Radioulnar Synostosis with Amegakaryocytic Thrombocytopenia: Disease Characteristics Report

Scope and evidence date. This report treats radioulnar synostosis with amegakaryocytic thrombocytopenia (RUSAT) as an umbrella phenotype comprising HOXA11-associated RUSAT1 and MECOM-associated RUSAT2. For MECOM, the broader term MECOM-associated syndrome is often preferable because radioulnar synostosis (RUS), thrombocytopenia, or both may be absent. Evidence is predominantly aggregated case reports and small family cohorts rather than population registries or individual EHR-derived data. No disease-specific management guideline or randomized therapeutic trial was identified.

Table: Compact knowledge-base comparison of aggregate RUSAT and its HOXA11- and MECOM-associated subtypes, including identifiers, inheritance, phenotype, mechanism, ontology suggestions, and clinical implications.

1. Disease information

RUSAT is a rare, congenital, inherited bone-marrow-failure syndrome coupling abnormal forearm development—usually proximal fusion of the radius and ulna—with deficient megakaryopoiesis and thrombocytopenia that can progress to pancytopenia. The synostosis severely restricts pronation and supination. Molecularly related disease spans isolated RUS, congenital amegakaryocytic thrombocytopenia, aplastic anemia, and global marrow failure with or without skeletal anomalies. The original MECOM study states: “RUSAT is an inherited bone marrow failure syndrome, characterized by thrombocytopenia and congenital fusion of the radius and ulna.” (niihori2015mutationsinmecom pages 1-2)

Identifiers and synonyms

• Aggregate syndrome: MONDO:0011555, Orphanet:71289.
• RUSAT1/HOXA11-associated disease: OMIM 605432.
• RUSAT2/MECOM-associated disease: OMIM 616738, MONDO:0014758.
• Broader MECOM phenotype: MECOM-associated syndrome, MONDO:0100458.
• Synonyms include radio-ulnar synostosis–amegakaryocytic thrombocytopenia syndrome, RUSAT, congenital thrombocytopenia with radioulnar synostosis, and historically CTRUS. OpenTargets links the aggregate entity to both MECOM and HOXA11, with primary-literature support from PMIDs 26581901, 29540340, and 11101832. OSGEP appears as a low-score database association but is not an established RUSAT causal gene and should not be curated as such without independent validation. (OpenTargets Search: Radioulnar synostosis with amegakaryocytic thrombocytopenia-HOXA11,MECOM)
• No dedicated MeSH, ICD-10, or ICD-11 code was established in the retrieved evidence; coding ordinarily uses the relevant congenital limb-malformation and thrombocytopenia/bone-marrow-failure codes rather than a disease-specific code.

2. Etiology, risk, and protective factors

Genetic causes

RUSAT is principally a heterozygous germline transcription-factor disorder:

1. RUSAT1: heterozygous pathogenic HOXA11 variants. The landmark report identified HOXA11 disease in two unrelated families (Thompson & Nguyen, Nature Genetics, 1 December 2000; PMID 11101832; DOI: https://doi.org/10.1038/82511). Subsequent cohorts indicate very few molecularly confirmed HOXA11 families. (germeshausen2018mecomassociatedsyndromea pages 1-2)
2. RUSAT2/MECOM-associated syndrome: heterozygous pathogenic MECOM sequence variants or constitutional deletions affecting 3q26.2. Variants are often de novo, although multigenerational autosomal-dominant transmission occurs. (walne2018expandingthephenotypic pages 1-5, germeshausen2018mecomassociatedsyndromea pages 2-2)

Risk factors. Carrying a pathogenic germline allele is the only established primary risk factor. Family history increases prior probability but may be absent because of de novo mutation, incomplete penetrance, mild parental disease, or somatic rescue. Sex, ethnicity, consanguinity, age, lifestyle, toxins, occupation, infection, and prenatal exposure are not established etiologic risk factors. No founder mutation or reliable carrier-frequency estimate is known.

Protective factors. No inherited protective allele, diet, lifestyle, medication, or environmental exposure has been validated. A notable endogenous modifier is somatic genetic rescue: in four individuals, copy-neutral loss of heterozygosity across chromosome 3q duplicated the residual wild-type MECOM allele in an expanding hematopoietic clone and was associated with milder or resolving cytopenia. This is a post-zygotic disease modifier, not a clinically deployable preventive factor. (venugopal2024unravelingfacetsof pages 2-3)

Gene–environment interaction. None has been demonstrated. Infections can aggravate morbidity in already cytopenic or immunodeficient patients but do not cause the Mendelian syndrome.

3. Phenotypes

The most useful phenotype summary comes from a 2024 review of 64 MECOM-associated individuals. RUS occurred in 45.3%; other skeletal malformations in 42.2%; pancytopenia in 36/64 (56.2%); isolated thrombocytopenia in 16/64 (25.0%); and no cytopenia in 8/64 (12.5%). Reported extrahematologic frequencies were nail/facial abnormalities 23.4%, neurologic findings 17.2%, hearing impairment 14.1%, renal abnormalities 9.4%, precocious puberty 6.3%, and immune dysfunction such as B-cell deficiency or hypogammaglobulinemia 10/64 (15.6%). The paper prints cardiac malformations as “27/64, 26.6%”; because 27/64 is 42.2%, that internally inconsistent statistic should be verified against its supplement before database ingestion. (huang2024anovelmissense pages 3-5)

Core phenotypes and suggested HPO annotations

• Congenital proximal radioulnar synostosis—usually bilateral; stable structural defect but lifelong limitation of forearm rotation. Suggested: Radioulnar synostosis, Bilateral radioulnar synostosis, Limited forearm supination/pronation, Congenital onset. Functional impact ranges from mild compensation to difficulty feeding, dressing, personal hygiene, writing, and positioning the hand.
• Thrombocytopenia / amegakaryocytic thrombocytopenia—often neonatal or infantile, severe and persistent or occasionally improving. Suggested: Thrombocytopenia, Decreased megakaryocytes, Petechiae, Ecchymosis, Abnormal bleeding, Intracranial hemorrhage.
• Progressive marrow failure—thrombocytopenia may broaden to anemia, neutropenia, pancytopenia, hypocellular marrow, aplastic anemia, or MDS. Suggested: Pancytopenia, Anemia, Neutropenia, Hypocellular bone marrow, Bone marrow failure, Myelodysplasia. (germeshausen2018mecomassociatedsyndromea pages 4-5, walne2018expandingthephenotypic pages 8-13)
• Hand and lower-limb anomalies—clinodactyly, brachydactyly/brachymesophalangy, abnormal fifth phalanges, overlapping fingers, nail anomalies, hip dysplasia, and occasionally absent patella. Suggested: Clinodactyly, Brachydactyly, Abnormality of the fifth finger, Nail abnormality, Hip dysplasia, Patellar aplasia. (niihori2015mutationsinmecom pages 1-2, venugopal2024unravelingfacetsof pages 3-4)
• Immune phenotype—B-cell lymphopenia or hypogammaglobulinemia, with recurrent bacterial/fungal infection in severe cases. Suggested: B-cell lymphopenia, Hypogammaglobulinemia, Recurrent infection. (germeshausen2018mecomassociatedsyndromea pages 5-6, germeshausen2018mecomassociatedsyndromea pages 4-5)
• Other variable manifestations—sensorineural hearing loss, congenital heart defects, aortic dilatation, renal/urinary malformations, cleft palate, and occasional neurodevelopmental abnormalities. Suggested: Sensorineural hearing impairment, Congenital heart defect, Aortic dilatation, Renal hypoplasia, Cleft palate, Intellectual disability. (venugopal2024unravelingfacetsof pages 6-7, germeshausen2018mecomassociatedsyndromea pages 8-9, germeshausen2018mecomassociatedsyndromea pages 5-5)

No disease-specific EQ-5D, SF-36, PROMIS, or validated quality-of-life study was identified. Quality-of-life effects are inferred from bleeding, transfusion dependence, infection, transplantation, and upper-limb functional restriction.

4. Genetic and molecular information

Genes and representative variants

• HOXA11 encodes a homeobox transcription factor involved in limb patterning and hematopoietic differentiation. The established RUSAT1 lesion is germline and heterozygous; published human evidence remains limited to a few families. (germeshausen2018mecomassociatedsyndromea pages 1-2, niihori2015mutationsinmecom pages 1-2)
• MECOM encodes alternatively transcribed/spliced MDS1, MDS1-EVI1, and EVI1 zinc-finger transcription-factor isoforms. It contains ten zinc fingers and regulates hematopoietic stem/progenitor-cell maintenance. (venugopal2024unravelingfacetsof pages 1-2)

The 2015 discovery study identified NM_001105078:c.2266A>G (p.Thr756Ala), c.2252A>G (p.His751Arg), and c.2248C>T (p.Arg750Trp). All affected the conserved eighth C-terminal zinc finger or adjacent residues and were absent from 382 ancestry-matched controls and dbSNP, 1000 Genomes, HGVD, and ExAC. At least two were de novo. (niihori2015mutationsinmecom pages 1-2, niihori2015mutationsinmecom pages 2-3)

Other reported MECOM variants include p.His751Tyr, p.Gln759Leu, p.Pro760Ser, p.Cys766Arg, p.Glu758Lys, p.Pro760Ala, splice loss c.2208-1_2208delGA, and multiple frameshift/nonsense alleles and constitutional deletions. Missense variants associated with RUS cluster particularly around zinc fingers 8–9, whereas truncating variants are distributed more broadly and often produce severe marrow failure, although this is not an absolute genotype–phenotype rule. (walne2018expandingthephenotypic pages 1-5, germeshausen2018mecomassociatedsyndromea pages 4-5)

A January 2024 case identified de novo NM_001105078.3:c.2285G>A (p.Arg762Lys), absent from public databases and classified likely pathogenic under ACMG criteria. The literature review counted 64 distinct variants: missense 35/64 (54.7%), deletion 8/64 (12.5%), frameshift 6/64 (9.4%), nonsense 6/64 (9.4%), splice 5/64 (7.8%), and unreported class 4/64. (huang2024anovelmissense pages 3-5)

All established causal alleles are constitutional/germline; somatic MECOM overexpression or rearrangement in cancer is biologically distinct. Somatic copy-neutral 3q loss of heterozygosity may rescue germline disease. No validated modifier gene, disease-specific methylation signature, or causal epigenetic lesion has been established. Large constitutional 3q26 deletions involving MECOM can cause severe multisystem disease; therefore, copy-number analysis is important when sequencing is negative. (germeshausen2018mecomassociatedsyndromea pages 9-9, venugopal2024unravelingfacetsof pages 2-3)

5. Environmental information

No toxin, radiation exposure, pollutant, smoking, alcohol, diet, exercise pattern, occupational exposure, or infectious agent is known to initiate RUSAT. Viral testing in reported infants was used to exclude acquired congenital cytopenia rather than establish causation. Environmental and public-health interventions therefore do not prevent the primary disorder.

6. Mechanism and pathophysiology

Ordered causal chain

1. A heterozygous germline HOXA11 or MECOM lesion leads to abnormal activity or dosage of a developmental transcription factor.
2. In MECOM missense disease, disruption of conserved zinc-finger structure leads to reduced or altered DNA binding; in truncating/deletion disease, haploinsufficiency is inferred to lead to reduced MECOM function. (niihori2015mutationsinmecom pages 2-3, germeshausen2018mecomassociatedsyndromea pages 4-5)
3. Altered transcription-factor function results in dysregulation of hematopoietic stem/progenitor-cell self-renewal and survival; the exact target network remains incompletely defined. (venugopal2024unravelingfacetsof pages 1-2, germeshausen2018mecomassociatedsyndromea pages 7-7)
4. Reduced HSPC maintenance leads to depletion of early progenitors and impaired megakaryopoiesis, resulting in absent/reduced megakaryocytes and congenital thrombocytopenia. (germeshausen2018mecomassociatedsyndromea pages 5-5)
5. Continued progenitor exhaustion leads to multilineage failure, causing anemia, neutropenia, pancytopenia, aplastic marrow, and—occasionally—dysplasia or myeloid malignancy.
6. Parallel developmental branch: altered HOXA11/MECOM transcription during embryonic limb-bud patterning leads to abnormal segmentation/remodeling of radius and ulna, resulting in congenital proximal RUS; this developmental link is strongly genotype-associated but its intervening molecular steps remain inferred. (niihori2015mutationsinmecom pages 3-5)
7. Additional branches: developmental transcriptional disturbance can lead to hand, cardiac, renal, auditory, and B-cell abnormalities; exact tissue-specific pathways are incompletely demonstrated.
8. In some individuals, somatic copy-neutral 3q loss of heterozygosity duplicates the wild-type MECOM allele and results in clonal hematopoietic rescue. Conversely, age-related acquisition of ASXL1, DNMT3A, TET2, ETV6, or 20q-loss clones may lead to improved short-term cellular fitness but potentially increase dysplasia/malignancy risk. (venugopal2024unravelingfacetsof pages 2-3)

Demonstrated versus inferred mechanisms

Structural modeling placed p.Arg750Trp at a predicted DNA-contact residue and implicated p.His751Arg in zinc-finger folding. ChIP-qPCR directly demonstrated reduced occupancy at RUNX1 exon 1 for p.Arg750Trp and p.His751Arg and at the CD109 promoter for p.Arg750Trp. Reporter assays showed enhanced suppression of AP-1 signaling—interpreted as a gain-of-function effect—and attenuated suppression of TGF-β-responsive transcription—partial loss of function. The authors appropriately concluded: “These functional assays suggest that transcriptional dysregulation by mutant EVI1 could be associated with the development of RUSAT.” (niihori2015mutationsinmecom pages 1-2, niihori2015mutationsinmecom pages 3-5)

MPL is not a proven uniform downstream mediator. MECOM and MPL correlate positively in human AML, whereas murine work suggested Evi1 can repress Mpl. Patient CD34+CD38-low cells retained detectable MPL, and very high thrombopoietin was interpreted as secondary to depletion of MPL-expressing cells rather than direct proof of MECOM-mediated MPL suppression. (germeshausen2018mecomassociatedsyndromea pages 7-7, germeshausen2018mecomassociatedsyndromea pages 5-5)

Suggested GO terms: DNA-binding transcription-factor activity; regulation of transcription by RNA polymerase II; hematopoietic stem-cell maintenance; stem-cell self-renewal; megakaryocyte differentiation; platelet formation; embryonic limb morphogenesis; regulation of apoptotic process; TGF-β receptor signaling; AP-1-mediated transcription. Suggested CL terms: hematopoietic stem cell, hematopoietic multipotent progenitor cell, megakaryocyte progenitor, megakaryocyte, platelet, B lymphocyte, osteoblast/chondrocyte lineage cells. These are annotation suggestions, not all experimentally demonstrated disease-cell targets.

No disease-specific single-cell atlas, spatial transcriptomic dataset, metabolomic/lipidomic signature, or multi-omics diagnostic classifier was identified.

7. Anatomical structures affected

• Primary: proximal radius and ulna, elbow/forearm rotational unit; bone marrow and circulating blood.
• Secondary/variable: fingers, phalanges, nails, patella and hip; heart and aorta; kidneys/urinary tract; inner ear/auditory pathway; immune/B-cell compartment.
• Tissues/cells: developing skeletal connective tissue and cartilage/bone; hematopoietic stem/progenitor cells; megakaryocytes; B lymphocytes.
• Subcellular: MECOM and HOXA11 are nuclear transcription factors; relevant GO cellular-component annotations include nucleus, chromatin, and transcription regulator complex.
• Localization: RUS is usually proximal and bilateral, although unilateral or radiographically subtle disease can occur. Suggested UBERON concepts: radius, ulna, forearm, elbow joint, bone marrow, heart, aorta, kidney, inner ear.

8. Temporal development

The skeletal lesion is prenatal and congenital, generally structurally stable. Hematologic onset ranges from fetal hydrops or neonatal hemorrhage to childhood or late-adult disease. In the 2024 15-person cohort, onset ranged from in utero to late adulthood, and one carrier remained comparatively well into the sixth decade. (venugopal2024unravelingfacetsof pages 6-7, venugopal2024unravelingfacetsof pages 2-3)

Typical untreated trajectories are: isolated stable RUS; congenital thrombocytopenia that remains isolated or transiently improves; or thrombocytopenia progressing variably to pancytopenia and marrow failure. Somatic rescue may produce spontaneous hematologic remission, whereas clonal hematopoiesis and dysplasia may emerge with age. Critical intervention periods are severe neonatal bleeding and the transition to transfusion dependence, severe neutropenia, recurrent infection, cytogenetic abnormality, or dysplasia.

9. Inheritance and population

Inheritance is autosomal dominant, with both de novo and familial variants. Penetrance is incomplete and expressivity exceptionally variable, including discordant skeletal and hematologic findings within families. Genetic anticipation is not established. Germline/gonadal mosaicism is theoretically possible but not quantified. No confirmed founder effect, ethnic enrichment, sex bias, incidence, or prevalence estimate exists; fewer than 100 MECOM-associated individuals had been reported by 2024, and HOXA11-confirmed disease is rarer still. These counts reflect publication ascertainment, not population prevalence. (germeshausen2018mecomassociatedsyndromea pages 2-2, venugopal2024unravelingfacetsof pages 1-2)

A 2024 cohort reported 12 losses among 16 pregnancies (75%) in five mothers with detailed histories, versus quoted general-population loss rates of 15–25%. Some losses also occurred in wild-type relatives and fetal genotypes were unavailable, so this striking association is hypothesis-generating rather than a penetrance estimate. (venugopal2024unravelingfacetsof pages 2-3)

10. Diagnostics

Recommended approach

1. CBC with differential, reticulocytes, smear, and bleeding assessment. Repeat serially because lineage involvement evolves.
2. Bone-marrow aspirate/biopsy when cytopenia is unexplained or progressive: assess cellularity, megakaryocytes, dysplasia, fibrosis, cytogenetics, and acquired myeloid variants.
3. Bilateral forearm radiographs to detect proximal RUS, even if external deformity is subtle. Hand/foot imaging may document associated skeletal anomalies.
4. Germline testing: inherited-BMF/thrombocytopenia panel containing MECOM, HOXA11, MPL, RBM8A, and relevant differential genes, or trio WES/WGS. Include MECOM exon-level and 3q26 copy-number/structural-variant analysis.
5. Use nonhematopoietic DNA—cultured skin fibroblasts, hair follicles, or carefully interpreted buccal samples—after HSCT or if somatic rescue/clonal hematopoiesis may mask the germline allele. (venugopal2024unravelingfacetsof pages 6-7, niihori2015mutationsinmecom pages 1-2)
6. Baseline evaluations should include hearing, B-cell count and immunoglobulins, echocardiography/aortic imaging, renal ultrasound and renal function, and orthopedic functional assessment.

The 2024 p.Arg762Lys case illustrates diagnostic severity: neutrophils 0.07×10⁹/L, hemoglobin 17 g/L, platelets 1×10⁹/L, hypocellular marrow with megakaryocyte depletion, B cells 0.09×10⁹/L, bilateral superior RUS, clinodactyly/brachydactyly, and subarachnoid hemorrhage. Infection, autoimmune, coagulation, hemoglobinopathy, chromosome-breakage, and karyotype studies were unrevealing; trio WES established diagnosis. (huang2024anovelmissense pages 1-3, huang2024anovelmissense pages 3-5)

Differential diagnosis

Major alternatives are MPL-related congenital amegakaryocytic thrombocytopenia, thrombocytopenia-absent radius syndrome (RBM8A; absent radii with thumbs present rather than radioulnar fusion), Fanconi anemia, Diamond–Blackfan anemia, dyskeratosis congenita/telomere disorders, GATA2 deficiency, RUNX1/ETV6/ANKRD26-related thrombocytopenia, MYH9-related disease, neonatal alloimmune thrombocytopenia, congenital infection, sepsis/DIC, and other syndromic RUS disorders. Normal chromosome-breakage testing helps exclude Fanconi anemia but does not establish RUSAT. (germeshausen2018mecomassociatedsyndromea pages 4-5, walne2018expandingthephenotypic pages 8-13, germeshausen2018mecomassociatedsyndromea pages 1-2)

CMA/karyotype/FISH are useful when a constitutional deletion or acquired clone is suspected. Mitochondrial, repeat-expansion, liquid-biopsy, metabolomic, and epigenomic testing have no established disease-specific role. Population newborn screening is unavailable; cascade testing is appropriate after a familial variant is found.

11. Outcome and prognosis

There are no reliable 5- or 10-year survival rates. Prognosis depends chiefly on bleeding severity, depth and progression of marrow failure, infection, donor availability and HSCT complications, and acquisition of dysplastic/malignant clones. Severe neonatal disease may cause intracranial hemorrhage, sepsis, or early death; other carriers remain mildly affected into adulthood. Reported morbidity includes transfusion dependence, recurrent infection, transplant toxicity, hearing impairment, and permanent upper-limb restriction. (germeshausen2018mecomassociatedsyndromea pages 4-5)

Among 80 previously reported MECOM-associated individuals, four myeloid malignancies—three adult MDS and one pediatric AML—were reported, approximately 5%; this likely underestimates lifetime risk because many patients undergo early HSCT. The 2024 study added aplasia with dysplasia and another MDS case and found age-related clonal hematopoiesis in all three older cohort members. Long-term CBC, marrow/cytogenetic, and molecular surveillance is therefore reasonable, although no evidence-based interval is established. (venugopal2024unravelingfacetsof pages 1-2)

12. Treatment and current applications

No drug corrects the germline transcription-factor defect. Management is individualized in an inherited-BMF center.

• Supportive hematology: platelet and red-cell transfusions for clinically significant bleeding/anemia; antimicrobial treatment and prevention according to neutropenia/immune status; avoid unnecessary immune suppression when inherited failure is likely. IVIG and corticosteroids may be used initially when immune or alloimmune thrombocytopenia is suspected but do not correct RUSAT marrow failure. Suggested NCIT concepts: platelet transfusion, red-blood-cell transfusion, anti-infective therapy, supportive care. (huang2024anovelmissense pages 3-5, germeshausen2018mecomassociatedsyndromea pages 4-5)
• Allogeneic HSCT: the only established definitive treatment for progressive or severe hematopoietic failure. It corrects donor-derived hematopoiesis but not congenital skeletal or other fixed organ abnormalities. Outcomes are case-based and include successful count normalization as well as deaths from transplant complications or sepsis. (germeshausen2018mecomassociatedsyndromea pages 4-5)
• In the 2024 p.Arg762Lys case, matched-unrelated-donor HSCT at 16 months reduced transfusion and infection frequency; at age four, neutrophils were 3.82×10⁹/L, hemoglobin 122 g/L, and platelets 317×10⁹/L. This is individual-level evidence, not a response-rate estimate. (huang2024anovelmissense pages 3-5)
• Orthopedic care: occupational/physical therapy and adaptive strategies for mild functional impairment. Corrective derotational osteotomy may improve hand position in severe fixed pronation but does not restore a normal proximal joint; evidence is extrapolated from congenital RUS generally, not RUSAT-specific cohorts.
• Hearing, renal, cardiac, and immune care should be phenotype directed. Aortic dilatation warrants cardiology follow-up; one of three affected individuals in the 2024 cohort progressed to a surgically significant aneurysm. (venugopal2024unravelingfacetsof pages 6-7, venugopal2024unravelingfacetsof pages 5-6)

No approved gene therapy, RNA therapy, targeted small molecule, or disease-specific interventional trial was identified. Somatic wild-type-allele rescue provides a biological rationale for future gene-corrected autologous transplantation or direct editing, but this remains expert translational speculation, not clinical evidence. (venugopal2024unravelingfacetsof pages 6-7)

13. Prevention

Primary lifestyle prevention is not possible. Effective prevention is genetic and complication focused:

• Genetic counseling: a heterozygous affected parent ordinarily has a 50% transmission risk per conception, but phenotype cannot be predicted reliably because expressivity is variable and somatic rescue may modify blood findings.
• Reproductive options: familial-variant prenatal diagnosis and preimplantation genetic testing are technically feasible; counseling should discuss uncertain severity and the preliminary pregnancy-loss signal.
• Secondary prevention: cascade testing, early CBCs and forearm imaging in at-risk relatives, and rapid genetic evaluation of congenital thrombocytopenia can prevent diagnostic delay and inappropriate immune therapy.
• Tertiary prevention: bleeding precautions, timely transfusion, infection prevention, avoidance of marrow-toxic exposure when possible, HSCT before irreversible complications, and surveillance for cytopenic progression, dysplasia, clonal hematopoiesis, hearing loss, renal/cardiac disease, and aortic dilatation.
• Vaccination follows standard and transplant/immunodeficiency-specific schedules; there is no disease-specific vaccine or chemoprophylaxis.

14. Other species and natural disease

No well-established naturally occurring veterinary equivalent, breed predisposition, zoonotic transmission, or cross-species infectious susceptibility was identified. The relevant orthologues are conserved Hoxa11 and Mecom/Evi1 in laboratory species. RUSAT is noninfectious and has no zoonotic potential.

15. Model organisms and experimental systems

• Mouse: heterozygous deletion of Evi1 exon 4 markedly reduces early marrow hematopoietic cells; other Evi1 models support stemness-gene expression, HSC survival/self-renewal, embryonic limb and cardiac roles. These models reproduce aspects of hematopoietic/developmental biology but not consistently the complete human RUSAT phenotype. (germeshausen2018mecomassociatedsyndromea pages 7-7)
• Junbo mouse: an Evi1 p.Asn782Ile-equivalent allele predisposes to otitis media and hearing loss; it is useful for auditory biology but does not prove that human RUSAT hearing loss has the same mechanism. (niihori2015mutationsinmecom pages 3-5)
• Cellular assays: transfected-cell ChIP-qPCR and AP-1/TGF-β reporters demonstrate variant-dependent DNA-binding and transcriptional abnormalities. Patient lymphoblastoid cells carrying p.Glu758Lys showed modestly reduced MECOM protein in three experiments (P=0.041 and 0.035 versus controls). Limitations include nonphysiologic expression and use of cells that are not primary HSPCs or developing limb tissue. (niihori2015mutationsinmecom pages 3-5, walne2018expandingthephenotypic pages 14-16)
• Patient hematopoietic samples: reduced CD34-high/CD38-low progenitors, retained low MPL expression, elevated thrombopoietin, marrow hypocellularity, and absent megakaryocytes provide direct human evidence of progenitor and megakaryocyte failure. (germeshausen2018mecomassociatedsyndromea pages 5-5)

No validated disease-specific zebrafish, rat, Drosophila, organoid, or iPSC model was identified in the retrieved evidence.

Recent developments and expert interpretation

The most important 2023–2024 advance is recognition that apparent “nonpenetrance” may reflect somatic genetic rescue, while older patients can develop clonal hematopoiesis, multilineage dysplasia, and MDS. In 15 newly described cases, seven had spontaneous resolution, attenuation, or late onset; four of six evaluable mild/resolving cases showed copy-neutral 3q loss of heterozygosity encompassing MECOM. This finding changes diagnostic practice: blood can be a misleading germline sample, and longitudinal marrow/genomic surveillance deserves consideration. (venugopal2024unravelingfacetsof pages 2-3)

A second advance is continued expansion of the variant spectrum and evidence that trio WES is clinically useful when congenital thrombocytopenia and skeletal findings coexist. The 2024 p.Arg762Lys case also documents normalization of counts after matched-unrelated HSCT. (huang2024anovelmissense pages 1-3, huang2024anovelmissense pages 3-5)

Authoritative interpretation favors “MECOM-associated syndrome” over restricting diagnosis to RUSAT2: neither RUS nor amegakaryocytic thrombocytopenia is obligatory, and disease can present as isolated orthopedic abnormality, isolated marrow failure, multisystem developmental disease, or late-onset cytopenia. (germeshausen2018mecomassociatedsyndromea pages 9-9, germeshausen2018mecomassociatedsyndromea pages 2-2)

Key primary sources

1. Thompson AA, Nguyen LT. Amegakaryocytic thrombocytopenia and radio-ulnar synostosis are associated with HOXA11 mutation. Nature Genetics. 1 December 2000. PMID: 11101832. https://doi.org/10.1038/82511
2. Niihori T, et al. Mutations in MECOM, Encoding Oncoprotein EVI1, Cause Radioulnar Synostosis with Amegakaryocytic Thrombocytopenia. American Journal of Human Genetics. 3 December 2015;97:848–854. PMID: 26581901. https://doi.org/10.1016/j.ajhg.2015.10.010 (niihori2015mutationsinmecom pages 1-2)
3. Germeshausen M, et al. MECOM-associated syndrome: a heterogeneous inherited bone marrow failure syndrome with amegakaryocytic thrombocytopenia. Blood Advances. March 2018;2:586–596. PMID: 29540340. https://doi.org/10.1182/bloodadvances.2018016501 (germeshausen2018mecomassociatedsyndromea pages 1-2)
4. Walne AJ, et al. Expanding the phenotypic and genetic spectrum of radioulnar synostosis associated hematological disease. Haematologica. July 2018;103:e284–e287. PMID: 29519864. https://doi.org/10.3324/haematol.2017.183855 (walne2018expandingthephenotypic pages 1-5)
5. Huang D, et al. A novel missense mutation in the MECOM gene in a Chinese boy with radioulnar synostosis with amegakaryocytic thrombocytopenia. BMC Pediatrics. January 2024;24:62. https://doi.org/10.1186/s12887-024-04552-1 (huang2024anovelmissense pages 1-3)
6. Venugopal P, et al. Unraveling facets of MECOM-associated syndrome: somatic genetic rescue, clonal hematopoiesis, and phenotype expansion. Blood Advances. 9 July 2024;8:3437–3443. https://doi.org/10.1182/bloodadvances.2023012331 (venugopal2024unravelingfacetsof pages 1-2)

Evidence limitations: RUSAT is ultra-rare; most statistics pool heterogeneous MECOM genotypes and ascertainment pathways. Frequencies are therefore descriptive of published cases, not unbiased penetrance estimates. HOXA11-specific natural-history and treatment data are particularly sparse, and most management recommendations are extrapolated from inherited marrow-failure and congenital-RUS practice.

References

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3. (germeshausen2018mecomassociatedsyndromea pages 1-2): Manuela Germeshausen, Phil Ancliff, Jaime Estrada, Markus Metzler, Eva Ponstingl, Horst Rütschle, Dirk Schwabe, Richard H. Scott, Sule Unal, Angela Wawer, Bernward Zeller, and Matthias Ballmaier. Mecom-associated syndrome: a heterogeneous inherited bone marrow failure syndrome with amegakaryocytic thrombocytopenia. Blood advances, 2 6:586-596, Mar 2018. URL: https://doi.org/10.1182/bloodadvances.2018016501, doi:10.1182/bloodadvances.2018016501. This article has 145 citations and is from a peer-reviewed journal.

4. (niihori2015mutationsinmecom pages 3-5): Tetsuya Niihori, Meri Ouchi-Uchiyama, Yoji Sasahara, Takashi Kaneko, Yoshiko Hashii, Masahiro Irie, Atsushi Sato, Yuka Saito-Nanjo, Ryo Funayama, Takeshi Nagashima, Shin-ichi Inoue, Keiko Nakayama, Keiichi Ozono, Shigeo Kure, Yoichi Matsubara, Masue Imaizumi, and Yoko Aoki. Mutations in mecom, encoding oncoprotein evi1, cause radioulnar synostosis with amegakaryocytic thrombocytopenia. American journal of human genetics, 97 6:848-54, Dec 2015. URL: https://doi.org/10.1016/j.ajhg.2015.10.010, doi:10.1016/j.ajhg.2015.10.010. This article has 162 citations and is from a highest quality peer-reviewed journal.

5. (germeshausen2018mecomassociatedsyndromea pages 7-7): Manuela Germeshausen, Phil Ancliff, Jaime Estrada, Markus Metzler, Eva Ponstingl, Horst Rütschle, Dirk Schwabe, Richard H. Scott, Sule Unal, Angela Wawer, Bernward Zeller, and Matthias Ballmaier. Mecom-associated syndrome: a heterogeneous inherited bone marrow failure syndrome with amegakaryocytic thrombocytopenia. Blood advances, 2 6:586-596, Mar 2018. URL: https://doi.org/10.1182/bloodadvances.2018016501, doi:10.1182/bloodadvances.2018016501. This article has 145 citations and is from a peer-reviewed journal.

6. (germeshausen2018mecomassociatedsyndromea pages 4-5): Manuela Germeshausen, Phil Ancliff, Jaime Estrada, Markus Metzler, Eva Ponstingl, Horst Rütschle, Dirk Schwabe, Richard H. Scott, Sule Unal, Angela Wawer, Bernward Zeller, and Matthias Ballmaier. Mecom-associated syndrome: a heterogeneous inherited bone marrow failure syndrome with amegakaryocytic thrombocytopenia. Blood advances, 2 6:586-596, Mar 2018. URL: https://doi.org/10.1182/bloodadvances.2018016501, doi:10.1182/bloodadvances.2018016501. This article has 145 citations and is from a peer-reviewed journal.

7. (walne2018expandingthephenotypic pages 8-13): Amanda Walne, Hemanth Tummala, Alicia Ellison, Shirleny Cardoso, Jasmin Sidhu, Gabriela Sciuccati, Tom Vulliamy, and Inderjeet Dokal. Expanding the phenotypic and genetic spectrum of radioulnar synostosis associated hematological disease. Haematologica, 103:e284-e287, Jul 2018. URL: https://doi.org/10.3324/haematol.2017.183855, doi:10.3324/haematol.2017.183855. This article has 34 citations.

8. (niihori2015mutationsinmecom pages 1-2): Tetsuya Niihori, Meri Ouchi-Uchiyama, Yoji Sasahara, Takashi Kaneko, Yoshiko Hashii, Masahiro Irie, Atsushi Sato, Yuka Saito-Nanjo, Ryo Funayama, Takeshi Nagashima, Shin-ichi Inoue, Keiko Nakayama, Keiichi Ozono, Shigeo Kure, Yoichi Matsubara, Masue Imaizumi, and Yoko Aoki. Mutations in mecom, encoding oncoprotein evi1, cause radioulnar synostosis with amegakaryocytic thrombocytopenia. American journal of human genetics, 97 6:848-54, Dec 2015. URL: https://doi.org/10.1016/j.ajhg.2015.10.010, doi:10.1016/j.ajhg.2015.10.010. This article has 162 citations and is from a highest quality peer-reviewed journal.

9. (germeshausen2018mecomassociatedsyndromea pages 2-2): Manuela Germeshausen, Phil Ancliff, Jaime Estrada, Markus Metzler, Eva Ponstingl, Horst Rütschle, Dirk Schwabe, Richard H. Scott, Sule Unal, Angela Wawer, Bernward Zeller, and Matthias Ballmaier. Mecom-associated syndrome: a heterogeneous inherited bone marrow failure syndrome with amegakaryocytic thrombocytopenia. Blood advances, 2 6:586-596, Mar 2018. URL: https://doi.org/10.1182/bloodadvances.2018016501, doi:10.1182/bloodadvances.2018016501. This article has 145 citations and is from a peer-reviewed journal.

10. (venugopal2024unravelingfacetsof pages 1-2): Parvathy Venugopal, Peer Arts, Lucy C. Fox, Annet Simons, Devendra K. Hiwase, Peter G. Bardy, Annette Swift, David M. Ross, Lize F. D. van Vulpen, Arjan Buijs, Kelly L. Bolton, Bartlomiej Getta, Eliska Furlong, Tina Carter, Ingrid Krapels, Marlijn Hoeks, Adila Al Kindy, Farah Al Kindy, Sonja de Munnik, Pamela Evans, Mahalia S. B. Frank, Adam M. Bournazos, Sandra T. Cooper, Thuong Thi Ha, Matilda R. Jackson, Luis Arriola-Martinez, Kerry Phillips, Yvonne Brennan, Madhura Bakshi, Karen Ambler, Song Gao, Karin S. Kassahn, Rosalie Kenyon, Kevin Hung, Milena Babic, Alan McGovern, Lesley Rawlings, Cassandra Vakulin, Lucas Dejong, Rema Fathi, Simon McRae, Nicholas Myles, Dariusz Ladon, Marjolijn Jongmans, Roland P. Kuiper, Nicola K. Poplawski, Pasquale Barbaro, Piers Blombery, Anna L. Brown, Christopher N. Hahn, and Hamish S. Scott. Unraveling facets of mecom-associated syndrome: somatic genetic rescue, clonal hematopoiesis, and phenotype expansion. Jun 2024. URL: https://doi.org/10.1182/bloodadvances.2023012331, doi:10.1182/bloodadvances.2023012331. This article has 9 citations and is from a peer-reviewed journal.

11. (venugopal2024unravelingfacetsof pages 2-3): Parvathy Venugopal, Peer Arts, Lucy C. Fox, Annet Simons, Devendra K. Hiwase, Peter G. Bardy, Annette Swift, David M. Ross, Lize F. D. van Vulpen, Arjan Buijs, Kelly L. Bolton, Bartlomiej Getta, Eliska Furlong, Tina Carter, Ingrid Krapels, Marlijn Hoeks, Adila Al Kindy, Farah Al Kindy, Sonja de Munnik, Pamela Evans, Mahalia S. B. Frank, Adam M. Bournazos, Sandra T. Cooper, Thuong Thi Ha, Matilda R. Jackson, Luis Arriola-Martinez, Kerry Phillips, Yvonne Brennan, Madhura Bakshi, Karen Ambler, Song Gao, Karin S. Kassahn, Rosalie Kenyon, Kevin Hung, Milena Babic, Alan McGovern, Lesley Rawlings, Cassandra Vakulin, Lucas Dejong, Rema Fathi, Simon McRae, Nicholas Myles, Dariusz Ladon, Marjolijn Jongmans, Roland P. Kuiper, Nicola K. Poplawski, Pasquale Barbaro, Piers Blombery, Anna L. Brown, Christopher N. Hahn, and Hamish S. Scott. Unraveling facets of mecom-associated syndrome: somatic genetic rescue, clonal hematopoiesis, and phenotype expansion. Jun 2024. URL: https://doi.org/10.1182/bloodadvances.2023012331, doi:10.1182/bloodadvances.2023012331. This article has 9 citations and is from a peer-reviewed journal.

12. (huang2024anovelmissense pages 3-5): Duo-wen Huang, Mingyan Jiang, Yiping Zhu, Dong-jun Li, Xiaoxi Lu, and Ju Gao. A novel missense mutation in the mecom gene in a chinese boy with radioulnar synostosis with amegakaryocytic thrombocytopenia. BMC Pediatrics, Jan 2024. URL: https://doi.org/10.1186/s12887-024-04552-1, doi:10.1186/s12887-024-04552-1. This article has 2 citations and is from a peer-reviewed journal.

13. (venugopal2024unravelingfacetsof pages 3-4): Parvathy Venugopal, Peer Arts, Lucy C. Fox, Annet Simons, Devendra K. Hiwase, Peter G. Bardy, Annette Swift, David M. Ross, Lize F. D. van Vulpen, Arjan Buijs, Kelly L. Bolton, Bartlomiej Getta, Eliska Furlong, Tina Carter, Ingrid Krapels, Marlijn Hoeks, Adila Al Kindy, Farah Al Kindy, Sonja de Munnik, Pamela Evans, Mahalia S. B. Frank, Adam M. Bournazos, Sandra T. Cooper, Thuong Thi Ha, Matilda R. Jackson, Luis Arriola-Martinez, Kerry Phillips, Yvonne Brennan, Madhura Bakshi, Karen Ambler, Song Gao, Karin S. Kassahn, Rosalie Kenyon, Kevin Hung, Milena Babic, Alan McGovern, Lesley Rawlings, Cassandra Vakulin, Lucas Dejong, Rema Fathi, Simon McRae, Nicholas Myles, Dariusz Ladon, Marjolijn Jongmans, Roland P. Kuiper, Nicola K. Poplawski, Pasquale Barbaro, Piers Blombery, Anna L. Brown, Christopher N. Hahn, and Hamish S. Scott. Unraveling facets of mecom-associated syndrome: somatic genetic rescue, clonal hematopoiesis, and phenotype expansion. Jun 2024. URL: https://doi.org/10.1182/bloodadvances.2023012331, doi:10.1182/bloodadvances.2023012331. This article has 9 citations and is from a peer-reviewed journal.

14. (germeshausen2018mecomassociatedsyndromea pages 5-6): Manuela Germeshausen, Phil Ancliff, Jaime Estrada, Markus Metzler, Eva Ponstingl, Horst Rütschle, Dirk Schwabe, Richard H. Scott, Sule Unal, Angela Wawer, Bernward Zeller, and Matthias Ballmaier. Mecom-associated syndrome: a heterogeneous inherited bone marrow failure syndrome with amegakaryocytic thrombocytopenia. Blood advances, 2 6:586-596, Mar 2018. URL: https://doi.org/10.1182/bloodadvances.2018016501, doi:10.1182/bloodadvances.2018016501. This article has 145 citations and is from a peer-reviewed journal.

15. (venugopal2024unravelingfacetsof pages 6-7): Parvathy Venugopal, Peer Arts, Lucy C. Fox, Annet Simons, Devendra K. Hiwase, Peter G. Bardy, Annette Swift, David M. Ross, Lize F. D. van Vulpen, Arjan Buijs, Kelly L. Bolton, Bartlomiej Getta, Eliska Furlong, Tina Carter, Ingrid Krapels, Marlijn Hoeks, Adila Al Kindy, Farah Al Kindy, Sonja de Munnik, Pamela Evans, Mahalia S. B. Frank, Adam M. Bournazos, Sandra T. Cooper, Thuong Thi Ha, Matilda R. Jackson, Luis Arriola-Martinez, Kerry Phillips, Yvonne Brennan, Madhura Bakshi, Karen Ambler, Song Gao, Karin S. Kassahn, Rosalie Kenyon, Kevin Hung, Milena Babic, Alan McGovern, Lesley Rawlings, Cassandra Vakulin, Lucas Dejong, Rema Fathi, Simon McRae, Nicholas Myles, Dariusz Ladon, Marjolijn Jongmans, Roland P. Kuiper, Nicola K. Poplawski, Pasquale Barbaro, Piers Blombery, Anna L. Brown, Christopher N. Hahn, and Hamish S. Scott. Unraveling facets of mecom-associated syndrome: somatic genetic rescue, clonal hematopoiesis, and phenotype expansion. Jun 2024. URL: https://doi.org/10.1182/bloodadvances.2023012331, doi:10.1182/bloodadvances.2023012331. This article has 9 citations and is from a peer-reviewed journal.

16. (germeshausen2018mecomassociatedsyndromea pages 8-9): Manuela Germeshausen, Phil Ancliff, Jaime Estrada, Markus Metzler, Eva Ponstingl, Horst Rütschle, Dirk Schwabe, Richard H. Scott, Sule Unal, Angela Wawer, Bernward Zeller, and Matthias Ballmaier. Mecom-associated syndrome: a heterogeneous inherited bone marrow failure syndrome with amegakaryocytic thrombocytopenia. Blood advances, 2 6:586-596, Mar 2018. URL: https://doi.org/10.1182/bloodadvances.2018016501, doi:10.1182/bloodadvances.2018016501. This article has 145 citations and is from a peer-reviewed journal.

17. (germeshausen2018mecomassociatedsyndromea pages 5-5): Manuela Germeshausen, Phil Ancliff, Jaime Estrada, Markus Metzler, Eva Ponstingl, Horst Rütschle, Dirk Schwabe, Richard H. Scott, Sule Unal, Angela Wawer, Bernward Zeller, and Matthias Ballmaier. Mecom-associated syndrome: a heterogeneous inherited bone marrow failure syndrome with amegakaryocytic thrombocytopenia. Blood advances, 2 6:586-596, Mar 2018. URL: https://doi.org/10.1182/bloodadvances.2018016501, doi:10.1182/bloodadvances.2018016501. This article has 145 citations and is from a peer-reviewed journal.

18. (niihori2015mutationsinmecom pages 2-3): Tetsuya Niihori, Meri Ouchi-Uchiyama, Yoji Sasahara, Takashi Kaneko, Yoshiko Hashii, Masahiro Irie, Atsushi Sato, Yuka Saito-Nanjo, Ryo Funayama, Takeshi Nagashima, Shin-ichi Inoue, Keiko Nakayama, Keiichi Ozono, Shigeo Kure, Yoichi Matsubara, Masue Imaizumi, and Yoko Aoki. Mutations in mecom, encoding oncoprotein evi1, cause radioulnar synostosis with amegakaryocytic thrombocytopenia. American journal of human genetics, 97 6:848-54, Dec 2015. URL: https://doi.org/10.1016/j.ajhg.2015.10.010, doi:10.1016/j.ajhg.2015.10.010. This article has 162 citations and is from a highest quality peer-reviewed journal.

19. (germeshausen2018mecomassociatedsyndromea pages 9-9): Manuela Germeshausen, Phil Ancliff, Jaime Estrada, Markus Metzler, Eva Ponstingl, Horst Rütschle, Dirk Schwabe, Richard H. Scott, Sule Unal, Angela Wawer, Bernward Zeller, and Matthias Ballmaier. Mecom-associated syndrome: a heterogeneous inherited bone marrow failure syndrome with amegakaryocytic thrombocytopenia. Blood advances, 2 6:586-596, Mar 2018. URL: https://doi.org/10.1182/bloodadvances.2018016501, doi:10.1182/bloodadvances.2018016501. This article has 145 citations and is from a peer-reviewed journal.

20. (huang2024anovelmissense pages 1-3): Duo-wen Huang, Mingyan Jiang, Yiping Zhu, Dong-jun Li, Xiaoxi Lu, and Ju Gao. A novel missense mutation in the mecom gene in a chinese boy with radioulnar synostosis with amegakaryocytic thrombocytopenia. BMC Pediatrics, Jan 2024. URL: https://doi.org/10.1186/s12887-024-04552-1, doi:10.1186/s12887-024-04552-1. This article has 2 citations and is from a peer-reviewed journal.

21. (venugopal2024unravelingfacetsof pages 5-6): Parvathy Venugopal, Peer Arts, Lucy C. Fox, Annet Simons, Devendra K. Hiwase, Peter G. Bardy, Annette Swift, David M. Ross, Lize F. D. van Vulpen, Arjan Buijs, Kelly L. Bolton, Bartlomiej Getta, Eliska Furlong, Tina Carter, Ingrid Krapels, Marlijn Hoeks, Adila Al Kindy, Farah Al Kindy, Sonja de Munnik, Pamela Evans, Mahalia S. B. Frank, Adam M. Bournazos, Sandra T. Cooper, Thuong Thi Ha, Matilda R. Jackson, Luis Arriola-Martinez, Kerry Phillips, Yvonne Brennan, Madhura Bakshi, Karen Ambler, Song Gao, Karin S. Kassahn, Rosalie Kenyon, Kevin Hung, Milena Babic, Alan McGovern, Lesley Rawlings, Cassandra Vakulin, Lucas Dejong, Rema Fathi, Simon McRae, Nicholas Myles, Dariusz Ladon, Marjolijn Jongmans, Roland P. Kuiper, Nicola K. Poplawski, Pasquale Barbaro, Piers Blombery, Anna L. Brown, Christopher N. Hahn, and Hamish S. Scott. Unraveling facets of mecom-associated syndrome: somatic genetic rescue, clonal hematopoiesis, and phenotype expansion. Jun 2024. URL: https://doi.org/10.1182/bloodadvances.2023012331, doi:10.1182/bloodadvances.2023012331. This article has 9 citations and is from a peer-reviewed journal.

22. (walne2018expandingthephenotypic pages 14-16): Amanda Walne, Hemanth Tummala, Alicia Ellison, Shirleny Cardoso, Jasmin Sidhu, Gabriela Sciuccati, Tom Vulliamy, and Inderjeet Dokal. Expanding the phenotypic and genetic spectrum of radioulnar synostosis associated hematological disease. Haematologica, 103:e284-e287, Jul 2018. URL: https://doi.org/10.3324/haematol.2017.183855, doi:10.3324/haematol.2017.183855. This article has 34 citations.

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.

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: Orphanet, OMIM.

3 of 6 terms resolved to a current term; the rest could not be looked up either way.