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Mediator Complex Disorders ("MEDopathies") — Landscape & KB Gap Analysis

Compiled 2026-07-30. Scope: every germline human Mendelian disease associated with a subunit of the Mediator transcriptional coactivator complex (the "MEDopathies"), plus the somatic and refuted/provisional associations. This is a research/landscape survey — a map of the disease space and of the PubMed literature dismech does and does not yet cite. All PMIDs were verified to exist on PubMed; every PMID marked NEW was fetched into references_cache/ during this survey and (where cited in the KB) snippet-validated.

What the Mediator complex is

The Mediator is a ~30-subunit assembly that bridges gene-specific transcription factors at enhancers and RNA polymerase II at promoters. It is organised into head, middle, tail, and a dissociable CDK8 kinase module (CKM). The CKM is a four-part cap: a kinase (CDK8 or its paralog CDK19), cyclin C (CCNC), a scaffold (MED12 or MED12L), and a large subunit (MED13 or MED13L). Germline variants across the complex converge on dysregulated Pol II transcription during development, producing a family of overlapping neurodevelopmental / neurodegenerative syndromes now collectively termed MEDopathies (Fazio 2025, PMID:41465117; Guillouet 2025, PMID:40081376).

Master table — germline mediatorpathies

Module abbreviations: CKM = CDK8 kinase module; H = head; M = middle; T = tail; core = structural core. "In KB?" refers to coverage as of this survey.

Gene Module Disease (abbrev) OMIM pheno MONDO Inh. In KB?
MED12 CKM FG syndrome 1 / Opitz-Kaveggia (FGS1) 305450 MONDO:0010590 XLR ✅ subtype
MED12 CKM Lujan (Lujan-Fryns) syndrome 309520 MONDO:0010655 XLR ✅ (noted)
MED12 CKM X-linked Ohdo, Maat-Kievit-Brunner type 300895 MONDO:0010477 XLR ❌ gap
MED12 CKM Hardikar syndrome (female-specific) 301068 MONDO:0012997 XL (females) ❌ gap
MED12 CKM Female syndromic NDD — — XL de novo ❌ gap
MED12 CKM X-linked partial epilepsy without ID — — XLR ❌ gap
MED12L CKM Nizon-Isidor syndrome (NIZIDS) 618872 MONDO:0030030 AD ❌ gap
MED13 CKM Intellectual dev. disorder 61 (MRD61) 618009 MONDO:0032485 AD ✅ subtype + own file
MED13L CKM MED13L syndrome (MRFACD) 616789 MONDO:0014773 AD ✅ subtype
CDK8 CKM ID w/ hypotonia & behavioral abn. (IDDHBA) 618748 MONDO:0032897 AD ❌ gap
CDK19 CKM Developmental & epileptic enceph. 87 (DEE87) 618916 MONDO:0030059 AD ❌ gap
MED11 H Neurodegen. w/ resp. failure, seizures (NDDRSB) 620327 MONDO:0957225 AR ❌ gap
MED17 H Infantile cerebral+cerebellar atrophy / MCPHA 613668 MONDO:0013351 AR ❌ gap
MED20 H Infantile basal ganglia degeneration + dystonia — (gene *612915) — AR ❌ gap (provisional)
MED27 core NDD w/ spasticity, cataracts, cerebellar hypoplasia (NEDSCAC) 619286 MONDO:0859137 AR ❌ gap
MED25 T Basel-Vanagaite-Smirin-Yosef syndrome (BVSYS) 616449 MONDO:0014643 AR ❌ gap
MED23 T AR intellectual dev. disorder 18 (MRT18) 614249 MONDO:0013651 AR ✅ subtype
MED16 T Guillouet-Gordon syndrome (GGNS) 621220 MONDO:0979227 AR ❌ gap (new 2025 gene)

By module — detail and key PubMed anchors

CDK8 kinase module (CKM)

MED12 (Xq13.1) is a single gene producing an allelic series — model each as a distinct entity, not a variant of one syndrome, because the mechanism differs by allele class (male missense hotspots vs. female loss-of-function). GeneReviews: MED12-Related Disorders (NBK1676; PMID:20301719). - FGS1 / Opitz-Kaveggia — recurrent p.R961W. Discovery PMID:17334363 (Risheg 2007, Nat Genet) NEW to KB; clinical cohort PMID:19938245 (already cited); behavioral PMID:18973276. - Lujan syndrome — p.N1007S. PMID:17369503 (already cited). - Shared mechanism — R961W/N1007S disrupt a Mediator constraint on GLI3-dependent SHH signalling: PMID:23091001 (Zhou 2012, PNAS) NEW to KB. - X-linked Ohdo (MKB type) — PMID:23395478 (Vulto-van Silfhout 2013, AJHG) NEW. - Hardikar syndrome (female-specific, LoF) — PMID:33244166 (Li 2021, Genet Med) NEW; further delineation PMID:41821414 (Warmoeskerken 2026). - Female syndromic NDD — PMID:33244165 (Polla 2021, Genet Med) NEW. - X-linked partial epilepsy without ID — PMID:36894399 (Yang 2023) — newest, benign-end phenotype. - Somatic MED12 (exon-2 Q44 gain-of-function; keep architecturally separate from germline): uterine leiomyoma PMID:21868628 (Mäkinen 2011, Science); also breast fibroadenoma, phyllodes tumor, leiomyosarcoma/CRC. dismech already models the somatic arm in Uterine_Leiomyoma.yaml and Breast_Fibroadenoma.yaml.

MED12L (3q25.1) — Nizon-Isidor syndrome: ID, prominent speech delay, hypotonia, variable congenital heart defects. Discovery PMID:31155615 (Nizon 2019, Genet Med) NEW; case series + mitotic-instability observation PMID:40838347 (Stewart 2026).

CDK8 (13q12.13) — IDDHBA: de novo kinase-domain missense (hypomorphic); hypotonia, mild-moderate ID, behavioral abnormalities, facial dysmorphism, congenital heart disease. Discovery PMID:30905399 (Calpena 2019, AJHG) NEW; mechanism PMID:33067521; phenotype expansion PMID:38193604.

CDK19 (6q21) — DEE87: de novo kinase-domain missense; hypotonia, global delay, epileptic encephalopathy/infantile spasms. Discovery PMID:32330417 (Chung 2020, AJHG) NEW; LoF/GoF dichotomy PMID:33495529; infantile spasms PMID:33568421.

MED13 / MED13L — already well covered in the KB. Useful mechanism additions: MED13L→cyclin C mislocalization/mitochondrial dysfunction PMID:35198885 (Chang 2022, iScience) NEW; cortical-neurogenesis priming PMID:40775066 (already cited).

Head module

MED17 (11q21) — MCPHA / infantile cerebral and cerebellar atrophy with postnatal progressive microcephaly: normal at birth, then postnatal microcephaly, spasticity, epilepsy, profound psychomotor retardation; MRI cerebral+cerebellar atrophy, poor myelination. Caucasus-Jewish founder p.L371P. Discovery PMID:20950787 (Kaufmann 2010, AJHG) NEW; milder compound-het siblings PMID:26004231; phenotype expansion PMID:30345598; founder natural history PMID:33756211; novel allele PMID:36508181.

MED11 (17p13.1) — NDDRSB (lethal): congenital microcephaly, neonatal respiratory failure, refractory myoclonic seizures, exaggerated startle, progressive neurodegeneration, premature death; recurrent homozygous C-terminal R109X destabilizes the MED11-MED22-MED17 bundle. Single defining paper PMID:36001086 (Calì 2022, Genet Med) NEW.

MED20 (6q22.31) — infantile basal ganglia degeneration + brain atrophy with infantile-onset spasticity and childhood-onset dystonia. Provisional: one family (2 sibs, homozygous p.G114Ala); the authors state proof of pathogenicity awaits unrelated patients. PMID:25446406 (Vodopiutz 2015, Eur J Pediatr) NEW. No OMIM phenotype #.

Structural core

MED27 (9q34.3) — NEDSCAC: global developmental delay, ID, axial hypotonia with distal spasticity, dystonia, cerebellar hypoplasia; congenital cataracts and seizures in severe cases. Discovery PMID:33443317 (Meng 2021, Ann Neurol) NEW — note the syndrome-defining paper is Ann Neurol, not Brain; the Brain 2023 paper (PMID:37517035, "ponto-cerebello-lental degeneration") is the follow-up cohort. Further: PMID:39296199 (Wu 2024); mechanism PMID:41017421 (Yiliyaer 2025).

Tail module

MED25 (19q13.33) — BVSYS (eye-intellectual-disability syndrome): severe ID with eye (cataract, microcornea, coloboma), brain (incl. polymicrogyria), cardiac and palatal anomalies; founder p.Y39C impairs MED25 incorporation into Mediator. Discovery PMID:25792360 (Basel-Vanagaite 2015, Hum Genet) NEW; p.I173T Lebanese founder PMID:30800049 / PMID:31602195; delineation PMID:32324310; polymicrogyria PMID:32816121.

MED23 (6q23.2) — already covered (MRT18). Useful additions: ketogenic-diet-responsive refractory epilepsy PMID:27311965 (Lionel 2016, AJMG A) NEW; genotype-phenotype PMID:39144687 (Bamaga 2024).

MED16 (19p13.3) — Guillouet-Gordon syndrome: a new (2025) Mediator disease gene — biallelic variants → MCA-ID MEDopathy with craniofacial defects, limb anomalies, and heart defects (predominantly tetralogy of Fallot). Discovery PMID:40081376 (Guillouet 2025, AJHG) NEW.

Refuted / provisional / negative associations (curate with care)

  • MED25 → CMT2B2 (Charcot-Marie-Tooth 2B2) is REFUTED. The original p.A335V association (Leal 2009, PMID:19290556) was reassigned by the same group to a homozygous PNKP variant: PMID:30039206 (Leal 2018, Neurogenetics). CMT2B2 (OMIM 605589) is now a PNKP disorder. dismech's Charcot-Marie-Tooth_Disease_Type_2.yaml currently lists "CMT2B2 (MED25)" in passing — this should be corrected (MED25 recorded only as a historical/refuted association, or the parenthetical updated to PNKP).
  • MED14 (Xp11.4) — emerging/provisional, not an established OMIM phenotype. Two single-family X-linked reports: T-B+NK+ immunodeficiency (PMID:35967429, Sertori 2022) and a VACTERL-like malformation report (Sertori 2025, Genes & Diseases — no PubMed PMID at survey time). Curate only as candidate.
  • CCNC (cyclin C) — no verified germline neurodevelopmental disorder despite being a core CKM subunit. Its only germline human disease link is a contiguous CCNC+PRDM13 duplication causing North Carolina macular dystrophy (retinal, not NDD; PMID:28973654, already reflected in North_Carolina_Macular_Dystrophy.yaml). Cyclin C is mechanistically implicated downstream of MED13L loss (PMID:35198885), not as a primary disease gene. Do not create a CCNC NDD entry. Watch for confusion with CCNK (cyclin K), a different gene causing a distinct NDD (PMID:29979980) — not part of the CKM.
  • No established germline Mendelian disease (report as negatives): MED1, MED15 (within 22q11.2 del region; somatic RCC fusions only), MED19, MED21, MED22, MED26, MED28, MED30, MED31. Guard against MED31 ≠ MRT31 (OMIM 614329 is a different locus).

KB action summary

Already covered: MED13, MED13L, MED12 (FGS1/Lujan), MED23 — as subtypes of kb/disorders/Mediator_Complex_Neurodevelopmental_Disorder.yaml, plus a dedicated MED13_Syndrome.yaml, and the somatic MED12 tumor arm.

Recommended additions (this survey acts on the germline neurodevelopmental set): add CDK8, CDK19, MED12L, MED11, MED17, MED20, MED27, MED25 (BVSYS), MED16 as subtypes of the Mediator grouping entry, and enrich the MED12 subtype with the Ohdo / Hardikar / female-NDD allelic series and the GLI3-SHH mechanism. All defining PMIDs above marked NEW were fetched and, where cited, snippet-validated.

Deferred (evidence tier / scope): MED20 and MED14 are single-family/provisional — MED20 is added with an explicit provisional flag; MED14 is left as a candidate note. MED12 somatic tumors stay in their existing tumor entries. The MED25-CMT2B2→PNKP correction to Charcot-Marie-Tooth_Disease_Type_2.yaml is flagged here for a follow-up.

Key references (verified)

FGS1 17334363 · Lujan 17369503 · SHH/GLI3 23091001 · Ohdo 23395478 · Hardikar 33244166 · female NDD 33244165 · MED12 epilepsy 36894399 · MED12L/Nizon-Isidor 31155615, 40838347 · CDK8 30905399, 33067521, 38193604 · CDK19 32330417, 33495529, 33568421 · MED17 20950787, 26004231, 30345598, 33756211, 36508181 · MED11 36001086 · MED20 25446406 · MED27 33443317, 37517035, 39296199, 41017421 · MED25 BVSYS 25792360, 30800049, 31602195, 32324310, 32816121 · MED25→PNKP reassignment 30039206 · MED23 21868677, 27311965, 30847200, 36824420, 39144687 · MED16 40081376 · MED13L cyclin C 35198885 · umbrella review (Fazio 2025) 41465117 · somatic MED12 21868628.