ミトコンドリア病と鑑別を要する臨床表現型を呈しCYP27A1遺伝子エクソン1に新規フレームシフト変異(c. 43_44delGG)を認めた脳腱黄色腫症の1例

Junpei Koge, Shintaro Hayashi, Hiroo Yamaguchi, Takahisa Tateishi, Hiroyuki Murai, Jun-ichi Kira

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.