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PubMed This is a summary of 18 peer-reviewed journal articles Updated
Neurology

The Biology of CTX and Why It Is Often Misdiagnosed

At a Glance

Cerebrotendinous Xanthomatosis (CTX) is a rare genetic disorder caused by an enzyme defect that leads to toxic cholestanol buildup. It is often misdiagnosed as MS, ADHD, or dementia. Unique signs of CTX include juvenile cataracts, chronic diarrhea, and painless lumps on the Achilles tendons.

Understanding why Cerebrotendinous Xanthomatosis (CTX) happens requires looking at a specific biological “blueprint” error. While the results of this error can look like other well-known conditions, the biology behind CTX is unique.

The Biology: A Missing Step in the Process

Every person has a gene called CYP27A1 [1]. This gene provides instructions for making an enzyme called sterol 27-hydroxylase [2].

Think of this enzyme as a worker on an assembly line. Its job is to take cholesterol and turn it into bile acids, which your body needs for digestion. In CTX, this worker is missing or unable to do the job [3][4].

Because the root cause is this genetic “assembly line” error, simply changing your diet to eat less cholesterol will not stop the disease; targeted medical treatment is required.

  • The Breakdown: Because the assembly line stops, the body cannot make enough of the primary bile acid it needs (called chenodeoxycholic acid) [5].
  • The Toxic Shortcut: To compensate, the body tries to use a different, “backup” path. This path unfortunately creates high levels of cholestanol and bile alcohols [2][5].
  • The Buildup: These substances cannot be easily cleared and begin to settle in the brain, nerves, and tendons, eventually causing damage [5][6].

Why It Is Often Misdiagnosed

Because CTX is rare and its symptoms are so varied, doctors often reach for more common diagnoses first. The “buildup” in the brain can mimic several different conditions:

1. Multiple Sclerosis (MS)

CTX can cause white matter lesions in the brain that look similar to the inflammation seen in Multiple Sclerosis [7]. Both conditions can cause walking difficulties (ataxia) and balance issues. However, MS is an autoimmune condition, while CTX is a metabolic one [7][8].

2. Adult ADHD

In adolescents and young adults, the “brain fog,” impulsivity, and difficulty focusing caused by CTX-related neurotoxicity are often mistaken for Attention-Deficit/Hyperactivity Disorder (ADHD) [9][10]. While ADHD is a common neurodevelopmental condition, in CTX, these symptoms are signs of a progressive metabolic buildup [11].

3. Frontotemporal Dementia (FTD)

In older adults, CTX can cause changes in personality, aggression, or a loss of social filters. These are the hallmarks of Behavioral Variant Frontotemporal Dementia (bvFTD) [9][10]. Because both involve the frontal lobes of the brain, the behavioral symptoms can be nearly identical [11].

The Key Differentiators: Solving the Mystery

The secret to distinguishing CTX from these “look-alike” conditions lies in the symptoms that seem “out of place.” Doctors look for a combination of neurological issues plus these three metabolic markers:

  • Juvenile Cataracts: If a patient has neurological issues and a history of cataracts before age 20, it is a major clue for CTX [12][13]. Primary MS or ADHD does not cause early cataracts.
  • Chronic Diarrhea: Unexplained, long-term diarrhea since infancy is a common CTX sign that isn’t found in dementia or MS [12][14].
  • Tendon Xanthomas: The presence of painless lumps on the Achilles tendons is perhaps the most specific sign of CTX [15][16].

If a person has “brain symptoms” but also has any of these three “body symptoms,” specialists will typically order a cholestanol blood test to confirm if a metabolic disorder is the true cause [17][18].

Common questions in this guide

Why is CTX often misdiagnosed as Multiple Sclerosis?
CTX can cause brain lesions, walking difficulties, and balance issues that look very similar to MS. However, MS is an autoimmune disease, while CTX is a metabolic disorder caused by a specific missing enzyme.
How can doctors tell the difference between CTX and adult ADHD?
While the brain fog, difficulty focusing, and impulsivity of CTX can mimic ADHD, CTX is a progressive metabolic condition. Doctors look for other physical signs, like a history of chronic diarrhea or early cataracts, to distinguish CTX from primary ADHD.
What are the key signs that point to CTX instead of frontotemporal dementia?
In addition to cognitive decline or personality changes, patients with CTX usually have physical symptoms not found in standard dementia. These "out of place" clues include a history of juvenile cataracts, childhood diarrhea, or painless lumps on their Achilles tendons.
Can eating a low-cholesterol diet stop CTX from getting worse?
No, simply reducing cholesterol in your diet will not stop CTX. The condition is caused by a missing enzyme that disrupts normal biological processes, so it requires targeted medical therapy to prevent the toxic buildup of cholestanol.
What test is used to confirm a diagnosis of CTX?
If a doctor suspects CTX based on a combination of neurological symptoms and physical signs like tendon lumps or early cataracts, they will typically order a specific blood test to check for high levels of cholestanol.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.How does the pattern of brain lesions on my (or my child's) MRI specifically point to CTX rather than Multiple Sclerosis?
  2. 2.If I have psychiatric symptoms but not tendon xanthomas yet, is biochemical testing for cholestanol still the next best step?
  3. 3.Can you help me understand the difference between the cognitive decline seen in CTX and that of frontotemporal dementia?
  4. 4.Are my cataracts considered 'juvenile-onset,' and how does that help confirm a metabolic diagnosis?
  5. 5.Since CTX is often misdiagnosed as ADHD, how can we distinguish between primary ADHD and CTX-related behavioral changes?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (18)
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    Cerebrotendinous Xanthomatosis: A Treatable Genetic Disease Not to Be Missed.

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    Long-term MRI Findings in Patients With Cerebrotendinous Xanthomatosis Treated With Chenodeoxycholic Acid.

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This page explains the biology and misdiagnosis of Cerebrotendinous Xanthomatosis (CTX) for educational purposes only. Always consult your neurologist or genetic specialist for an accurate diagnosis and medical advice.

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