Cerebrotendinous xanthomatosis (CTX)

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People with Cerebrotendinous xanthomatosis (CTX) cannot break down certain forms of cholesterol properly. This is because they have a deficiency of a mitochondrial enzyme called sterol 27-hydroxylase. This enzyme deficiency leads to an accumulation of fats and increasing numbers of xanthomas in body tissues, which result in the symptoms seen.

The signs and symptoms do vary considerably from individual to individual. Chronic diarrhoea in infancy is common. In about 75% of cases the first sign is clouding of the lens of the eye (cataract) in childhood. Xanthomas develop in the tendons in adolescence or young adulthood. These are most commonly in the Achilles tendon (which connects the heel of the foot to the calf muscles), but also in tendons of the elbows, hands, knees and neck. Tendon xanthomas may cause discomfort and interfere with tendon flexibility.

In adulthood, progressive neurological problems begin. These include dementia, seizures, hallucinations, depression, and difficulty with coordinating movements (ataxia) and speech (dysarthria). Slow deterioration in intellectual abilities occurs in the 20s in more than 50% of people with the disorder.

Progressively brittle bones that are prone to fracture can occur and there is an increased risk of developing heart (cardiovascular) disease.

Currently there is no consensus on the prevalence of CTX, with estimates varying from 0.1 to 5 per 100,000 people worldwide. The condition is more common among people of northern European heritage, at-least 1 per 50,000 people.

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Diagnosis

Unexplained childhood onset cataracts associated with infantile chronic diarrhoea and intellectual disability or deterioration strongly suggest the possibility of CTX.

The diagnosis is made on the basis of clinical findings, biochemical test results and/or genetic test results. Classic findings include elevated levels of cholestanol and bile alcohols in serum and urine and changes seen on an MRI scan of the brain. Genetic testing can confirm the diagnosis, or establish it in a family member of someone already diagnosed.

Treatment

Early diagnosis and long-term treatment with a medication called chenodeoxycholic acid improves neurological symptoms and contributes to a better prognosis. Sometimes another medication called HMG-CoA reductase inhibitors are also given but these can cause adverse side effects.

Cataracts can be removed by surgery when necessary. Epilepsy, spasticity, and parkinsonism can be treated using standard therapies. Calcium and vitamin D supplements can improve osteoporosis and coenzyme Q10 (CoQ10) treatment may improve muscle weakness.

Genetics and Inheritance

Genetic testing methods change over time. A consultant geneticist from an NHS genetic clinic can arrange testing of the CYP27A1 gene, where needed, review the inheritance pattern and provide up-to-date management advice. Families are welcome to seek advice from genetic clinics at various times of life. For example, when an individual with CTX or their siblings want more details as they get older, they could ask about the condition for themselves.

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