RASGEF1B is a guanine nucleotide exchange factor (GEF) that exhibits highly specific activity toward RAP2A, a member of the Ras-like G-protein family 1. Unlike other GEFs, RASGEF1B demonstrates remarkable specificity, functioning exclusively on Rap2 while showing no activity toward Rap1 or other Ras subfamily members 1. The protein localizes to early endosomes and heavy membrane fractions, where it can trigger Ras activity through the canonical Ras-Raf-MEK-ERK pathway 2. RASGEF1B expression is induced in macrophages by Toll-like receptor (TLR) agonists, particularly TLR3 and TLR4, through MyD88-independent pathways, and during infections with protozoan parasites 2. The gene shows tissue-specific developmental expression patterns in zebrafish, including somites, brain regions, and retinal tissues 3. Clinically, RASGEF1B has emerged as a disease-relevant gene, with haploinsufficiency contributing to 4q21 microdeletion syndrome characterized by growth restriction, mental retardation, and speech delays 4. The gene has also been identified as a potential biomarker in genome-wide association studies of parathyroid hormone levels and white-coat hypertension effect, suggesting broader physiological roles 56.