Causes of diabetes insipidus

Diabetes insipidus is caused by problems with a chemical called vasopressin (AVP), which is also known asantidiuretic hormone (ADH) .

AVP is produced by the hypothalamus and stored in the pituitary gland until needed. The hypothalamus is an area of the brain that controls mood and appetite. The pituitary gland is located below your brain, behind the bridge of your nose.

AVP regulates the level of water in your body by controlling the amount of urine your kidneys produce. When the level of water in your body decreases, your pituitary gland releases AVP to conserve water and stop the production of urine.

In diabetes insipidus, AVP fails to properly regulate your body's level of water, and allows too much urine to be produced and passed from your body.

There are two main types of diabetes insipidus:

• cranial diabetes insipidus wherethe body doesn't produce enough AVP, so excessive amounts of water are lost in large amounts of urine
• nephrogenic diabetes insipidus where AVP is produced at the right levels but, for a variety of reasons, the kidneys don't respond to itin the normal way.

Possible underlying causes for both types of diabetes insipidus are described below.

Cranial diabetes insipidus

The three most common causes of cranial diabetes insipidus are:

• a Brain tumour, malignant (cancerous) that damages the hypothalamus or pituitary gland
• a severe head injury that damages the hypothalamus or pituitary gland
• complications that occur during brain or pituitary surgery

No cause can be found for about a third of all cases of cranial diabetes insipidus. These cases, known as idiopathic, appear to be related to the immune system attacking the normal, healthy cells producing AVP. It's unclear what causes the immune system to do this.

Less common causes of cranial diabetic insipidus include:

• cancers that spread from another part of the body to the brain
• Wolfram syndrome, which is a rare genetic disorder that also causes vision loss
• brain damage caused by a sudden loss of oxygen, which can occur during a stroke or drowning
• infections, such as meningitis and encephalitis , that can damage the brain

Nephrogenic diabetes insipidus

Your kidneys contain nephrons, which are tiny intricate structures that filter waste products from the blood and help produce urine. They also control how much water is reabsorbed into your body and how much is passedin theurine.

In a healthy person, AVP acts as asignal to the nephrons to reabsorb water into the body. In nephrogenic diabetes insipidus, the nephrons in the kidney aren't able to respond to this signal, leading to excessive water loss in large amounts of urine. Your thirst increases to try to balance this loss from the body.

Nephrogenic diabetes insipidus can be congenital (present at birth) or acquired (where it develops later in life as a result of an external factor). These are described in more detail below.

Congenital nephrogenic diabetes insipidus

Two genetic mutations (abnormal changes in genes that leads to them not working properly) have been identified that cause congenital nephrogenic diabetes insipidus.

The first, known as the AVPR2 gene mutation, is responsible for 90% of all cases of congenital diabetes insipidus. However, it's still rare, occurring in an estimated1 in 250,000 births.

The AVPR2 gene mutation can only be passed down by mothers (who may appear to not be affected) to their sons (who are affected).

The remaining 10% of cases of congenital nephrogenic diabetes insipidus are caused by the AQP2 gene mutation, which can affect both males and females.

It's a medication that's often used to treat bipolar disorder . Long-term lithium use can damage the cells of the kidneys so they no longer respond to AVP.

Just over half of all people on long-term lithium therapy develop some degree of nephrogenic diabetes insipidus. Stopping lithium treatment often restores normal kidney function, although in many cases the damage to the kidneys is permanent.

Due to these risks, it's recommended that you have kidney function tests every three months if you're taking lithium.

It sends messages to the body controlling movement, speech and senses.

Genetic

Genetic is a term that refers to genes, the characteristics inherited from a family member.

Kidney

Kidneys are a pair of bean-shaped organs located at the back of the abdomen, which remove waste and extra fluid from the blood and pass them out of the body as urine.

Pituitary gland

The pituitary gland is a pea-sized gland in the centre of the head, which hangs below the brain and produces hormones.