rs1000940 — RABEP1 RABEP1 Metabolic-Immune Regulatory Variant

RABEP1 — When Cellular Trafficking Shapes Drug-Induced Glucose Risk

The cell's ability to retrieve, sort, and recycle surface receptors is controlled by an elaborate endosomal highway. RABEP1 (Rab GTPase-binding effector protein 1, also known as Rabaptin-5) is a key traffic controller along this highway, coordinating the fusion of clathrin-coated vesicles with early endosomes and regulating how receptors — including the insulin receptor — are recycled back to the cell surface or degraded. When psychiatric medications stress this system, small genetic differences in RABEP1 translate into measurable differences in fasting glucose.

The rs1000940 variant sits deep within an intron of RABEP1 on chromosome 17p13.3. Although intronic, it tags a haplotype associated with meaningful differences in how fasting glucose responds to weight-gain-inducing psychotropic drugs — a context in which the normal metabolic buffering of endosomal trafficking is challenged.

The Mechanism

RABEP1 operates at the interface between clathrin-coated vesicles and early endosomes¹¹ clathrin-coated vesicles and early endosomes
Clathrin-coated vesicles form at the plasma membrane during receptor endocytosis; early endosomes are the first intracellular sorting compartment they encounter. It functions as a symmetrical scaffold, distributing across both compartments and providing the tethering complex (together with Rab5 and EEA1) that drives heterotypic vesicle fusion. This positions RABEP1 as a gatekeeper for how efficiently endocytosed receptors — including the insulin receptor and glucose transporter-linked machinery — are recycled versus degraded.

A 2022 study identified an additional role: RABEP1 recruits the autophagy initiator RB1CC1/FIP200 and ATG16L1²² RB1CC1/FIP200 and ATG16L1
These proteins nucleate the autophagosome membrane; RABEP1 brings them to damaged early endosomes to initiate selective organelle clearance to endosomes damaged by environmental stress or intracellular pathogens, coupling endosomal homeostasis to the autophagy pathway. In the context of antipsychotic treatment — which disrupts hypothalamic energy sensing, hepatic glucose output, and pancreatic insulin secretion — altered RABEP1 activity could shift the balance of receptor recycling in metabolically active tissues.

The Evidence

The primary evidence comes from a pharmacogenomics study by Delacrétaz et al. (2017)³³ Delacrétaz et al. (2017)
Gene, 628:8-15 — first study to identify RABEP1 rs1000940 as a glucose modifier in psychotropic-treated patients examining 357 Caucasian psychiatric patients receiving weight-gain-inducing psychotropic drugs, with replication in 140 additional patients. G-allele carriers of rs1000940 A>G showed significantly lower fasting glucose across both samples (−0.16 mmol/l, p<0.001 in discovery; −0.77 mmol/l, p=0.03 in replication). The A/A genotype was thus associated with higher fasting glucose in the treated setting.

The study used Classification and Regression Trees (CART) methodology alongside linear mixed models, identifying rs1000940 as one of two variants (the other being SH2B1 rs3888190, a leptin signalling gene) that together predicted differential metabolic trajectories under psychotropic treatment. The authors note this was "the first human study" to observe this association, making the evidence level emerging but biologically plausible.

Second-generation antipsychotics produce glucose dysregulation via multiple mechanisms: M3 muscarinic receptor antagonism in the pancreas suppresses insulin secretion; central hypothalamic effects impair glucose sensing; direct hepatic effects increase glucose output; and leptin insensitivity disrupts appetite-glucose coupling. RABEP1 variation may modulate the endosomal component of insulin receptor trafficking across these metabolically active tissues.

Population frequencies show notable ancestry variation: the G (lower-glucose) allele is most common in East Asian populations (~62%) and least common in African populations (~24%), with Europeans and Latinos at ~30-32%.

Practical Actions

Psychiatric patients carrying the AA genotype face elevated fasting glucose risk during psychotropic treatment. Baseline and periodic fasting glucose monitoring is warranted before and during treatment with weight-gain-inducing agents. Metformin has demonstrated efficacy in reducing antipsychotic-induced glucose dysregulation and can be considered as a co-prescription in at-risk patients.

Interactions

The SH2B1 rs3888190 variant, identified in the same Delacrétaz et al. study, affects LDL cholesterol under psychotropic treatment. Carriers of both rs1000940 AA (higher glucose risk) and rs3888190 A-allele (higher LDL risk) may face a compounded cardiometabolic burden during psychotropic treatment, warranting heightened metabolic surveillance.