Adrenoleukodystrophy is a rare inherited condition that affects the nervous system and the adrenal glands, causing progressive damage to the protective covering of nerve cells in the brain. Understanding this disease, its warning signs, and available treatments can help families navigate this challenging diagnosis.
Epidemiology
Adrenoleukodystrophy is a rare genetic disease that touches lives across the globe, though it remains uncommon enough that many people have never heard of it. The condition affects approximately 1 in 15,000 to 1 in 21,000 individuals worldwide, with no particular ethnic or racial group showing significantly higher rates than others.[4][2]
The disease shows a distinct pattern in how it affects males and females, primarily because of how it is inherited. Males experience more severe symptoms than females who carry the disease. Among boys with the genetic mutation, about 35 to 40 percent will develop the childhood cerebral form of ALD, which is the most aggressive type.[2] While females who carry the mutation are highly unlikely to develop the childhood brain form of the disease, approximately half may experience neurological symptoms later in adulthood, typically related to spinal cord and nerve problems rather than the brain damage seen in boys.[2]
The age at which symptoms appear varies considerably depending on the type of ALD. The childhood cerebral form typically emerges between ages 4 and 10, while the adult-onset form, called adrenomyeloneuropathy (a condition affecting the spinal cord and nerves), usually begins between ages 21 and 35.[1][4] Some individuals may experience only problems with their adrenal glands without neurological symptoms.
Causes
Adrenoleukodystrophy stems from a change, or mutation, in a specific gene called ABCD1. This gene contains the instructions for making a protein known as ALDP, which plays a crucial role in breaking down certain types of fats in the body.[2][4] When this gene is faulty, the protein it produces doesn’t work properly, leading to a cascade of problems throughout the body.
The ABCD1 gene is located on the X chromosome, one of the two chromosomes that determine biological sex. Women have two X chromosomes, while men have one X and one Y chromosome. This location explains why the disease affects males and females differently. Because males have only one X chromosome, they don’t have a backup if the ABCD1 gene on that chromosome is defective. Females, having two X chromosomes, usually have one functioning copy that can partially compensate for the faulty one, making their symptoms typically milder or delayed until later in life.[7]
When the ALDP protein doesn’t function correctly, the body cannot break down very-long-chain fatty acids (VLCFAs), which are fat molecules with particularly long chemical structures. These fatty acids then accumulate in various tissues throughout the body, especially in the brain, nervous system, and adrenal glands.[1][2] Scientists believe this buildup causes inflammation and damage, though the exact mechanisms are still being studied.
Risk Factors
The primary risk factor for developing adrenoleukodystrophy is having a family history of the condition. Because ALD is an X-linked genetic disorder, certain patterns of inheritance create higher risk for specific family members.
Males born to mothers who carry the ABCD1 mutation face the highest risk. Each son of a carrier mother has a 50 percent chance of inheriting the condition. Brothers of boys diagnosed with ALD should be tested, as they may also carry the mutation. Similarly, male relatives on the mother’s side of the family, including uncles and male cousins through maternal aunts, may be at risk.[7]
Females who inherit the mutation become carriers and, while they may not develop severe childhood symptoms, approximately half will experience neurological problems as adults. These typically involve the spinal cord rather than the brain. Daughters of carrier mothers have a 50 percent chance of becoming carriers themselves.[2]
Unlike many diseases where lifestyle factors or environmental exposures play a role, ALD is purely genetic. There are no known behaviors, dietary habits, or external factors that increase or decrease the likelihood of developing the condition if someone has the genetic mutation. The disease does not skip generations in the traditional sense, though it may appear to because female carriers often have mild or no symptoms, making the family history unclear until a male child is diagnosed.
Having a family member diagnosed with ALD should prompt genetic counseling and testing for other relatives. Many states now include ALD in newborn screening programs, allowing early detection even when family history is unknown.[2][9]
Symptoms
The symptoms of adrenoleukodystrophy vary dramatically depending on which form of the disease a person develops and when it begins. Babies with ALD appear completely normal at birth and develop typically during infancy, which is why early symptoms can be easy to miss or attribute to other causes.[3]
In the childhood cerebral form, boys typically begin showing symptoms between ages 4 and 10. The earliest signs are often behavioral changes that parents or teachers might notice at school. A child who previously did well academically may suddenly struggle with reading, writing, or understanding what others say. Memory problems may emerge, and the child may have difficulty following instructions or completing tasks they could do before.[2][5]
Behavioral difficulties are common and troubling for families. Children may become withdrawn, pulling away from friends and activities they once enjoyed. Others may develop aggressive behaviors or show unusual hyperactivity. Poor school performance often prompts the initial medical evaluation that leads to diagnosis. As the disease progresses, more serious neurological symptoms appear, including seizures, vision problems, hearing loss, and difficulty swallowing. Without treatment, children with this form typically experience progressive loss of abilities, eventually becoming unable to speak, see, or move voluntarily.[2][5]
Many individuals with ALD also develop adrenal insufficiency, also called Addison’s disease, where the adrenal glands fail to produce adequate amounts of essential hormones, particularly cortisol. This can occur with or without neurological symptoms. Signs of adrenal problems include decreased appetite, weight loss, muscle weakness, fatigue, and increased skin pigmentation. Adrenal insufficiency can be life-threatening if not recognized and treated, especially during times of stress or illness.[1][4]
The adult-onset form, called adrenomyeloneuropathy, progresses more slowly than the childhood cerebral form. Men with this type typically notice symptoms beginning in their twenties or thirties. The most common complaint is progressive stiffness and weakness in the legs, which gradually worsens over years. Walking becomes increasingly difficult, and many eventually require mobility aids. Other symptoms include problems with bladder and bowel control, sexual dysfunction, and pain or unusual sensations in the hands and feet.[1][4]
Some adults with ALD also develop brain involvement similar to the childhood form, though this occurs in only about one in five affected men. When this happens, cognitive decline, personality changes, and loss of coordination can occur relatively rapidly. Female carriers who develop symptoms typically experience a milder version of adrenomyeloneuropathy in adulthood, usually with less severe disability than affected males.[1][6]
Prevention
Because adrenoleukodystrophy is an inherited genetic condition, there is no way to prevent someone who has the mutation from potentially developing the disease. However, several approaches can help identify ALD early, prevent life-threatening complications, and potentially stop disease progression if caught at the right time.
Newborn screening represents one of the most important advances in ALD prevention and early detection. Many states in the United States now include ALD in routine newborn screening programs, which test a small blood sample taken from a baby’s heel shortly after birth. While ALD was added to the Recommended Uniform Screening Panel in 2016, only about 30 states currently test for the disease, though more are expected to begin soon.[2][9] Early identification through newborn screening allows monitoring to begin immediately, potentially catching the disease before symptoms appear when treatment is most effective.
For families with a known history of ALD, genetic counseling is essential. A genetic counselor can explain inheritance patterns, discuss testing options for family members, and help families understand their risks. Pregnant women who are known carriers or who have a family history of ALD may choose to have prenatal testing, including amniocentesis (testing fluid from around the baby) or chorionic villus sampling (testing a small sample of placental tissue), to determine if their baby has inherited the condition.[7]
While there’s no proven way to prevent the disease from developing in someone with the mutation, regular monitoring is crucial. Boys and men with ALD should have their adrenal function tested periodically, as adrenal insufficiency can develop at any time and requires lifesaving hormone replacement therapy. Regular brain MRI scans are recommended for boys with ALD to detect early signs of cerebral involvement when treatment options like stem cell transplantation or gene therapy might still be effective.[2][12]
Treatment of adrenal insufficiency with hormone replacement is well-established and can prevent life-threatening adrenal crises. However, this treatment doesn’t affect the neurological aspects of the disease. For the adult form of ALD, there are currently limited preventive options, though research into various treatments continues.[13]
Pathophysiology
Understanding what happens inside the body in adrenoleukodystrophy helps explain why the disease causes such devastating effects. The process begins at the cellular level with the malfunction of tiny structures called peroxisomes, which are responsible for breaking down certain types of fats.
In healthy individuals, peroxisomes contain the ALDP protein, which acts like a transporter, moving very-long-chain fatty acids into the peroxisome where they can be broken down and eliminated. When the ABCD1 gene is mutated, the ALDP protein either doesn’t form correctly or doesn’t work properly. Without functional ALDP, very-long-chain fatty acids cannot enter the peroxisomes to be processed, so they accumulate in the body’s tissues.[4][6]
These accumulated fatty acids are particularly harmful in three main areas: the brain, the spinal cord and peripheral nerves, and the adrenal glands. In the brain, the buildup of very-long-chain fatty acids triggers inflammation that damages the myelin sheath, the protective fatty coating around nerve cells. Myelin acts like insulation on electrical wires, allowing nerve signals to travel quickly and efficiently. When myelin is destroyed, nerve cells cannot communicate properly with the rest of the body, disrupting everything from movement to thinking to sensory processing.[1][4]
The process of myelin destruction in childhood cerebral ALD happens rapidly and progressively. What begins as small areas of damage visible on brain imaging scans can spread quickly, involving more and more of the brain’s white matter (the parts of the brain rich in myelin-covered nerve fibers). This progressive demyelination (loss of myelin) explains why children with cerebral ALD lose skills they previously had, as the connections between different parts of the brain and between the brain and body break down.[2][5]
Scientists aren’t entirely certain why some individuals with the ABCD1 mutation develop rapid brain inflammation while others experience slower progression affecting mainly the spinal cord. Research suggests the accumulation of very-long-chain fatty acids causes oxidative stress, a type of cellular damage from unstable molecules. Recent studies also indicate that the mutation may affect how brain cell junctions work and may compromise the blood-brain barrier, the protective boundary that normally keeps harmful substances out of the brain.[19]
In the spinal cord form of the disease, the damage occurs more slowly and affects specific nerve tracts—the long nerve fibers that carry signals up and down the spinal cord. The corticospinal tracts (which control voluntary movement) and the dorsal columns (which carry sensory information about position and vibration) are particularly vulnerable. This explains why people with adrenomyeloneuropathy develop progressive leg stiffness and difficulty walking, as these nerve pathways gradually deteriorate.[13]
The adrenal glands, which sit atop the kidneys and produce essential hormones including cortisol, also accumulate very-long-chain fatty acids. This buildup damages the outer layer of the adrenal gland called the adrenal cortex, preventing it from making adequate amounts of hormones. Without enough cortisol, the body cannot properly respond to stress, regulate blood pressure, or maintain normal energy levels. This is why adrenal insufficiency can become life-threatening, especially during illness or injury when the body needs extra cortisol.[4][5]
Blood tests in individuals with ALD show elevated levels of very-long-chain fatty acids, which serves as a key diagnostic marker. However, the level of these fatty acids in the blood doesn’t correlate well with how severe someone’s symptoms are or predict which form of the disease they will develop. This lack of correlation suggests that other factors beyond just fatty acid accumulation contribute to disease progression, though researchers are still working to understand what those factors might be.[6]
