Expanding the phenotypic spectrum of TUBB4A-associated hypomyelinating leukoencephalopathies.
OBJECTIVE
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.


METHODS
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.


RESULTS
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.


CONCLUSIONS
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.
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.
Satoko
S
Miyatake
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.
Hitoshi
H
Osaka
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.
Masaaki
M
Shiina
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.
Masayuki
M
Sasaki
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.
Jun-Ichi
J
Takanashi
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.
Kazuhiro
K
Haginoya
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.
Takahito
T
Wada
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.
Masafumi
M
Morimoto
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.
Naoki
N
Ando
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.
Yoji
Y
Ikuta
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.
Mitsuko
M
Nakashima
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.
Yoshinori
Y
Tsurusaki
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.
Noriko
N
Miyake
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.
Kazuhiro
K
Ogata
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. naomat@yokohama-cu.ac.jp hsaitsu@yokohama-cu.ac.jp.
Naomichi
N
Matsumoto
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. naomat@yokohama-cu.ac.jp hsaitsu@yokohama-cu.ac.jp.
Hirotomo
H
Saitsu
D000293:Adolescent; D000328:Adult; D001479:Basal Ganglia / Q000473:pathology; D002531:Cerebellum / Q000473:pathology; D002648:Child; D002675:Child, Preschool; D004252:DNA Mutational Analysis; D003711:Demyelinating Diseases / Q000150:complications / Q000235:genetics*; D059472:Exome / Q000235:genetics; D005260:Female; D020022:Genetic Predisposition to Disease; D006801:Humans; D007223:Infant; D056784:Leukoencephalopathies / Q000150:complications / Q000235:genetics*; D008297:Male; D008958:Models, Molecular; D009154:Mutation / Q000235:genetics*; D010641:Phenotype; D014404:Tubulin / Q000235:genetics*; D055815:Young Adult
C582076:TUBB4A protein, human; D014404:Tubulin