Megumi Tsuji

Rapid detection of a mutation causing X-linked leucoencephalopathy by exome sequencing

Background Conventional PCR-based direct sequencing of candidate genes for a family with X-linked leucoencephalopathy with unknown aetiology failed to identify any causative mutations. Objective To carry out exome sequencing of entire transcripts of the whole X chromosome to investigate a family with X linked leucoencephalopathy. Methods and results Next-generation sequencing of all the transcripts of the X chromosome, after liquid-based genome partitioning, was performed on one of the two affected male subjects (the proband) and an unaffected male subject (his brother). A nonsense mutation in MCT8 (c.1102A→T (p.R368X)) was identified in the proband. Subsequent PCR-based direct sequencing of other family members confirmed the presence of this mutation, hemizygous in the other affected brother and heterozygous in the probands mother and maternal grandmother. MCT8 mutations usually cause abnormal thyroid function in addition to neurological abnormalities, but this proband had normal thyroid function. Conclusion Single-lane exome next-generation sequencing is sufficient to fully analyse all the transcripts of the X chromosome. This method is particularly suitable for mutation screening of X-linked recessive disorders and can avoid biases in candidate gene choice.

Acute encephalopathy in children with Dravet syndrome

Purpose:  The occurrence of acute encephalopathy in children with Dravet syndrome has been reported sporadically. This study clarified the features of acute encephalopathy in children with Dravet syndrome.

Paradoxical increase in seizure frequency with valproate in nonketotic hyperglycinemia.

Nonketotic hyperglycinemia (NKH), or glycine encephalopathy, is an autosomal recessive disorder caused by a defect in the glycine cleavage enzyme system. In neonatal-onset NKH, patients manifest lethargy, hypotonia, apnea, and intractable epileptic seizures that are not specific to this disease. We experienced a 6-year-old girl with spastic quadriplegia, intractable epilepsy, and mental retardation, all initially regarded as sequelae of neonatal meningitis. The seizure frequency was transiently increased when valproate was started. Head MRI revealed progressive brain atrophy and white matter loss with high intensity signals on T2-weighted and diffusion-weighted images, which prompted us to conduct further metabolic workups. High glycine levels led us to suspect NKH, and we confirmed this diagnosis by the non-invasive, (13)C-glycine breath test. DNA sequencing revealed novel Leu885Pro/Trp897Cys mutations in the glycine decarboxylase gene that were transmitted from both parents. Sodium benzoate and dextromethorphan dramatically decreased her hypertonicity. Our case shows that paradoxical increases in seizure frequency following valproate can be a clue for a diagnosis of NKH, and that a correct diagnosis of NKH can greatly alter the quality of life in such patients.

5,10-Methylenetetrahydrofolate reductase deficiency with progressive polyneuropathy in an infant.

5,10-Methylenetetrahydrofolate reductase (MTHFR) deficiency is the most prevalent inborn error of folate metabolism, and has variable clinical manifestations from asymptomatic to severe psychomotor retardation, microcephalus and seizure. In untreated infantile cases, it predominantly affects the central nervous system, which is sometimes fatal. On the other hand, peripheral nerve involvement is uncommon. We present a severe infantile case of MTHFR deficiency that manifested unilateral phrenic nerve palsy with communicating hydrocephalus, developmental delay and died at 11months of age. An enzymatic study confirmed MTHFR deficiency with residual activity of 0.75% of mean control values in cultured fibroblasts. Mutation analysis of the MTHFR gene revealed homozygous, tandem missense mutations c.[446G>T; 447C>T] in exon 3 of the MTHFR gene converting glycine to valine (Gly149Val). In MTHFR deficiency, betaine may improve the symptoms if started immediately after birth by reducing the level of serum homocysteine and increasing that of methionine. Our results show that we should be aware of possible inborn errors of folate metabolism such as MTHFR deficiency, in infants with unexplained developmental delay manifesting rapidly progressive polyneuropathy.

Enhanced long-term potentiation in mature rats in a model of epileptic spasms with betamethasone-priming and postnatal N-methyl-D-aspartate administration.

Patients with epileptic spasms are at high risk for learning and memory impairment later in life. We examined whether synaptic plasticity is affected in the adult hippocampus, a structure responsible for learning and memory, using an animal model of epileptic spasms of unknown cause.

Acute encephalopathy in a patient with Dravet syndrome.

Dravet syndrome (severe myoclonic epilepsy in infancy) is an epileptic syndrome with various types of seizures that begin in the first year of life and may result in intellectual impairment. Mutations of the SCN1A gene are the most prevalent genetic cause of Dravet syndrome. In this study, we report a 12-year-old girl with Dravet syndrome carrying an SCN1A mutation, c.2785Cdel (L929del fsX934). She had an episode of status epilepticus and persistent lethargy after 48 h of acute febrile illness that was preceded by an annual flu vaccination. Low voltage activities detected by electroencephalogram and elevated neuron-specific enolase/interleukin-6 concentrations in the cerebrospinal fluid suggested acute encephalopathy. MRI showed abnormalities in the bilateral thalami, cerebellum and brainstem. These abnormalities were protracted over a month. The biochemical and MRI characteristics of this case are different from any known type of encephalopathy, and may suggest a vulnerability of neurons expressing mutant SCN1A in the brain.

Phenotype of GABA-transaminase deficiency

Objective: We report a case series of 10 patients with γ-aminobutyric acid (GABA)–transaminase deficiency including a novel therapeutic trial and an expanded phenotype. Methods: Case ascertainment, literature review, comprehensive evaluations, and long-term treatment with flumazenil. Results: All patients presented with neonatal or early infantile-onset encephalopathy; other features were hypotonia, hypersomnolence, epilepsy, choreoathetosis, and accelerated linear growth. EEGs showed burst-suppression, modified hypsarrhythmia, multifocal spikes, and generalized spike-wave. Five of the 10 patients are currently alive with age at last follow-up between 18 months and 9.5 years. Treatment with continuous flumazenil was implemented in 2 patients. One patient, with a milder phenotype, began treatment at age 21 months and has continued for 20 months with improved alertness and less excessive adventitious movements. The second patient had a more severe phenotype and was 7 years of age at initiation of flumazenil, which was not continued. Conclusions: GABA-transaminase deficiency presents with neonatal or infantile-onset encephalopathy including hypersomnolence and choreoathetosis. A widened phenotypic spectrum is reported as opposed to lethality by 2 years of age. The GABA-A benzodiazepine receptor antagonist flumazenil may represent a therapeutic strategy.

SAD-B kinase regulates pre-synaptic vesicular dynamics at hippocampal Schaffer collateral synapses and affects contextual fear memory

Synapses of amphids defective (SAD)‐A/B kinases control various steps in neuronal development and differentiation, such as axon specifications and maturation in central and peripheral nervous systems. At mature pre‐synaptic terminals, SAD‐B is associated with synaptic vesicles and the active zone cytomatrix; however, how SAD‐B regulates neurotransmission and synaptic plasticity in vivo remains unclear. Thus, we used SAD‐B knockout (KO) mice to study the function of this pre‐synaptic kinase in the brain. We found that the paired‐pulse ratio was significantly enhanced at Shaffer collateral synapses in the hippocampal CA1 region in SAD‐B KO mice compared with wild‐type littermates. We also found that the frequency of the miniature excitatory post‐synaptic current was decreased in SAD‐B KO mice. Moreover, synaptic depression following prolonged low‐frequency synaptic stimulation was significantly enhanced in SAD‐B KO mice. These results suggest that SAD‐B kinase regulates vesicular release probability at pre‐synaptic terminals and is involved in vesicular trafficking and/or regulation of the readily releasable pool size. Finally, we found that hippocampus‐dependent contextual fear learning was significantly impaired in SAD‐B KO mice. These observations suggest that SAD‐B kinase plays pivotal roles in controlling vesicular release properties and regulating hippocampal function in the mature brain.

Long-term home non-invasive positive pressure ventilation in children: Results from a single center in Japan

BACKGROUND Non-invasive positive pressure ventilation (NPPV) in children has recently increased worldwide and is used not only for neuromuscular diseases but for various other diseases. However, there have been few observational studies on long-term NPPV in children in Japan. METHODS Based on medical records, we retrospectively evaluated patients aged ≤20 years who were initiated long-term NPPV at our hospital from January 2001 to December 2015. RESULTS A total of 53 patients on long-term NPPV were identified; 38 (72%) had severe motor and intellectual disabilities (SMID). Compared to those with non-neuromuscular diseases, those with neuromuscular diseases had significantly more planned initiations and less frequent use of oxygen. Regarding patient outcome, 34 patients continued NPPV (64%), and there were three discontinues (6%), seven tracheostomies (13%), and nine deaths (17%). The continuation rate was high among those with neuromuscular disorders (15/19 cases, 79%) and that of tracheotomy was high in those with metabolic/degenerative diseases (3/9 cases, 33%). Ten patients transitioned to adult care, accounting for 29% of the 34 continuing patients. CONCLUSION This is the first observational study on long-term NPPV use in children in Japan that examined outcomes in patients with a range of disorders. The initiation situation, management, and outcomes differed between patients with neuromuscular and non-neuronal muscular diseases. Long-term use of NPPV is possible in many cases, including children with SMID, but can be challenging to continue in patients with progressive diseases such as metabolic/degenerative diseases. Careful discussions regarding the management of each patient are necessary.