What are the genetic changes related to neurohypophyseal diabetes insipidus ?
The familial form of neurohypophyseal diabetes insipidus is caused by mutations in the AVP gene. This gene provides instructions for making a hormone called vasopressin or antidiuretic hormone (ADH). This hormone, which is produced and stored in the brain, helps control the body's water balance.  The kidneys filter the blood to remove waste and excess fluid, which are stored in the bladder as urine. ADH controls the balance between fluid intake and urine excretion. Normally, when a person's fluid intake is low or when a lot of fluid is lost (for example, through sweating), the brain releases more ADH into the bloodstream. High levels of this hormone direct the kidneys to reabsorb more water and to make less urine. When fluid intake is adequate, the brain releases less ADH. Lower levels of this hormone cause the kidneys to reabsorb less water and to make more urine.  Mutations in the AVP gene result in progressive damage to the brain cells where ADH is produced. These cells ultimately die, causing a shortage of ADH. Without this hormone, the kidneys do not reabsorb water as they should, and the body makes excessive amounts of urine. These problems with water balance are characteristic of neurohypophyseal diabetes insipidus.  The acquired form of neurohypophyseal diabetes insipidus results when the areas of the brain that produce or store ADH are damaged by head injuries, brain tumors, brain surgery, certain diseases and infections, or bleeding in the brain. A loss of ADH disrupts the body's water balance, leading to excessive urine production and the other features of the disorder.  In 30 to 50 percent of all cases of neurohypophyseal diabetes insipidus, the cause of the disorder is unknown. Studies suggest that some of these cases may have an autoimmune basis. Autoimmune disorders occur when the immune system malfunctions and attacks the body's own tissues and organs. For unknown reasons, in some people with neurohypophyseal diabetes insipidus the immune system appears to damage the brain cells that normally produce ADH.