Usefulness of cholestanol levels in the diagnosis and follow-up of patients with cerebrotendinous xanthomatosis

Clinicogenetic characterization of cerebrotendinous xanthomatosis in Brazil

There are few cerebrotendineous xanthomatosis (CTX) case series and observational studies including a significant number of Latin American patients. We describe a multicenter Brazilian cohort of patients with CTX highlighting their clinical phenotype, recurrent variants and assessing possible genotype-phenotype correlations. We analyzed data from all patients with clinical and molecular or biochemical diagnosis of CTX regularly followed at six genetics reference centers in Brazil between March 2020 and August 2023. We evaluated 38 CTX patients from 26 families, originating from 4 different geographical regions in Brazil. Genetic analysis identified 13 variants in the CYP27A1 gene within our population, including 3 variants that had not been previously described. The most frequent initial symptom of CTX in Brazil was cataract (27%), followed by xanthomas (24%), chronic diarrhea (13.5%), and developmental delay (13.5%). We observed that the median age at loss of ambulation correlates with the age of onset of neurological symptoms, with an average interval of 10 years (interquartile range 6.9 to 11 years). This study represents the largest CTX case series ever reported in South America. We describe phenotypic characteristics and report three new pathogenic or likely pathogenic variants.

[A case of cerebrotendinous xanthomatosis mimicking the clinical phenotype of mitochondrial disease with a novel frame-shift mutation (c. 43_44 delGG) in CYP27A1 gene exon 1]

A 37-old-male with a history of early childhood mental retardation was admitted to our hospital. He experienced recurrent syncopes at 23 years old, and at age 35 gait disturbance and hearing impairment developed gradually and worsened over time. His grandparents were in a consanguineous marriage. He was of short stature and absent of tendon xanthomas. Neurological examinations revealed scanning speech, dysphagia, right sensorineural hearing loss, spasticity in both upper and lower extremities, and spastic gait. Tendon reflexes were brisk throughout, and Babinski and Chaddock reflexes were both positive bilaterally. Laboratory tests revealed elevated lactate and pyruvate concentrations in both serum and cerebrospinal fluid. Fluid attenuated inversion recovery magnetic resonance imaging showed high intensity lesions in the bilateral cerebellar hemispheres, pyramidal tracts in the brainstem, and internal capsules symmetrically. Brain magnetic resonance spectroscopy measurements revealed an elevated lactate/creatine plus phosphocreatine ratio and a decreased N-acetyl-aspartate/creatine plus phosphocreatine ratio in the cerebellum. At this point, mitochondrial diseases, particularly myoclonic epilepsy with ragged-red fibers (MERRF), to be the most likely cause. We performed a biopsy of his left biceps brachii muscle, showing variations in fiber size with occasional central nuclei and very few ragged-red fibers. Blood mitochondrial respiratory enzyme assays showed normal values with elevated citrate synthase activity, and mitochondrial DNA analyses for MERRF revealed no pathogenic mutations. We then explored other possibilities and detected an elevated serum cholestanol concentration of 20.4 μg/ml (reference value <4.0) and genetic analysis by direct sequencing method disclosed a novel frame-shift mutation (c. 43_44delGG) in CYP27A1 gene exon1, leading to a diagnosis of cerebrotendinous xanthomatosis (CTX). This case emphasizes importance of awareness of CTX as a possibility when patients present with clinical phenotypes mimicking mitochondrial diseases, but with negative results for muscle pathology or genetic analyses. The measurements of serum cholestanol concentrations might be useful in diagnosing such atypical cases.

[Laboratory diagnosis of a rare congenital neurodegenerative disease: cerebrotendinous xanthomatosis]

Cerebrotendinous xanthomatosis is a rare neurodegenerative disease characterized by the accumulation of cholesterol and cholestanol in the brain and the tendons caused by mutations of the gene encoding sterol 27-hydroxylase (CYP27A1), which is involved in bile acid synthesis. The diagnosis is often missed and delayed because of the variable clinical presentation of the disease. Blood testing for cerebrotendinous xanthomatosis is routinely performed using gas chromatography-mass spectrometry measurement of elevated cholestanol level, and the diagnosis is confirmed by molecular genetic analysis. Early recognition and initiation of chenodeoxycholic acid therapy with hydoxymethyl‑glutaryl‑Coenzyme-A reductase inhibitors is critical to prevent irreversible neurological damage and permanent disability. The authors summarize the current knowledge about the pathomechanism, laboratory diagnosis and therapeutic options of cerebrotendinous xanthomatosis.