RAB3IL1 (RAB3A interacting protein like 1) is a guanine nucleotide exchange factor (GEF) that activates small GTPases regulating intracellular trafficking and exocytosis. As a GEF, RAB3IL1 catalyzes the exchange of GDP to GTP on multiple Rab proteins, converting them to their active forms 1. RAB3IL1 functions as a dual Rab-binding protein, serving as a GEF for Rab3A, Rab8A, and Rab8B, while also binding Rab11a and Rab11b through a distinct carboxy-terminal domain 1. In human sperm exocytosis, GRAB (the protein product encoded by RAB3IL1) is recruited by the Rab27A-Rabphilin3a complex and exhibits GEF activity toward Rab3A during the acrosome reaction 2. Regarding disease relevance, RAB3IL1 has been implicated in multiple pathologies. Genetic variants in RAB3IL1 are associated with autism spectrum disorder and language impairments, with structural equation modeling identifying rs2524290 as a causal SNP linking ASD with language deficits 3. RAB3IL1 was identified as a novel ferroptosis regulator in male infertility; Rab3il1 knockdown induces ferroptosis via SLC7A11 translocation, disrupting the blood-testis barrier in idiopathic non-obstructive azoospermia 4. RAB3IL1 additionally serves as a hub gene in unstable atherosclerotic plaque progression 5 and functions as a prognostic indicator for hepatocellular carcinoma outcome 6. These findings position RAB3IL1 as a multifunctional protein relevant to neurodevelopmental, reproductive, cardiovascular, and oncological diseases.