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Meckel Syndrome

Disease Pathophysiology Research Report

2026-02-02
Falcon MONDO:0018921 Model: Edison Scientific Literature 13 citations

Disease Pathophysiology Research Report

Target Disease

  • Disease Name: Meckel syndrome (Meckel–Gruber syndrome, MKS)
  • MONDO ID: MONDO:0019391
  • Category: Genetic (autosomal recessive ciliopathy)

Summary and Key Concepts

Meckel syndrome is a perinatally lethal, multisystem ciliopathy caused by biallelic variants in genes encoding components of the ciliary transition zone (TZ) and associated complexes. The TZ functions as a selective diffusion and gating barrier that establishes ciliary membrane composition and controls receptor and intraflagellar transport (IFT) trafficking. Disruption of TZ modules (MKS, NPHP, B9) and their linkage to basal body/IFT assemblies impairs ciliogenesis and cilia-based signaling (notably Hedgehog and Wnt/PCP), leading to severe developmental malformations of the brain, kidney, liver, and limbs (e.g., occipital encephalocele, cystic renal dysplasia, hepatic ductal plate malformation, polydactyly). Recent work further indicates that proteolytic processing of TMEM67 by ADAMTS9 acts as a molecular switch that uncouples its roles in Wnt signaling vs. TZ assembly/ciliogenesis, offering a direct genotype-to-mechanism framework for MKS (preprint) (mill2023primaryciliaas pages 31-36, kalot2024primaryciliaand pages 11-12, ahmed2024twofunctionalforms pages 5-8, ahmed2024twofunctionalforms pages 1-5).

Table (click to expand)
Gene/Protein (HGNC) Complex/Module Primary localization (cellular component) Principal function / mechanism (1–2 lines) Pathways implicated Evidence (citation IDs, DOI/URL, month year)
TMEM67 MKS module Ciliary transition zone / ciliary membrane / basal body TZ scaffold required for ciliogenesis; extracellular CRD acts as Wnt co-receptor; ADAMTS9 cleavage produces a TZ-localizing C-terminal form and a surface form that mediates Wnt signaling. Non-canonical/canonical Wnt; ciliogenesis; TZ assembly (indirectly affects HH) (ahmed2024twofunctionalforms pages 5-8) https://doi.org/10.1101/2024.09.04.611229, Sep 2024; (kalot2024primaryciliaand pages 11-12) https://doi.org/10.3389/fneph.2023.1331847, Jan 2024; (mill2023primaryciliaas pages 31-36) https://doi.org/10.1038/s41576-023-00587-9, Apr 2023
MKS1 MKS module Transition zone / basal body TZ scaffold component required for basal body docking and ciliogenesis; influences apical actin remodeling (RhoA–ROCK) needed for basal body anchoring. Ciliogenesis; actin/RhoA-mediated basal body docking; epithelial morphogenesis (kalot2024primaryciliaand pages 11-12) https://doi.org/10.3389/fneph.2023.1331847, Jan 2024; (mill2023primaryciliaas pages 31-36) https://doi.org/10.1038/s41576-023-00587-9, Apr 2023
CEP290 TZ / NPHP-associated module Transition zone / connecting cilium (photoreceptors); ciliary necklace / Y-link region Architectures ciliary membrane and TZ substructure; required for proper localization of TZ proteins and trafficking of photoreceptor/ciliary cargo. Intraflagellar transport / ciliary trafficking; Hedgehog (via receptor localization) (dubaicUnknownyearofthethesis pages 24-26) thesis (no DOI), unknown year; (mill2023primaryciliaas pages 31-36) https://doi.org/10.1038/s41576-023-00587-9, Apr 2023
CC2D2A MKS / TZ Transition zone TZ assembly factor that interacts with CEP290; required for ciliogenesis and TZ integrity. Ciliary trafficking; developmental signalling (HH/Wnt consequences) (dubaicUnknownyearofthethesis pages 24-26) thesis (no DOI), unknown year; (mill2023primaryciliaas pages 31-36) https://doi.org/10.1038/s41576-023-00587-9, Apr 2023
TMEM216 MKS module Transition zone / basal body TZ/transitional membrane protein needed for basal body docking and ciliogenesis; biallelic loss leads to severe MKS phenotypes. Planar cell polarity / Wnt-PCP, ciliogenesis, actin remodeling (RhoA axis) (kalot2024primaryciliaand pages 11-12) https://doi.org/10.3389/fneph.2023.1331847, Jan 2024; (kalot2024primaryciliaand pages 19-20) https://doi.org/10.3389/fneph.2023.1331847, Jan 2024
TMEM231 MKS module Transition zone TZ component implicated in TZ assembly and stable recruitment of other TZ proteins; contributes to diffusion barrier function. Ciliogenesis; TZ gating affecting HH/Wnt signalling (dubaicUnknownyearofthethesis pages 24-26) thesis (no DOI), unknown year; (mill2023primaryciliaas pages 31-36) https://doi.org/10.1038/s41576-023-00587-9, Apr 2023
B9D1 (B9-domain) / MKS-associated Transition zone / basal body B9-domain containing TZ protein; part of TZ/B9 complex that helps establish diffusion barrier and TZ architecture; pathogenic variants reported in MKS pedigrees. TZ gate formation; ciliogenesis; developmental signalling (mill2023primaryciliaas pages 31-36) https://doi.org/10.1038/s41576-023-00587-9, Apr 2023; (dubaicUnknownyearofthethesis pages 24-26) thesis (no DOI), unknown year
RPGRIP1L NPHP/MKS-associated Transition zone / basal body TZ scaffold/gate protein required for selective entry of proteins into cilium; loss perturbs TZ barrier and signaling receptor localization. Ciliary receptor trafficking (HH, PDGFR), ciliogenesis (dubaicUnknownyearofthethesis pages 24-26) thesis (no DOI), unknown year; (mill2023primaryciliaas pages 31-36) https://doi.org/10.1038/s41576-023-00587-9, Apr 2023
RSG1 CPLANE–TZ link Basal body / transition zone interface Small GTPase linking the CPLANE complex to TZ architecture; required for CPLANE-dependent recruitment of IFT and normal TZ assembly. CPLANE → IFT recruitment → ciliogenesis; impacts TZ assembly and thus ciliary signalling (kalot2024primaryciliaand pages 19-20) https://doi.org/10.3389/fneph.2023.1331847, Jan 2024; (mill2023primaryciliaas pages 31-36) https://doi.org/10.1038/s41576-023-00587-9, Apr 2023
INPP5E (not classic MKS) lipid regulator at cilium Ciliary membrane / axoneme 5-phosphatase that controls ciliary phosphoinositide composition (PIP levels), essential for ciliary protein localization, ciliogenesis and HH signaling fidelity. PI lipid signaling in cilium; Hedgehog pathway; ciliogenesis (mill2023primaryciliaas pages 31-36) https://doi.org/10.1038/s41576-023-00587-9, Apr 2023; (kalot2024primaryciliaand pages 19-20) https://doi.org/10.3389/fneph.2023.1331847, Jan 2024
Transition zone (concept) TZ (MKS / NPHP modules) Transition zone (membrane, Y-links, ciliary necklace) Diffusion/barrier gate at cilium base assembled from MKS/NPHP/B9 modules; controls selective trafficking of receptors/IFT, thereby organizing ciliary signalling and enabling tissue-specific developmental programmes. Hedgehog, Wnt/PCP, TGF-β/BMP, receptor trafficking / IFT-dependent signalling (mill2023primaryciliaas pages 31-36) https://doi.org/10.1038/s41576-023-00587-9, Apr 2023; (dubaicUnknownyearofthethesis pages 24-26) thesis (no DOI), unknown year; (ahmed2024twofunctionalforms pages 5-8) https://doi.org/10.1101/2024.09.04.611229, Sep 2024

Table: Compact reference table of key Meckel syndrome (MKS) genes/modules, their cellular localization, primary mechanisms, implicated pathways, and supporting evidence (selected recent reviews and mechanistic studies). This aids mapping genotype→cellular defect→pathway for MKS pathophysiology.

1. Core Pathophysiology

  • Transition zone (TZ) gate dysfunction is the central mechanism in MKS. The TZ is a membrane-proximal subcompartment that forms a selective barrier and trafficking hub for entry/exit of proteins, coordinating IFT-A/B complexes and motor-driven cargo movement; defects mislocalize signaling receptors (e.g., PTCH1, SMO, GPR161), perturb ciliary phosphoinositides, and disrupt cilia-mediated pathway fidelity (HH, TGF-β, Wnt) (mill2023primaryciliaas pages 31-36).
  • MKS/NPHP/B9 modules assemble the TZ and interact with basal body components. Loss of MKS-module proteins (e.g., TMEM67, MKS1, TMEM216) prevents basal body docking and ciliogenesis via aberrant RhoA–ROCK–actin remodeling, blocking epithelial morphogenesis and ciliogenesis (kalot2024primaryciliaand pages 11-12, kalot2024primaryciliaand pages 19-20).
  • New mechanistic insight: ADAMTS9 cleaves the extracellular domain of TMEM67 to create two functional forms—a non-cleaved, surface Wnt co-receptor form and a C-terminal fragment that localizes to the TZ to promote ciliogenesis. A non-cleavable Tmem67 mouse retains Wnt signaling but exhibits ciliogenesis defects that phenocopy null alleles, indicating proteolysis-driven partitioning of TMEM67 functions (bioRxiv, Sept 5, 2024) (ahmed2024twofunctionalforms pages 1-5, ahmed2024twofunctionalforms pages 5-8).
  • CEP290 shapes TZ substructure (ciliary necklace/Y-links) and organizes protein distribution within the connecting cilium; its loss restricts other TZ proteins proximally and abrogates outer segment formation (photoreceptor model), highlighting TZ architectural dependence (Journal of Cell Science, 2025) (mill2023primaryciliaas pages 31-36, dubaicUnknownyearofthethesis pages 24-26).

2. Dysregulated Molecular Pathways

  • Hedgehog (HH) signaling: The primary cilium orchestrates HH via ciliary trafficking of PTCH1, SMO, GPR161, and GLI processing; defective TZ gating/IFT trafficking perturbs HH gradient interpretation, contributing to midline CNS and limb patterning defects (mill2023primaryciliaas pages 31-36).
  • Wnt/planar cell polarity (PCP): TMEM67’s extracellular domain serves as a Wnt co-receptor (Wnt5a/ROR2 axis), while its TZ-localized form scaffolds ciliogenesis. Loss of MKS proteins also perturbs PCP/cytoskeletal polarity, coupling to epithelial morphogenesis and renal tubule architecture (ahmed2024twofunctionalforms pages 5-8, kalot2024primaryciliaand pages 11-12).
  • Actin/RhoA pathways: MKS1/TMEM67/TMEM216 regulate apical actin remodeling for basal body docking; hyperactivated RhoA disrupts docking and ciliogenesis (kalot2024primaryciliaand pages 11-12, kalot2024primaryciliaand pages 19-20).
  • Additional cilia-regulated pathways: TGF-β/BMP and PDGFRα signaling require intact ciliary trafficking; TZ dysfunction is predicted to broadly impair these signaling hubs (mill2023primaryciliaas pages 31-36).

3. Cellular Processes Affected

4. Key Molecular Players

5. Cellular Components (GO/CC)

6. Disease Progression: Genotype → Mechanism → Organ-level Malformations

7. Phenotypic Manifestations (clinical and HP terms)

8. Recent Developments and Latest Research (2023–2025 prioritized)

9. Current Applications and Real-world Implementations

  • Prenatal genetics: Diagnostic algorithms for fetuses with bilateral polycystic kidneys integrate ultrasound features with chromosomal microarray and exome sequencing; MKS represents a substantial fraction of such cases, guiding counseling and management (Simonini 2023) (kalot2024primaryciliaand pages 19-20).
  • Pathway-aware variant interpretation: Recognition that MKS genes localize to TZ/MKS modules and perturb HH/Wnt/PCP helps interpret variants of uncertain significance and to predict organ involvement patterns (mill2023primaryciliaas pages 31-36, kalot2024primaryciliaand pages 11-12).

10. Expert Opinions and Authoritative Analysis

11. Relevant Statistics and Data

Gene/Protein Annotations with Ontologies

Phenotype Associations (HP terms)

Cell Type Involvement (CL terms)

Anatomical Locations (UBERON terms)

Chemical Entities (CHEBI)

Evidence Items (recent, with URLs/dates)

Notes and Limitations

References (by citation IDs)

References

  1. (mill2023primaryciliaas pages 31-36): Pleasantine Mill, Søren T. Christensen, and Lotte B. Pedersen. Primary cilia as dynamic and diverse signalling hubs in development and disease. Nature reviews. Genetics, 24:421-441, Apr 2023. URL: https://doi.org/10.1038/s41576-023-00587-9, doi:10.1038/s41576-023-00587-9. This article has 370 citations.

  2. (kalot2024primaryciliaand pages 11-12): Rita K. Kalot, Zachary T Sentell, Thomas M. Kitzler, and Elena Torban. Primary cilia and actin regulatory pathways in renal ciliopathies. Frontiers in Nephrology, Jan 2024. URL: https://doi.org/10.3389/fneph.2023.1331847, doi:10.3389/fneph.2023.1331847. This article has 11 citations and is from a poor quality or predatory journal.

  3. (ahmed2024twofunctionalforms pages 5-8): Manu Ahmed, Sydney Fischer, Karyn L. Robert, Karen I. Lange, Michael W. Stuck, Sunayna Best, Colin A. Johnson, Gregory J. Pazour, Oliver E. Blacque, and Sumeda Nandadasa. Two functional forms of the meckel-gruber syndrome protein tmem67 generated by proteolytic cleavage by adamts9 mediate wnt signaling and ciliogenesis. bioRxiv, Sep 2024. URL: https://doi.org/10.1101/2024.09.04.611229, doi:10.1101/2024.09.04.611229. This article has 0 citations and is from a poor quality or predatory journal.

  4. (ahmed2024twofunctionalforms pages 1-5): Manu Ahmed, Sydney Fischer, Karyn L. Robert, Karen I. Lange, Michael W. Stuck, Sunayna Best, Colin A. Johnson, Gregory J. Pazour, Oliver E. Blacque, and Sumeda Nandadasa. Two functional forms of the meckel-gruber syndrome protein tmem67 generated by proteolytic cleavage by adamts9 mediate wnt signaling and ciliogenesis. bioRxiv, Sep 2024. URL: https://doi.org/10.1101/2024.09.04.611229, doi:10.1101/2024.09.04.611229. This article has 0 citations and is from a poor quality or predatory journal.

  5. (dubaicUnknownyearofthethesis pages 24-26): M Dubaic. Of the thesis: primary cilia function in development and disease. Unknown journal, Unknown year.

  6. (kalot2024primaryciliaand pages 19-20): Rita K. Kalot, Zachary T Sentell, Thomas M. Kitzler, and Elena Torban. Primary cilia and actin regulatory pathways in renal ciliopathies. Frontiers in Nephrology, Jan 2024. URL: https://doi.org/10.3389/fneph.2023.1331847, doi:10.3389/fneph.2023.1331847. This article has 11 citations and is from a poor quality or predatory journal.