LGI4

LGI4 is a secreted, glycosylated leucine-rich repeat protein that functions as a paracrine ligand essential for peripheral nervous system myelination and glial development. Schwann cell-secreted LGI4 signals through axonal ADAM22 (and also ADAM11/ADAM23) to drive axonal sorting, Schwann cell differentiation, and myelin formation, and promotes proliferation and differentiation of glial-restricted progenitors across sensory, sympathetic, and enteric ganglia (PMID:16341215, PMID:20220021, PMID:21068328). Disease-causing mutations primarily impair LGI4 trafficking and secretion through the endomembrane system rather than ADAM22 binding per se, and biallelic loss-of-function mutations in human LGI4 cause arthrogryposis multiplex congenita with peripheral nerve hypomyelination (PMID:28318499, PMID:34288120). IgG4 autoantibodies targeting the LGI4–ADAM22 complex suppress Schwann cell myelination programs by reducing Krox20 expression, linking disrupted LGI4 signaling to chronic inflammatory demyelinating polyneuropathy (PMID:36631269).

1. 2005 High

   The identification of LGI4 as the gene disrupted in claw paw mice established that a Schwann cell-secreted factor is required for axonal sorting and peripheral myelination, answering the question of whether an extrinsic signal drives PNS myelin initiation.

   Evidence Mouse claw paw mutant genetics, siRNA knockdown in neuron–Schwann cell cocultures, exogenous LGI4 rescue assay

   PMID:16341215

   Open questions at the time

   • Receptor identity on axons unknown
   • Mechanism by which LGI4 promotes Schwann cell differentiation not defined
   • Whether LGI4 acts in glia outside myelinating Schwann cells untested
2. 2008 High

   Biochemical identification of ADAM22, ADAM23, and ADAM11 as direct LGI4-binding partners revealed the receptor family mediating LGI4 signaling, expanding the receptor landscape beyond a single candidate.

   Evidence Immunoprecipitation/mass spectrometry and quantitative cell-ELISA binding assays

   PMID:18974846

   Open questions at the time

   • Relative contributions of ADAM11, ADAM22, and ADAM23 to myelination not dissected
   • Downstream intracellular signaling pathway unknown
3. 2010 High

   Cell-type-specific conditional knockouts demonstrated that LGI4 is required in Schwann cells and ADAM22 on axons, establishing a directional paracrine signaling axis and showing LGI4 binds ADAM22 directly without cofactors; genetic epistasis further showed LGI4–ADAM22 signaling controls glial progenitor proliferation and differentiation across sensory, sympathetic, and enteric ganglia.

   Evidence Schwann cell- and neuron-specific conditional KO mice, direct binding assays, compound-mutant epistasis analysis across multiple ganglia

   PMID:20220021 PMID:21068328

   Open questions at the time

   • Intracellular signaling cascade downstream of ADAM22 engagement not characterized
   • Whether LGI4 acts in CNS glia undetermined
   • Structural basis of LGI4–ADAM22 interaction unknown
4. 2014 Medium

   Discovery of an LGI4–ADAM23 paracrine axis in breast cancer showed that LGI4 function extends beyond neural development, with LGI4 from ADAM23-negative cells promoting proliferation and invasion of neighboring ADAM23-positive cells.

   Evidence LGI4 knockdown in heterotypic breast cancer cell cocultures with proliferation and invasion assays

   PMID:24662834

   Open questions at the time

   • Downstream oncogenic pathway not identified
   • In vivo relevance in tumor models not tested
   • Specificity of LGI4 versus other LGI family members in this context unclear
5. 2017 High

   Identification of biallelic LGI4 mutations in human arthrogryposis multiplex congenita patients established LGI4 as essential for human PNS myelination and demonstrated that mutations cause aberrant splicing and impaired secretion.

   Evidence Whole-exome sequencing of affected families, patient-derived iPSC secretion and splicing assays, sciatic nerve electron microscopy

   PMID:28318499

   Open questions at the time

   • Whether therapeutic LGI4 replacement could rescue myelination in patients untested
   • Genotype-phenotype correlation across different mutation types incomplete
6. 2021 Medium

   Functional dissection of patient missense mutations showed the primary pathomechanism is impaired endomembrane trafficking and secretion, not loss of ADAM22 binding or myelination-promoting activity, refining the disease model.

   Evidence Cell-based secretion assays, ADAM22 binding assays, and myelination coculture assays with panel of mutant LGI4 proteins

   PMID:34288120

   Open questions at the time

   • Quality control mechanism recognizing and retaining mutant LGI4 in the ER/Golgi not identified
   • Not independently replicated
   • Whether chaperone-based rescue of secretion is feasible untested
7. 2023 Medium

   Detection of anti-LGI4/ADAM22 IgG4 autoantibodies in CIDP patients that suppress Krox20 expression in Schwann cells linked disrupted LGI4 signaling to acquired inflammatory neuropathy, extending pathological relevance beyond genetic disease.

   Evidence Patient serum IgG application to Schwann cell cultures, cell-based binding assays with co-expressed LGI4 and ADAM22, RT-qPCR for Krox20

   PMID:36631269

   Open questions at the time

   • Prevalence of anti-LGI4 autoantibodies across CIDP cohorts not established
   • Whether autoantibodies block LGI4 binding to ADAM22 or disrupt a downstream step not resolved
   • Pathogenicity in animal passive-transfer models not demonstrated
8. 2025 Medium

   Demonstration that IGF2BP2 stabilizes LGI4 mRNA in an m6A-dependent manner in intestinal epithelial cells revealed an epitranscriptomic regulatory layer for LGI4 expression and an anti-inflammatory role for LGI4 via suppression of MEK1/2-ERK1/2 signaling.

   Evidence meRIP-qPCR, RIP, mRNA stability assays, IGF2BP2 KO mice, AAV9-mediated LGI4 rescue in DSS colitis model

   PMID:40663812

   Open questions at the time

   • Receptor mediating LGI4 anti-inflammatory signaling in gut epithelium not identified
   • Whether m6A regulation of LGI4 mRNA operates in Schwann cells unknown
   • Mechanism linking LGI4 to MEK/ERK suppression not defined

• Key unresolved questions include the intracellular signaling cascade downstream of ADAM22 engagement by LGI4, the structural basis of the LGI4–ADAM22 interaction, the quality control mechanism governing LGI4 endomembrane trafficking, and whether LGI4 functions in the CNS.
• No crystal or cryo-EM structure of LGI4 or LGI4–ADAM22 complex
• Downstream transcriptional program beyond Krox20 induction not mapped
• Whether LGI4 cardiac channelosome function is physiologically relevant requires peer-reviewed confirmation