| domain | finding/statistic | evidence type | interpretation/limitation |
|---|---|---|---|
| Molecular definition | FG syndrome 1 / Opitz-Kaveggia syndrome is the molecularly confirmed MED12-associated disorder caused by recurrent MED12 c.2881C>T (p.Arg961Trp, p.R961W) (pqac-00000002, pqac-00000005) | Human clinical genetics + review | Important to distinguish from broader “FG syndrome” phenotypes that are genetically heterogeneous and often MED12-negative (pqac-00000002, pqac-00000003) |
| Molecularly confirmed cohort | 23 affected males from 10 families with MED12 p.Arg961Trp; broader paper also discusses 30 live-born affected males in 10 families and compares 48 clinically diagnosed but mutation-negative cases (pqac-00000000, pqac-00000001) | Human cohort/case series | Denominators vary by analysis subset and by availability of records; avoid mixing molecularly confirmed cases with historical phenotypic FG cases (pqac-00000000, pqac-00000001) |
| Inheritance | X-linked disorder affecting males; heterozygous females reported as clinically unaffected and intellectually normal in the core cohort (pqac-00000000, pqac-00000004, pqac-00000013) | Human pedigree/cohort | Evidence supports male-limited expression in known families, but formal penetrance estimates are not established (pqac-00000013) |
| Core early phenotype | Infantile hypotonia and constipation in 23/23 affected males (pqac-00000013) | Human cohort/case series | Strongest recurring early clinical features; useful for recognition but not specific outside the syndromic context (pqac-00000011, pqac-00000013) |
| Neuroanatomy | Corpus callosum agenesis/hypoplasia in 13/13 imaged individuals (pqac-00000000, pqac-00000013) | Human imaging within cohort | High frequency among imaged patients, but denominator is only those who underwent neuroimaging (pqac-00000013) |
| Gastrointestinal/anorectal anomalies | Anal anomaly (fistula/stenosis/atresia) in 11/19 (pqac-00000000, pqac-00000013) | Human cohort/case series | Denominator reflects patients with evaluable data; severe constipation can also occur without a major structural anal defect (pqac-00000003, pqac-00000013) |
| Cardiac anomalies | Congenital cardiac anomaly in 11/18 (pqac-00000000, pqac-00000013) | Human cohort/case series | Substantial but not universal; supports baseline cardiology evaluation in suspected cases (pqac-00000011, pqac-00000013) |
| Craniofacial features | Small ears in 12/13 where specifically measured/supported (pqac-00000014) | Human cohort/case series | One of the more discriminating facial findings, but facial gestalt remains composite rather than single-feature based (pqac-00000000, pqac-00000011) |
| Head size | Macrocephaly reported with denominator variation: 15/18 in one summary, 7/18 absolute macrocephaly in another analysis (pqac-00000014, pqac-00000013) | Human cohort/case series | Variation likely reflects different definitions/ascertainment (absolute vs relative macrocephaly, age-specific data); should be reported with denominator and wording preserved (pqac-00000000, pqac-00000014) |
| Diagnostic performance | Historical clinical algorithm for targeted MED12 p.Arg961Trp testing showed 100% sensitivity and 90% specificity (pqac-00000001, pqac-00000016) | Human diagnostic study | Useful as historical triage, but modern practice generally prioritizes sequencing-based diagnosis; performance derived from limited retrospective cohorts (pqac-00000002, pqac-00000016) |
| Mechanism: immediate-early genes | In patient EBV-immortalized lymphoblastoid cells, MED12 p.Arg961Trp dysregulated immediate-early genes, with JUN downregulation and FOS upregulation; promoter Pol II/MED12 recruitment paralleled expression changes (pqac-00000010) | Human patient-cell functional study | Mechanistic evidence is from lymphoblastoid cells, so tissue relevance to brain/gut/heart phenotypes is inferential rather than directly demonstrated (pqac-00000010) |
| Mechanism: SHH/GLI3 | In patient lymphoblast cell lines, MED12-related XLID variants including FG-associated p.Arg961Trp showed elevated GLI3-dependent SHH target-gene transcripts such as CREB5, BMP4, and NEUROG2 (pqac-00000009) | Human patient-cell functional study | Supports pathway-selective transcriptional dysregulation; does not fully explain organ-specific manifestations or phenotypic variability (pqac-00000007, pqac-00000009) |
| Mechanistic synthesis | Expert review concludes p.Arg961Trp causes selective MED12 pathway dysfunction affecting enhancer/transcriptional control rather than complete loss of MED12 function (pqac-00000007, pqac-00000008) | Expert review/mechanistic synthesis | Current model integrates REST/IEG/SHH findings, but no unified causal chain has been proven across all affected tissues (pqac-00000007, pqac-00000008) |
| Prognosis/natural history | Early deaths/deceased male infants occurred in many families, but after infancy prognosis improves; some affected males were functioning well in the 5th-6th decades and hypotonia may improve with age (pqac-00000000, pqac-00000013) | Human natural history within cohort | Mortality is concentrated early; long-term adult survival is clearly possible, but formal survival curves are unavailable (pqac-00000013) |
| Treatment landscape | No disease-modifying therapy, validated biomarker-directed treatment, or FG syndrome 1-specific interventional clinical trial was identified; management is supportive and multidisciplinary (pqac-00000012, pqac-00000013) | Review + cohort-based expert management | Current care targets complications and development rather than MED12-specific molecular correction; evidence base is largely expert opinion and case-series practice (pqac-00000012) |


*Table: This table summarizes the most actionable evidence for molecularly confirmed FG syndrome 1, including defining variant, cohort size, major phenotype frequencies, mechanism, diagnostic performance, prognosis, and treatment gaps. It is useful for separating MED12 p.Arg961Trp-associated disease from the broader heterogeneous FG phenotype.*