Nobutsune Ishikawa

Polycomb-group complex 1 acts as an E3 ubiquitin ligase for Geminin to sustain hematopoietic stem cell activity

Polycomb-group (PcG) genes encode multimeric nuclear protein complexes, PcG complex 1 and 2. PcG complex 2 was proved to induce transcription repression and to further methylate histone H3 at lysine-27 (H3K27). Subsequently PcG complex 1 is recruited through recognition of methylated H3K27 and maintains the transcription silencing by mediating monoubiquitination of histone H2A at lysine-119. Genetic evidence demonstrated a crucial role for PcG complex 1 in stem cells, and Bmi1, a member of PcG complex 1, was shown to sustain adult stem cells through direct repression of the INK4a locus encoding cyclin-dependent kinase inhibitor, p16CKI, and p19ARF. The molecular functions of PcG complex 1, however, remain insufficiently understood. In our study, deficiency of Rae28, a member of PcG complex 1, was found to impair ubiquitin-proteasome-mediated degradation of Geminin, an inhibitor of DNA replication licensing factor Cdt1, and to increase protein stability. The resultant accumulation of Geminin, based on evidence from retroviral transduction experiments, presumably eliminated hematopoietic stem cell activity in Rae28-deficient mice. Rae28 mediates recruiting Scmh1, which provides PcG complex 1 an interaction domain for Geminin. Moreover, PcG complex 1 acts as the E3 ubiquitin ligase for Geminin, as we demonstrated in vivo as well as in vitro by using purified recombinant PcG complex 1 reconstituted in insect cells. Our findings suggest that PcG complex 1 supports the activity of hematopoietic stem cells, in which high-level Geminin expression induces quiescence securing genome stability, by enhancing cycling capability and hematopoietic activity through direct regulation of Geminin.

Neurodevelopmental abnormalities associated with severe congenital neutropenia due to the R86X mutation in the HAX1 gene

Objective: Severe congenital neutropenia (SCN), also known as Kostmann syndrome (SCN3, OMIM 610738), includes a variety of haematological disorders caused by different genetic abnormalities. Mutations in ELA2 are most often the cause in autosomal dominant or sporadic forms. Recently, mutations in HAX1 have been identified as the cause of some autosomal recessive forms of SCN, including those present in the original pedigree first reported by Kostmann. We sought to determine the relationship between HAX1 gene mutations and the clinical characteristics of Japanese cases of SCN. Methods: The genes implicated in SCN (ELA2, HAX1, Gfi-1, WAS, and P14) were analysed in 18 Japanese patients with SCN. The clinical features of these patients were obtained from medical records. Immunoblotting of HAX1 was performed on cell extracts from peripheral blood leucocytes from patients and/or their parents. Results: We found five patients with HAX1 deficiency and 11 patients with mutations in the ELA2 gene. In HAX1 deficiency, a homozygous single base pair substitution (256C>T), which causes the nonsense change R86X, was identified in three affected individuals. Two sibling patients showed a compound heterozygous mutation consisting of a single base pair substitution (256C>T) and a 59 bp deletion at nucleotides 376–434. There was no detectable phenotype in any heterozygous carrier. All patients with HAX1 deficiency had experienced developmental delay. Three patients carrying R86X also suffered from epileptic seizures. In contrast, no SCN patient with heterozygous mutations in the ELA2 gene suffered from any neurodevelopmental abnormality. Conclusions: These findings suggest that the R86X mutation in the HAX1 gene is an abnormality in Japanese SCN patients with HAX1 deficiency and may lead to neurodevelopmental abnormalities and severe myelopoietic defects.

The novel IFNGR1 mutation 774del4 produces a truncated form of interferon-γ receptor 1 and has a dominant-negative effect on interferon-γ signal transduction

Background: Patients with interferon-γ receptor 1 (IFNγR1) deficiency show selective susceptibility to intracellular pathogens such as mycobacteria. IFNγR1 deficiency is an inherited immunodeficiency disorder, which can be either recessive or dominant. Dominant forms of IFNγR1 deficiency are known to be associated with mutations that introduce a premature stop codon in the intracellular domain of IFNγR1. One such mutation, 818del4, is believed to be the most common type. Although these mutations are presumed to exert a dominant-negative effect on IFNγ signal transduction, the underlying molecular mechanism is unresolved. Objective: We characterised the 774del4 mutant of IFNγR1 using a gene-expression system to examine the effects of this mutation on IFNγ signal transduction. Results: We identified a novel dominant mutation in IFNGR1, designated 774del4, which produced a truncated form of IFNγR1 in a patient with recurrent mycobacterial infections. IFNγR1 was overexpressed on the surfaces of CD14-positive cells from the peripheral blood of this patient, and STAT1 phosphorylation in response to high doses of IFNγ was partially deficient. We expressed two truncated forms of IFNγR1, 774del4 and 818del4, in HEK 293 cells using transient transfection and found that these mutants overexpressed IFNγR1 on the cell surface because of impaired receptor stability, which resulted in a dominant-negative effect on IFNγ signal transduction. Conclusion: Like the 818del4 mutation, 774del4 produces a truncated form of IFNγR1, which has a dominant-negative effect on IFNγ signal transduction through altered receptor stability.

Different neuroradiological findings during two stroke-like episodes in a patient with a congenital disorder of glycosylation type Ia

Congenital disorders of glycosylation type Ia (CDG-Ia) are the most common type of CDG and are characterized by liver dysfunction, coagulation disorders, mental retardation, hypotonia, cerebellar dysfunction, polyneuropathy, seizures, and stroke-like episodes. Stroke-like episodes occur in 40-55% of cases, but their etiology is not fully understood. Although it has been stated that an epileptic process may cause the stroke-like episodes, there is no clear evidence of ischemic stroke. Here, we describe two stroke-like episodes in a patient with CDG. We performed radiological studies during each episode and obtained two distinct magnetic resonance imaging (MRI) findings: one revealed an ischemic stroke, and the other demonstrated marked edema followed by focal necrosis. This is the first direct evidence of ischemic stroke, and we report that another process may affect the etiology in the same patient.

Detection of Autoantibodies against NMDA-Type Glutamate Receptor in a Patient with Recurrent Optic Neuritis and Transient Cerebral Lesions

We describe the case of a Japanese girl with recurrent optic neuritis and transient cerebral lesions. Antibodies against N-methyl-d-aspartate (NMDA)-type glutamate receptors were detected in both serum and cerebrospinal fluid. Results of this case study suggest that the development of autoantibodies against NMDA-type glutamate receptors may play a role in the pathogenesis of central nervous system demyelinating diseases.

Craniosynostosis in a patient with a de novo 15q15-q22 deletion†

Interstitial deletions involving the chromosomal band 15q15 are very rare. A total of five cases were previously reported. Here another case of a 15q15.2‐q22.2 deletion is reported, presenting with severe craniosynostosis of coronary, metopic, and sagittal sutures. The chromosome 15 with the 17.7‐Mb deletion was of the paternal origin. A critical region for craniosynostosis may be located at the 734‐kb segment at 15q15.2. Interestingly, the entire FBN1 gene was deleted in this patient.

Recurrent acute cerebellar ataxia associated with anti-cardiolipin antibodies.

Various autoantibodies are detected in patients with acute cerebellar ataxia (ACA). Although an autoimmune process may contribute to the mechanism of ACA, its pathophysiology is not completely understood. We report a girl with recurrent ACA and anti-cardiolipin antibodies. Her cerebral blood flow imaging showed hypoperfusion in the cerebellum, which improved when the anti-cardiolipin antibodies disappeared. Our case suggests that vasculopathy or non-vascular neurotoxicity in the cerebellum caused by antiphospholipid antibodies leads to acute cerebellar ataxia.

Compound heterozygosity in GPR56 with bilateral frontoparietal polymicrogyria.

Polymicrogyria is caused by a diverse etiology, one of which is gene mutation. At present, only one gene (GPR56) is known to cause polymicrogyria, which leads to a distinctive phenotype termed bilateral frontoparietal polymicrogyria (BFPP). BFPP is an autosomal recessive inherited human brain malformation with abnormal cortical lamination. Here, we identified compound heterozygous GPR56 mutations in a patient with BFPP. The proband was a Japanese female born from non-consanguineous parents. She presented with mental retardation, developmental motor delay, epilepsy exhibiting the feature of Lennox-Gastaut syndrome, exotropia, bilateral polymicrogyria with a relatively spared perisylvian region, bilateral patchy-white-matter MRI signal changes, and hypoplastic pontine basis. GPR56 sequence analysis revealed a c.107G>A substitution leading to a p.S36N, and a c.113G>A leading to a p.R38Q. Although affected individuals with compound heterozygosity in GPR56 have not been previously described, we presume that compound heterozygosity of these two mutations in a ligand binding domain within the extracellular N-terminus of protein could result in BFPP. In addition, we observed unusually less involvement of perisylvian cortex for polymicrogyria, and Lennox-Gastaut syndrome for epilepsy, which are likely common features in patients with BFPP caused by GPR56 mutations.

A case of frontal lobe epilepsy in which amplitude-integrated EEG combined with conventional EEG was useful for evaluating clusters of seizures

Accurate evaluation of status epilepticus or clusters of seizures in patients with epilepsy is a critical issue in epilepsy care units. Although the need for continuous electroencephalographic monitoring has been recognized, it has been difficult to evaluate the frequency of ictal changes in electroencephalography (EEG) data in real time. Amplitude-integrated EEG (aEEG) has been reported to be useful for neuromonitoring, particularly in newborn infants. However, few reports of the utility of aEEG in older children with epilepsy have been published. We employed aEEG in combination with conventional EEG in an 11-year old boy presenting with clusters of seizures and were able to accurately evaluate the frequency of seizures in real time. The combination of aEEG and conventional EEG may be a useful tool in both neonatal intensive care units and epilepsy care units.

Late-onset epileptic spasms in a patient with 22q13.3 deletion syndrome

Patients with 22q13.3 deletion syndrome present with diverse neurological problems such as global developmental delays, hypotonia, delayed or absent speech, autistic behavior, and epilepsy. Seizures occur in up to one-third of patients with 22q13.3 deletion syndrome; however, only a few reports have provided details regarding the seizure manifestations. The present report describes a patient with 22q13.3 deletion syndrome who presented with late-onset epileptic spasms (ES) and electroencephalography features like Lennox-Gastaut syndrome. An array comparative genomic hybridization analysis revealed that a chromosomal deletion of this patient included SHANK3. To the best of our knowledge, this is the first confirmed case of late-onset ES occur in patients with 22q13.3 deletion syndrome with a SHANK3 deletion.