X-linked adrenoleukodystrophy

X-linked adrenoleukodystrophy is a genetic disorder that mainly affects the nervous system and the adrenal glands, which are located on top of each kidney. In this disorder, the fatty covering (myelin) that insulates nerves in the brain and spinal cord tends to deteriorate (a condition called demyelination). The loss of myelin reduces the ability of the nerves to relay information to the brain. In addition, damage to the outer layer of the adrenal glands (adrenal cortex) causes a shortage of certain hormones (adrenocortical insufficiency). Adrenocortical insufficiency may cause weakness, weight loss, skin changes, vomiting, and coma.

There are four distinct types of X-linked adrenoleukodystrophy: a childhood cerebral form, an adrenomyeloneuropathy type, an adrenal insufficiency only form, and a type called asymptomatic.

The childhood cerebral form of X-linked adrenoleukodystrophy typically occurs in boys. Girls are rarely affected with this type. If not treated, affected boys experience learning and behavioral problems that usually begin between the ages of 4 and 10. Over time the symptoms can worsen, and children may have difficulty reading, writing, understanding speech, and comprehending written material. Additional signs and symptoms of the cerebral form include aggressive behavior, vision problems, difficulty swallowing, poor coordination, and impaired adrenal gland function. The rate at which this disorder progresses is variable but can be extremely rapid, often leading to total disability within a few years. The life expectancy of individuals with this type depends on whether early diagnosis and treatment are available. Without treatment, individuals with the cerebral form of X-linked adrenoleukodystrophy usually survive only a few years after symptoms begin.

Signs and symptoms of the adrenomyeloneuropathy type appear between early adulthood and middle age. Affected individuals develop progressive stiffness and weakness in their legs (paraparesis), experience urinary and genital tract disorders, and often show changes in behavior and intellectual function. Most people with the adrenomyeloneuropathy type also have adrenocortical insufficiency. Some severely affected individuals develop cerebral X-linked adrenoleukodystrophy. 

People with X-linked adrenoleukodystrophy whose only symptom is adrenocortical insufficiency are said to have the adrenal insufficiency only form. In these individuals, adrenocortical insufficiency can begin anytime between the first year of life and adulthood. However, most affected individuals develop the additional features of cerebral X-linked adrenoleukodystrophy in childhood or the adrenomyeloneuropathy type by the time they reach middle age. The life expectancy of individuals with the adrenal insufficiency form depends on the severity of the signs and symptoms, but typically this is the mildest of the three types.

Children with the asymptomatic form do not appear to have any symptoms of X-linked adrenoleukodystrophy, but medical testing may show brain or biochemical abnormalities. Some individuals with the asymptomatic form may develop features of other types of X-linked adrenoleukodystrophy later in life.

Rarely, individuals with X-linked adrenoleukodystrophy develop multiple features of the disorder in adolescence or early adulthood. In addition to adrenocortical insufficiency, these individuals usually have psychiatric disorders and a loss of intellectual function (dementia). It is unclear whether these individuals have a distinct form of the condition or a variation of one of the previously described types.

For reasons that are unclear, different forms of X-linked adrenoleukodystrophy can be seen in affected individuals within the same family.