| Domain | Knowledge-base content | Suggested ontology terms/IDs | Evidence caveat |
|---|---|---|---|
| Disease identity | Non-syndromic X-linked intellectual disability (NS-XLID) is a genetically heterogeneous X-linked neurodevelopmental disease group in which intellectual disability is the only consistent shared feature; additional neurologic, behavioral, or dysmorphic findings may occur but are variable and gene-/family-specific. Exact disease-level knowledge is aggregated from literature/reviews and should not be overgeneralized to every gene-defined subtype. (pqac-00000000, pqac-00000001, pqac-00000002, pqac-00000009) | MONDO:0019181; term label: non-syndromic X-linked intellectual disability | “Nonsyndromic” does **not** mean absence of all other findings; rather, no consistent syndromic pattern across cases. Scope overlaps with syndromic XLID for many genes. |
| Synonyms / scope | Non-specific X-linked intellectual disability; nonsyndromal X-linked intellectual disability; NS-XLID; historical: non-syndromic X-linked mental retardation. (pqac-00000001, pqac-00000002, pqac-00000009) | term suggestions; verify release | Historical terminology in older papers may use outdated language. |
| Core phenotype | Intellectual disability is the defining phenotype, often mild to severe depending on gene/variant. (pqac-00000001, pqac-00000009) | HP:0001249 Intellectual disability | Frequency at disease-group level cannot be meaningfully quantified because NS-XLID aggregates many disorders. |
| Core phenotype | Developmental delay / global developmental delay may precede formal ID diagnosis in childhood. (pqac-00000021, pqac-00000026, pqac-00000027) | HP:0001263 Global developmental delay; HP:0011344 Severe global developmental delay | More typical in pediatric case series; adult historical families may be described primarily as ID. |
| Core phenotype | Speech/language delay or poor/absent speech is common in several gene-specific forms. (pqac-00000021, pqac-00000026, pqac-00000028, pqac-00000029) | HP:0000750 Delayed speech and language development; HP:0001344 Expressive language delay | Strongly gene-dependent; not universal across all NS-XLID genes. |
| Core phenotype | Hypotonia / muscle weakness reported in subsets, including SLC9A7-related cases. (pqac-00000021) | HP:0001252 Hypotonia; HP:0001324 Muscle weakness | Variable and not specific; may reflect particular gene mechanisms. |
| Core phenotype | Seizures/epilepsy occur in some NS-XLID genes (for example IQSEC2-, GLRA2-, ATP2B3-related cases) but are inconsistent at disease-group level. (pqac-00000008, pqac-00000026, pqac-00000028, pqac-00000029) | HP:0001250 Seizure; HP:0002123 Generalized myoclonic seizure (term suggestion; verify release if subtyped) | Presence of seizures can shift some cases toward broader neurodevelopmental syndromes; use gene-level assertion when possible. |
| Core phenotype | Autism spectrum features / autistic traits / behavioral abnormalities / psychiatric problems may occur in subsets. (pqac-00000008, pqac-00000012, pqac-00000026) | HP:0000729 Autism; HP:0000708 Behavioral abnormality | HPO choice should be tailored to reported feature (autism, aggression, hyperactivity, anxiety, etc.). |
| Anatomy | Primary organ/system affected: brain, especially forebrain/cerebral cortex and synaptic networks underlying cognition and behavior. (pqac-00000011, pqac-00000013, pqac-00000020) | UBERON:0000955 brain; UBERON:0000956 cerebral cortex | Disease-level anatomy is inferred from shared neurodevelopmental biology rather than uniform lesion localization. |
| Tissue / cell types | Principal affected tissue: nervous tissue; relevant cell types include excitatory neurons, inhibitory neurons, and broader cortical/hippocampal neuronal populations. (pqac-00000013, pqac-00000016, pqac-00000019, pqac-00000020) | CL:0000540 neuron; term suggestions: excitatory neuron, inhibitory neuron, cortical neuron, hippocampal neuron; verify release | Exact CL subtype should match gene/mechanism-specific evidence; many papers infer rather than directly prove target cell types. |
| Subcellular compartments | Recurrently implicated compartments include synapse, presynaptic vesicle, postsynaptic density, dendritic spine, nucleus/chromatin, Golgi/TGN/post-Golgi vesicles, endosome, and mitochondrion for some genes. (pqac-00000006, pqac-00000011, pqac-00000013, pqac-00000021, pqac-00000022, pqac-00000023) | GO:0045202 synapse; GO:0098793 presynapse; GO:0014069 postsynaptic density; GO:0043197 dendritic spine; GO:0005654 nucleoplasm; GO:0005794 Golgi apparatus; GO:0005802 trans-Golgi network; GO:0005768 endosome; GO:0005739 mitochondrion | Use gene-level annotation for highest confidence; not every compartment applies to every NS-XLID gene. |
| Major mechanism | Synaptic function/plasticity defects: vesicle trafficking, neurotransmitter release, postsynaptic signaling, receptor trafficking, dendritic spine regulation. Representative genes include GDI1, IL1RAPL1, SYN1, SYP, DLG3, GRIA3, IQSEC2, NLGN3, NLGN4, RAB39B, OPHN1, PAK3, TSPAN7. (pqac-00000006, pqac-00000008, pqac-00000013) | GO:0007268 chemical synaptic transmission; GO:0016079 synaptic vesicle exocytosis; GO:0048167 regulation of synaptic plasticity | Shared pathway category is review-derived; representative genes vary in evidence strength. |
| Major mechanism | Cytoskeleton / Rho- and Arf-family GTPase signaling affecting dendrites and spines. Representative genes include IQSEC2, OPHN1, PAK3, FGD1. (pqac-00000008, pqac-00000013) | GO:0032956 regulation of actin cytoskeleton organization; GO:0007015 actin filament organization | Often downstream of synaptic signaling; phenotype correlations remain incomplete. |
| Major mechanism | Transcription, chromatin, RNA processing, translation regulation. Representative genes include HCFC1, KDM5C, MECP2, MED12, PQBP1, RPS6KA3, THOC2, UPF3B, ZNF711, AFF2, ATRX, DDX3X. (pqac-00000006, pqac-00000011, pqac-00000012) | GO:0006357 regulation of transcription by RNA polymerase II; GO:0006338 chromatin remodeling; GO:0000398 mRNA splicing; GO:0000184 nuclear-transcribed mRNA catabolic process, nonsense-mediated decay | Many of these genes also cause syndromic XLID; classify carefully at variant/disorder level. |
| Major mechanism | Ubiquitination / proteostasis dysregulation, including neuronal proliferation/differentiation and substrate turnover. Representative genes include HUWE1, MID2, RLIM, USP9X. (pqac-00000006, pqac-00000012) | GO:0016567 protein ubiquitination; GO:0032436 positive regulation of proteasomal ubiquitin-dependent protein catabolic process | Evidence is stronger for some genes than others; downstream neuronal effects remain incompletely resolved. |
| Major mechanism | Membrane transport / ion homeostasis / metabolism. Representative genes include SLC6A8, CLCN4, SLC16A2, SLC25A5, NDUFA1, ACSL4, ATP2B3, GLRA2. (pqac-00000010, pqac-00000026, pqac-00000029) | GO term suggestions: transmembrane transport, ion homeostasis, creatine transmembrane transporter activity, mitochondrial ATP transport; verify release | Some genes produce broader syndromic/metabolic phenotypes outside strict NS-XLID. |
| Major mechanism | Golgi/TGN pH regulation and glycosylation defects. Best current gene-specific example: SLC9A7 p.Leu515Phe causing altered Golgi acidification and aberrant glycosylation with abnormal transferrin N-glycosylation. (pqac-00000021, pqac-00000022, pqac-00000023) | GO:0051453 regulation of intracellular pH; GO:0006486 protein glycosylation; GO:0005794 Golgi apparatus; GO:0005802 trans-Golgi network | Mechanism currently best established for SLC9A7-related NS-XLID, not the entire disease group. |
| Causal genes / heterogeneity | Highly heterogeneous disorder group. Review-level counts reported ~56 genes implicated in NS-XLID, with many overlapping syndromic genes; 146 total XLID genes reported by 2020 review, and disease-target databases list additional associated genes. (pqac-00000001, pqac-00000005, pqac-00000009, pqac-00000000) | Gene symbols only; disease-group curation should link to gene-specific disorder records where possible | Gene lists change with reclassification; some historical genes remain uncertain/questioned. |
| Inheritance | Usually X-linked inheritance affecting males more often; female carriers may be unaffected or mildly/variably affected, influenced by X-chromosome inactivation and gene escape status. (pqac-00000009, pqac-00000014, pqac-00000020, pqac-00000025) | HP:0001417 X-linked inheritance; term suggestion: X-linked recessive inheritance; verify release | Some genes act through dominant, de novo, mosaic, or dosage-sensitive mechanisms in females. |
| Diagnostics | Recommended workup typically includes clinical evaluation/family history, FMR1 testing, chromosomal microarray, and next-generation sequencing (panel, exome, or genome) with segregation analysis and variant interpretation under ACMG/AMP. (pqac-00000014, pqac-00000015) | NCIT term suggestions: Genetic Testing, Chromosomal Microarray Analysis, Whole Exome Sequencing, Whole Genome Sequencing; verify release | No single disease-specific laboratory biomarker exists for NS-XLID as a group. |
| Diagnostics | Exome/genome sequencing now outperforms CMA/panels for unexplained GDD/ID broadly; targeted XLID panels may still help in suggestive pedigrees. In one XLID panel study, 17 candidate variants were identified in 16/61 unrelated males after negative karyotype/FMR1 testing. (pqac-00000015) | NCIT term suggestions: Whole Exome Sequencing, Next-Generation Sequencing Panel; verify release | Yield figures vary by cohort design and inclusion criteria; many statistics are for GDD/ID broadly, not NS-XLID alone. |
| Diagnostics | Functional follow-up may include RNA studies, biochemical assays, and gene-specific tests; example: urine creatine/creatinine ratio and brain MRS for SLC6A8 deficiency; transferrin glycosylation for SLC9A7-related disease. (pqac-00000008, pqac-00000015, pqac-00000022) | LOINC/NCIT term suggestions; CHEBI: creatine (verify ontology mapping in KB) | These are gene-specific adjuncts, not universal NS-XLID diagnostics. |
| Diagnostics in females | Extreme skewing of X-inactivation in females with idiopathic ID can enrich for pathogenic findings; in one 2023 cohort, 11/136 informative women (8%) had >=90% skewing and WES found pathogenic variants in 8/11 (73%). (pqac-00000025) | term suggestions: skewed X-chromosome inactivation; verify release | Evidence pertains to idiopathic ID in females, not a diagnostic criterion for all NS-XLID. |
| Treatment / management | No disease-modifying therapy is established for NS-XLID as a disease group. Current care is supportive and individualized: developmental therapies, speech-language therapy, special education, behavioral/psychiatric management, and antiseizure treatment when indicated. (pqac-00000014, pqac-00000016, pqac-00000017) | NCIT term suggestions: Supportive Care, Speech Therapy, Occupational Therapy, Physical Therapy, Special Education, Anticonvulsant Therapy; verify release | Management is phenotype- and gene-specific; evidence base often extrapolated from broader neurodevelopmental care. |
| Advanced therapeutics | Research directions include gene therapy, selective X-reactivation, dosage-controlled transgene strategies, and circuit/synapse-targeted interventions; these remain experimental and are mostly not NS-XLID-specific. (pqac-00000016, pqac-00000017, pqac-00000018, pqac-00000019) | NCIT term suggestions: Gene Therapy, CRISPR-based Gene Editing, RNA Therapy; verify release | Most therapeutic development is for specific syndromic X-linked NDDs; translation to NS-XLID is unresolved. |
| Prevention / counseling | Genetic counseling, cascade testing, carrier testing, reproductive counseling, and when a familial pathogenic variant is known, options such as prenatal diagnosis or preimplantation genetic testing. (pqac-00000014, pqac-00000026, pqac-00000029) | NCIT term suggestions: Genetic Counseling, Carrier Screening, Prenatal Genetic Testing, Preimplantation Genetic Testing; verify release | Prevention is primarily genetic/reproductive rather than environmental because NS-XLID is a monogenic/heterogeneous genetic disease group. |
| Epidemiology | Intellectual disability overall affects ~1% of the population; males are affected more often. XLID accounts for an estimated 5-10% of ID in males, but disease-specific prevalence for NS-XLID is not well established because it comprises many rare gene-defined disorders. (pqac-00000009, pqac-00000014, pqac-00000026) | No exact disease-level prevalence ID recommended | Avoid presenting a single prevalence for MONDO:0019181 as if it were a uniform entity. |
| Natural history / prognosis | Usually childhood-onset and lifelong. Course is generally chronic/stable in terms of core cognitive impairment, while associated features (seizures, behavior, speech limitations) depend on the causal gene and comorbidities. (pqac-00000009, pqac-00000021, pqac-00000026) | term suggestions: childhood onset; chronic course; verify release | Prognosis cannot be generalized across all NS-XLID subtypes. |
| Models | Model systems include mouse models, human iPSCs, and cellular assays; current 2024 work emphasizes mosaic female models, reporter-based strategies, dual-eGRASP/synaptic assays, electrophysiology, imaging, and human iPSC approaches to resolve circuit heterogeneity. (pqac-00000016, pqac-00000017, pqac-00000019, pqac-00000020) | NCIT term suggestions: Disease Model, Induced Pluripotent Stem Cell, Mouse Model; CL:0000000 cell (generic, term suggestion for specific derived neurons); verify release | Much model literature is from broader XLID/X-linked NDDs, not exclusively strict NS-XLID. |
| Exemplary gene-specific subtype | SLC9A7-related NS-XLID: recurrent p.Leu515Phe reported in two unrelated families; associated with moderate-severe ID, speech delay, hypotonia/muscle weakness, reserved personality, clinodactyly; mechanism involves TGN/post-Golgi alkalinization and abnormal glycosylation. (pqac-00000021, pqac-00000022, pqac-00000023, pqac-00000024) | Gene: SLC9A7; GO/UBERON/HPO terms above as applicable | Useful exemplar of mechanistic depth, but not representative of all NS-XLID mechanisms. |


*Table: This table provides a compact, ontology-ready summary of nonsyndromic X-linked intellectual disability for knowledge-base use. It emphasizes heterogeneous gene-dependent biology and highlights that intellectual disability is the only consistent shared feature across the disease group.*