A 5-year-old boy presented with profound developmental delay. On neurologic examination, he had significant spasticity and dystonia with constant movements of his limbs. Of note, developmental delay and hypotonia were initially noticed at 6 months of age at which time a thorough investigation was initiated that included plasma amino acids, urine organic acids, carnitine, congenital disorders of glycosylation-transferrin test, creatine kinase, magnetic resonance imaging (MRI) brain/spine, chromosomal microarray, and electromyography. All tests including MRI were reported normal at that time. At 2 years of age, the patient was unable to completely control his head and needed assistance to walk or stand. During his visit at 5 years of age, a repeat MRI of the brain was performed, which showed diffuse hypomyelination with small putamen and marked cerebellar volume loss (Fig. 1a, b). What is your diagnosis?

中文翻译：

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锥体外系运动伴髓鞘减少

一名 5 岁男孩出现严重发育迟缓。在神经系统检查中，他有明显的痉挛和肌张力障碍，四肢不断运动。值得注意的是，发育迟缓和肌张力减退最初是在 6 个月大时被发现的，当时开始了一项彻底的调查，包括血浆氨基酸、尿液有机酸、肉碱、先天性糖基化转铁蛋白测试、肌酸激酶、磁共振成像。 MRI) 脑/脊柱、染色体微阵列和肌电图。当时报告的所有测试包括 MRI 都正常。2岁时，患者无法完全控制自己的头部，需要帮助才能行走或站立。在他 5 岁时就诊期间，对他的大脑进行了重复 MRI，表现为弥漫性髓鞘形成及小壳核和显着的小脑体积损失（图 1a、b）。你的诊断是什么？