Klotho, GDNF, IGF-1, and GLP-1 Signaling Pathways in Autism

Abstract

Autism spectrum disorder (ASD) is a heterogeneous neurodevelopmental condition characterized by deficits in social communication and restricted, repetitive behaviors. Although traditionally linked to synaptic protein dysfunction and neurotransmitter imbalance, growing evidence suggests that broader intracellular signaling networks critically regulate the neurodevelopmental processes disrupted in ASD. This review synthesizes current evidence on four interconnected signaling pathways, Klotho, GDNF/GFRA-1, IGF-1, and GLP-1, and examines their potential roles in ASD pathophysiology within a unified mechanistic framework. These pathways regulate fundamental processes, including neuronal survival, synaptogenesis, dendritic maturation, myelination, modulation of oxidative stress, neuroinflammation, and metabolic homeostasis. Importantly, they converge on shared intracellular cascades such as PI3K/Akt, MAPK/ERK, mTOR, and Wnt/β-catenin, which are increasingly implicated in ASD-related abnormalities in synaptic plasticity and circuit organization. Experimental models demonstrate that dysregulation of these signaling systems can impair hippocampal function, alter excitatory-inhibitory balance, and disrupt structural connectivity. Among them, IGF-1 has shown promising translational potential in clinical trials for syndromic ASD, while GLP-1 receptor agonists and Klotho modulation represent emerging therapeutic avenues. The GDNF/GFRA-1 axis further highlights the importance of trophic support in maintaining synaptic integrity and neuronal resilience. By integrating molecular, preclinical, and clinical findings, this review proposes that convergent dysregulation of trophic and metabolic signaling pathways may contribute to ASD heterogeneity. A systems-level understanding of these interconnected mechanisms may facilitate biomarker development and support the advancement of stratified, pathway-targeted therapeutic strategies.

Study at a Glance

Study Snapshot

Study Facts Table

What Researchers Actually Did

Verma and colleagues conducted a narrative integrative review synthesizing molecular, preclinical, and available clinical evidence across four signaling systems: Klotho, GDNF/GFRA-1, IGF-1, and GLP-1. The authors mapped each pathway’s receptor biology, downstream intracellular cascades, brain expression patterns, and developmental dynamics, then positioned each within the context of ASD pathophysiology. They drew on animal models, human genetic and biomarker studies, in vitro experiments, and clinical trial data to build a unified mechanistic framework arguing that convergent dysregulation of trophic and metabolic signaling, rather than single-gene or single-transmitter defects, may explain a portion of ASD biological heterogeneity.

A structured evidence summary table catalogued 11 preclinical and clinical datasets covering interventions ranging from recombinant IGF-1 in Phelan-McDermid syndrome to semaglutide in BTBR mice to exenatide in LPS-exposed rats. The authors explicitly graded the four pathways by translational strength, positioning IGF-1 as clinically supported, GLP-1 as early translational, GDNF/GFRA-1 as preclinical, and Klotho as hypothesis-generating. Throughout, shared downstream nodes, particularly PI3K/Akt/mTOR and MAPK/ERK, were highlighted as potential network hubs linking these otherwise distinct ligand-receptor systems.

Key Findings: Primary Outcomes

• IGF-1 (strongest evidence): Two crossover trials in Phelan-McDermid syndrome (n=9 each) found recombinant IGF-1 well tolerated, with reported improvements in sensory responsiveness and repetitive behaviors; one trial showed gains in social impairment scores and reduced hyperactivity. Neither trial reported statistically significant change across all primary endpoints.
• GLP-1 (preclinical signal): Semaglutide in BTBR mice (60 µg/kg/day × 6 weeks) markedly reduced autism-like behaviors and restored DNA damage/repair pathways and oxidative balance. A pharmacogenetic Mendelian randomization study reported genetically proxied GLP-1R activation associated with lower ASD risk (OR approximately 0.55), though the authors acknowledge this is assumption-dependent indirect inference.
• GDNF/GFRA-1 (observational): Plasma GDNF increases following auditory integration therapy in ASD individuals correlated with decreases in SRS and CARS severity scores. Conditional deletion of GFRA-1 in forebrain neurons in mice impaired dendritic branching, spine density, and pattern-separation tasks. No interventional human data exist.
• Klotho (biomarker signal only): One small study (100 ASD children vs. 100 controls in Iraq) found lower serum soluble Klotho (AUC 0.888 for discriminating ASD) with a negative correlation with malondialdehyde. No causal or interventional human data exist.
• Shared downstream convergence: All four pathways engage PI3K/Akt, MAPK/ERK, mTOR, and/or Wnt/β-catenin. The authors propose that network-level dysregulation at these shared hubs, rather than pathway-specific defects, may generate ASD heterogeneity.

Key Findings: Secondary Outcomes and Subgroup Analyses

• IGF-1 trials in Rett syndrome (MECP2 mutations, n=12 girls; mecasermin 240 µg/kg BID × 17 weeks) reported increased CSF IGF-1 levels, improved apnea measures, and improved anxiety scores, with small sample size limiting inference.
• Trofinetide (an IGF-1 derivative) in a Phase III Rett syndrome trial (n=208) achieved improvements in RSBQ and CGI-I scores but was associated with diarrhea and vomiting.
• 4-hydroxyisoleucine (a natural activator of IGF-1 and GLP-1 signaling) administered orally in a propionic acid rat ASD model (50 and 100 mg/kg) improved behavioral deficits, neuroinflammation, neurotransmitter balance, and white-matter histology.
• Multi-omics analyses in human cohorts (Chinese Han and SFARI SPARK) linked IGF1R genetic burden to ASD risk and identified IGF-1R enrichment in parvalbumin interneurons, consistent with an excitatory-inhibitory imbalance mechanism.
• A single adolescent case report described reductions in compulsive eating and behavioral improvements with liraglutide (titrated to 2.4 mg/day × 36 weeks) in an ASD individual; no generalizability can be inferred.

Results: Adverse Events and Safety Profile

This review does not report primary safety data. The referenced IGF-1 trials document generally favorable tolerability in pediatric populations with neurodevelopmental disorders. Trofinetide was associated with diarrhea and vomiting. GLP-1 receptor agonists carry well-characterized safety profiles from metabolic disease registrations. The authors flag theoretical long-term risks of IGF-1 (excessive cell growth, cancer) and note that optimal dosing, treatment windows, and pediatric safety data for GLP-1 receptor agonists in ASD populations remain unanswered. Klotho and GDNF-targeted interventions have no ASD-specific safety data.

Statistical Approach and Rigor

As a narrative review, this paper does not apply meta-analytic statistics or formal risk-of-bias tools. The authors summarize findings qualitatively and organize evidence by pathway and study type. The evidence table (Table 1) is descriptive rather than quantitatively synthesized. No PRISMA methodology is declared, no systematic search strategy is reported, and no formal GRADE assessment is applied. The review acknowledges heterogeneity across study designs, species, and populations without quantifying it. The Mendelian randomization data for GLP-1R (OR approximately 0.55 for ASD risk) is cited from a single external study without meta-analytic pooling or sensitivity analysis. The Klotho biomarker AUC of 0.888 derives from one small regional cohort of uncertain representativeness.

Clinical Bottom Line: IGF-1 is the one pathway in this review with controlled human trial data in ASD; the remaining three are mechanistically interesting but not yet clinically actionable outside of research settings.

Why This Matters Clinically

ASD research has long centered on synaptic scaffolding proteins, GABA/glutamate balance, and ion channel dysfunction. This review makes a conceptually useful argument: those targets may be downstream of upstream trophic and metabolic signaling failures that are pharmacologically accessible through agents already in clinical use or development. If even one of these pathways, most plausibly IGF-1 or GLP-1 signaling, proves modifiable in well-characterized ASD subgroups, it opens a stratification framework: rather than treating autism generically, clinicians could identify patients with low IGF-1 bioavailability, impaired GDNF signaling, or neuroinflammatory profiles and direct targeted therapy accordingly. That goal is worth pursuing. The distance between that goal and the current evidence, however, is considerable.

CED Clinical Relevance

At CED Clinic, patients often present with questions about metabolic and trophic interventions, including GLP-1 receptor agonists that are increasingly discussed across neurological and psychiatric indications. This review provides a structured molecular rationale for why these pathways are biologically plausible in ASD, while also making explicit what is not yet known. For patients on GLP-1 receptor agonists for metabolic comorbidities, the preclinical and early genetic evidence adds mechanistic context without changing prescribing decisions. For families asking about IGF-1, the review accurately conveys that syndromic ASD trials show signals of benefit but that idiopathic ASD remains unanswered. Klotho and GDNF discussions belong firmly in the context of future research, not current clinical planning.

Fits What We Already Know

The review situates itself within a well-established literature linking PI3K/Akt/mTOR hyperactivation to ASD, particularly tuberous sclerosis complex and PTEN-related syndromes (cited: Sharma and Mehan 2021; Pagani et al. 2021). The role of BDNF/TrkB in synaptic plasticity and its disruption in ASD provides an established precedent for trophic signaling as a disease-relevant target. The authors correctly note that IGF-1’s mechanism, restoring AMPA receptor function and LTP in Shank3-deficient mice (Bozdagi et al. 2013; Shcheglovitov et al. 2013), aligns with the broader synaptic deficit model of ASD. The inclusion of GLP-1 extends a growing literature on metabolic-neurological interface signaling that has been productive in Alzheimer’s and Parkinson’s disease research (Athauda et al. 2017; Gejl et al. 2016), though the extrapolation to neurodevelopmental disorders requires more than mechanistic analogy.

What This Study Teaches Us

The review offers a structured, accessible map of four signaling pathways that share downstream molecular real estate with each other and with established ASD risk mechanisms. Its core contribution is organizational: demonstrating that Klotho, GDNF/GFRA-1, IGF-1, and GLP-1 are not isolated curiosities but members of an interconnected network whose convergence on PI3K/Akt and related cascades makes them candidates for systems-level investigation. It also communicates honestly, if not always prominently, that the evidence gradient is steep: one pathway has human trial data, one has preclinical signals and genetic epidemiology, and two have mechanistic plausibility and little else.

What It Does Not Show

• It does not demonstrate that modulating any of these pathways improves outcomes in idiopathic ASD.
• It does not establish causality between pathway dysregulation and ASD symptomatology in humans.
• The IGF-1 trial data cited are from small crossover studies in a specific genetic syndrome; these results do not generalize to the broader ASD population.
• The Klotho and GDNF biomarker associations reported in humans are from small, single-cohort observational studies with no causal inference.
• The Mendelian randomization finding for GLP-1R and ASD risk is indirect, assumption-dependent, and requires clinical trial validation.
• The review does not address long-term safety of any of these interventions in pediatric neurodevelopmental populations.

Fits the Broader Conversation

This review joins a growing body of work arguing that ASD heterogeneity demands a shift from symptom-targeted to mechanism-based therapeutics. It adds to an emerging discussion, already active in the IGF-1 and mTOR literature, about stratifying ASD by biological pathway rather than behavioral phenotype alone. The inclusion of GLP-1 is timely, given the rapid expansion of GLP-1 receptor agonist indications and the parallel interest in their central nervous system effects. Whether Klotho and GDNF will follow IGF-1 from mechanistic candidate to clinical target depends on whether the field can generate the longitudinal, well-characterized cohort data that this review, to its credit, explicitly identifies as missing.

Teaches Us: Families

Scientists are investigating whether certain signaling proteins in the brain, molecules that act like chemical messengers supporting neuron growth, survival, and connection, may be disrupted in some people with autism. This review looks at four of those proteins: Klotho, GDNF, IGF-1, and GLP-1. Of the four, only IGF-1 has been tested in human clinical trials for autism, and those trials were in a specific genetic type of autism called Phelan-McDermid syndrome. The results suggested IGF-1 was safe and produced some improvements in behavior, but the studies were small. The other three proteins are being studied in animals or cells right now, not yet in people with autism. This research is promising because it suggests autism may involve disruptions in biological pathways that could eventually be treated with targeted medicines, but we are not yet there for most of these pathways.

Teaches Us: Clinicians

This review constructs a molecular framework linking four trophic-metabolic signaling axes to ASD pathophysiology through shared downstream nodes (PI3K/Akt, MAPK/ERK, mTOR, Wnt/β-catenin). For the clinician, the operationally relevant takeaway is the evidence gradient: IGF-1 has phase II/III crossover trial data in SHANK3-related and MECP2-related syndromes; GLP-1 receptor agonists have preclinical signals, one Mendelian randomization study, and a case report; GDNF/GFRA-1 has small observational human correlations; Klotho has one small biomarker study. The review identifies five discrete translational gaps: absence of longitudinal pathway data in characterized ASD cohorts, lack of validated CNS biomarkers for stratification, no powered idiopathic ASD trials for any pathway, unknown pediatric safety profiles for GLP-1 agonists in this context, and no human interventional data for Klotho or GDNF/GFRA-1. Biomarker-guided stratification (IGF-1 serum levels, IGF1R expression, downstream p-

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