Adrenoleukodystrophy is a disease caused by a mutation in the ABCD1 gene that is located on the X chromosome. It is a neurodegenerative disease in which the protective myelin sheath covering the nerve fibers in the brain and spinal cord gradually deteriorate. This demyelination causes injury to the brain leading to the behavioral and neurological symptoms seen in the patients. The disease also affects the adrenal glands causing them not to produce enough steroid hormones.
Who is affected by ALD?
Because the mutated gene causing the disease is on the X chromosome, men are at higher risk of developing ALD. This is because men have only one X chromosome while women have two. So even if a woman inherits a mutated copy of the ABCD1 gene, the other healthy copy of the gene located on the other X chromosome can compensate. However, carrier women or those who have one faulty copy of the ABCD1 gene may also develop symptoms of ALD later in life.
ALD does not discriminate based on ethnicity and is reported in similar frequency in populations around the world.
How common is ALD?
According to the U.S. National Library of Medicine, the prevalence of ALD is 1 in 20,000 to 50,000 individuals worldwide.
In the U.S., 1 in every 21,000 men is thought to be affected by ALD while 1 in 16,800 women are thought to be ALD carriers.
As per a newborn screening conducted in the state of New York, the incidence of ALD at birth was estimated to be 1 in 15,000. Among the 700,000 newborns screened in a three-year period, 45 babies were diagnosed with ALD.
How common are the different types of ALD?
ALD had three distinct types based on the symptoms and age of disease onset: childhood cerebral ALD (CALD), adrenomyeloneuropathy (AMN), and Addison’s disease.
According to combined data describing the distribution of ALD types in different regions of the world, CALD is the most common, with around 33 to 57 percent of all reported cases. Addison’s disease is the least reported with about 10 percent of all cases, while AMN represents around 25 to 46 percent of all ALD cases. The exception to this pattern is the Netherlands where AMN is the most common type with 46 percent of reported cases.
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