant spectrum: recurrent likely-pathogenic hotspots in a highly constrained gene

ClinVar (RefSeq NM_001085049.3) lists recurrent NS-causing missense variants classified as Likely pathogenic:

Of 297 MRAS ClinVar records, only these missense point variants are pathogenic/likely-pathogenic for NS (the other "Pathogenic" entries are large 3q copy-number variants unrelated to the point-mutation mechanism). Population-constraint metrics from gnomAD (ENSG00000158186, chr3:138,347,648–138,405,534) show MRAS is strongly intolerant to both missense and loss-of-function variation: missense Z = 3.16 (observed/expected = 0.555), pLI = 0.99, LoF o/e = 0.19 (4 observed vs 20.9 expected). The pathogenic residues Gly23, Thr68, and Gln71 are conserved codons that are established mutational hotspots across the RAS protein family. All reported disease variants are germline, de novo, and absent from population databases.

"Gly23 and Thr68 are highly conserved residues, and the corresponding codons are known hotspots for RASopathy-associated mutations in other RAS proteins" — PMID: 31108500

Finding 5 — Clinical phenotype and epidemiology: an ultra-rare NS subtype with disproportionately severe, early-onset HCM

NS11 shares the core multisystem Noonan phenotype but is distinguished by its severe cardiac involvement. Noonan syndrome overall affects ~1:1,000–2,500 live births (Roberts et al. 2013), is autosomal dominant, and features distinctive facies, short stature, congenital heart disease (pulmonary valve stenosis, HCM), developmental delay/learning difficulties, cryptorchidism, lymphatic dysplasia, bleeding diathesis, and renal anomalies. NS11/MRAS accounts for only a handful of reported individuals worldwide — <1% of molecularly solved NS. Reported MRAS patients uniformly presented with HCM, often with neonatal/infantile onset and severe course (including one neonatal death from cardiac failure).

"Noonan syndrome is a genetic multisystem disorder characterised by distinctive facial features, developmental delay, learning difficulties, short stature, congenital heart disease, renal anomalies, lymphatic malformations, and bleeding difficulties" — PMID: 23312968

"hypertrophic cardiomyopathy in RASopathies (R-HCM) is associated with higher prevalence of congestive heart failure and shows increased prevalence and severity of left ventricular outflow tract obstruction" — PMID: 34776080

RASopathy-associated HCM (R-HCM) shows higher rates of congestive heart failure and left ventricular outflow tract (LVOT) obstruction than sarcomeric HCM, consistent with the severe HCM-predominant presentation of MRAS cases.

Finding 6 — M-Ras biology and evolutionary conservation inform model-organism relevance

M-Ras is a RAS-family GTPase with a single orthologue conserved from nematode to human, and it evolved independently of R-Ras (Keduka et al. 2009). In ascidian, Ci-Mras is expressed in the neural complex and its knockdown perturbs FGF–Ras–MAPK-dependent neural/notochord development; mammalian M-Ras mediates NGF-induced neuronal differentiation in PC12 cells. Beyond the SHOC2–PP1c–RAF branch, M-Ras also signals via RA-GEF-2 to activate Rap1, regulating integrin-mediated adhesion (Yoshikawa et al. 2007). Disease modeling to date is primarily via patient-derived iPSC-cardiomyocytes carrying p.Gly23Val, which reproduce hypertrophy and abnormal calcium handling.

"A single Mras orthologue exists from nematode to mammalian" — PMID: 18977283

"activated M-Ras potently induced lymphocyte function-associated antigen 1 (LFA-1)-mediated cell aggregation" — PMID: 17538012

Finding 7 — p.Gly23Val causes ~40-fold constitutive activation; iPSC-CMs prove necessity and sufficiency for cardiac hypertrophy

Higgins et al. (2017; JCI Insight) performed molecular-dynamics simulations predicting that p.Gly23Val damages the effector-interaction regions and the GTP-binding site; ectopic-expression experiments revealed a 40-fold increase in M-Ras activation versus wild-type, with enhanced RAS/MAPK signaling and downstream gene-expression changes. Higgins et al. (2019; Circ Genom Precis Med) used CRISPR/Cas9 isogenic-corrected patient iPSC-cardiomyocytes to demonstrate that the variant is both necessary and sufficient to elicit hypertrophy — larger cell size, hypertrophic gene-expression changes, and impaired Ca²⁺ handling (irregular Ca²⁺ transients).

"ectopic expression experiments revealed a 40-fold increase in MRAS activation for p.Gly23Val-MRAS compared with WT-MRAS" — PMID: 28289718

"p.Gly23Val-MRAS is both necessary and sufficient to elicit a cardiac hypertrophy phenotype in iPSC-CMs" — PMID: 31638832

This is among the strongest causal evidence in any RASopathy: an isogenic-control experiment directly linking a single point variant to the defining clinical phenotype.

Finding 8 — Diagnosis and multidisciplinary management

Diagnosis of NS is clinical (van der Burgt criteria) with molecular confirmation; because MRAS is one of >20 RASopathy genes, testing uses multigene NGS panels/exome rather than single-gene tests (Tartaglia 2022). Short stature is treated with recombinant human growth hormone; a phase 3 RCT (REAL8, NCT05330325) showed once-weekly somapacitan non-inferior/superior to daily GH (height velocity 10.4 vs 9.2 cm/yr). Bleeding diathesis affects up to ~40–65% of NS patients — partial factor XI/VII deficiency, platelet dysfunction, and shear-related acquired von Willebrand syndrome with pulmonary stenosis — warranting hemostatic screening before surgery. Severe/obstructive HCM refractory to standard therapy is managed with off-label MEK inhibition (trametinib) or mTOR inhibitors. Cancer surveillance follows RASopathy guidelines.

"Daily growth hormone (GH) injections are indicated for the treatment of short stature in children with Noonan syndrome" — PMID: 41774755

"Nearly 40% of patients with the Noonan syndrome had a bleeding diathesis and >90% of them had platelet function and/or coagulation abnormalities" — PMID: 24753526

The 15 Disease-Characteristic Domains

1. Disease Information

Overview. NS11 is a rare autosomal-dominant developmental disorder within the RASopathy family (disorders of RAS–MAPK dysregulation). It is the MRAS-related form of Noonan syndrome, characterized by classic Noonan features plus a characteristically severe, frequently neonatal/infantile hypertrophic cardiomyopathy.

Key identifiers. - OMIM: #618499 (Noonan syndrome 11) - MONDO: 0032786 - Gene: MRAS (HGNC:7227), 3q22.3; Ensembl ENSG00000158186; gene OMIM 608435 - RefSeq: NM_001085049.3 - ICD-10: Q87.1 (congenital malformation syndromes predominantly affecting stature) — code used for Noonan syndrome broadly; ICD-11: LD2F.11 (Noonan syndrome and Noonan-related syndromes) - MeSH: Noonan Syndrome (D009634) — no NS11-specific MeSH term - Orphanet: Noonan syndrome (ORPHA:648) — no separate NS11 subtype code

Synonyms/alternative names. Noonan syndrome 11; NS11; MRAS-related Noonan syndrome; M-Ras/R-Ras3–related Noonan syndrome.

Data source type. Information is derived from aggregated disease-level resources (OMIM, ClinVar, gnomAD) and from individual patient case reports (the handful of published NS11 cases), not from EHR-scale cohorts — reflecting the ultra-rare nature of the disease.

2. Etiology

Causal factor. Purely genetic: de novo germline activating missense variants in MRAS. No environmental or infectious cause.

Genetic risk factors. The disease-causing variants are themselves the sole "risk factor." Recurrent hotspots: p.Gly23Val, p.Gly23Arg, p.Thr68Ile, p.Gln71Arg (and likely-pathogenic p.Pro120Leu). MRAS is highly constrained (missense Z = 3.16, pLI = 0.99), so any missense change at a conserved GTP-handling residue is likely deleterious. No NS11-specific modifier genes are established.

Environmental risk factors. None known. As with all de novo dominant conditions, advanced paternal age is a general (inferred) risk factor for de novo point mutations, not specifically demonstrated for MRAS.

Protective factors. None identified. Given strong purifying selection at MRAS, no protective alleles are documented.

Gene–environment interactions. None established. NS11 is a monogenic, fully genetically determined condition.

3. Phenotypes

NS11 shares the core Noonan phenotype, with cardiac hypertrophy as the distinguishing severe feature. Frequencies below are largely extrapolated from broader NS and RASopathy-HCM literature given the tiny NS11 case count.

Quality-of-life impact. Dominated by cardiac morbidity (heart-failure symptoms, exercise intolerance, procedural risk), short stature, and neurodevelopmental/learning needs. Bleeding tendency complicates surgery. Formal EQ-5D/SF-36 data specific to NS11 are not available.

4. Genetic/Molecular Information

• Causal gene: MRAS (M-Ras/R-Ras3), 3q22.3, HGNC:7227; gene OMIM 608435; disease OMIM #618499.
• Variant classification (ACMG/AMP, per ClinVar): Likely pathogenic — p.Gly23Val (c.68G>T), p.Gly23Arg (c.67G>C), p.Thr68Ile (c.203C>T), p.Gln71Arg (c.212A>G), p.Pro120Leu (c.359C>T).
• Variant type: Missense single-nucleotide substitutions affecting conserved GTP-binding/hydrolysis residues.
• Allele frequency: Absent from population databases (gnomAD) — consistent with de novo pathogenic origin.
• Somatic vs germline: Germline, de novo. Somatic MRAS variation is not a recognized oncogenic driver comparable to KRAS/HRAS/NRAS.
• Functional consequence: Gain of function via impaired intrinsic and GAP-stimulated GTPase activity → constitutive GTP loading.
• Modifier genes: None established for NS11.
• Epigenetic information: No NS11-specific DNA-methylation or chromatin signature described.
• Chromosomal abnormalities: Not part of the point-mutation NS11 mechanism; large 3q22 CNVs in ClinVar represent a separate contiguous-gene entity.

5. Environmental Information

Not applicable. NS11 is a monogenic de novo dominant disorder. No environmental factors, lifestyle factors, or infectious agents are implicated in causation or triggering. Standard cardiac-risk lifestyle considerations apply generically to any HCM patient but are not disease-specific.

6. Mechanism / Pathophysiology

Ordered causal chain (initiating lesion → clinical manifestation):

1. A de novo germline missense variant in MRAS (e.g., c.68G>T, p.Gly23Val) alters a conserved GTP-binding/hydrolysis residue → impairs intrinsic and GAP-stimulated GTP hydrolysis (demonstrated; ~40-fold increased activation for p.Gly23Val).
2. Impaired hydrolysis → M-Ras accumulates in the constitutively active, GTP-bound state with constitutive plasma-membrane targeting and prolonged non-raft localization (demonstrated).
3. Active GTP–M-Ras → enhanced binding to the SHOC2–PP1c (PPP1CB) holophosphatase (demonstrated: enhanced binding to PPP1CB and SHOC2).
4. SHOC2–PP1c → dephosphorylates the inhibitory Ser259 site of RAF → relieves 14-3-3-mediated RAF autoinhibition (demonstrated for the M-Ras–SHOC2–PP1c module).
5. RAF activation → hyperactivation of the MEK→ERK (MAPK) cascade (demonstrated: increased MAPK signaling), with a branch to increased PI3K–AKT signaling (demonstrated, variable).
6. ERK/AKT hyperactivation in developing tissues → dysregulated cell proliferation, differentiation, growth, and survival (inferred from RASopathy biology).
7. In cardiomyocytes → cardiomyocyte hypertrophy, hypertrophic gene-expression program, and impaired Ca²⁺ handling (demonstrated in iPSC-CMs; variant necessary and sufficient) → hypertrophic cardiomyopathy (clinical manifestation).
8. In craniofacial, skeletal, hematopoietic, lymphatic, and neural lineages → distinctive facies, short stature, bleeding diathesis, lymphatic dysplasia, and developmental delay (inferred by analogy to other RASopathies).

  MRAS missense (Gly23/Thr68/Gln71)
    │  impairs GTP hydrolysis
    ▼
  Constitutive GTP–M-Ras  ── membrane-targeted, non-raft
    │  enhanced binding
    ▼
      SHOC2 – PP1c (PPP1CB) holophosphatase
    │  dephosphorylates RAF-pSer259
    ▼
RAF (relieved autoinhibition)
    ├──────────────► MEK ──► ERK  (MAPK; main axis)
    └──────────────► PI3K ──► AKT  (variable branch)
                   │
                   ▼
  cardiomyocyte hypertrophy + Ca²⁺ dyshandling
                   │
                   ▼
 SEVERE HYPERTROPHIC CARDIOMYOPATHY
(+ facies, short stature, bleeding, lymphatic, DD)

• Molecular pathways: RAS–RAF–MEK–ERK (MAPK; KEGG hsa04010); PI3K–AKT (KEGG hsa04151); Rap1 signaling via RA-GEF-2 (secondary M-Ras branch).
• Cellular processes: Dysregulated proliferation, differentiation, growth, survival (GO:0008283, GO:0030154); cardiomyocyte hypertrophy (GO:0003300); abnormal Ca²⁺ handling.
• Protein dysfunction: Gain-of-function GTPase locked in active conformation (UniProt O14807, MRAS_HUMAN); no misfolding/aggregation — the defect is functional (constitutive signaling).
• GO biological-process suggestions: GO:0007265 (Ras protein signal transduction), GO:0000165 (MAPK cascade), GO:0043410 (positive regulation of MAPK cascade).
• Cell types (CL): cardiac muscle cell / cardiomyocyte (CL:0000746; CL:0002094 regular cardiac myocyte).
• Molecular profiling: iPSC-CM transcriptomics showed a hypertrophic gene-expression signature; no large-scale proteomic/metabolomic/lipidomic NS11-specific datasets exist.
• Functional genomics: CRISPR/Cas9 isogenic correction (Higgins 2019) is the key functional-genomics evidence.

7. Anatomical Structures Affected

• Primary organ: Heart — specifically the myocardium/left ventricle (UBERON:0002084 heart left ventricle; UBERON:0002349 myocardium), with hypertrophy and LVOT obstruction. Pulmonary valve (UBERON:0002146) with stenosis.
• Secondary/body systems: Cardiovascular (primary); lymphatic (UBERON:0006558 lymphatic vessel — chylothorax, lymphangiectasia); hematologic (bleeding diathesis); musculoskeletal/growth (short stature); craniofacial (distinctive facies); nervous system (developmental delay); genitourinary (cryptorchidism, occasional renal anomalies).
• Tissue/cell level: Cardiac muscle tissue; cardiomyocytes (CL:0000746). Connective tissue, lymphatic endothelium, and hematopoietic lineages secondarily involved.
• Subcellular level (GO cellular component): Plasma membrane (GO:0005886) — constitutive membrane targeting of mutant M-Ras; non-raft membrane microdomains; cytoplasm. Sarcoplasmic-reticulum Ca²⁺-handling machinery is functionally affected in cardiomyocytes.
• Localization/lateralization: Cardiac hypertrophy is typically biventricular/asymmetric septal as in HCM generally; systemic features are bilateral/symmetric.

8. Temporal Development

• Onset: Congenital to neonatal/infantile. HCM in reported MRAS cases presents very early, often neonatally (one neonatal death from cardiac failure).
• Onset pattern: Congenital structural/functional cardiac disease with progressive hypertrophy; facies present at birth; short stature emerges postnatally.
• Progression: Cardiac hypertrophy can be rapidly progressive in infancy — a poor-prognosis pattern shared with other early-onset RASopathy HCM. Course is otherwise chronic and lifelong.
• Disease course: Non-cardiac features (facies, stature, learning) are stable/chronic; cardiac disease is the dominant driver of morbidity/mortality and can progress to heart failure.
• Remission patterns: No spontaneous remission of the genetic disorder; treatment-induced regression of HCM observed with MEK inhibition in RASopathy HCM broadly.
• Critical periods: The neonatal/infantile window is the critical period of cardiac vulnerability and the key window for intervention (e.g., MEK-inhibitor rescue).

9. Inheritance and Population

• Epidemiology: No standalone NS11 prevalence/incidence figures exist. Noonan syndrome overall: ~1:1,000–2,500 live births. NS11 is <1% of molecularly solved NS — ultra-rare, a handful of reported individuals worldwide.
• Inheritance: Autosomal dominant; reported cases are de novo.
• Penetrance: Presumed high/complete for the cardiac phenotype in reported cases (all had HCM), though the sample is too small for formal estimates.
• Expressivity: Variable, as in NS generally.
• Genetic anticipation: Not applicable (not a repeat-expansion disorder).
• Germline mosaicism: Not documented for MRAS; possible in principle for any de novo dominant condition (inferred).
• Founder effects / consanguinity: Not applicable (de novo dominant; no founder alleles).
• Carrier frequency: Not applicable (dominant, de novo; variants absent from gnomAD).
• Population demographics: No ethnic predisposition known; reported cases span different populations. Sex ratio: NS overall is roughly equal; NS11 case count too small to assess. Age distribution: presents in infancy/childhood.

10. Diagnostics

• Clinical diagnosis: Van der Burgt criteria for Noonan syndrome (facies + one or more of: cardiac defect, short stature, family history, other features).
• Genetic testing (recommended approach): Multigene RASopathy NGS panel or exome/genome sequencing — the standard, because MRAS is one of >20 RASopathy genes. Single-gene MRAS testing is inefficient. WGS/WES both have high utility; targeted panels are cost-effective first-line. Chromosomal microarray/karyotype/FISH are not primary tools (point-mutation disorder). Mitochondrial and repeat-expansion testing are not applicable.
• Variant interpretation: ClinVar/ClinGen and ACMG/AMP criteria; de novo occurrence (PS2), absence from gnomAD (PM2), hotspot residue (PM1), and functional gain-of-function data (PS3) support pathogenicity.
• Cardiac diagnostics: Echocardiography (HCM, LVOT gradient, pulmonary stenosis), ECG, cardiac MRI, and heart-failure biomarkers (BNP/NT-proBNP — generic).
• Hematologic workup: Bleeding time, PT/aPTT, factor XI/VII assays, platelet-function testing, von Willebrand multimer analysis — especially before invasive procedures.
• Omics-based diagnostics: Not routinely used; research iPSC-CM models exist.
• Differential diagnosis: Other RASopathies (PTPN11, SOS1, RAF1, RIT1, SHOC2, PPP1CB, LZTR1, etc.), sarcomeric HCM, and other syndromic HCM causes (metabolic/mitochondrial). Molecular testing resolves the distinction.
• Screening: No population newborn screening exists; cascade testing is limited by the de novo nature. Prenatal findings (increased nuchal translucency, cardiac hypertrophy, polyhydramnios) may prompt targeted testing.

11. Outcome / Prognosis

• Prognosis driver: Severity and onset of HCM. Early-onset (before ~6 months) NS-HCM carries high mortality; NS11 cases have included neonatal death from cardiac failure.
• Survival/mortality: No NS11-specific survival statistics. By analogy, RASopathy-HCM with heart failure has worse surgical risk and mortality than sarcomeric HCM.
• Morbidity: Heart failure, LVOT obstruction, arrhythmia risk, bleeding complications, growth failure, developmental/learning needs.
• Recovery potential: The genetic disorder is lifelong, but MEK-inhibitor therapy has produced regression of HCM in RASopathy patients, offering a route to improved cardiac outcomes.
• Prognostic factors: Age at HCM onset, LVOT obstruction, heart-failure signs, treatment response.
• Prognostic biomarkers: No validated NS11-specific molecular biomarkers; cardiac imaging metrics and natriuretic peptides are used clinically.

12. Treatment

• Pharmacotherapy / targeted therapy (emerging): MEK1/2 inhibitor trametinib (off-label/compassionate use) can reverse or attenuate severe NS-associated HCM and lymphatic disease; a trial is registered (NCT06555237). mTOR inhibitors (rapamycin/everolimus) have been used for severe RASopathy HCM. Rigosertib (dual RAS/MAPK + PI3K/AKT inhibitor) reversed HCM in RAF1-NS models. NCIT terms: Trametinib (NCIT:C77908); Sirolimus/Rapamycin (NCIT:C1212).
• Growth: Recombinant human growth hormone for short stature; once-weekly somapacitan shown non-inferior/superior to daily GH in NS (REAL8 RCT). NCIT: Recombinant Human Growth Hormone (NCIT:C1834).
• Cardiac supportive/interventional: Standard HCM management (beta-blockers, avoidance of dehydration), surgical/catheter relief of LVOT/pulmonary stenosis; RVOT stenting and staged strategies used to bridge infants (trametinib-then-surgery approaches reported in NS-HCM broadly).
• Hematologic: Hemostatic optimization before surgery.
• Rehabilitative/supportive: Developmental and educational support; physical/occupational/speech therapy; nutritional support for feeding difficulties.
• Pharmacogenomics: No NS11-specific pharmacogenomic guidance; the genotype itself (RAS-MAPK activation) is the rationale for pathway-targeted therapy (precision-medicine approach).
• Treatment outcomes/adverse events: Trametinib case reports show short-term symptomatic improvement across NS-HCM; moderate side effects (skin, GI) reported; long-term data lacking. Formal response rates in MRAS patients specifically are not yet published.
• Cancer surveillance: Per RASopathy guidelines (RAS-MAPK genes carry variable tumor risk).

13. Prevention

• Primary prevention: Not possible — de novo genetic origin.
• Secondary prevention: Early cardiac surveillance (echocardiography) after molecular/clinical diagnosis to detect and treat HCM early; early hemostatic evaluation before procedures.
• Tertiary prevention: Aggressive management of HCM (targeted MEK/mTOR inhibition, heart-failure care, obstruction relief) to prevent decompensation; developmental support to optimize function.
• Immunization/behavioral/public-health/environmental interventions: Not applicable (no environmental etiology). Standard childhood immunizations apply.
• Genetic counseling: Central to care. Recurrence risk for parents of a de novo case is low (but non-zero due to possible germline mosaicism). An affected individual has 50% transmission risk (autosomal dominant). Prenatal/preimplantation genetic testing is available once the familial variant is known.

14. Other Species / Natural Disease

• Taxonomy/orthologues: MRAS is conserved with a single orthologue from nematode to human. Mouse Mras (NCBI Gene 17532); ascidian Ci-Mras; zebrafish and other vertebrate orthologues exist.
• Natural disease in other species: No naturally occurring MRAS-related Noonan-like disease is documented in companion animals or wildlife (OMIA). Veterinary relevance is therefore minimal.
• Comparative biology: M-Ras evolved independently of R-Ras; its neural/developmental function is conserved between mammals and ascidian, and it functions in FGF–Ras–MAPK-dependent development — underscoring cross-species conservation of the affected pathway.
• Transmission/zoonosis: Not applicable (non-infectious genetic disorder).

15. Model Organisms

• Cellular/in vitro (primary model): Patient-derived iPSC-cardiomyocytes carrying p.Gly23Val, with CRISPR/Cas9 isogenic-corrected controls — the definitive NS11 model. It recapitulates cardiomyocyte hypertrophy, hypertrophic gene expression, and impaired Ca²⁺ handling, and established that the variant is necessary and sufficient for the cardiac phenotype (PMID: 31638832). Ectopic-expression cell systems quantified the ~40-fold activation (PMID: 28289718).
• In vitro biochemistry: Cell-based assays of GTP loading, SHOC2/PPP1CB binding, and MAPK/PI3K-AKT readouts (Motta 2020).
• Invertebrate/other: Ascidian Ci-Mras knockdown models demonstrate conserved neural/notochord roles; PC12 cells model M-Ras-dependent neuronal differentiation.
• Mammalian genetic models: No published Mras knock-in mouse specifically modeling NS11 was identified; general RASopathy mouse models (Ptpn11, Raf1 knock-ins) inform pathway biology and MEK-inhibitor efficacy, and transgenic Raf1 models were used for the rigosertib study.
• Model characteristics/limitations: iPSC-CMs excellently model the cardiac phenotype and drug response but do not capture systemic/developmental features (facies, stature, lymphatics) or whole-organism physiology. A dedicated Mras animal model remains a gap.
• Resources: MGI (Mras, mouse gene 17532), Cellosaurus (patient iPSC lines), Alliance of Genome Resources for orthology.

Mechanistic Model / Interpretation

NS11 is mechanistically among the best-understood RASopathies at the "single-variant → single-phenotype" level, despite its rarity. The unifying model is constitutive RAS–MAPK activation driven by a hydrolysis-dead M-Ras GTPase that hyperengages the SHOC2–PP1c–RAF module. Three lines of orthogonal evidence converge:

The therapeutic corollary is direct: because the phenotype is driven by MEK/ERK output, pharmacologic MEK inhibition is a mechanism-matched therapy, and multiple RASopathy case reports (RIT1, RAF1, PTPN11) show that trametinib can reverse severe HCM and lymphatic disease — a strong rationale for its use in NS11, pending genotype-specific data.

Evidence Base

Limitations and Knowledge Gaps

1. Tiny case count. Only a handful of molecularly proven NS11 patients are published. All frequency, penetrance, expressivity, and prognosis statements beyond "HCM is characteristic and severe" are extrapolated from broader NS/RASopathy cohorts, not from NS11-specific data.
2. No NS11-specific epidemiology. Prevalence, incidence, sex ratio, and survival are not directly measured.
3. No dedicated in vivo model. The definitive model is iPSC-CMs; a Mras knock-in mouse recapitulating the systemic phenotype is not published — limiting study of extra-cardiac features and whole-organism drug testing.
4. Genotype-specific therapy data absent. MEK-inhibitor efficacy is documented in other RASopathy genotypes (RIT1, RAF1, PTPN11) but not yet specifically in MRAS patients; efficacy is inferred from shared downstream mechanism.
5. Extra-cardiac mechanism largely inferred. The causal steps from ERK hyperactivation to facies, stature, lymphatic, and neurodevelopmental features are inferred by analogy, not demonstrated in MRAS tissue.
6. No episignature/epigenetic, proteomic, metabolomic, or lipidomic profiling specific to NS11.
7. p.Pro120Leu and p.Gln71Arg have less functional characterization than the Gly23/Thr68 hotspots.

Proposed Follow-up Experiments / Actions

1. International case registry. Aggregate all molecularly confirmed MRAS patients (GeneMatcher/collaborative networks) to define true frequency, phenotypic range, cardiac natural history, and mortality.
2. Generate an Mras knock-in mouse (e.g., p.Gly23Val) to model the systemic phenotype, test MEK/mTOR/rigosertib in vivo, and study extra-cardiac mechanisms.
3. Genotype-specific trametinib data. Prospectively capture MEK-inhibitor response in MRAS patients within trials such as NCT06555237; report cardiac imaging and biomarker endpoints.
4. Functional characterization of p.Gln71Arg and p.Pro120Leu (GTP loading, SHOC2/PPP1CB binding, MAPK/PI3K-AKT output) to confirm gain-of-function and refine ACMG classification.
5. iPSC-CM drug screens comparing trametinib, mTOR inhibitors, rigosertib, and SHOC2/PPP1CB-directed strategies on MRAS-mutant cardiomyocytes; test rescue of Ca²⁺ handling.
6. Structural studies / AlphaFold-informed modeling of mutant M-Ras–SHOC2–PP1c to identify the interface for potential allosteric inhibitors.
7. Episignature analysis of MRAS patients to determine whether NS11 carries a distinguishing DNA-methylation signature useful for VUS resolution.

Report compiled from 5 investigation iterations, 8 confirmed findings, and 61 reviewed papers. Evidence types: human clinical (case reports/cohorts), in vitro (iPSC-CMs, biochemistry), model organism (ascidian, PC12; pathway-level mouse models), and computational (molecular-dynamics, constraint metrics).

Artifacts

• OpenScientist final report
• OpenScientist final report

Reference Validation

Checked with linkml-reference-validator 0.2.1.

All extracted references resolved successfully.

Term Validation

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

Terms whose name is worth a second look

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

• HP:0001263 (1 mention) - the report calls it "Developmental delay / learning difficulty"; HP calls it Global developmental delay, and lists "Developmental delay, global" among its other names
• HP:0001642 (1 mention) - the report calls it "Pulmonary valve stenosis"; HP calls it Pulmonic stenosis, and lists "Pulmonary valve stenosis" among its other names
• HP:0000465 (1 mention) - the report calls it "Webbed/broad neck"; HP calls it Webbed neck
• HP:0001892 (1 mention) - the report calls it "Bleeding diathesis"; HP calls it Abnormal bleeding, and lists "Bleeding diathesis" among its other names
• HP:0000028 (1 mention) - the report calls it "Cryptorchidism (males)"; HP calls it Cryptorchidism

Terms named inconsistently

The report gives these identifiers more than one name of its own:

• HGNC:7227 - called "MRAS", "Gene:* MRAS"

Prefixes with no resolver

Terms carrying these prefixes were not checked either way, because no configured ontology covers them. An unrecognised prefix may name an ontology this run could not reach as easily as one that does not exist, so nothing here is evidence of fabrication: ORPHA.

28 of 30 terms resolved to a current term; the rest could not be looked up either way.