Adrenoleukodystrophy
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Adrenoleukodystrophy (ALD) is a degenerative disorder of nerve fibers. It is a type of leukodystrophy. Leukodystrophies are dysmyelinating disorders, in which there is an abnormal myelin formation due to a metabolic disturbance affecting the white matter. They are different from demyelinating disorders such as multiple sclerosis, in which myelin is formed normally, but is lost by immunologic dysfunction or other reasons.
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Symptoms
The clinical presentations largely depend on the age of onset of the disease. The most frequent type is the childhood-onset one, which is characterized by failure to develop, seizures, ataxia, adrenal insufficiency and degeneration of visual and auditory function.
In adolescent-onset form, the spinal cord dysfunction is more prominent and therefore is called adrenomyeloneuropathy. The patients usually present with weakness and numbness of the limbs and urination or defecation problems.
Adult and neonatal forms of the disease are also present, but they are extremely rare. Some patients may present with sole findings of adrenal insufficiency (Addison's disease).
Diagnosis
The diagnosis is established by clinical findings and the detection of serum long chain fatty acid levels. MRI examination reveals white matter abnormalities, and neuroimaging findings of this disease are quite reminiscent of the findings of multiple sclerosis. Genetic testing for the analysis of the defective gene is available in some centers.
Pathophysiology
The most common form of ALD is X-linked (the defective gene is on the X chromosome, location Xq28), and is characterized by excessive accumulation of very long chain fatty acids (VLCFA) - fatty acids chains with 24-30 carbon atoms (particularly hexacosanoate, C26) in length (normally less than 20). This was originally described by Moser et al in 1981.
The gene (ABCD1 or "ATP-binding cassette, subfamily D, member 1") codes for a protein that transfers fatty acids into peroxisomes, the cellular organelles where the fatty acids undergo β-oxidation (Mosser et al 1993). A dysfunctional gene leads to the accumulation of long-chain fatty acids.
The precise mechanisms through which high VLCFA concentrations cause the disease are still (2005) unknown, but accumulation is severe in the organs affected.
Treatment
There is no definite treatment for the disease. Some dietary treatments, e.g., Lorenzo's oil, have been used with limited success. Bone marrow transplantation may be helpful for some mild cases.
Reference
- Moser HW, Moser AB, Frayer KK, Chen W, Schulman JD, O'Neill BP, Kishimoto Y. Adrenoleukodystrophy: increased plasma content of saturated very long chain fatty acids. Neurology 1981;31:1241-9. PMID 7202134.
- Mosser J, Douar AM, Sarde CO, Kioschis P, Feil R, Moser H, Poustka AM, Mandel JL, Aubourg P. Putative X-linked adrenoleukodystrophy gene shares unexpected homology with ABC transporters. Nature 1993;361:726-30. PMID 8441467.
External link
- Template:OMIM
- Adrenoleukodystrophy - NIH/NINDS (http://www.ninds.nih.gov/health_and_medical/disorders/adrenolu_doc.htm)
- The role of peroxisomes in X-linked ALD (http://www.peroxisome.org/Scientist/Biochemistry/XALD.html)