HESX1 is a homeobox transcription factor essential for anterior forebrain, pituitary, and midline structure development 1. During embryogenesis, HESX1 is expressed in prospective forebrain tissue and becomes restricted to Rathke's pouch, the anterior pituitary primordium, until approximately E15.5 in mice 2. The protein functions as a sequence-specific DNA-binding transcription repressor that binds palindromic PIII sequences and forms heterodimers with PROP1 to antagonize PROP1 activation 3. Notably, HESX1 expression persists in adult human pituitaries, suggesting an ongoing role in pituitary cell maintenance and function 2. Loss-of-function HESX1 mutations cause septo-optic dysplasia (SOD), characterized by optic nerve hypoplasia, midline defects (agenesis of septum pellucidum, corpus callosum abnormalities), and pituitary hormone deficiencies 14. Missense mutations within the homeodomain that abolish DNA-binding capacity have been documented in familial SOD cases 1. HESX1 mutations also contribute to combined pituitary hormone deficiency and hypogonadotropic hypogonadism through disrupted hypothalamic-pituitary axis development 5. Recent evidence implicates HESX1 in monogenic absence seizure epilepsies, though the mechanistic link remains unclear 6. The variable penetrance and expressivity of HESX1-related disorders likely reflect contributions from both genetic and environmental factors 7.