Why do GLP-1 drugs work better for some people than others? This large genetic study suggests inherited differences in drug-target genes may shape both weight-loss success and the risk of nausea and vomiting.
Study: Genetic predictors of GLP1 receptor agonist weight loss and side effects. Image Credit: Kotcha K / Shutterstock
In a recent study published in the journal Nature, researchers conducted a large-scale genome-wide association study (GWAS; overall survey cohort n = 27,885 participants) to investigate the genetic basis of variability in GLP-1 receptor agonist response. Study analyses identified a missense variant in GLP1R associated with enhanced weight-loss efficacy.
Each copy of the effect allele was shown to predict an additional 0.76 kg of weight loss in the sample cohort. Furthermore, genetic variation in GLP1R and GIPR was linked to medication-induced nausea and vomiting, with the GIPR association seen only in patients utilizing tirzepatide.
Together, these findings highlight that common genetic variation in drug-target genes directly contributes to patient response and the risk of adverse events.
Obesity Treatment Background and Incretin Variability
Obesity has been established as one of the most prevalent and physiologically harmful public health conditions of modern society. The condition is associated with a spectrum of metabolic and cardiovascular diseases and is highlighted as a primary risk factor for type 2 diabetes (T2D) and certain cancers.
Alarmingly, global obesity prevalence is increasing at unprecedented rates, with government reports indicating that the condition impacts ~40% of all adults in the United States (US). While traditional pharmacological and lifestyle-based interventions demonstrated limited success in helping obesity patients achieve sustained weight loss, the relatively recent development of incretin mimetics has revolutionized current therapeutic strategies.
These novel pharmacological interventions primarily comprise glucagon-like peptide-1 (GLP-1) receptor agonists and dual GLP-1/GIP receptor agonists, which function by mimicking the effects of gastrointestinal hormones that stimulate endogenous insulin secretion, delay gastric emptying, and suppress appetite.
However, clinical trials have reported significant inter-patient efficacy variability: while the average weight reduction was 10.2% across the intervention cohort, nearly 32.2% of patients achieved less than a 5% reduction (or experienced weight gain), while 4.9% lost over 25%.
GLP-1 GWAS Study Design
The present study aimed to identify genetic contributors to this significant inter-person variability. The study comprised a large-scale genome-wide association study (GWAS) using self-reported data from 27,885 23andMe research participants (82.4% female; median age = 52 years) who had previously utilized GLP-1 medications.
The cohort’s summary statistics revealed a median pre-treatment Body Mass Index (BMI) of 35.1 kg/m², with participants’ ancestry groups including European (78.3%), Latino (12.9%), and African American (4.2%) populations.
The study validated the self-report data by analyzing a subset of 909 participants who shared their Electronic Health Record (EHR) data via Apple HealthKit. Although this EHR data showed smaller median BMI changes than self-reports (-5.79% vs -11.8%), the two datasets were found to be reasonably statistically correlated (Pearson r = 0.57).
The study’s primary outcome of interest (“efficacy phenotype”) was defined as the participant-specific percentage change in BMI from baseline (Δ BMI%). Statistical analyses comprised linear model fitting, with models notably incorporating non-genetic factors: age, sex, pre-treatment BMI, drug type, dosage, and time on drug.
GLP1R and GIPR Genetic Findings
Linear model results revealed that non-genetic factors collectively explained 21.4% of the variance in BMI loss. Participants’ T2D status was further confirmed as a significant negative predictor of weight loss (P = 2.0 × 10-73), with patients with a T2D diagnosis losing an average of 2.87 percentage points less than those without.
GWAS results identified a robust genome-wide significant association on chromosome 6 at the GLP1R locus. This missense variant (p.Pro7Leu) was found to confer an additional 0.641% reduction in BMI per effect allele.
The study observed that the effect allele for this variant was most common in individuals of European ancestry (40%) and least common in those of African ancestry (7%). Meta-analysis across ancestral groups confirmed the strength of the observed association (P = 1.1 × 10-12).
Side effect analysis revealed distinct genetic drivers for nausea and vomiting. Variants near GLP1R were associated with these side effects, and co-localization analysis suggested that the genetic signals for weight loss and gastrointestinal side effects share a causal variant, implying that increased efficacy is biologically linked to greater susceptibility to nausea and vomiting.
Finally, the study identified a second major signal at the GIPR locus that specifically influences vomiting in tirzepatide users. Individuals carrying the C allele (risk allele) demonstrated a 1.83-fold increased odds of vomiting compared to those with the protective G allele.
Precision Medicine Implications for GLP-1 Therapy
The present study findings strongly suggest that patient-specific variation in drug-target genes directly modulates therapeutic response. While the genetic effect sizes are currently modest, they may enable stratifying patients by efficacy and risk from the outset of treatment.
This study, therefore, lays the foundation for precision medicine in obesity, potentially allowing clinicians to better optimize drug selection and dosage escalation based on each patient’s unique genetic landscape as predictive models improve, undergo further validation, and are shown to add clinically meaningful value beyond non-genetic factors.
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