HESX1 mutations contribute to development of septo-optic dysplasia (SOD), a condition that can be diagnosed with the presence of two or more features of the classical triad: (i) optic nerve hypoplasia, (ii) pituitary hormone abnormalities, and (iii) midline brain defects, including agenesis of the septum pellucidum and/or corpus callosum [21]. Here, HESX1 is linked to Septo-optic dysplasia.