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Adrenoleukodystrophy (ALD) is an inherited metabolic storage disorder. An inherited disorder means that the disease is caused by faulty genes passed on from parents to children. Genes are instructions that tell the body how to make all the different substances the body needs to work properly.

The affected gene in ALD is on the X chromosome. Chromosomes are thread-like strands of DNA that carry genetic information about your body. Since boys with ALD have only one X chromosome, they will typically have severe disease. Girls with ALD, who usually have one faulty gene and one normal gene, often have milder disease. About 1 out of every 3 boys born with ALD will have the most severe form called cerebral X-linked ALD. X-linked ALD is rare. It affects about 1 in 20,000 individuals worldwide, according to the National Institutes of Health. 

The faulty gene involved in ALD prevents the body from being able to break down (metabolize) certain fatty acids. Fatty acids make up the fat in our bodies and the fat we eat. These fatty acids build up in the brain, nervous system, and adrenal glands (small glands that sit on the kidneys). This keeps nerve cells from sending signals throughout the body. As a result, those severely affected with ALD will have problems with movement, memory, learning, speaking, and other mental functions.

In a family with a history of ALD, some boys can be diagnosed with ALD when there are no signs of central nervous system damage. Boys diagnosed with ALD before symptoms appear must be watched carefully for signs the ALD is affecting the central nervous system. A doctor with experience treating patients with ALD will schedule regular brain scans to watch for these signs.

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