Adrenomyeloneuropathy (AMN) is the adult-onset form of adrenoleukodystrophy, an inherited condition caused by a mutation in the ABCD1 gene located on the X chromosome. As an X-linked condition, men are at higher risk of developing AMN, but milder symptoms have also been reported in women.
AMN constitutes about 25-46 percent of all ALD cases reported worldwide. Patients usually show symptoms around ages 20-30.
The ABCD1 gene provides instructions to synthesize the adrenoleukodystrophy protein (ALDP). ALDP is responsible for the transport of certain molecules such as very long-chain fatty acids (VLCFA) to a specialized compartment in the cell called peroxisomes, where they are broken down. The mutation in the gene results in the insufficient production of ALDP, causing the accumulation of VLCFA. This causes the breakdown of the protective sheath covering the nerve fibers in the brain and spinal cord.
In AMN, VLCFA accumulation can affect either only the spinal cord or both the brain and spinal cord.
The disease can also affect the adrenal glands, located on top of the kidneys, preventing them from supplying adequate levels of essential hormones such as cortisol and aldosterone.
The occurrence and severity of AMN symptoms vary from person to person. The most common symptoms include:
- Leg muscle spasticity and weakness that can worsen over time
- Difficulty walking and changes in walking pattern
- Impaired muscle coordination (ataxia)
- Speech difficulty
- Adrenal insufficiency
- Sexual dysfunction or impotence
- Poor bladder control
- Weight loss
- Mild numbness and tingling in the hands and feet (peripheral neuropathy)
If the brain is affected, it may lead to additional symptoms such as behavioral changes, seizures, loss of eyesight, and impaired hearing.
Based on the symptoms reported, a blood test is often the first diagnostic test that detects elevated levels of VLCFA in patients. The blood test can be followed by genetic testing to identify the mutation and confirm the diagnosis.
Magnetic resonance imaging (MRI) of the brain and spinal cord is used to determine whether there is cerebral involvement or if only the spinal cord has been affected. MRI also helps monitor the progression of AMN. Brain MRI can show signs of the condition even before the development of any neurological symptoms.
Based on the symptoms observed in the patient, multiple treatment options are available. For most AMN patients, physiotherapy can help build muscle strength to manage spasticity and improve walking.
Corticosteroid replacement therapy is used to treat adrenal insufficiency. Cortisol can be replaced by oral glucocorticoids such as Cortef (oral hydrocortisone developed by Pfizer. Aldosterone insufficiency is commonly treated using oral mineralocorticoids such as Florinef (fludrocortisone).
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