| Domain | Established findings | Quantitative evidence in defining 7-person cohort | Suggested ontology terms | Evidence limitations |
|---|---|---|---|---|
| Disease identity | Distinct Mendelian neurodevelopmental disorder caused by **HDAC4** missense variants affecting the major 14-3-3 regulatory motif; distinguished from **HDAC4 haploinsufficiency/2q37 deletion syndrome (BDMR)** by phenotype and proposed mechanism (pqac-00000011, pqac-00000012) | Defining cohort: **7 unrelated individuals** (pqac-00000011, pqac-00000009) | Suggested: **MONDO:0859232**; **OMIM:619797**; NCBI Gene/ HGNC for **HDAC4** | MONDO/OMIM identifiers are disease-resource mappings; cohort size comes from one discovery report |
| Causal gene / variant class | **Heterozygous de novo missense variants** in **HDAC4** clustering at residues **242-248** around phospho-Ser246 within the 14-3-3 binding site; variants reported to alter **Thr244, Glu247, or Pro248** (pqac-00000011, pqac-00000009) | **7/7 de novo**; **5/7** affect **Pro248** (pqac-00000011, pqac-00000009) | Suggested: Sequence Ontology **missense_variant**; HP suggested **De novo mutation** if phenotype-modeling requires; GO suggested **protein binding**, **protein localization** | Full per-patient HGVS list was not fully recoverable from the parsed table extract |
| Core neurodevelopmental phenotype | Universal developmental delay / intellectual disability with central hypotonia; all school-age individuals required special education, with one relatively milder case (pqac-00000009) | **DD/ID 7/7**; **hypotonia 7/7** (pqac-00000009) | Suggested HPO: **Developmental delay (HP:0001263)**, **Intellectual disability (HP:0001249)**, **Central hypotonia (HP:0011443)** | Severity stratification and milestone ages were incompletely extractable from the malformed table |
| Seizures / neurologic features | Epilepsy is common; one case had infantile spasms refractory to medication, two had generalized seizures beginning in mid-childhood; movement abnormalities included hand stereotypies or dystonic limb movements (pqac-00000009) | **Seizures 3/7** (pqac-00000009) | Suggested HPO: **Seizure (HP:0001250)**, **Infantile spasms (HP:0012469)**, **Stereotypy (HP:0000733)**, **Dystonia (HP:0001332)** | Frequency for movement disorder/stereotypies was described narratively, not fully tabulated in available extract |
| Sleep | Sleep disturbance reported in a subset (pqac-00000009) | **3/7** (pqac-00000009) | Suggested HPO: **Sleep disturbance (HP:0002360)** | Type/severity of sleep disorder not consistently specified |
| Brain imaging | Variable, nonspecific brain MRI abnormalities occurred in most imaged cases (pqac-00000009, pqac-00000008) | **MRI nonspecific changes 5/7** (pqac-00000009) | Suggested HPO: **Abnormality of brain MRI (HP:0410263)** | Specific neuroanatomical lesions were not consistently detailed in accessible text |
| Craniofacial / oral phenotype | Recurrent facial features included hypertelorism, full lower lip, long palpebral fissures, frontal hair upsweep, widely spaced teeth, and large ears; significant drooling in early childhood was common (pqac-00000009) | Multi-case recurrent features reported qualitatively; exact counts not fully recoverable except statement that **at least 6/7** had **dental anomalies, hypertelorism and/or hip defects** (pqac-00000008, pqac-00000012) | Suggested HPO: **Hypertelorism (HP:0000316)**, **Long palpebral fissure (HP:0000639)**, **Full lower lip (HP:0000179)**, **Widely spaced teeth (HP:0000687)**, **Large ears (HP:0000400)**, **Drooling (HP:0002307)** | Individual feature frequencies are incompletely extractable from the parsed PDF table |
| Feeding / swallowing | Swallowing difficulties and/or drooling are highlighted as distinguishing features compared with BDMR (pqac-00000012) | Cohort-wide count not fully extractable; described as clinically recurrent/common (pqac-00000009, pqac-00000012) | Suggested HPO: **Dysphagia (HP:0002015)**, **Feeding difficulties (HP:0011968)**, **Drooling (HP:0002307)** | Exact numerator/denominator for swallowing problems unavailable in accessible text |
| Skeletal / orthopedic phenotype | Hip dislocation or subluxation, progressive scoliosis/kyphosis, and joint laxity/hypermobility were frequent; delayed anterior fontanel closure seen in two cases (pqac-00000009, pqac-00000012) | **Hip dislocation/subluxation 4/7**; **scoliosis/kyphosis 5/7**; **delayed fontanel closure 2/7** (pqac-00000009) | Suggested HPO: **Hip dislocation (HP:0002827)**, **Hip subluxation (HP:0001388)**, **Scoliosis (HP:0002650)**, **Kyphosis (HP:0002808)**, **Joint hypermobility (HP:0001382)**, **Delayed closure of the anterior fontanelle (HP:0001476)** | Progression details were narrative; some features grouped together (e.g., scoliosis/kyphosis) |
| Growth | Growth was generally unremarkable except relatively large head size in one case (pqac-00000009) | No robust abnormal-growth frequency; authors state growth parameters were “generally unremarkable” (pqac-00000009) | Suggested HPO: **Relative macrocephaly (HP:0004482)** if supported case-wise | Limited anthropometric summary only |
| Negative / distinguishing features | Unlike BDMR/2q37 deletion syndrome, the cohort lacked reported autism, obesity, and brachydactyly type E; also lacked BDMR-typical broad face/brachycephaly/broad upturned nose (pqac-00000009, pqac-00000012) | **Autism 0/7 reported**; **obesity 0/7 reported**; **brachydactyly type E 0/7 reported** (pqac-00000009, pqac-00000012) | Suggested HPO negatives for curation only if allowed: absence of **Autistic behavior (HP:0000729)**, **Obesity (HP:0001513)**, **Brachydactyly type E (HP:0005863)** | These are reported absences in a small cohort, not proof of impossibility |
| Molecular mechanism | Variants impair phosphorylation-dependent **14-3-3** interaction at the key HDAC4 shuttling motif, reducing cytoplasmic sequestration and supporting a **gain-of-function via increased nuclear HDAC4 activity**; downstream effects on **RUNX2** and **MEF2C** are proposed (pqac-00000012, pqac-00000008, pqac-00000009) | Functional assay showed **~2-fold reduced 14-3-3β binding** for **p.Thr244Lys** and **p.Glu247Gly** in HEK-293 co-immunoprecipitation assays (pqac-00000012) | Suggested GO: **protein binding (GO:0005515)**, **protein localization to nucleus / nucleocytoplasmic transport** (suggested only), **negative regulation of transcription by RNA polymerase II (GO:0000122)**; suggested CL: **HEK-293 cell** not a CL term, so avoid strict CL assertion | Reduced binding is experimentally shown only for two variants; increased nuclear activity and transcriptional consequences are strongly inferred/proposed rather than directly measured in patient tissue |
| Differential diagnosis | Should be distinguished from **2q37 deletion syndrome / brachydactyly-mental retardation syndrome (BDMR)** caused by HDAC4 loss-of-function or larger deletions; defining differences include more severe DD/ID and presence of swallowing difficulties/drooling, congenital hip defects, progressive kyphoscoliosis, delayed fontanel closure, and absence of autism/obesity/brachydactyly E (pqac-00000011, pqac-00000012, pqac-00000004) | Comparator evidence includes a **103-individual** 2q37 deletion cohort supporting HDAC4 as major contributor to BDMR but with different/overlapping features (pqac-00000004, pqac-00000006) | Suggested MONDO/OMIM differential: **2q37 deletion syndrome / BDMR (OMIM:600430)** | Differential interpretation depends on small n for OMIM 619797 and heterogeneous comparator deletions |
| Diagnostics / management implication | Diagnosis currently depends on sequencing-based detection of **HDAC4** missense variants in the 242-248 motif and clinical correlation; no disease-specific interventional trial or established targeted therapy identified in available evidence (pqac-00000009, pqac-00000008) | Cohort identified by **WES/clinical exome sequencing**, with Sanger confirmation (pqac-00000009) | Suggested NCIT: **Whole Exome Sequencing**, **Sanger Sequencing** | No validated biomarker, natural-history study, or evidence-based treatment algorithm found in retrieved sources |


*Table: This table summarizes the defining clinical and mechanistic evidence for Neurodevelopmental Disorder with Central Hypotonia and Dysmorphic Facies (OMIM 619797) from the foundational 7-person cohort. It is useful for rapid knowledge-base curation because it separates established observations, explicit cohort counts, suggested ontology mappings, and evidence limitations.*