ARHGEF40 (also known as SOLO) functions as a guanine nucleotide exchange factor (GEF) that specifically activates RhoA and RhoC small GTPases 1. The protein plays a crucial role in cytoskeletal organization by promoting actin stress fiber formation and force-induced stress fiber reinforcement through RhoA/ROCK signaling activation 1. ARHGEF40 directly binds to keratin-8/keratin-18 (K8/K18) intermediate filaments through multiple sites, and this interaction is essential for tensile force-induced RhoA activation and consequent actin cytoskeletal reinforcement 1. The protein's DH-PH domain is responsible for its interaction with RhoA, and deletion of this domain abolishes binding and blocks Wnt signaling activation 2. In disease contexts, ARHGEF40 has emerging clinical significance. It is overexpressed in non-small cell lung cancer, where it promotes proliferation and invasion via the AKT-Wnt axis 2. The gene has been identified as a novel susceptibility gene for hereditary melanoma 3 and is associated with lung function in Korean populations 4. Additionally, de novo missense variants at position p.Arg225 have been identified in individuals with multiple congenital anomalies and developmental delay, suggesting an autosomal dominant disease relationship 5.