Publications by authors named "Chihiro Ohba"

37 Publications

ATP6V0A1 encoding the a1-subunit of the V0 domain of vacuolar H-ATPases is essential for brain development in humans and mice.

Nat Commun 2021 04 8;12(1):2107. Epub 2021 Apr 8.

Department of Biochemistry, Hamamatsu University School of Medicine, Hamamatsu, Japan.

Vacuolar H-ATPases (V-ATPases) transport protons across cellular membranes to acidify various organelles. ATP6V0A1 encodes the a1-subunit of the V0 domain of V-ATPases, which is strongly expressed in neurons. However, its role in brain development is unknown. Here we report four individuals with developmental and epileptic encephalopathy with ATP6V0A1 variants: two individuals with a de novo missense variant (R741Q) and the other two individuals with biallelic variants comprising one almost complete loss-of-function variant and one missense variant (A512P and N534D). Lysosomal acidification is significantly impaired in cell lines expressing three missense ATP6V0A1 mutants. Homozygous mutant mice harboring human R741Q (Atp6v0a1) and A512P (Atp6v0a1) variants show embryonic lethality and early postnatal mortality, respectively, suggesting that R741Q affects V-ATPase function more severely. Lysosomal dysfunction resulting in cell death, accumulated autophagosomes and lysosomes, reduced mTORC1 signaling and synaptic connectivity, and lowered neurotransmitter contents of synaptic vesicles are observed in the brains of Atp6v0a1 mice. These findings demonstrate the essential roles of ATP6V0A1/Atp6v0a1 in neuronal development in terms of integrity and connectivity of neurons in both humans and mice.
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http://dx.doi.org/10.1038/s41467-021-22389-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8032687PMC
April 2021

Comprehensive analysis of coding variants highlights genetic complexity in developmental and epileptic encephalopathy.

Nat Commun 2019 06 7;10(1):2506. Epub 2019 Jun 7.

Department of Human Genetics, Yokohama City University Graduate School of Medicine, 3-9 Fukuura, Kanazawa-ku, Yokohama, 236-0004, Japan.

Although there are many known Mendelian genes linked to epileptic or developmental and epileptic encephalopathy (EE/DEE), its genetic architecture is not fully explained. Here, we address this incompleteness by analyzing exomes of 743 EE/DEE cases and 2366 controls. We observe that damaging ultra-rare variants (dURVs) unique to an individual are significantly overrepresented in EE/DEE, both in known EE/DEE genes and the other non-EE/DEE genes. Importantly, enrichment of dURVs in non-EE/DEE genes is significant, even in the subset of cases with diagnostic dURVs (P = 0.000215), suggesting oligogenic contribution of non-EE/DEE gene dURVs. Gene-based analysis identifies exome-wide significant (P = 2.04 × 10) enrichment of damaging de novo mutations in NF1, a gene primarily linked to neurofibromatosis, in infantile spasm. Together with accumulating evidence for roles of oligogenic or modifier variants in severe neurodevelopmental disorders, our results highlight genetic complexity in EE/DEE, and indicate that EE/DEE is not an aggregate of simple Mendelian disorders.
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http://dx.doi.org/10.1038/s41467-019-10482-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6555845PMC
June 2019

Identification of novel compound heterozygous mutations in ACO2 in a patient with progressive cerebral and cerebellar atrophy.

Mol Genet Genomic Med 2019 07 20;7(7):e00698. Epub 2019 May 20.

Department of Embryology, Institute for Developmental Research, Aichi Human Service Center, Kasugai, Japan.

Background: The tricarboxylic acid (TCA) cycle is a sequence of catabolic reactions within the mitochondrial matrix, and is a central pathway for cellular energy metabolism. Genetic defects affecting the TCA cycle are known to cause severe multisystem disorders.

Methods: We performed whole exome sequencing of genomic DNA of a patient with progressive cerebellar and cerebral atrophy, hypotonia, ataxia, seizure disorder, developmental delay, ophthalmological abnormalities and hearing loss. We also performed biochemical studies using patient fibroblasts.

Results: We identified new compound heterozygous mutations (c.1534G > A, p.Asp512Asn and c.1997G > C, p.Gly666Ala) in ACO2, which encodes aconitase 2, a component of the TCA cycle. In patient fibroblasts, the aconitase activity was reduced to 15% of that of the control, and the aconitase 2 level decreased to 36% of that of the control. As such a decrease in aconitase 2 in patient fibroblasts was partially restored by proteasome inhibition, mutant aconitase 2 was suggested to be relatively unstable and rapidly degraded after being synthesized. In addition, the activity of the father-derived variant of aconitase 2 (p.Gly666Ala), which had a mutation near the active center, was 55% of that of wild-type.

Conclusion: The marked reduction of aconitase activity in patient fibroblasts was due to the combination of decreased aconitase 2 amount and activity due to mutations. Reduced aconitase activity directly suppresses the TCA cycle, resulting in mitochondrial dysfunction, which may lead to symptoms similar to those observed in mitochondrial diseases.
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http://dx.doi.org/10.1002/mgg3.698DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6625133PMC
July 2019

Genetic landscape of Rett syndrome-like phenotypes revealed by whole exome sequencing.

J Med Genet 2019 06 6;56(6):396-407. Epub 2019 Mar 6.

Division of Pediatrics, Tokyo Metropolitan Tobu Medical Center for Persons with Developmental and Multiple Disabilities, Tokyo, Japan.

Background: Rett syndrome (RTT) is a characteristic neurological disease presenting with regressive loss of neurodevelopmental milestones. Typical RTT is generally caused by abnormality of methyl-CpG binding protein 2 (). Our objective to investigate the genetic landscape of -negative typical/atypical RTT and RTT-like phenotypes using whole exome sequencing (WES).

Methods: We performed WES on 77 -negative patients either with typical RTT (n=11), atypical RTT (n=22) or RTT-like phenotypes (n=44) incompatible with the RTT criteria.

Results: Pathogenic or likely pathogenic single-nucleotide variants in 28 known genes were found in 39 of 77 (50.6%) patients. WES-based CNV analysis revealed pathogenic deletions involving six known genes (including ) in 8 of 77 (10.4%) patients. Overall, diagnostic yield was 47 of 77 (61.0 %). Furthermore, strong candidate variants were found in four novel genes: a de novo variant in each of ATPase H transporting V0 subunit A1 (), ubiquitin-specific peptidase 8 () and microtubule-associated serine/threonine kinase 3 (), as well as biallelic variants in nuclear receptor corepressor 2 ().

Conclusions: Our study provides a new landscape including additional genetic variants contributing to RTT-like phenotypes, highlighting the importance of comprehensive genetic analysis.
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http://dx.doi.org/10.1136/jmedgenet-2018-105775DOI Listing
June 2019

De novo mutations of the ATP6V1A gene cause developmental encephalopathy with epilepsy.

Brain 2018 06;141(6):1703-1718

Pediatric Neurology, Neurogenetics and Neurobiology Unit and Laboratories, Children's Hospital A. Meyer-University of Florence, Florence, Italy.

V-type proton (H+) ATPase (v-ATPase) is a multi-subunit proton pump that regulates pH homeostasis in all eukaryotic cells; in neurons, v-ATPase plays additional and unique roles in synapse function. Through whole exome sequencing, we identified de novo heterozygous mutations (p.Pro27Arg, p.Asp100Tyr, p.Asp349Asn, p.Asp371Gly) in ATP6V1A, encoding the A subunit of v-ATPase, in four patients with developmental encephalopathy with epilepsy. Early manifestations, observed in all patients, were developmental delay and febrile seizures, evolving to encephalopathy with profound delay, hypotonic/dyskinetic quadriparesis and intractable multiple seizure types in two patients (p.Pro27Arg, p.Asp100Tyr), and to moderate delay with milder epilepsy in the other two (p.Asp349Asn, p.Asp371Gly). Modelling performed on the available prokaryotic and eukaryotic structures of v-ATPase predicted p.Pro27Arg to perturb subunit interaction, p.Asp100Tyr to cause steric hindrance and destabilize protein folding, p.Asp349Asn to affect the catalytic function and p.Asp371Gly to impair the rotation process, necessary for proton transport. We addressed the impact of p.Asp349Asn and p.Asp100Tyr mutations on ATP6V1A expression and function by analysing ATP6V1A-overexpressing HEK293T cells and patients' lymphoblasts. The p.Asp100Tyr mutant was characterized by reduced expression due to increased degradation. Conversely, no decrease in expression and clearance was observed for p.Asp349Asn. In HEK293T cells overexpressing either pathogenic or control variants, p.Asp349Asn significantly increased LysoTracker® fluorescence with no effects on EEA1 and LAMP1 expression. Conversely, p.Asp100Tyr decreased both LysoTracker® fluorescence and LAMP1 levels, leaving EEA1 expression unaffected. Both mutations decreased v-ATPase recruitment to autophagosomes, with no major impact on autophagy. Experiments performed on patients' lymphoblasts using the LysoSensor™ probe revealed lower pH of endocytic organelles for p.Asp349Asn and a reduced expression of LAMP1 with no effect on the pH for p.Asp100Tyr. These data demonstrate gain of function for p.Asp349Asn characterized by an increased proton pumping in intracellular organelles, and loss of function for p.Asp100Tyr with decreased expression of ATP6V1A and reduced levels of lysosomal markers. We expressed p.Asp349Asn and p.Asp100Tyr in rat hippocampal neurons and confirmed significant and opposite effects in lysosomal labelling. However, both mutations caused a similar defect in neurite elongation accompanied by loss of excitatory inputs, revealing that altered lysosomal homeostasis markedly affects neurite development and synaptic connectivity. This study provides evidence that de novo heterozygous ATP6V1A mutations cause a developmental encephalopathy with a pathomechanism that involves perturbations of lysosomal homeostasis and neuronal connectivity, uncovering a novel role for v-ATPase in neuronal development.
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http://dx.doi.org/10.1093/brain/awy092DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5972584PMC
June 2018

variants in and cause neurodevelopmental disorders.

Ann Clin Transl Neurol 2018 03 29;5(3):280-296. Epub 2018 Jan 29.

Department of Biochemistry Hamamatsu University School of Medicine 1-20-1 Handayama, Higashi-ku Hamamatsu 431-3192 Japan.

Objective: () and () isoforms of Calcium/calmodulin-dependent protein kinase II (CaMKII) play a pivotal role in neuronal plasticity and in learning and memory processes in the brain. Here, we explore the possible involvement of - and -CaMKII variants in neurodevelopmental disorders.

Methods: Whole-exome sequencing was performed for 976 individuals with intellectual disability, developmental delay, and epilepsy. The effect of and variants on CaMKII structure and firing of neurons was evaluated by computational structural analysis, immunoblotting, and electrophysiological analysis.

Results: We identified a total of five de novo and variants in three and two individuals, respectively. Seizures were common to three individuals with variants. Using a minigene splicing assay, we demonstrated that a splice site variant caused skipping of exon 11 leading to an in-frame deletion of the regulatory segment of CaMKII . By structural analysis, four missense variants are predicted to impair the interaction between the kinase domain and the regulatory segment responsible for the autoinhibition of its kinase activity. The Thr286/Thr287 phosphorylation as a result of release from autoinhibition was increased in three mutants when the mutants were stably expressed in Neuro-2a neuroblastoma cells. Expression of a CaMKII mutant in primary hippocampal neurons significantly increased A-type K currents, which facilitated spike repolarization of single action potentials.

Interpretation: Our data highlight the importance of CaMKII and CaMKII and their autoinhibitory regulation in human brain function, and suggest the enhancement of A-type K currents as a possible pathophysiological basis.
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http://dx.doi.org/10.1002/acn3.528DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5846454PMC
March 2018

De novo HDAC8 mutation causes Rett-related disorder with distinctive facial features and multiple congenital anomalies.

Brain Dev 2018 May 5;40(5):406-409. Epub 2018 Mar 5.

Department of Pediatrics, Research Center for Children, Research Center for Rett Syndrome, St. Mary's Hospital, Kurume, Fukuoka 830-8543, Japan. Electronic address:

We present a unique 11-year-old girl showing clinical features of Rett-related disorder with distinctive facial features and multiple congenital anomalies including ocular hypertelorism, arched eyebrows, a broad nose, dental anomalies, congenital heart disease, truncal obesity, and epilepsy. A novel de novo mutation in histone deacetylase 8 (HDAC8) (c.652G > T, p.Gly218Cys) was confirmed by whole exome sequencing and Sanger sequencing. X-chromosome inactivation analysis on DNA isolated from peripheral blood lymphocytes revealed a completely skewed pattern associated with an inactive maternal allele. Late clinical loss of acquired purposeful hand movements and psychomotor deterioration may be a feature of Rett-related disorder, while distinctive facial features and multiple congenital anomalies are reminiscent of Cornelia de Lange syndrome.
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http://dx.doi.org/10.1016/j.braindev.2017.12.013DOI Listing
May 2018

Biallelic Variants in CNPY3, Encoding an Endoplasmic Reticulum Chaperone, Cause Early-Onset Epileptic Encephalopathy.

Am J Hum Genet 2018 02 27;102(2):321-329. Epub 2018 Jan 27.

Department of Biochemistry, Hamamatsu University School of Medicine, Hamamatsu 431-3192, Japan. Electronic address:

Early-onset epileptic encephalopathies, including West syndrome (WS), are a group of neurological disorders characterized by developmental impairments and intractable seizures from early infancy. We have now identified biallelic CNPY3 variants in three individuals with WS; these include compound-heterozygous missense and frameshift variants in a family with two affected siblings (individuals 1 and 2) and a homozygous splicing variant in a consanguineous family (individual 3). All three individuals showed hippocampal malrotation. In individuals 1 and 2, electroencephalography (EEG) revealed characteristic fast waves and diffuse sharp- and slow-wave complexes. The fast waves were clinically associated with seizures. CNPY3 encodes a co-chaperone in the endoplasmic reticulum and regulates the subcellular distribution and responses of multiple Toll-like receptors. The amount of CNPY3 in lymphoblastoid cells derived from individuals 1 and 2 was severely lower than that in control cells. Cnpy3-knockout mice exhibited spastic or dystonic features under resting conditions and hyperactivity and anxiolytic behavior during the open field test. Also, their resting EEG showed enhanced activity in the fast beta frequency band (20-35 Hz), which could mimic the fast waves in individuals 1 and 2. These data suggest that CNPY3 and Cnpy3 perform essential roles in brain function in addition to known Toll-like receptor-dependent immune responses.
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http://dx.doi.org/10.1016/j.ajhg.2018.01.004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5985471PMC
February 2018

Novel recessive mutations in MSTO1 cause cerebellar atrophy with pigmentary retinopathy.

J Hum Genet 2018 Mar 16;63(3):263-270. Epub 2018 Jan 16.

Department of Human Genetics, Graduate School of Medicine, Yokohama City University, Yokohama, Japan.

Misato 1, mitochondrial distribution and morphology regulator (encoded by the MSTO1 gene), is involved in mitochondrial distribution and morphology. Recently, MSTO1 mutations have been shown to cause clinical manifestations suggestive of mitochondrial dysfunction, such as muscle weakness, short stature, motor developmental delay, and cerebellar atrophy. Both autosomal dominant and recessive modes of inheritance have been suggested. We performed whole-exome sequencing in two unrelated patients showing cerebellar atrophy, intellectual disability, and pigmentary retinopathy. Three novel mutations were identified: c.836 G > A (p.Arg279His), c.1099-1 G > A (p.Val367Trpfs*2), and c.79 C > T (p.Gln27*). Both patients had compound heterozygous mutations with a combination of protein-truncation mutation and missense mutation, the latter shared by them both. This survey of two patients with recessive and novel MSTO1 mutations provides additional clinical and genetic information on the pathogenicity of MSTO1 in humans.
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http://dx.doi.org/10.1038/s10038-017-0405-8DOI Listing
March 2018

Epileptic apnea in a patient with inherited glycosylphosphatidylinositol anchor deficiency and PIGT mutations.

Brain Dev 2018 Jan 17;40(1):53-57. Epub 2017 Jul 17.

Department of Child Neurology, National Center Hospital, National Center of Neurology and Psychiatry, Tokyo, Japan.

We report an 11-month-old boy with acetazolamide-responsive epileptic apnea and inherited glycosylphosphatidylinositol (GPI)-anchor deficiency who presented with decreased serum alkaline phosphatase associated with compound PIGT mutations. The patient exhibited congenital anomalies, severe intellectual disability, and seizures, including epileptic apnea with epileptiform discharges from bilateral temporal areas. Brain magnetic resonance imaging revealed delayed myelination and progressive atrophy of the brainstem, cerebellum, and cerebrum. Whole-exome sequencing revealed compound heterozygous mutations in PIGT (c.250G>T, p.Glu84X and c.1096G>T, p.Gly366Trp), which encodes a subunit of the GPI transamidase complex. Flow cytometry revealed decreased expression of CD16 (a GPI anchor protein) on granulocytes, supporting the putative pathogenicity of the mutations. Phenobarbital, clonazepam, and potassium bromide decreased the frequency of tonic seizure and acetazolamide decreased epileptic apnea. To our knowledge, this is the first reported case of intractable seizures accompanied by epileptic apnea associated with GPI anchor deficiency and a compound PIGT mutation.
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http://dx.doi.org/10.1016/j.braindev.2017.06.005DOI Listing
January 2018

Neuroimaging findings in Joubert syndrome with C5orf42 gene mutations: A milder form of molar tooth sign and vermian hypoplasia.

J Neurol Sci 2017 May 1;376:7-12. Epub 2017 Mar 1.

Department of Human Genetics, Yokohama City University Graduate School of Medicine, Yokohama, Japan.

Purpose: Little is known regarding neuroimaging-genotype correlations in Joubert syndrome (JBTS). To elucidate one of these correlations, we investigated the neuroimaging findings of JBTS patients with C5orf42 mutations.

Materials And Methods: Neuroimaging findings in five JBTS patients with C5orf42 mutations were retrospectively assessed with regard to the infratentorial and supratentorial structures on T1-magnetization prepared rapid gradient echo (MPRAGE), T2-weighted images, and color-coded fractional anisotropy (FA) maps; the findings were compared to those in four JBTS patients with mutations in other genes (including three with AHI1 and one with TMEM67 mutations).

Results: In C5orf42-mutant patients, the infratentorial magnetic resonance (MR) images showed normal or minimally thickened and minimally elongated superior cerebellar peduncles (SCP), normal or minimally deepened interpeduncular fossa (IF), and mild vermian hypoplasia (VH). However, in other patients, all had severe abnormalities in the SCP and IF, and moderate to marked VH. Supratentorial abnormalities were found in one individual in other JBTS. In JBTS with all mutations, color-coded FA maps showed the absence of decussation of the SCP (DSCP).

Conclusion: The morphological neuroimaging findings in C5orf42-mutant JBTS were distinctly mild and made diagnosis difficult. However, the absence of DSCP on color-coded FA maps may facilitate the diagnosis of JBTS.
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http://dx.doi.org/10.1016/j.jns.2017.02.065DOI Listing
May 2017

A novel mutation in the proteolytic domain of LONP1 causes atypical CODAS syndrome.

J Hum Genet 2017 Jun 2;62(6):653-655. Epub 2017 Feb 2.

Department of Pediatric Neurology, Miyagi Children's Hospital, Miyagi, Japan.

Cerebral, ocular, dental, auricular, skeletal (CODAS) syndrome is a rare autosomal recessive multisystem disorder caused by mutations in LONP1. It is characterized by intellectual disability, cataracts, delayed tooth eruption, malformed auricles and skeletal abnormalities. We performed whole-exome sequencing on a 12-year-old Japanese male with severe intellectual disability, congenital bilateral cataracts, spasticity, hypotonia with motor regression and progressive cerebellar atrophy with hyperintensity of the cerebellar cortex on T2-weighted images. We detected compound heterozygous mutation in LONP1. One allele contained a paternally inherited frameshift mutation (p.Ser100Glnfs*46). The other allele contained a maternally inherited missense mutation (p.Arg786Trp), which was predicted to be pathogenic by web-based prediction tools. The two mutations were not found in Exome Variant Server or our 575 in-house control exomes. Some features were not consistent with CODAS syndrome but overlapped with Marinesco-Sjögren syndrome, a multisystem disorder caused by a mutation in SIL1. An atypical mutation site may result in atypical presentation of the LONP1 mutation.
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http://dx.doi.org/10.1038/jhg.2017.11DOI Listing
June 2017

Biallelic TBCD Mutations Cause Early-Onset Neurodegenerative Encephalopathy.

Am J Hum Genet 2016 Oct 22;99(4):950-961. Epub 2016 Sep 22.

Department of Human Genetics, Yokohama City University Graduate School of Medicine, Yokohama 236-0004, Japan.

We describe four families with affected siblings showing unique clinical features: early-onset (before 1 year of age) progressive diffuse brain atrophy with regression, postnatal microcephaly, postnatal growth retardation, muscle weakness/atrophy, and respiratory failure. By whole-exome sequencing, we identified biallelic TBCD mutations in eight affected individuals from the four families. TBCD encodes TBCD (tubulin folding co-factor D), which is one of five tubulin-specific chaperones playing a pivotal role in microtubule assembly in all cells. A total of seven mutations were found: five missense mutations, one nonsense, and one splice site mutation resulting in a frameshift. In vitro cell experiments revealed the impaired binding between most mutant TBCD proteins and ARL2, TBCE, and β-tubulin. The in vivo experiments using olfactory projection neurons in Drosophila melanogaster indicated that the TBCD mutations caused loss of function. The wide range of clinical severity seen in this neurodegenerative encephalopathy may result from the residual function of mutant TBCD proteins. Furthermore, the autopsied brain from one deceased individual showed characteristic neurodegenerative findings: cactus and somatic sprout formations in the residual Purkinje cells in the cerebellum, which are also seen in some diseases associated with mitochondrial impairment. Defects of microtubule formation caused by TBCD mutations may underlie the pathomechanism of this neurodegenerative encephalopathy.
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http://dx.doi.org/10.1016/j.ajhg.2016.08.005DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5065661PMC
October 2016

Impaired neuronal KCC2 function by biallelic SLC12A5 mutations in migrating focal seizures and severe developmental delay.

Sci Rep 2016 07 20;6:30072. Epub 2016 Jul 20.

Department of Human Genetics, Graduate School of Medicine, Yokohama City University, 3-9 Fukuura, Yokohama 236-0004, Japan.

Epilepsy of infancy with migrating focal seizures (EIMFS) is one of the early-onset epileptic syndromes characterized by migrating polymorphous focal seizures. Whole exome sequencing (WES) in ten sporadic and one familial case of EIMFS revealed compound heterozygous SLC12A5 (encoding the neuronal K(+)-Cl(-) co-transporter KCC2) mutations in two families: c.279 + 1G > C causing skipping of exon 3 in the transcript (p.E50_Q93del) and c.572 C >T (p.A191V) in individuals 1 and 2, and c.967T > C (p.S323P) and c.1243 A > G (p.M415V) in individual 3. Another patient (individual 4) with migrating multifocal seizures and compound heterozygous mutations [c.953G > C (p.W318S) and c.2242_2244del (p.S748del)] was identified by searching WES data from 526 patients and SLC12A5-targeted resequencing data from 141 patients with infantile epilepsy. Gramicidin-perforated patch-clamp analysis demonstrated strongly suppressed Cl(-) extrusion function of E50_Q93del and M415V mutants, with mildly impaired function of A191V and S323P mutants. Cell surface expression levels of these KCC2 mutants were similar to wildtype KCC2. Heterologous expression of two KCC2 mutants, mimicking the patient status, produced a significantly greater intracellular Cl(-) level than with wildtype KCC2, but less than without KCC2. These data clearly demonstrated that partially disrupted neuronal Cl(-) extrusion, mediated by two types of differentially impaired KCC2 mutant in an individual, causes EIMFS.
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http://dx.doi.org/10.1038/srep30072DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4951812PMC
July 2016

A female case of aromatic l-amino acid decarboxylase deficiency responsive to MAO-B inhibition.

Brain Dev 2016 Nov 29;38(10):959-963. Epub 2016 Jun 29.

Department of Pediatrics, Jichi Medical University, Japan.

Background: Aromatic l-amino acid decarboxylase (AADC) deficiency is an autosomal recessive disorder, caused by defects in the DDC gene. AADC catalyzes the synthesis of the neurotransmitters dopamine and serotonin from l-dopa and 5-HT respectively. Most patients are bed ridden for life, with little response to treatment. We now report one female patient who improved her motor and cognitive function after being prescribed a MAO-B inhibitor.

Case: A five years old female presented with the typical clinical features of AADC deficiency. She was floppy, with no head control, had intermittent limb dystonia, and an upward deviation of the eyes (oculogyric crisis). This patient possessed compound heterozygous mutations in DDC (p.Trp105Cys, p.Pro129Ser), with a CSF draw indicating abnormal patterns of biogenic amine metabolites, compatible with AADC deficiency.

Results: After her diagnosis at 3years of age, medication with levodopa and vitamin B6 failed to show any efficacy. Subsequent administration with a MAO-B inhibitor improved her psychomotor functions to the extent that at 5years of age she could walk several meters with support.

Conclusion: Our analyses of chemical findings, together with in silico structure predictions, lead us to hypothesize that this patient retained some AADC activity. In these cases, accurate diagnosis and early treatment should improve patient outcome.
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http://dx.doi.org/10.1016/j.braindev.2016.06.002DOI Listing
November 2016

The first genetically confirmed Japanese patient with mucolipidosis type IV.

Clin Case Rep 2016 May 13;4(5):509-12. Epub 2016 Apr 13.

Department of Human Genetics Graduate School of Medicine Yokohama City University Yokohama Japan.

Mucolipidosis type IV (MLIV) is a rare neurodegenerative disorder characterized by severe psychomotor delay and visual impairment. We report the brain pathology in the first Japanese patient of MLIV with a novel homozygous missense mutation in MCOLN1. We detected the localized increase in p62-reactive astrocytes in the basal ganglia.
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http://dx.doi.org/10.1002/ccr3.540DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4856247PMC
May 2016

De novo GABRA1 mutations in Ohtahara and West syndromes.

Epilepsia 2016 Apr 25;57(4):566-73. Epub 2016 Feb 25.

Department of Human Genetics, Yokohama City University Graduate School of Medicine, Yokohama, Japan.

Objective: GABRA1 mutations have been identified in patients with familial juvenile myoclonic epilepsy, sporadic childhood absence epilepsy, and idiopathic familial generalized epilepsy. In addition, de novo GABRA1 mutations were recently reported in a patient with infantile spasms and four patients with Dravet syndrome. Those reports suggest that GABRA1 mutations are associated with infantile epilepsy including early onset epileptic encephalopathies. In this study, we searched for GABRA1 mutations in patients with infantile epilepsy to investigate the phenotypic spectrum of GABRA1 mutations.

Methods: In total, 526 and 145 patients with infantile epilepsy were analyzed by whole-exome sequencing and GABRA1-targeted resequencing, respectively.

Results: We identified five de novo missense GABRA1 mutations in six unrelated patients. A p.R112Q mutation in the long extracellular N-terminus was identified in a patient with infantile epilepsy; p.P260L, p.M263T, and p.M263I in transmembrane spanning domain 1 (TM1) were identified in three unrelated patients with West syndrome and a patient with Ohtahara syndrome, respectively; and p.V287L in TM2 was identified in a patient with unclassified early onset epileptic encephalopathy. Four of these mutations have not been observed previously.

Significance: Our study suggests that de novo GABRA1 mutations can cause early onset epileptic encephalopathies, including Ohtahara syndrome and West syndrome.
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http://dx.doi.org/10.1111/epi.13344DOI Listing
April 2016

Milder progressive cerebellar atrophy caused by biallelic SEPSECS mutations.

J Hum Genet 2016 Jun 18;61(6):527-31. Epub 2016 Feb 18.

Department of Human Genetics, Graduate School of Medicine, Yokohama City University, Yokohama, Japan.

Cerebellar atrophy is recognized in various types of childhood neurological disorders with clinical and genetic heterogeneity. Genetic analyses such as whole exome sequencing are useful for elucidating the genetic basis of these conditions. Pathological recessive mutations in Sep (O-phosphoserine) tRNA:Sec (selenocysteine) tRNA synthase (SEPSECS) have been reported in a total of 11 patients with pontocerebellar hypoplasia type 2, progressive cerebellocerebral atrophy or progressive encephalopathy, yet detailed clinical features are limited to only four patients. We identified two new families with progressive cerebellar atrophy, and by whole exome sequencing detected biallelic SEPSECS mutations: c.356A>G (p.Asn119Ser) and c.77delG (p.Arg26Profs*42) in family 1, and c.356A>G (p.Asn119Ser) and c.467G>A (p.Arg156Gln) in family 2. Their development was slightly delayed regardless of normal brain magnetic resonance imaging (MRI) in infancy. The progression of clinical symptoms in these families is evidently slower than in previously reported cases, and the cerebellar atrophy milder by brain MRI, indicating that SEPSECS mutations are also involved in milder late-onset cerebellar atrophy.
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http://dx.doi.org/10.1038/jhg.2016.9DOI Listing
June 2016

De novo KCNB1 mutations in infantile epilepsy inhibit repetitive neuronal firing.

Sci Rep 2015 Oct 19;5:15199. Epub 2015 Oct 19.

Department of Human Genetics, Yokohama City University Graduate School of Medicine, Yokohama, Japan.

The voltage-gated Kv2.1 potassium channel encoded by KCNB1 produces the major delayed rectifier potassium current in pyramidal neurons. Recently, de novo heterozygous missense KCNB1 mutations have been identified in three patients with epileptic encephalopathy and a patient with neurodevelopmental disorder. However, the frequency of KCNB1 mutations in infantile epileptic patients and their effects on neuronal activity are yet unknown. We searched whole exome sequencing data of a total of 437 patients with infantile epilepsy, and found novel de novo heterozygous missense KCNB1 mutations in two patients showing psychomotor developmental delay and severe infantile generalized seizures with high-amplitude spike-and-wave electroencephalogram discharges. The mutation located in the channel voltage sensor (p.R306C) disrupted sensitivity and cooperativity of the sensor, while the mutation in the channel pore domain (p.G401R) selectively abolished endogenous Kv2 currents in transfected pyramidal neurons, indicating a dominant-negative effect. Both mutants inhibited repetitive neuronal firing through preventing production of deep interspike voltages. Thus KCNB1 mutations can be a rare genetic cause of infantile epilepsy, and insufficient firing of pyramidal neurons would disturb both development and stability of neuronal circuits, leading to the disease phenotypes.
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http://dx.doi.org/10.1038/srep15199DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4609934PMC
October 2015

De novo KIF1A mutations cause intellectual deficit, cerebellar atrophy, lower limb spasticity and visual disturbance.

J Hum Genet 2015 Dec 10;60(12):739-42. Epub 2015 Sep 10.

Department of Human Genetics, Yokohama City University, Graduate School of Medicine, Yokohama, Japan.

Recently, de novo KIF1A mutations were identified in patients with intellectual disability, spasticity and cerebellar atrophy and/or optic nerve atrophy. In this study, we analyzed a total of 62 families, including 68 patients with genetically unsolved childhood cerebellar atrophy, by whole-exome sequencing (WES). We identified five de novo missense KIF1A mutations, including only one previously reported mutation (p.Arg316Trp). All the mutations are located in the motor domain of KIF1A. In all patients, initial symptom onset was during the infantile period, and included developmental delay in three patients and gait disturbance in two. Thereafter, they showed gait disturbances, exaggerated deep tendon reflexes, cerebellar symptoms and cerebellar atrophy on brain magnetic resonance imaging. Four patients showed lower limb spasticity, upper limb clumsiness and visual disturbances. Nerve conduction study revealed peripheral neuropathy in three patients. This study further delineates clinical features of de novo KIF1A mutations. Genetic testing of KIF1A should be considered in children with developmental delay, cerebellar atrophy and pyramidal features.
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http://dx.doi.org/10.1038/jhg.2015.108DOI Listing
December 2015

De novo KCNT1 mutations in early-onset epileptic encephalopathy.

Epilepsia 2015 Sep 3;56(9):e121-8. Epub 2015 Jul 3.

Department of Human Genetics, Graduate School of Medicine, Yokohama City University, Yokohama, Japan.

KCNT1 mutations have been found in epilepsy of infancy with migrating focal seizures (EIMFS; also known as migrating partial seizures in infancy), autosomal dominant nocturnal frontal lobe epilepsy, and other types of early onset epileptic encephalopathies (EOEEs). We performed KCNT1-targeted next-generation sequencing (207 samples) and/or whole-exome sequencing (229 samples) in a total of 362 patients with Ohtahara syndrome, West syndrome, EIMFS, or unclassified EOEEs. We identified nine heterozygous KCNT1 mutations in 11 patients: nine of 18 EIMFS cases (50%) in whom migrating foci were observed, one of 180 West syndrome cases (0.56%), and one of 66 unclassified EOEE cases (1.52%). KCNT1 mutations occurred de novo in 10 patients, and one was transmitted from the patient's mother who carried a somatic mosaic mutation. The mutations accumulated in transmembrane segment 5 (2/9, 22.2%) and regulators of K(+) conductance domains (7/9, 77.8%). Five of nine mutations were recurrent. Onset ages ranged from the neonatal period (<1 month) in five patients (5/11, 45.5%) to 1-4 months in six patients (6/11, 54.5%). A generalized attenuation of background activity on electroencephalography was seen in six patients (6/11, 54.5%). Our study demonstrates that the phenotypic spectrum of de novo KCNT1 mutations is largely restricted to EIMFS.
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http://dx.doi.org/10.1111/epi.13072DOI Listing
September 2015

Somatic Mutations in the MTOR gene cause focal cortical dysplasia type IIb.

Ann Neurol 2015 Sep 3;78(3):375-86. Epub 2015 Jul 3.

Department of Human Genetics, Yokohama City University Graduate School of Medicine, Yokohama, Japan.

Objective: Focal cortical dysplasia (FCD) type IIb is a cortical malformation characterized by cortical architectural abnormalities, dysmorphic neurons, and balloon cells. It has been suggested that FCDs are caused by somatic mutations in cells in the developing brain. Here, we explore the possible involvement of somatic mutations in FCD type IIb.

Methods: We collected a total of 24 blood-brain paired samples with FCD, including 13 individuals with FCD type IIb, 5 with type IIa, and 6 with type I. We performed whole-exome sequencing using paired samples from 9 of the FCD type IIb subjects. Somatic MTOR mutations were identified and further investigated using all 24 paired samples by deep sequencing of the entire gene's coding region. Somatic MTOR mutations were confirmed by droplet digital polymerase chain reaction. The effect of MTOR mutations on mammalian target of rapamycin (mTOR) kinase signaling was evaluated by immunohistochemistry and Western blotting analyses of brain samples and by in vitro transfection experiments.

Results: We identified four lesion-specific somatic MTOR mutations in 6 of 13 (46%) individuals with FCD type IIb showing mutant allele rates of 1.11% to 9.31%. Functional analyses showed that phosphorylation of ribosomal protein S6 in FCD type IIb brain tissues with MTOR mutations was clearly elevated, compared to control samples. Transfection of any of the four MTOR mutants into HEK293T cells led to elevated phosphorylation of 4EBP, the direct target of mTOR kinase.

Interpretation: We found low-prevalence somatic mutations in MTOR in FCD type IIb, indicating that activating somatic mutations in MTOR cause FCD type IIb.
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http://dx.doi.org/10.1002/ana.24444DOI Listing
September 2015

Compound heterozygous GFM2 mutations with Leigh syndrome complicated by arthrogryposis multiplex congenita.

J Hum Genet 2015 Sep 28;60(9):509-13. Epub 2015 May 28.

Department of Pediatrics, Sapporo Medical University School of Medicine, Sapporo, Japan.

Defects in the mitochondrial translation apparatus can impair energy production in affected tissues and organs. Most components of this apparatus are encoded by nuclear genes, including GFM2, which encodes a mitochondrial ribosome recycling factor. A few patients with mutations in some of these genes have been reported to date. Here, we present two female siblings with arthrogryposis multiplex congenita, optic atrophy and severe mental retardation. The younger sister had a progressive cerebellar atrophy and bilateral neuropathological findings in the brainstem. Although her cerebrospinal fluid (CSF) levels of lactate and pyruvate were not increased, brain magnetic resonance spectroscopy showed a lactate peak. Additionally, her CSF lactate/pyruvate and serum beta-hydroxybutyrate/acetoacetate ratios were high, and levels of oxidative phosphorylation in skin fibroblasts were reduced. We therefore diagnosed Leigh syndrome. Genomic investigation confirmed the presence of compound heterozygous GFM2 mutations (c.206+4A>G and c.2029-1G>A) in both siblings, causing aberrant splicing with premature stop codons (p.Gly50Glufs*4 and p.Ala677Leufs*2, respectively). These findings suggest that GFM2 mutations could be causative of a phenotype of Leigh syndrome with arthrogryposis multiplex congenita.
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http://dx.doi.org/10.1038/jhg.2015.57DOI Listing
September 2015

De novo SHANK3 mutation causes Rett syndrome-like phenotype in a female patient.

Am J Med Genet A 2015 Jul 30;167(7):1593-6. Epub 2015 Apr 30.

Departments of Pediatrics and Child Health, Kurume University School of Medicine, Kurume, Fukuoka, Japan.

Rett syndrome (RTT) is a neurodevelopmental disorder predominantly affecting females. Females with the MECP2 mutations exhibit a broad spectrum of clinical manifestations ranging from classical Rett syndrome to asymptomatic carriers. Mutations of genes encoding cyclin-dependent kinase-like 5 (CDKL5) and forkhead box G1 (FOXG1) are also found in early onset RTT variants. Here, we present the first report of a female patient with RTT-like phenotype caused by SHANK3 (SH3 and multiple ankylin repeat domain 3) mutation, indicating that the clinical spectrum of SHANK3 mutations may extend to RTT-like phenotype in addition to (severe) developmental delay, absence of expressive speech, autistic behaviors and intellectual disability.
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http://dx.doi.org/10.1002/ajmg.a.36775DOI Listing
July 2015

GRIN1 mutations cause encephalopathy with infantile-onset epilepsy, and hyperkinetic and stereotyped movement disorders.

Epilepsia 2015 Jun 10;56(6):841-8. Epub 2015 Apr 10.

Department of Human Genetics, Graduate School of Medicine, Yokohama City University, Yokohama, Japan.

Objective: Recently, de novo mutations in GRIN1 have been identified in patients with nonsyndromic intellectual disability and epileptic encephalopathy. Whole exome sequencing (WES) analysis of patients with genetically unsolved epileptic encephalopathies identified four patients with GRIN1 mutations, allowing us to investigate the phenotypic spectrum of GRIN1 mutations.

Methods: Eighty-eight patients with unclassified early onset epileptic encephalopathies (EOEEs) with an age of onset <1 year were analyzed by WES. The effect of mutations on N-methyl-D-aspartate (NMDA) receptors was examined by mapping altered amino acids onto three-dimensional models.

Results: We identified four de novo missense GRIN1 mutations in 4 of 88 patients with unclassified EOEEs. In these four patients, initial symptoms appeared within 3 months of birth, including hyperkinetic movements in two patients (2/4, 50%), and seizures in two patients (2/4, 50%). Involuntary movements, severe developmental delay, and intellectual disability were recognized in all four patients. In addition, abnormal eye movements resembling oculogyric crises and stereotypic hand movements were observed in two and three patients, respectively. All the four patients exhibited only nonspecific focal and diffuse epileptiform abnormality, and never showed suppression-burst or hypsarrhythmia during infancy. A de novo mosaic mutation (c.1923G>A) with a mutant allele frequency of 16% (in DNA of blood leukocytes) was detected in one patient. Three mutations were located in the transmembrane domain (3/4, 75%), and one in the extracellular loop near transmembrane helix 1. All the mutations were predicted to impair the function of the NMDA receptor.

Significance: Clinical features of de novo GRIN1 mutations include infantile involuntary movements, seizures, and hand stereotypies, suggesting that GRIN1 mutations cause encephalopathy resulting in seizures and movement disorders.
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http://dx.doi.org/10.1111/epi.12987DOI Listing
June 2015

Sporadic infantile-onset spinocerebellar ataxia caused by missense mutations of the inositol 1,4,5-triphosphate receptor type 1 gene.

J Neurol 2015 May 21;262(5):1278-84. Epub 2015 Mar 21.

Department of Child Neurology, National Center of Neurology and Psychiatry, 4-1-1 Ogawahigashi-cho, Kodaira, Tokyo, 187-8551, Japan,

Mutations in the inositol 1,4,5-triphosphate receptor type 1 gene (ITPR1) have been identified in families with early-onset spinocerebellar ataxia type 29 (SCA29) and late-onset SCA15, but have not been found in sporadic infantile-onset cerebellar ataxia. We examined if mutations of ITPR1 are also involved in sporadic infantile-onset SCA. Sixty patients with childhood-onset cerebellar atrophy of unknown etiology and their families were examined by whole-exome sequencing. We found de novo heterozygous ITPR1 missense mutations in four unrelated patients with sporadic infantile-onset, nonprogressive cerebellar ataxia. Patients displayed nystagmus, tremor, and hypotonia from very early infancy. Nonprogressive ataxia, motor delay, and mild cognitive deficits were common clinical findings. Brain magnetic resonance imaging revealed slowly progressive cerebellar atrophy. ITPR1 missense mutations cause infantile-onset cerebellar ataxia. ITPR1-related SCA includes sporadic infantile-onset cerebellar ataxia as well as SCA15 and SCA29.
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http://dx.doi.org/10.1007/s00415-015-7705-8DOI Listing
May 2015

Preparation of molecule-responsive microsized hydrogels via photopolymerization for smart microchannel microvalves.

Macromol Rapid Commun 2015 Mar 26;36(6):515-9. Epub 2015 Jan 26.

Department of Chemistry and Materials Engineering, Kansai University, 3-3-35, Yamate-cho, Suita, Osaka, 564-8680, Japan.

Microdevices designed for practical environmental pollution monitoring need to detect specific pollutants such as dioxins. Bisphenol A (BPA) has been widely used as a monomer for the synthesis of polycarbonate and epoxy resins. However, the recent discovery of its high potential ability to disrupt human endocrine systems has made the development of smart systems and microdevices for its detection and removal necessary. Molecule-responsive microsized hydrogels with β-cycrodextrin (β-CD) as ligands are prepared by photopolymerization using a fluorescence microscope. The molecule-responsive micro-hydrogels show ultra-quick shrinkage in response to target BPA. Furthermore, the flow rate of a microchannel is autonomously regulated by the molecule-responsive shrinking of their hydrogels as smart microvalves.
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http://dx.doi.org/10.1002/marc.201400676DOI Listing
March 2015

Detecting copy-number variations in whole-exome sequencing data using the eXome Hidden Markov Model: an 'exome-first' approach.

J Hum Genet 2015 Apr 22;60(4):175-82. Epub 2015 Jan 22.

Department of Human Genetics, Yokohama City University Graduate School of Medicine, Yokohama, Japan.

Whole-exome sequencing (WES) is becoming a standard tool for detecting nucleotide changes, and determining whether WES data can be used for the detection of copy-number variations (CNVs) is of interest. To date, several algorithms have been developed for such analyses, although verification is needed to establish if they fit well for the appropriate purpose, depending on the characteristics of each algorithm. Here, we performed WES CNV analysis using the eXome Hidden Markov Model (XHMM). We validated its performance using 27 rare CNVs previously identified by microarray as positive controls, finding that the detection rate was 59%, or higher (89%) with three or more targets. XHMM can be effectively used, especially for the detection of >200 kb CNVs. XHMM may be useful for deletion breakpoint detection. Next, we applied XHMM to genetically unsolved patients, demonstrating successful identification of pathogenic CNVs: 1.5-1.9-Mb deletions involving NSD1 in patients with unknown overgrowth syndrome leading to the diagnosis of Sotos syndrome, and 6.4-Mb duplication involving MECP2 in affected brothers with late-onset spasm and progressive cerebral/cerebellar atrophy confirming the clinical suspect of MECP2 duplication syndrome. The possibility of an 'exome-first' approach for clinical genetic investigation may be considered to save the cost of multiple investigations.
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http://dx.doi.org/10.1038/jhg.2014.124DOI Listing
April 2015

Early onset epileptic encephalopathy caused by de novo SCN8A mutations.

Epilepsia 2014 Jul 2;55(7):994-1000. Epub 2014 Jun 2.

Department of Human Genetics, Graduate School of Medicine, Yokohama City University, Yokohama, Japan; Department of Clinical Neurology and Stroke Medicine, Yokohama City University, Yokohama, Japan.

Objective: De novo SCN8A mutations have been reported in patients with epileptic encephalopathy. Herein we report seven patients with de novo heterozygous SCN8A mutations, which were found in our comprehensive genetic analysis (target capture or whole-exome sequencing) for early onset epileptic encephalopathies (EOEEs).

Methods: A total of 163 patients with EOEEs without mutations in known genes, including 6 with malignant migrating partial seizures in infancy (MMPSI), and 60 with unclassified EOEEs, were analyzed by target capture (28 samples) or whole-exome sequencing (135 samples).

Results: We identified de novo SCN8A mutations in 7 patients: 6 of 60 unclassified EOEEs (10.0%), and one of 6 MMPSI cases (16.7%). The mutations were scattered through the entire gene: four mutations were located in linker regions, two in the fourth transmembrane segments, and one in the C-terminal domain. The type of the initial seizures was variable including generalized tonic-clonic, atypical absence, partial, apneic attack, febrile convulsion, and loss of tone and consciousness. Onset of seizures was during the neonatal period in two patients, and between 3 and 7 months of age in five patients. Brain magnetic resonance imaging (MRI) showed cerebellar and cerebral atrophy in one and six patients, respectively. All patients with SCN8A missense mutations showed initially uncontrollable seizures by any drugs, but eventually one was seizure-free and three were controlled at the last examination. All patients showed developmental delay or regression in infancy, resulting in severe intellectual disability.

Significance: Our data reveal that SCN8A mutations can cause variable phenotypes, most of which can be diagnosed as unclassified EOEEs, and rarely as MMPSI. Together with previous reports, our study further indicates that genetic testing of SCN8A should be considered in children with unclassified severe epilepsy.
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http://dx.doi.org/10.1111/epi.12668DOI Listing
July 2014

PIGA mutations cause early-onset epileptic encephalopathies and distinctive features.

Neurology 2014 May 4;82(18):1587-96. Epub 2014 Apr 4.

From the Department of Pediatrics (M.K., K.H.), Yamagata University Faculty of Medicine, Yamagata; Department of Human Genetics (H.S., C.O., M.N., Y.T., N. Miyake, N. Matsumoto), Yokohama City University Graduate School of Medicine, Yokohama; Department of Immunoregulation (Y.M., T.K.), Research Institute for Microbial Diseases, and WPI Immunology Frontier Research Center, Osaka University, Suita; Division of Neurology (K.K., R.M., S.-i.H.), Saitama Children's Medical Center, Saitama; Division of Neurology (S.W.), Miyagi Children's Hospital, Sendai; Division of Neurology (M.I., H.O.), Clinical Research Institute, Kanagawa Children's Medical Center, Yokohama; Department of Pediatrics (K.M.), Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama; Department of Pediatrics (R.T.), Aomori Prefectural Central Hospital, Aomori; and Department of Pediatrics (H.O.), Jichi Medical School, Tochigi, Japan.

Objective: To investigate the clinical spectrum caused by mutations in PIGA at Xp22.2, which is involved in the biosynthesis of the glycosylphosphatidylinositol (GPI) anchor, among patients with early-onset epileptic encephalopathies (EOEEs).

Methods: Whole-exome sequencing was performed as a comprehensive genetic analysis for a cohort of 172 patients with EOEEs including early myoclonic encephalopathy, Ohtahara syndrome, and West syndrome, and PIGA mutations were carefully investigated.

Results: We identified 4 PIGA mutations in probands showing early myoclonic encephalopathy, West syndrome, or unclassified EOEE. Flow cytometry of blood granulocytes from patients demonstrated reduced expression of GPI-anchored proteins. Expression of GPI-anchored proteins in PIGA-deficient JY5 cells was only partially or hardly restored by transient expression of PIGA mutants with a weak TATA box promoter, indicating a variable loss of PIGA activity. The phenotypic consequences of PIGA mutations can be classified into 2 types, severe and less severe, which correlate with the degree of PIGA activity reduction caused by the mutations. Severe forms involved myoclonus and asymmetrical suppression bursts on EEG, multiple anomalies with a dysmorphic face, and delayed myelination with restricted diffusion patterns in specific areas. The less severe form presented with intellectual disability and treatable seizures without facial dysmorphism.

Conclusions: Our study confirmed that PIGA mutations are one genetic cause of EOEE, suggesting that GPI-anchor deficiencies may be an underlying cause of EOEE.
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http://dx.doi.org/10.1212/WNL.0000000000000389DOI Listing
May 2014