| Entity / identifier | Causal gene and inheritance | Hallmark phenotype / course | Mechanism / evidence | Diagnostic / treatment implications |
|---|---|---|---|---|
| **Aggregate RUSAT syndrome** — MONDO:0011555; Orphanet:71289 | Genetically heterogeneous; established causes are heterozygous germline variants in **HOXA11** or **MECOM**, usually autosomal dominant, frequently de novo, with variable expressivity and incomplete penetrance (pqac-00000000, pqac-00000001) | Congenital proximal radioulnar synostosis with amegakaryocytic thrombocytopenia; thrombocytopenia may progress to pancytopenia, hypocellular marrow, and global bone-marrow failure. Either skeletal or hematologic manifestations can occasionally be absent in molecularly related disease. Suggested HPO: **Radioulnar synostosis**, **Thrombocytopenia**, **Pancytopenia**, **Hypocellular bone marrow**, **Decreased megakaryocytes** (pqac-00000001, pqac-00000008) | Developmental transcription-factor dysfunction links forelimb patterning to hematopoietic and megakaryocytic failure. The precise downstream causal network remains incompletely resolved (pqac-00000020, pqac-00000023) | Evaluate CBC/smear, marrow cellularity and megakaryocytes, bilateral forearm radiographs, family history, and germline **HOXA11/MECOM** testing. Severe marrow failure requires transfusion/infection support and consideration of allogeneic HSCT; orthopedic intervention is based on functional limitation (pqac-00000029, pqac-00000030) |
| **RUSAT1 / HOXA11-associated disease** — OMIM:605432 | **HOXA11**; heterozygous germline, autosomal dominant; familial cases established, with markedly variable hematologic expression (pqac-00000001, pqac-00000008) | Usually congenital bilateral RUS and thrombocytopenia from birth; reported spectrum ranges from no major hematologic problems to early bone-marrow failure. Additional findings can include clinodactyly, hip dysplasia, and sensorineural hearing loss. Suggested HPO: **Congenital onset**, **Abnormality of forearm**, **Clinodactyly**, **Sensorineural hearing impairment** (pqac-00000001, pqac-00000026) | HOXA11 is a homeobox transcription factor required for limb development and hematopoietic differentiation. Human genotype–phenotype evidence is strong, but subtype-specific downstream targets and pathway causality remain less well characterized than for MECOM (pqac-00000021, pqac-00000026) | Confirm with germline HOXA11 sequencing after clinical/radiographic recognition; include deletion/CNV analysis if sequencing is unrevealing. Monitor serial blood counts and marrow function. HSCT treats progressive marrow failure but does not correct congenital synostosis (pqac-00000001, pqac-00000030) |
| **RUSAT2 / MECOM-associated syndrome** — MONDO:0014758; OMIM:616738 | **MECOM**; pathogenic heterozygous germline variants or constitutional deletions; autosomal dominant, often de novo, with variable expressivity, incomplete penetrance, and occasional somatic genetic rescue (pqac-00000006, pqac-00000017, pqac-00000018) | Continuous spectrum from isolated RUS without cytopenia to congenital amegakaryocytic thrombocytopenia, pancytopenia, aplastic anemia, MDS, or severe neonatal BMF without RUS. Other features include clinodactyly/brachydactyly, cardiac or renal anomalies, B-cell deficiency, hearing loss, and vascular disease. In a 64-case literature summary: RUS 45.3%, pancytopenia 56.2%, thrombocytopenia 25.0%, and no cytopenia 12.5%. Suggested HPO: **B-cell lymphopenia**, **Aplastic anemia**, **Myelodysplasia**, **Congenital heart defect**, **Renal malformation** (pqac-00000016, pqac-00000028) | MECOM/EVI1 zinc-finger variants impair DNA occupancy and alter AP-1 and TGF-β transcriptional responses; patient and mouse evidence supports reduced HSPC maintenance/self-renewal. MPL downregulation is not consistently demonstrated. Somatic copy-neutral 3q loss of heterozygosity can duplicate the wild-type allele and rescue hematopoiesis (pqac-00000014, pqac-00000023, pqac-00000018) | Use an inherited-BMF panel or trio WES/WGS with MECOM SNV/indel and CNV analysis; test nonhematopoietic DNA after HSCT or when somatic rescue is suspected. Assess CBC, marrow, B cells/immunoglobulins, hearing, renal and cardiac anatomy, and forearm radiographs. HSCT can normalize hematopoiesis; 2024 evidence supports long-term surveillance for clonal hematopoiesis, dysplasia, and myeloid malignancy (pqac-00000016, pqac-00000028) |


*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.*