Yutaka Negishi

Two patients with acute rotavirus encephalitis associated with cerebellar signs and symptoms

Rotavirus, one of the major causes of severe gastroenteritis in children, occasionally causes central nervous system complications. Recently several patients with acute encephalitis/encephalopathy due to rotavirus associated with cerebellar signs and symptoms have been reported. The condition is characterized by disturbances of consciousness at onset and cerebellar signs and symptoms such as hypotonia, ataxia, dysmetria, and speech disorders, including mutism, slow speech, and dysarthria at convalescence. We report two patients (3-year-old girl, 2-year-old boy) who developed acute encephalitis due to rotavirus and showed cerebellar signs and symptoms. Both patients had characteristic history of consciousness disturbances subsequent to several days of diarrhea, vomiting and fever, and cerebellar symptoms such as hypotonia, ataxia, dysmetria, and speech disorders during the recovery period. Electroencephalography showed diffuse high-voltage delta wave activity in each patient. Brain magnetic resonance imaging showed cerebellar edema in the acute phase followed by cerebellar atrophy on follow-up images in both patients. In the first patient, diffusion-weighted images (DWI) revealed high signals at the left cerebellar peduncle region and apparent diffusion coefficient (ADC) maps showed decreased ADC values of the lesion in the acute phase. The first patient had dysmetria at 1-year follow-up. However, she had normal motor and cognitive functions and could lead her daily life without impairment. In the second patient, no further symptoms were apparent at 1-year follow-up. Acute encephalitis/encephalopathy due to rotavirus with cerebellar signs and symptoms might be diagnosed on DWI, by demonstrating decreased ADC values in acute phase.

Novel splicing mutation in the ASXL3 gene causing Bainbridge-Ropers syndrome

Bainbridge–Ropers syndrome (BRPS) is characterized by severe developmental delay, feeding problems, short stature, characteristic facal appearance including arched eyebrows and anteverted nares, and ulnar deviation of the hands. BRPS is caused by a heterozygous mutation in the additional sex combs‐like 3 (ASXL3) gene. We describe a patient with severe developmental delay, feeding problems, short stature, autism, and sleep disturbance with a heterozygous de novo splicing mutation in the ASXL3 gene. Reported disease‐causing mutations in ASXL3 are located mostly in the first half of exon 11, analogous to ASXL1 mutations of which result in Bohring–Opitz syndrome (BOS). Our findings suggest that the expression of the truncated ASXL3 protein, including ASXN and ASXH domains, give rise to BRPS, which is distinct from but overlaps with BOS.

A combination of genetic and biochemical analyses for the diagnosis of PI3K-AKT-mTOR pathway-associated megalencephaly

BackgroundConstitutive activation of the PI3K-AKT-mTOR pathway (mTOR pathway) underlies megalencephaly in many patients. Yet, prevalence of the involvement of the PI3K-AKT-mTOR pathway in patients with megalencephaly remains to be elucidated, and molecular diagnosis is challenging. Here, we have successfully established a combination of genetic and biochemical methods for diagnosis of mTOR pathway-associated megalencephaly, and have attempted to delineate the clinical characteristics of the disorder.MethodsThirteen patients with an increased head circumference and neurological symptoms participated in the study. To evaluate the activation of the mTOR pathway, we performed western blot analysis to determine the expression levels of phosphorylated S6 ribosomal protein (phospho-S6 protein) in lymphoblastoid cell lines from 12 patients. Multiplex targeted sequencing analysis for 15 genes involved in the mTOR pathway was performed on 12 patients, and whole-exome sequencing was performed on one additional patient. Clinical features and MRI findings were also investigated.ResultsWe identified pathogenic mutations in six (AKT3, 1 patient; PIK3R2, 2 patients; PTEN, 3 patients) of the 13 patients. Increased expression of phospho-S6 protein was demonstrated in all five mutation-positive patients in whom western blotting was performed, as well as in three mutation-negative patients. Developmental delay, dysmorphic facial features were observed in almost all patients. Syndactyly/polydactyly and capillary malformations were not observed, even in patients with AKT3 or PIK3R2 mutations. There were no common phenotypes or MRI findings among these patients.ConclusionsA combination of genetic and biochemical methods successfully identified mTOR pathway involvement in nine of 13 (approximately 70%) patients with megalencephaly, indicating a major contribution of the pathway to the pathogenesis of megalencephaly. Our combined approach could be useful to identify patients who are suitable for future clinical trials using an mTOR inhibitor.

Truncating mutation in NFIA causes brain malformation and urinary tract defects.

Chromosome 1p32-p31 deletion syndrome involving the Nuclear factor I/A (NFIA) gene is characterized by corpus callosum hypoplasia or defects and urinary tract defects. Herein we report on a case resembling the 1p32-p31 deletion syndrome carrying a de novo truncating mutation (c.1094delC; p.Pro365Hisfs*32) in the NFIA gene, confirming that haploinsufficiency of the NFIA gene is a major determinant of this syndrome.

Homoplasmy of a mitochondrial 3697G>A mutation causes Leigh syndrome

Herein we report on three siblings with Leigh syndrome (LS) harboring a homoplasmic m.3697G>A mutation (G131S) in the MT-ND1 gene. The siblings’ phenotypically normal mother had the same, albeit heteroplasmic, mutation. Complex I deficiency (8% of average control values) was demonstrated in a biceps brachii muscle from one of the patients. Heteroplasmic m.3697G>A has been reported in patients with Leber’s hereditary optic neuropathy, mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes and Stüve–Wiedemann syndrome. Because all three patients in this series carried m.3697G>A in a homoplasmic manner and had LS, we suggest that homoplasmy of m.3697G>A may cause the LS phenotype.

Biallelic mutations in SZT2 cause a discernible clinical entity with epilepsy, developmental delay, macrocephaly and a dysmorphic corpus callosum

Mutations in SZT2 were first reported in 2013 as a cause of early-onset epileptic encephalopathy. Because only five reports have been published to date, the clinical features associated with SZT2 remain unclear. We herein report an additional patient with biallelic mutations in SZT2. The proband, a four-year-old girl, showed developmental delay and seizures from two years of age. Her seizures were not intractable and readily controlled by valproate. She showed mildly dysmorphic facies with macrocephaly, high forehead, and hypertelorism, and also had pectus carinatum. An EEG showed epileptic discharges which rarely occurred. A brain MRI revealed a short and thick corpus callosum. Whole-exome sequencing detected compound heterozygous biallelic mutations (c.8596dup (p.Tyr2866Leufs∗42) and c.2930-17_2930-3delinsCTCGTG) in SZT2, both of which were novel and predicted to be truncating. This case suggested a broad phenotypic spectrum arises from SZT2 mutations, forming a continuum from epileptic encephalopathy and severe developmental delay to mild intellectual disability without epilepsy. The characteristic thick and short corpus callosum observed in 7/8 cases with epilepsy, including the proband, but not in three non-syndromic cases, appears to be specific, and thus useful for indicating the possibility of SZT2 mutations. This feature has the potential to make loss of SZT2 a clinically discernible disorder despite a wide clinical spectrum.

Defects in autophagosome-lysosome fusion underlie Vici syndrome, a neurodevelopmental disorder with multisystem involvement

Vici syndrome (VICIS) is a rare, autosomal recessive neurodevelopmental disorder with multisystem involvement characterized by agenesis of the corpus callosum, cataracts, cardiomyopathy, combined immunodeficiency, developmental delay, and hypopigmentation. Mutations in EPG5, a gene that encodes a key autophagy regulator, have been shown to cause VICIS, however, the precise pathomechanism underlying VICIS is yet to be clarified. Here, we describe detailed clinical (including brain MRI and muscle biopsy) and genetic features of nine Japanese patients with VICIS. Genetic dissection of these nine patients from seven families identified 14 causative mutations in EPG5. These included five nonsense, two frameshift, three splicing, one missense, and one multi-exon deletion mutations, and two initiation codon variants. Furthermore, cultured skin fibroblasts (SFs) from two affected patients demonstrated partial autophagic dysfunction. To investigate the function of EPG5, siRNA based EPG5 knock-down, and CRISPR/Cas9 mediated EPG5 knock-out HeLa cells were generated. EPG5-depleted cells exhibited a complete block of autophagic flux caused by defective autophagosome-lysosome fusion. Unexpectedly, endocytic degradation was normal in both VICIS SFs and EPG5 depleted cells, suggesting that EPG5 function is limited to the regulation of autophagosome-lysosome fusion.

Role of a heterotrimeric G-protein, Gi2, in the corticogenesis: Possible involvement in periventricular nodular heterotopia and intellectual disability

We analyzed the role of a heterotrimeric G‐protein, Gi2, in the development of the cerebral cortex. Acute knockdown of the α‐subunit (Gαi2) with in utero electroporation caused delayed radial migration of excitatory neurons during corticogenesis, perhaps because of impaired morphology. The migration phenotype was rescued by an RNAi‐resistant version of Gαi2. On the other hand, silencing of Gαi2 did not affect axon elongation, dendritic arbor formation or neurogenesis at ventricular zone in vivo. When behavior analyses were conducted with acute Gαi2‐knockdown mice, they showed defects in social interaction, novelty recognition and active avoidance learning as well as increased anxiety. Subsequently, using whole‐exome sequencing analysis, we identified a de novo heterozygous missense mutation (c.680C>T; p.Ala227Val) in the GNAI2 gene encoding Gαi2 in an individual with periventricular nodular heterotopia and intellectual disability. Collectively, the phenotypes in the knockdown experiments suggest a role of Gαi2 in the brain development, and impairment of its function might cause defects in neuronal functions which lead to neurodevelopmental disorders.

Fulminant encephalopathy with marked brain edema and bilateral thalamic lesions.

We encountered two children with acute encephalopathy associated with unique clinical manifestations. Both the patients had status epilepticus at onset and neuroimaging studies revealed marked brain edema and bilateral thalamic lesions. Although they were treated with steroids and immunoglobulin, their outcomes were very poor. A thermolabile variant of carnitine palmitoyltransferase II and an elevated interleukin-6 level in cerebrospinal fluid were observed in one patient each. The constellation of clinical and neuroimaging findings in our patients is apparently not consistent with any established subtype of acute encephalopathy/encephalitis.

CTCF deletion syndrome: clinical features and epigenetic delineation

Background Heterozygous mutations in CTCF have been reported in patients with distinct clinical features including intellectual disability. However, the precise pathomechanism underlying the phenotype remains to be uncovered, partly because of the diverse function of CTCF. Here we describe extensive clinical and genetic investigation for two patients with a microdeletion encompassing CTCF. Methods We performed genetic examination including comprehensive investigation of X chromosome inactivation and DNA methylation profiling at imprinted loci and genome-wide. Results Two patients showed comparable clinical features to those in a previous report, indicating that haploinsufficiency of CTCF was the major determinant of the microdeletion syndrome. Despite the haploinsufficiency of CTCF, X chromosome inactivation was normal. DNA methylation at imprinted loci was normal, but hypermethylation at CTCF binding sites was demonstrated, of which PRKCZ and FGFR2 were identified as candidate genes. Conclusions This study confirms that haploinsufficiency of CTCF causes distinct clinical features, and that a microdeletion encompassing CTCF could cause a recognisable CTCF deletion syndrome. Perturbed DNA methylation at CTCF binding sites, not at imprinted loci, may underlie the pathomechanism of the syndrome.