| Feature | clEDS1 / **TNXB** | clEDS2 / **AEBP1** | Evidence notes |
|---|---|---|---|
| Molecular definition | Biallelic pathogenic **TNXB** variants causing complete tenascin-X deficiency | Biallelic pathogenic **AEBP1** variants causing loss or dysfunction of aortic carboxypeptidase-like protein (ACLP) | Both are autosomal-recessive monogenic extracellular-matrix disorders; TNXB haploinsufficiency and CAH-X are related but distinct entities (pqac-00000000, pqac-00000004) |
| Protein function | Tenascin-X is an extracellular-matrix glycoprotein that regulates collagen deposition and matrix organization and interacts with collagen fibrils/decorin | ACLP binds several fibrillar collagens through its discoidin domain, enhances collagen polymerization, and contributes to development, repair, fibrosis, fibroblast proliferation, and collagen-producing-cell differentiation | Human and model evidence supports disrupted collagen-rich matrix organization rather than a primary collagen-gene defect (pqac-00000008, pqac-00000016) |
| Core phenotype | Generalized joint hypermobility, hyperextensible skin, easy bruising, and generalized tissue fragility | Joint hypermobility **11/11**, skin hyperextensibility **11/11**, easy bruising **10/11** in the 2023 aggregated series | clEDS2 percentages derive from only 11 reported individuals and are vulnerable to ascertainment bias (pqac-00000001, pqac-00000004) |
| Scarring distinction | Classically resembles classical EDS but usually lacks the typical atrophic scars of COL5A1/COL5A2-related classical EDS | Atrophic scarring occurred in **9/11**, so absence of atrophic scars is not a reliable clEDS2 discriminator | The “classical-like without atrophic scarring” rule applies most strongly to TNXB-related clEDS1, not uniformly to clEDS2 (pqac-00000001, pqac-00000014) |
| Additional phenotype clues | Muscle weakness, myalgia, fatigability, edema without cardiac failure, distal joint changes, and possible neuropathy; in one TNX-deficient dataset, mild–moderate weakness was **80%**, reduced vibration sense **60%**, axonal polyneuropathy **40%**, and mild myopathic biopsy findings **20%** | Hair loss or thinning was reported in **6/11** and may be a useful distinguishing clue; osteoporosis, poor wound healing, redundant skin, and marfanoid features have also been described | TNXB neuromuscular percentages came from a small EDS/TNX-deficiency cohort; the clEDS2 hair-loss observation requires confirmation in larger series (pqac-00000007, pqac-00000004) |
| Vascular concerns | Easy bruising and hematomas are prominent; severe arterial events have been reported but are not sufficiently quantified for precise risk estimates | Among 11 reported individuals, **2/11** had arterial aneurysm and/or dissection; reported findings include vertebral-artery dissection, splenic-artery dilatation, arterial tortuosity, and an aortic-root aneurysm requiring surgery | Cardiovascular surveillance has been proposed for clEDS2, but evidence remains case-series level rather than guideline-grade (pqac-00000004) |
| Cardiac findings | Valve or structural cardiac abnormalities can occur, especially in the distinct CAH-X spectrum, but clEDS1-specific frequencies are uncertain | Mitral-valve prolapse was reported in **4/11** | Do not transfer CAH-X cardiac-frequency estimates directly to biallelic TNXB clEDS1 (pqac-00000001, pqac-00000004) |
| Gastrointestinal and pelvic-floor concerns | A 2024 summary of a nine-patient TNXB cohort reported gastrointestinal complications in all patients, including perforation, diverticulitis, bleeding, obstruction, rectal/anal prolapse, and gallstones | Potentially serious bowel complications have been emphasized in recent reports, but robust frequencies are unavailable | The clEDS1 observation is from a highly selected small cohort and should not be interpreted as population prevalence (pqac-00000002, pqac-00000004) |
| Variant spectrum and functional consequence | Missense, nonsense, frameshift, splice, deletion, and TNXA-derived/chimeric alleles occur; disease-producing biallelic variants generally cause absent or profoundly deficient tenascin-X | Reported pathogenic alleles include nonsense, frameshift, splice-site, and damaging missense variants; demonstrated consequences include nonsense-mediated decay, absent ACLP, and impaired collagen assembly | More than 75% of patients in one recent TNXB cohort reportedly carried TNXA-derived variation; AEBP1 functional nullizygosity is supported by RNA/protein studies (pqac-00000002, pqac-00000008, pqac-00000009) |
| Testing pitfalls | Technically difficult because **TNXB** lies in the complex RCCX locus and has a highly homologous pseudogene, **TNXA**; sequencing alone may miss exon conversions, TNXA/TNXB chimeras, or copy-number changes | Standard sequencing and deletion/duplication analysis are generally applicable, but missense variants may require segregation and functional evidence | TNXB testing should use validated locus-aware methods and copy-number/chimera analysis; long-read or genome/RNA approaches may resolve unsolved cases (pqac-00000010, pqac-00000012) |
| Important diagnostic distinction | Complete biallelic TNXB deficiency causes clEDS1; heterozygous TNXB deficiency may produce a hypermobility phenotype, while a CYP21A2–TNXB contiguous rearrangement produces **CAH-X** | AEBP1-related disease is not CAH-X and does not inherently cause congenital adrenal hyperplasia | Conflating these entities can distort inheritance, phenotype, and recurrence-risk counseling (pqac-00000000, pqac-00000001, pqac-00000009) |
| Mechanistic pathology | Tenascin-X deficiency reduces collagen density and alters matrix and elastic-fiber organization; TNX-null mouse skin has approximately **30% less collagen** despite relatively preserved fibril size and shape | ACLP deficiency impairs binding/polymerization of fibrillar collagen; patient skin shows reduced dermal collagen and ragged abnormal fibrils | Evidence includes human skin/fibroblasts, biochemical collagen-polymerization assays, and knockout mice (pqac-00000008, pqac-00000016) |
| Experimental models | **Tnxb−/− mouse:** reduced collagen deposition and mechanical allodynia; allodynia responded to gabapentin and a μ-opioid agonist but not indomethacin | **Aebp1−/− mouse:** abnormal/delayed wound repair associated with impaired fibroblast proliferation; patient-derived fibroblasts provide direct functional models | Models reproduce selected ECM, wound-healing, or pain mechanisms but do not establish the full human multisystem natural history (pqac-00000008, pqac-00000015, pqac-00000017) |
| Therapy status | No approved molecularly targeted, gene, RNA, or cell therapy; care is supportive and complication-directed | No approved molecularly targeted, gene, RNA, or cell therapy; care is supportive and complication-directed | Current management relies on multidisciplinary rehabilitation, pain treatment, tissue-protection and wound precautions, cardiovascular assessment, and genetic counseling; recommendations are largely extrapolated from broader EDS care (pqac-00000012, pqac-00000013) |
| Evidence maturity | Larger clinical experience than clEDS2, but still ultra-rare with no population-level natural-history estimates | Only 11 individuals were aggregated in the 2023 report; phenotype and complication frequencies remain provisional | Neither subtype has reliable incidence, prevalence, survival, penetrance, treatment-response, or quality-of-life statistics (pqac-00000002, pqac-00000004) |


*Table: Database-ready comparison of TNXB-related clEDS1 and AEBP1-related clEDS2, emphasizing molecular definitions, phenotype differences, testing pitfalls, mechanisms, models, and evidence limitations.*