rs1042044 — GLP1R Leu260Phe

GLP-1 Receptor Leu260Phe — A Common Variant With Wide-Ranging Effects

The GLP-1 receptor (GLP1R) mediates the actions of glucagon-like peptide 1¹¹ glucagon-like peptide 1
GLP-1 is an incretin hormone that stimulates insulin secretion, slows gastric emptying, and suppresses appetite, one of the body's most important metabolic hormones. GLP1R is also the target of blockbuster medications like semaglutide (Ozempic, Wegovy) and tirzepatide (Mounjaro). The rs1042044 variant causes a leucine-to-phenylalanine substitution at position 260, located in intracellular loop 2²² intracellular loop 2
the region of the receptor inside the cell that couples to G proteins and downstream signaling molecules of the receptor protein.

The Mechanism

The Leu260Phe substitution sits in the intracellular signaling domain of the GLP-1 receptor, where it can influence how the receptor communicates with downstream G proteins and beta-arrestins after ligand binding. Functional studies from the CATIE trial showed that cells expressing the Leu260 variant (A allele) display significantly reduced cell surface protein expression³³ significantly reduced cell surface protein expression
approximately 30-40% of wild-type levels but paradoxically show numerically greater calcium mobilization per receptor, suggesting each individual receptor may signal more efficiently. This creates a complex pharmacological profile: fewer receptors on the surface, but each one potentially more active.

The variant's location in intracellular loop 2 affects the receptor's interaction with intracellular signaling cascades including the cAMP pathway⁴⁴ cAMP pathway
cyclic AMP is the primary second messenger activated by GLP-1 receptor signaling and calcium-dependent insulin secretion. A Russian study in 174 subjects found that CA heterozygotes had significantly lower postprandial C-peptide and insulin responses compared to CC homozygotes, confirming reduced insulin secretory capacity in A allele carriers.

The Evidence

The strongest pharmacogenomic evidence comes from the CATIE antipsychotic trial⁵⁵ CATIE antipsychotic trial
Brandl EJ et al. GLP1R haplotypes correlate with altered response to multiple antipsychotics. Schizophr Res, 2015, which studied 597 Caucasian subjects across five antipsychotic medications. The GLP1R haplotype uniquely tagged by the rs1042044 Leu260 allele was associated with significantly better response to olanzapine (Cohen's d=-0.62, p=0.002) and risperidone (d=-0.62, p=0.006), but worse response to perphenazine (p=0.03) and ziprasidone (d=0.81, p=0.003). A recessive genetic model provided the best fit, meaning two copies of the A allele are needed for the full effect.

Beyond antipsychotic response, the variant has been linked to HPA axis function⁶⁶ HPA axis function
the hypothalamic-pituitary-adrenal axis controls cortisol secretion and stress responses. In a study of 77 preschool-aged children, those homozygous for the Phe260 allele (CC genotype) had significantly higher morning salivary cortisol levels (p=0.008), suggesting the GLP-1 receptor plays a role in stress hormone regulation from early life ⁷⁷ Beinfeld MC et al. J Psychiatr Res, 2010.

An Egyptian case-control study of 160 subjects found the AA genotype was associated with a 4.5-fold increased risk of papillary thyroid cancer ⁸⁸ Ibrahim AA et al. Gene, 2022, with higher GLP-1R mRNA and protein expression in tumour tissue of AA carriers. In Chinese postmenopausal women, the A allele carried a 2.76-fold increased risk of osteoporosis, with a significant gene-gene interaction with the GLP1R variant rs2268641 ⁹⁹ Xu et al. PLOS ONE, 2024.

Practical Implications

For most people, this variant's primary clinical relevance lies in antipsychotic pharmacogenomics. If you are prescribed olanzapine or risperidone, the AA genotype predicts better treatment response. Conversely, perphenazine and ziprasidone may be less effective. The variant does not predict antipsychotic-induced weight gain.

The associations with bone density and thyroid cancer are from smaller studies that require replication in larger cohorts before clinical action is warranted. However, the consistent direction of effects across multiple tissues (pancreas, brain, bone, thyroid) supports genuine functional significance of this receptor variant.

Interactions

The rs1042044 variant sits on the same gene as rs6923761 (Gly168Ser)¹⁰¹⁰ rs6923761 (Gly168Ser)
the most studied GLP1R pharmacogenomic variant, affecting GLP-1 agonist drug response, and the two variants tag different GLP1R haplotypes. In the CATIE trial, rs6923761 tagged haplotype 2 (associated with altered antipsychotic response via a dominant model), while rs1042044 tagged haplotype 1 (recessive model). These haplotypes have independent and sometimes opposing effects on drug response. A significant interaction between rs1042044 and rs2268641 has been documented for osteoporosis risk in Chinese postmenopausal women, where neither variant alone fully explains the effect.