X-linked adrenoleukodystrophy is a disorder that occurs most often in males. It mainly affects the nervous system and the adrenal glands, which are small glands located on top of each kidney. People with this disorder often have progressive destruction of the fatty covering (myelin) that insulates nerves in the brain and spinal cord. They may also have a shortage of certain hormones caused by damage to the outer layer of the adrenal glands (adrenal cortex). This hormonal deficiency is known as adrenocortical insufficiency.