Aidan Jack Seeger Foundation
What is ALD?
Adrenoleukodystrophy, or ALD, is a deadly genetic disease that affects 1 in 17,000 people. As it is an X-linked genetic disease, it most severely affects boys and men. This brain disorder destroys myelin, the protective sheath that surrounds the brain’s neurons — the nerve cells that allow us to think and to control our muscles. It knows no racial, ethnic or geographic barriers.
The most devastating form of ALD appears in childhood, generally between the ages of four and ten years old. Normal, healthy boys suddenly begin to regress. At first, they simply show behavioral problems, such as withdrawal or difficulty concentrating, vision problems, or coordination issues. Gradually, as the disease ravages their brain, their symptoms grow worse, including blindness, deafness, seizures, loss of muscle control, and progressive dementia. This relentless downward spiral leads to a vegetative state or death usually within 2-5 years of diagnosis. Demyelination is the stripping away of the fatty coating that keeps nerve pulses confined and maintains the integrity of nerve signals. This process inhibits the nerves ability to conduct properly, thereby causing neurological deficits. Demyelination is an inflammatory response and nerve cells throughout the brain are destroyed.
Adrenoleukodystrophy, or ALD, is an x-linked metabolic disorder, characterized by progressive neurologic deterioration due to demyelination of the cerebral white matter. Brain function declines as the protective myelin sheath is gradually stripped from the brain’s nerve cells. Without that sheath, the neurons cannot conduct action potentials—in other words, they stop telling the muscles and other elements of the central nervous system what to do.
This sequence of events appears to be related to an abnormal accumulation of saturated very-long-chain fatty acids (VLCFA) in the serum and tissues of the central nervous system, which sets off an abnormal immune response that leads to demyelination. It is unclear exactly how this chain of events works, but scientists do know that it has its roots in genetics.
ALD is caused by a genetic abnormality, commonly referred to as a “genetic mutation”, affecting the X chromosome, otherwise known as an “x-linked” condition. Everyone has two sex chromosomes: women have two X chromosomes and men have an X and a Y chromosome. If a woman inherits the abnormal X chromosome, she still has a normal, second X chromosome to help balance out the affects of the mutation. Boys and men do not have a second X chromosome, so if they inherit this genetic abnormality, they will most likely get the disease.
ALD takes several forms, which can vary widely in their severity and progression. They include:
Childhood Cerebral Demyelinating ALD. This is the most common form of ALD, representing about 45% of all ALD cases. It is characterized by an inflammatory process that destroys the myelin, causing relentless progressive deterioration to a vegetative state or death, usually within five years.
Although women who carry the ALD gene mutation do not generally develop the brain disease itself, some display mild symptoms of the disorder. These symptoms usually develop after age 35, and primarily include progressive stiffness, weakness, or paralysis of the lower limbs, numbness, pain in the joints, and urinary problems.