From the Departments of Human Genetics (S.M., M.N., Y.T., N. Miyake, N. Matsumoto, H.S.) and Biochemistry (M. Shiina, K.O.), Yokohama City University Graduate School of Medicine; Division of Neurology (H.O.), Clinical Research Institute, Kanagawa Children's Medical Center, Yokohama; Department of Pediatrics (H.O.), Jichi Medical School, Tochigi; Department of Child Neurology (M. Sasaki), National Center of Neurology and Psychiatry, Tokyo; Department of Pediatrics (J.-i.T.), Kameda Medical Center, Chiba; Department of Pediatric Neurology (K.H.), Takuto Rehabilitation Center for Children, Sendai; Genetic Counselling and Clinical Research Unit (T.W.), Kyoto University School of Public Health; Department of Pediatrics (M.M.), Graduate School of Medical Science, Kyoto Prefectural University of Medicine; Department of Neonatology and Pediatrics (N.A.), Nagoya City University Graduate School of Medical Sciences; and Department of Neurology (Y.I.), Tokyo Metropolitan Children's Medical Center, Japan.
Neurology. 2014 Jun 17;82(24):2230-7. doi: 10.1212/WNL.0000000000000535. Epub 2014 May 21.
We performed whole-exome sequencing analysis of patients with genetically unsolved hypomyelinating leukoencephalopathies, identifying 8 patients with TUBB4A mutations and allowing the phenotypic spectrum of TUBB4A mutations to be investigated.
Fourteen patients with hypomyelinating leukoencephalopathies, 7 clinically diagnosed with hypomyelination with atrophy of the basal ganglia and cerebellum (H-ABC), and 7 with unclassified hypomyelinating leukoencephalopathy, were analyzed by whole-exome sequencing. The effect of the mutations on microtubule assembly was examined by mapping altered amino acids onto 3-dimensional models of the αβ-tubulin heterodimer.
Six heterozygous missense mutations in TUBB4A, 5 of which are novel, were identified in 8 patients (6/7 patients with H-ABC [the remaining patient is an atypical case] and 2/7 patients with unclassified hypomyelinating leukoencephalopathy). In 4 cases with parental samples available, the mutations occurred de novo. Analysis of 3-dimensional models revealed that the p.Glu410Lys mutation, identified in patients with unclassified hypomyelinating leukoencephalopathy, directly impairs motor protein and/or microtubule-associated protein interactions with microtubules, whereas the other mutations affect longitudinal interactions for maintaining αβ-tubulin structure, suggesting different mechanisms in tubulin function impairment. In patients with the p.Glu410Lys mutation, basal ganglia atrophy was unobserved or minimal although extrapyramidal features were detected, suggesting its functional impairment.
TUBB4A mutations cause typical H-ABC. Furthermore, TUBB4A mutations associate cases of unclassified hypomyelinating leukoencephalopathies with morphologically retained but functionally impaired basal ganglia, suggesting that TUBB4A-related hypomyelinating leukoencephalopathies encompass a broader clinical spectrum than previously expected. Extrapyramidal findings may be a key for consideration of TUBB4A mutations in hypomyelinating leukoencephalopathies.
我们对遗传原因不明的脑白质营养不良低髓鞘化患者进行了全外显子组测序分析，发现 8 例 TUBB4A 突变患者，从而对 TUBB4A 突变的表型谱进行了研究。
对 14 例低髓鞘化脑白质营养不良患者进行全外显子组测序分析，其中 7 例临床诊断为基底节和小脑萎缩伴低髓鞘化（H-ABC），7 例为未分类的低髓鞘化脑白质营养不良。通过将突变的氨基酸映射到αβ-微管蛋白异二聚体的三维模型上来检测突变对微管组装的影响。
在 8 例患者（7 例 H-ABC 患者[另 1 例为非典型病例]和 2 例未分类的低髓鞘化脑白质营养不良患者）中发现了 6 个 TUBB4A 错义杂合突变，其中 5 个是新的。在 4 例有父母样本的病例中，突变是从头发生的。三维模型分析显示，在未分类的低髓鞘化脑白质营养不良患者中发现的 p.Glu410Lys 突变直接损害了运动蛋白和/或微管相关蛋白与微管的相互作用，而其他突变则影响维持αβ-微管蛋白结构的纵向相互作用，提示微管功能障碍的机制不同。在 p.Glu410Lys 突变患者中，尽管存在锥体外系特征，但基底节萎缩未观察到或轻微，提示其功能受损。
TUBB4A 突变导致典型的 H-ABC。此外，TUBB4A 突变与形态保留但功能受损的基底节相关的未分类低髓鞘化脑白质营养不良有关，提示 TUBB4A 相关的低髓鞘化脑白质营养不良的临床谱比以前预期的更广泛。锥体外系表现可能是考虑低髓鞘化脑白质营养不良中 TUBB4A 突变的关键。
