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Cerebrotendinous xanthomathosis (CTX) is a rare autosomal recessive leukodystrophy, which means both copies of the affected gene in each cell have mutations. The parents of an individual with this disease usually each carry one copy of the mutated gene, but do not show signs and symptoms of the condition. The affected gene is called CYP27A1, which provides instructions for producing an enzyme called sterol 27-hydroxylase. Mutations in sterol 27-hydroxylase impair its ability to break down cholesterol to a specific bile acid called chenodeoxycholic acid. As a result, a molecule called cholestanol, which is similar to cholesterol, accumulates in fatty nodules (xanthomas), blood, nerve cells, and the brain.
Clinical features develop slowly, and may present irregularly in variable combinations. The most common features are tendon xanthomas in the Achilles tendon, neurological dysfunction, and cataracts. As patients grow older, they develop progressive coronary arteriosclerosis, and osteoporosis that predisposes them to bone fractures. The central nervous system manifestations are gradual deterioration of intellectual function, which progresses to dementia, behavior and psychiatric manifestations, stiffness, gait difficulty, and speech slurring. Seizures occur in half of the symptomatic subjects. Chronic diarrhea is a frequent symptom. In children, cataracts may be the first manifestation of CTX, and xanthomatas may be absent in patients with severe neurological involvement.
CTX is one of the few treatable leukodystrophies. Long-term treatment with chenodeoxycholic acid (CDCA) normalizes bile acid synthesis, normalizes plasma and CSF concentration of cholestanol, and improves neurophysiologic findings.