FGD1 (FYVE, RhoGEF and PH domain containing 1) is a guanine nucleotide exchange factor that specifically activates CDC42, a Rho-family GTPase, by catalyzing the exchange of bound GDP for GTP 1. This activation regulates actin cytoskeleton organization, filopodium assembly, and cell shape through RhoGEF-mediated signal transduction 2. FGD1 contains functionally critical domains including RhoGEF, pleckstrin homology (PH), and FYVE domains that form a canonical signaling architecture conserved across the FGD family 1. Mutations in FGD1 cause Aarskog-Scott syndrome (AAS), an X-linked developmental disorder characterized by short stature, facial anomalies, skeletal deformities, and genitourinary malformations 3. A large patient cohort of 111 males with FGD1 variants revealed that short stature has prenatal onset and shows catch-up growth during the first decade, with most patients achieving low-normal adult stature 4. Intellectual disability is rare, though specific learning difficulties and attention-deficit hyperactivity disorder occur at elevated prevalence 4. Growth hormone treatment improved height outcomes in FGD1-related AAS patients with growth hormone deficiency 3. Beyond AAS, FGD1 was identified as one of 15 common differentially expressed genes shared between sarcopenia and type 2 diabetes mellitus, suggesting potential roles in muscle metabolism 5.