I guess this fits the category of rare deseases since not many are born with septo optic dysplasia.. it is estimated about 1 in 100,000 are born with septo optic dysplasia. The condition is actually a triad of conditions grouped as a syndrome. First is a midline brain defect know as agenesis of the septum pellucidum( sometimes the corpus callosum is also absent partailly absent or malformed). next is underdevelopment ( hypoplasia) of the optic nerve(s) along with nystagmus,poor vision in one or both eyes.. most paitients are blind in one or both eyes. The optic disk in the affected eye/s is also very small with a "double ring" sign a doctor can see with the othalmascope. the last of this triad is endocrine disorders such as pituitary ( lack of growth hormone) thyroid, sex hormones, thalamic dysfunctions with body temp dysregulation). At this time it is not known if septo optic dysplasia is hereditary or what causes it. Septo optic dysplasia used to be called De morsier's syndrome.