| Subtype | Causal gene / product | OMIM disease ID | Inheritance | Defining phenotype | Representative variants | Key evidence / limitations |
|---|---|---|---|---|---|---|
| ANXD1 | **RMRP** / noncoding RNA component of RNase MRP | **607095** | **Autosomal recessive; ultra-rare** | Most severe end of the CHH-AD spectrum; prenatal-onset extreme disproportionate short stature, severe spondyloepimetaphyseal dysplasia, brachydactyly, joint laxity, hypodontia; typically lacks the immunodeficiency/anemia/malignancy predisposition more characteristic of CHH (pqac-00000018, pqac-00000005) | **g.111_112insACTGTAGACATTCCT**, **g.90_91AG>GC**, **g.254C>G**; severe case with **g.195C>T** plus null **g.254_263delCTCAGCGCGG** (pqac-00000016, pqac-00000017, pqac-00000018, pqac-00000019) | Best mechanistic evidence among ANXD subtypes: RMRP mutations impair RNase MRP-mediated **pre-rRNA cleavage**, correlating with bone-dysplasia severity; reduced **cyclin B2 mRNA cleavage** tracks more with hair/immuno-hematologic features than with ANXD itself (pqac-00000018, pqac-00000019). Limitation: much evidence derives from the broader CHH-AD spectrum rather than large ANXD1 cohorts. |
| ANXD2 | **POP1** / hPOP1 protein, shared subunit of RNase MRP and RNase P complexes | **617396** | **Autosomal recessive; ultra-rare** | ANXD-like skeletal dysplasia spanning mild to severe presentations, including severe short stature and extensive skeletal abnormalities; considered part of the RNase-MRP–related skeletal dysplasia spectrum (pqac-00000004, pqac-00000005) | **p.Pro582Ser**, **p.Glu870fs*5**, **p.Asp511Tyr** (biallelic) (pqac-00000004) | Human evidence shows **markedly reduced RMRP abundance** and **elevated pre-5.8S rRNA** in at least one proband, supporting disturbed ribosome/RNase-MRP biology (pqac-00000004). Limitation: very small number of reported families/patients; phenotypic boundaries between mild POP1 skeletal dysplasia and ANXD2 remain incompletely defined. |
| ANXD3 | **NEPRO (C3orf17)** / NEPRO protein, reported to interact with RNase MRP subunits | **618853** | **Autosomal recessive; ultra-rare** | Severe short stature, brachydactyly, skin laxity, joint hypermobility/dislocations, platyspondyly/ovoid vertebrae, hypoplastic ilia/acetabulae, small femoral epiphyses, irregular metaphyses; 2023 case expanded phenotype to **atlantoaxial subluxation**, **dental anomalies**, and **sagittal craniosynostosis/scaphocephaly** (pqac-00000000, pqac-00000001, pqac-00000002, pqac-00000005) | Homozygous **c.280C>T, p.Arg94Cys** (apparent recurrent/founder variant in several reported patients) (pqac-00000001, pqac-00000005) | Recent direct evidence is strongest at the case-report level: before the 2023 report, only **five** ANXD3 patients had been described; the 2023 paper added one more and broadened the recognized phenotype (pqac-00000000, pqac-00000001, pqac-00000005). Limitation: mechanism is less resolved than for RMRP; patient numbers remain extremely small. |
| Cross-subtype summary | **RMRP / POP1 / NEPRO** | ANXD1 **607095**; ANXD2 **617396**; ANXD3 **618853** | **All currently recognized ANXD subtypes are autosomal recessive and ultra-rare** | Shared core picture: severe prenatal/early-childhood growth failure with marked skeletal dysplasia; subtype-specific extraskeletal findings are limited and evidence is mostly from individual case reports or tiny series (pqac-00000000, pqac-00000005, pqac-00000018) | Subtype-defining variants are heterogeneous except for recurrent **NEPRO p.Arg94Cys** in ANXD3 and multiple recurrent **RMRP** alleles in the CHH-AD spectrum (pqac-00000001, pqac-00000015, pqac-00000018) | Knowledge base should treat ANXD as an **ultra-rare Mendelian skeletal dysplasia with sparse epidemiology**: prevalence/incidence, penetrance, survival, and genotype-specific prognosis are not well quantified in current literature (pqac-00000000, pqac-00000004, pqac-00000005). |


*Table: This table summarizes the three recognized anauxetic dysplasia subtypes by gene, OMIM identifier, inheritance, phenotype, representative variants, and evidence strength. It is useful as a compact knowledge-base overview while highlighting that all forms are autosomal recessive and exceptionally rare.*