HESX1 Gene

Septo-optic dysplasia is a disorder of early brain development. Although its signs and symptoms vary, this condition is traditionally defined by three characteristic features: underdevelopment (hypoplasia) of the optic nerves, abnormal formation of structures along the midline of the brain, and pituitary hypoplasia.

The first major feature, optic nerve hypoplasia, is the underdevelopment of the optic nerves, which carry visual information from the eyes to the brain. In affected individuals, the optic nerves are abnormally small and make fewer connections than usual between the eyes and the brain. As a result, people with optic nerve hypoplasia have impaired vision in one or both eyes. Optic nerve hypoplasia can also be associated with unusual side-to-side eye movements (nystagmus) and other eye abnormalities.

The second characteristic feature of septo-optic dysplasia is the abnormal development of structures separating the right and left halves of the brain. These structures include the corpus callosum, which is a band of tissue that connects the two halves of the brain, and the septum pellucidum, which separates the fluid-filled spaces called ventricles in the brain. In the early stages of brain development, these structures may form abnormally or fail to develop at all. Depending on which structures are affected, abnormal brain development can lead to intellectual disability and other neurological problems.

The third major feature of this disorder is pituitary hypoplasia. The pituitary is a gland at the base of the brain that produces several hormones. These hormones help control growth, reproduction, and other critical body functions. Underdevelopment of the pituitary can lead to a shortage (deficiency) of many essential hormones. Most commonly, pituitary hypoplasia causes growth hormone deficiency, which results in slow growth and unusually short stature. Severe cases cause panhypopituitarism, a condition in which the pituitary produces no hormones. Panhypopituitarism is associated with slow growth, low blood sugar (hypoglycemia), genital abnormalities, and problems with sexual development.

The signs and symptoms of septo-optic dysplasia can vary significantly. Some researchers suggest that septo-optic dysplasia should actually be considered a group of related conditions rather than a single disorder. About one-third of people diagnosed with septo-optic dysplasia have all three major features; most affected individuals have two of the major features. In rare cases, septo-optic dysplasia is associated with additional signs and symptoms, including recurrent seizures (epilepsy), delayed development, and abnormal movements.