Childhood cerebral form - appears in mid-childhood (at ages 4 - 8)
Adrenomyeloneuropathy (AMN) - occurs in men ages 20 and up
Addison's Disease - adrenal gland does not produce enough steroid hormones, such as cortisone and testosterone
The disease is not limited to specific race.
Take A Closer Look
ALD affects peroxisomal fatty acid beta oxidation, which results in the formation of long fatty acid chains in certain body tissues. Peroxisomes are organelles found in eukaryotic cells, which are the cells that make up humans. Peroxisomes are responsible for breaking down fatty acid molecules into smaller forms to release energy. When fatty acids are not broken down properly, they begin to build up in areas such as the brain, nervous system, and adrenal glands.
Image of a eukaryotic cell depicting the processes involving VLCFAs (very-long chain fatty acids). VLCFAs build up in patients with ALD because the peroxisome is unable to break them down. All cells of the body, except red blood cells, have peroxisomes. The degredation (breaking down) of VLCFAs is ineffective because the ALDP (ALD protein) is missing or defective. ALDP is crucial for the transport of the VLCFA from the cell into the peroxisome.
The Genetics
Chromosomes
The affected gene is found on the recessive X-chromosome. The disease most commonly affects males in a severe form, since men only have one X-chromosome. In order for a female to have the disease, the gene must affect both X-chromosomes. Women may be a carrier with one affected X-chromosome; they carry the disease, but have a less severe form or are not affected by it at all.
About 1 out of every 3 boys born with ALD will have the most severe form called cerebral X-linked ALD. It affects about 1 in 20,000 individuals worldwide.
The ABCD1 gene is responsible for transporting fatty acids chains into peroxisomes and is the main gene affected by the disease.
Image of location of the mutation on the X-chromosome.