Adrenomyeloneuropathy

Adrenomyeloneuropathy (AMN) is caused by changes (mutations) in the ABCD1 gene. This gene gives the body instructions to make the adrenoleukodystrophy protein (ALDP) which helps transport certain types of fats (called very long-chain fatty acids) into the peroxisomes. Peroxisomes are structures in cells that contain enzymes used to help break down fats and other substances. Mutations in the ABCD1 gene cause low levels of functional ALDP, which then causes high levels of very long-chain fatty acids to build up in the body. High levels of these fats in the nervous system, adrenal glands, and testes disrupt their normal function, resulting in the features of AMN.

A diagnosis of adrenomyeloneuropathy (AMN) is typically suspected based on the presence of characteristic signs and symptoms. A blood test that measures the levels of a specific type of fat (very long-chain fatty acids) and/or genetic testing for a mutation in the ABCD1 gene can be used to confirm the diagnosis. Once a diagnosis is made, an MRI of the brain may be recommended to determine if the person has AMN with cerebral involvement (brain and spinal cord affected) or AMN without cerebral involvement (only spinal cord affected).

Adrenomyeloneuropathy (AMN) is inherited in an X-linked manner. A condition is considered X-linked if the responsible gene is located on the X chromosome, one of the two sex chromosomes. The Y chromosome is the other sex chromosome. Women have two X chromosomes and men have an X and a Y chromosome.

Because men have one copy of the X chromosome, a mutated copy of the responsible gene in each cell is enough to cause signs or symptoms of the condition. A man with an X-linked condition will pass the mutation to all of his daughters and none of his sons.

Because women have two X chromosomes, the effect of the mutation may be masked by the other, normal copy of the gene, on the other X chromosome. Women with one mutation are often referred to as "carriers" of an X-linked condition. In most cases, carrier women have no symptoms or are mildly affected. However, some may be just as severely affected as males with the condition. Women who carry an X-linked condition have a 50% chance of passing the mutation on with each pregnancy.

In AMN approximately 20% of women who carry one ABCD1 mutation will develop progressive stiffness and weakness in their legs, often in middle age or later. These women typically have normal adrenal function.

The long-term outlook (prognosis) for people with adrenomyeloneuropathy (AMN) varies depending on the subtype. In general, AMN with cerebral involvement (both brain and spinal cord affected) has a worse prognosis than AMN without cerebral involvement (only spinal cord affected). Many people without cerebral involvement are able to maintain successful personal and professional lives with physical therapy, management of bladder control issues, and counseling.

Approximately 40-45% of people affected by AMN show some degree of brain involvement on MRI. In some of these cases (around 10-20%), the brain involvement becomes severely progressive (worsening over time) and may lead to cognitive decline, behavioral abnormalities, physical disability, or even death.

Treatment of adrenomyeloneuropathy (AMN) varies based on the signs and symptoms in each person. For example, steroid replacement therapy may be prescribed in people with adrenal insufficiency. Physical therapy may also be recommended to help build and maintain muscle strength.