The symptoms of ALD are a result of absent or malfunctioning enzymes within the peroxisomes.  The peroxisomes are tiny structures in the cells of the body that help to break down large molecules of fats into smaller ones so that they can be used by the body.  In ALD, the peroxisomes cannot break down a type of fat called very long chain fatty acids, (VLCFA).  Because the VLCFA cannot be broken down, they accumulate throughout the body in the plasma, especially in the brain and the adrenal glands.  While it is unclear if the VLCFA cause the deterioration or are simply another symptom of the disease, the destruction of the myelin sheath surrounding the nerves leads to neurological problems, and the adrenal gland malfunction leads to Addison's Disease.

Part of the job of the adrenal glands is to use cholesterol to make  steroids.  These steroids are used to help the body properly use sodium and potassium and to break down proteins, carbohydrates and other fats.  Almost all males that are affected with ALD have problems with their adrenal glands functioning correctly.  One of the symptoms of an adrenal problem or Addison's Disease is dark skin.  Thus, boys often appear healthy with the appearance of a beautiful tan.  One way to differentiate between dark skin from Addison's and a tan is the even darker markings in the creases of the skin, as well as in scratches or scars.