"ALD is inherited as an X-linked recessive genetic disease. X-linked recessive genetic disorders are conditions caused by an abnormal gene on the X chromosome. Females have two X chromosomes but one of the X chromosomes is “turned off” and all of the genes on that chromosome are inactivated. Females who have a disease gene present on one of their X chromosomes are carriers for that disorder. Carrier females often do not display symptoms of the disorder because it is usually the X chromosome with the abnormal gene that is turned off. A male has one X chromosome and if he inherits an X chromosome that contains a disease gene, he will develop the disease. Males with X-linked disorders pass the disease gene to all of their daughters, who will be carriers. A male cannot pass an X-linked gene to his sons because males always pass their Y chromosome instead of their X chromosome to male offspring. Female carriers of an X-linked disorder have a 25% chance with each pregnancy to have a carrier daughter like themselves, a 25% chance to have a non-carrier daughter, a 25% chance to have a son affected with the disease, and a 25% chance to have an unaffected son." Says https://rarediseases.org/rare-diseases/adrenoleukodystrophy/.
In simple terms the disease only effects mostly males.
ALD is treated with Lorenzo oil and stem cell transplants.
Lorenzo oil is a combination of two fats from olive oil and rapeseed oil which has been proving effective in subsideing the symptoms of ALD in boys who are not yet symptomatic.
A stem cell transplant is for boys with ALD who have a Loes score lower than 8 or 9. A loes score is an MRI measure of the severity of the disease. These boys are generally considered candidates for stem cell transplantation. There are two sources for transplanted stem cells: umbilical cord blood or bone marrow. The goal of both of these treatments is to provide the patient with healthy stem cells that produce a functioning ALD protein, the protein that is lacking in people with ALD. Some of these actually make it into the brain halting or even reversing the brain damage.