Weight Loss with Cerebrotendinous Xanthomatosis (CTX): A South African Guide

The Biology Behind CTX

Sterol 27-hydroxylase (CYP27A1) catalyses the first step in the conversion of cholesterol side chain to a carboxyl group, ultimately producing CDCA and cholic acid. In CTX:

• The CDCA biosynthesis pathway is blocked
• Low CDCA fails to provide negative feedback on CYP7A1 (the rate-limiting enzyme for bile acid synthesis) — so the liver keeps producing cholesterol → cholestanol precursors
• Cholestanol (a 5α-reduced form of cholesterol) accumulates everywhere, including the blood-brain barrier and central nervous system
• Bile alcohols (hepatanol, pentahydroxy bile alcohol) accumulate in urine and serum

CTX prevalence is approximately 1–5 per 100,000. It is probably underdiagnosed in South Africa — the slowly progressive neurological picture (often misdiagnosed as multiple sclerosis, cerebellar ataxia of unknown cause, or premature dementia) means decades may pass before the correct diagnosis is made. Certain populations have higher carrier rates: Sephardic Jews of Moroccan origin have a higher prevalence due to a founder variant, but CTX occurs across all ethnicities including Black African populations.

Why Weight Management Matters in CTX

CTX creates two intersecting weight challenges:

1. Cardiovascular risk from cholestanol accumulation — atherosclerosis develops early; excess body weight accelerates this risk. Maintaining a healthy weight reduces cardiovascular burden on an already stressed system
2. Neurological impairment limiting activity — cerebellar ataxia, spastic paraparesis, and cognitive decline progressively reduce physical activity capacity, predisposing to weight gain from physical inactivity
3. Chronic diarrhoea and malabsorption — chronic diarrhoea (from bile acid malabsorption and GI cholestanol deposition) can impair nutrient absorption and paradoxically cause under-nutrition in some patients

The dietary approach must serve all three: support cardiovascular health, work within neurological limitations, and compensate for any malabsorption.

CDCA Replacement Therapy: The Cornerstone of Treatment

Before discussing diet, it's essential to understand that dietary management in CTX is adjunctive to medical treatment, not a replacement for it. The primary treatment is chenodeoxycholic acid (CDCA) oral replacement therapy at 750 mg/day (typically 250 mg three times daily). CDCA:

• Replaces the deficient bile acid, restoring negative feedback on bile acid synthesis
• Reduces CYP7A1 activity → less cholesterol → less cholestanol production
• Reduces serum cholestanol by 50–90% in many patients
• Arrests and sometimes reverses early neurological decline
• Reduces xanthoma size

In South Africa, CDCA (as Chenofalk or Ursofalk preparations) can be obtained but may require motivation through medical aid or compassionate access from the metabolic physician. Statins (especially simvastatin) are sometimes added to reduce cholesterol substrate further — they have a synergistic effect with CDCA in CTX. Unlike sitosterolaemia, statins ARE useful in CTX.

Dietary Strategy in CTX

Cholesterol Restriction: Meaningful but Not Extreme

Dietary cholesterol provides substrate for cholestanol synthesis via CYP27A1's normal role. Reducing dietary cholesterol reduces the cholesterol pool available for conversion to cholestanol. The recommendation is a moderately low cholesterol diet — not a zero-cholesterol approach (which is impractical and removes important nutrient-dense foods):

• Limit egg yolks to 3–4 per week (whole eggs; whites are fine without restriction)
• Choose lean cuts of meat; avoid organ meats (liver, kidney, brain — very high cholesterol)
• Limit full-fat dairy; use low-fat or reduced-fat versions
• Avoid prawns, squid, and shellfish in large quantities (relatively high cholesterol)
• Fish is excellent — omega-3 content provides cardiovascular protection

Anti-Atherogenic Eating for Cardiovascular Protection

Premature atherosclerosis is a leading cause of morbidity in CTX. A Mediterranean-style anti-inflammatory approach is ideal:

Managing Chronic Diarrhoea Through Diet

Chronic diarrhoea is a debilitating feature of CTX that precedes neurological symptoms by years and is caused by bile acid malabsorption and GI cholestanol deposition. Dietary strategies to manage diarrhoea:

• Soluble fibre — oats, psyllium husk, apple, banana, cooked lentils — binds excess bile acids in the gut, reducing diarrhoea (paradoxically, bile acid binders should not be used pharmacologically as they worsen CTX)
• Small, frequent meals — reduces large bile acid surges into the small intestine
• Low-fat meals — very high-fat meals trigger large bile acid secretion; moderate fat is better tolerated
• Probiotics — amasi (maas), plain yoghurt, kefir — support gut microbiome; may reduce diarrhoea frequency
• Avoid high-FODMAPs if sensitive — some CTX patients have co-existing IBS-type fermentation issues; a short trial of low-FODMAP (registered dietitian guided) can help
• Hydration — chronic diarrhoea depletes fluids and electrolytes; 8–10 glasses of water daily minimum; oral rehydration if diarrhoea is severe

Nutrient Supplementation Considerations

• Fat-soluble vitamins (A, D, E, K) — bile acid malabsorption impairs fat-soluble vitamin absorption; deficiencies are common; check levels annually and supplement if deficient under medical supervision
• Vitamin D — particularly important; deficiency worsens neurological function and bone health; South African sun helps but diarrhoea impairs absorption; test and supplement if below 50 nmol/L
• Calcium — malabsorption risk; dietary sources (dairy, leafy greens, sardines eaten with bones) are important; supplement with medical guidance if levels low
• CoQ10 — some mitochondrial overlap; preliminary supportive evidence in bile acid synthesis disorders; discuss with metabolic physician

Exercise with CTX: Working Around Neurological Limitations

Exercise is complicated in CTX because neurological deterioration progressively reduces capacity. The approach must adapt to the stage of disease:

Early CTX (minimal neurological symptoms)

• Regular moderate exercise is encouraged — reduces cardiovascular risk, supports weight management, maintains functional independence
• Aerobic exercise: brisk walking, cycling, swimming — 30 minutes most days
• Resistance training: moderate weights, compound movements; strengthens postural muscles that will be needed as neurological disease progresses
• Protect Achilles tendons from explosive loading (xanthomas may be present)

Established Ataxia / Spasticity

• Physiotherapy-guided exercise is essential — balance training, proprioception work, gait retraining; neurological physiotherapists at academic hospitals in SA
• Hydrotherapy — buoyancy reduces fall risk during exercise; warm water reduces spasticity; excellent for aerobic conditioning with gait impairment
• Seated exercises — stationary cycling, seated rowing, resistance bands — maintain cardiovascular fitness and muscle tone when standing exercise is unsafe
• Walking aids — use walking sticks, zimmerframe, or rollator as needed; falling with osteoporotic bones (possible from vitamin D/calcium malabsorption) is dangerous

Weight Loss Rate in CTX

Target slow, sustainable weight loss of 0.3–0.5 kg per week. Rapid weight loss is inappropriate in CTX for several reasons:

• Neurological function requires adequate energy — the brain is already under metabolic stress from cholestanol accumulation
• Rapid fat loss can mobilise fat-stored cholestanol, theoretically increasing circulating levels temporarily
• Muscle loss from crash dieting worsens mobility in a condition that already compromises motor function

CTX in South Africa: Getting Diagnosed and Treated

CTX is severely underdiagnosed in South Africa. Many patients are currently walking around with misdiagnoses. If you or a family member has:

• Achilles tendon xanthomas at a young age
• Early-onset cataracts (childhood or young adult)
• Unexplained cerebellar ataxia, spasticity, or cognitive decline
• Chronic diarrhoea of unknown cause
• Any combination of the above

Request serum cholestanol measurement and referral to a clinical geneticist or neurologist experienced in metabolic conditions.

Centres to contact:

• Division of Human Genetics, University of Cape Town / Groote Schuur Hospital
• Division of Human Genetics, University of the Witwatersrand / Charlotte Maxeke Johannesburg Academic Hospital
• Steve Biko Academic Hospital, University of Pretoria
• Dietitian support: ADSA (adsa.org.za)
• International CTX support: CTX Research Society (ctxresearch.org)

Key Takeaways

• CTX is caused by CYP27A1 mutations — bile acid synthesis is blocked, cholestanol accumulates in brain, tendons, and lens
• Cardinal signs: Achilles tendon xanthomas + cataracts + neurological deterioration + chronic diarrhoea + premature atherosclerosis
• CDCA replacement therapy (750 mg/day) is the disease-modifying treatment — dramatically reduces cholestanol and arrests neurological decline; UDCA is NOT equivalent
• Diet: moderate cholesterol restriction (limit organ meats, excess egg yolks, shellfish); anti-atherogenic Mediterranean approach; soluble fibre to manage diarrhoea
• South African staples that help: pilchards (omega-3), rooibos tea (antioxidant), olive oil, avocado, lentils, oats, amasi/yoghurt (probiotics)
• Fat-soluble vitamin deficiency (A, D, E, K) common due to malabsorption — check levels annually
• Exercise adapted to neurological stage: full aerobic activity early; physiotherapy + hydrotherapy as ataxia/spasticity develops
• Severely underdiagnosed in SA — if symptoms match, push for serum cholestanol testing