Mutations in Citron Kinase Cause Recessive Microlissencephaly with Multinucleated Neurons.

Primary microcephaly is a neurodevelopmental disorder that is caused by a reduction in brain size as a result of defects in the proliferation of neural progenitor cells during development. Mutations in genes encoding proteins that localize to the mitotic spindle and centrosomes have been implicated in the pathogenicity of primary microcephaly. In contrast, the contractile ring and midbody required for cytokinesis, the final stage of mitosis, have not previously been implicated by human genetics in the molecular mechanisms of this phenotype. Citron kinase (CIT) is a multi-domain protein that localizes to the cleavage furrow and midbody of mitotic cells, where it is required for the completion of cytokinesis. Rodent models of Cit deficiency highlighted the role of this gene in neurogenesis and microcephaly over a decade ago. Here, we identify recessively inherited pathogenic variants in CIT as the genetic basis of severe microcephaly and neonatal death. We present postmortem data showing that CIT is critical to building a normally sized human brain. Consistent with cytokinesis defects attributed to CIT, multinucleated neurons were observed throughout the cerebral cortex and cerebellum of an affected proband, expanding our understanding of mechanisms attributed to primary microcephaly.

The Neuropathology of MIRAGE Syndrome.

MIRAGE syndrome is a multisystem disorder characterized by myelodysplasia, infections, restriction of growth, adrenal hypoplasia, genital phenotypes, and enteropathy. Mutations in the sterile alpha motif domain containing 9 (SAMD9) gene which encodes a protein involved in growth factor signal transduction are thought to cause MIRAGE syndrome. SAMD9 mutations lead to an antiproliferative effect resulting in a multisystem growth restriction disorder. Though rare, a few patients with SAMD9 mutations were reported to have hydrocephalus and/or cerebellar hypoplasia on imaging. The neuropathologic features of MIRAGE syndrome have not been previously described. Here, we describe the postmortem neuropathologic examinations of 2 patients with a clinical diagnosis of MIRAGE syndrome and confirmed SAMD9 mutations. Common features included microcephaly, hydrocephalus, white matter abnormalities, and perivascular calcifications. One of the 2 cases showed marked cerebellar hypoplasia with loss of Purkinje and granule neurons as well as multifocal polymicrogyria and severe white matter volume loss; similar findings were not observed in the second patient. These cases demonstrate the variation in neuropathologic findings in patients with MIRAGE syndrome. Interestingly, the findings are similar to those reported in ataxia-pancytopenia syndrome caused by mutations in SAMD9L, a paralogue of SAMD9.

Genomic Analysis of Dysembryoplastic Neuroepithelial Tumor Spectrum Reveals a Diversity of Molecular Alterations Dysregulating the MAPK and PI3K/mTOR Pathways.

Dysembryoplastic neuroepithelial tumors (DNT) lacking key diagnostic criteria are challenging to diagnose and sometimes fall into the broader category of mixed neuronal-glial tumors (MNGT) or the recently described polymorphous low-grade neuroepithelial tumor of the young (PLNTY). We examined 41 patients with DNT, MNGT, or PLNTY for histologic features, genomic findings, and progression-free survival (PFS). Genomic analysis included sequence and copy number variants and RNA-sequencing. Classic DNT (n = 26) was compared with those with diffuse growth without cortical nodules (n = 15), 6 of which exhibited impressive CD34 staining classifying them as PLNTY. Genomic analysis was complete in 33, with sequence alterations recurrently identified in BRAF, FGFR1, NF1, and PDGFRA, as well as 7 fusion genes involving FGFR2, FGFR1, NTRK2, and BRAF. Genetic alterations did not distinguish between MNGTs, DNTs, or PLNTYs; however, FGFR1 alterations were confined to DNT, and PLNTYs contained BRAF V600E or FGFR2 fusion genes. Analysis of PFS showed no significant difference by histology or genetic alteration; however, numbers were small and follow-up time short. Further molecular characterization of a PLNTY-related gene fusion, FGFR2-CTNNA3, demonstrated oncogenic potential via MAPK/PI3K/mTOR pathway activation. Overall, DNT-MNGT spectrum tumors exhibit diverse genomic alterations, with more than half (19/33) leading to MAPK/PI3K pathway alterations.

An investigation of the expression of G1-phase cell cycle proteins in focal cortical dysplasia type IIB.

Balloon cells (BCs) are the pathologic hallmark of focal cortical dysplasia type IIB, a common cause of pharmacoresistent epilepsy. Expression of markers of cell immaturity and of the proliferation marker minichromosome maintenance protein 2 (mcm2) have been previously shown in BCs, suggesting that these cells might represent a pool of less-differentiated cells licensed for replication. An alternative explanation is that these cells are the remnants of early cortical plate cells that have failed to differentiate or to be eliminated during development and are arrested in the cell cycle, a hypothesis that this study aims to explore. Using immunohistochemical methods and semiquantitative analysis in 19 cases of focal cortical dysplasia (ages 1-81 years), we studied the expression of cell cycle proteins important either in regulating progression through the G1 phase or inducing cell arrest and promoting premature senescence. Only a small fraction of BCs expressed geminin, suggesting that few BCs enter the S phase or complete the cell cycle. Variable expression of nonphosphorylated retinoblastoma protein (Rb), cdk4, and p53 was noted in BCs. Cyclin E, D1, cdk2, phosphorylated Rb (795 and 807/811), and checkpoint 2 expression levels were low in BCs. These findings suggest early rather than late G1 arrest. Cell senescence could be induced by an undefined cerebral insult during development or alternatively represent a physiologic replicative senescence. These findings also suggest that dysregulation of cell cycle pathways may occur in focal cortical dysplasia, which opens further areas for exploration as potential new treatment avenues.

A Clinical, Neuropathological and Genetic Study of Homozygous A467T POLG-Related Mitochondrial Disease.

Mutations in the nuclear gene POLG (encoding the catalytic subunit of DNA polymerase gamma) are an important cause of mitochondrial disease. The most common POLG mutation, A467T, appears to exhibit considerable phenotypic heterogeneity. The mechanism by which this single genetic defect results in such clinical diversity remains unclear. In this study we evaluate the clinical, neuropathological and mitochondrial genetic features of four unrelated patients with homozygous A467T mutations. One patient presented with the severe and lethal Alpers-Huttenlocher syndrome, which was confirmed on neuropathology, and was found to have a depletion of mitochondrial DNA (mtDNA). Of the remaining three patients, one presented with mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS), one with a phenotype in the Myoclonic Epilepsy, Myopathy and Sensory Ataxia (MEMSA) spectrum and one with Sensory Ataxic Neuropathy, Dysarthria and Ophthalmoplegia (SANDO). All three had secondary accumulation of multiple mtDNA deletions. Complete sequence analysis of muscle mtDNA using the MitoChip resequencing chip in all four cases demonstrated significant variation in mtDNA, including a pathogenic MT-ND5 mutation in one patient. These data highlight the variable and overlapping clinical and neuropathological phenotypes and downstream molecular defects caused by the A467T mutation, which may result from factors such as the mtDNA genetic background, nuclear genetic modifiers and environmental stressors.

Chromosome band 7q34 deletions resulting in KIAA1549-BRAF and FAM131B-BRAF fusions in pediatric low-grade Gliomas.

The majority of pediatric low-grade gliomas (LGGs) are characterized by constitutive activation of the mitogen-activated protein kinase (MAPK) pathway through various mechanisms including BRAF mutations, inactivation of NF1, and KIAA1549-BRAF and FAM131B-BRAF fusions. The KIAA1549-BRAF fusion typically results from a 2.0 Mb tandem duplication in chromosome band 7q34. In the present study, single nucleotide polymorphism (SNP)-based array analysis of three LGGs demonstrated deletions in 7q34 that resulted in a BRAF fusion. Case 1 was likely a pilocytic astrocytoma (PA) with three deletions in 7q33q34 and an exon 15-9 KIAA1549-BRAF fusion. SNP array analysis of case 2, a possible dysembryoplastic neuroepithelial tumor (DNT), revealed a 2.6 Mb deletion, which included the 5' end of BRAF and extended to the 3' end of FAM131B. In case 3, deletions involving BRAF and FAM131B were observed in both a primary and a recurrent PA. RNA-based sequence analysis of cases 2 and 3 confirmed a fusion between FAM131B exon 2 and BRAF exon 9. The presence of fusion transcripts in these three LGGs highlights the utility of SNP array analysis to identify deletions that are suggestive of fusion proteins. BRAF fusions can result from multiple non-overlapping deletions, suggesting various complex mechanisms of formation.

Spectrum of neuropathophysiology in spinal muscular atrophy type I.

Neuropathologic findings within the central and peripheral nervous systems in patients with spinal muscular atrophy type I (SMA-I) were examined in relation to genetic, clinical, and electrophysiologic features. Five infants representing the full clinical spectrum of SMA-I were examined clinically for compound motor action potential amplitude and SMN2 gene copy number; morphologic analyses of postmortem central nervous system, neuromuscular junction, and muscle tissue samples were performed and SMN protein was assessed in muscle samples. The 2 clinically most severely affected patients had a single copy of the SMN2 gene; in addition to anterior horn cells, dorsal root ganglia, and thalamus, neuronal degeneration in them was widespread in the cerebral cortex, basal ganglia, pigmented nuclei, brainstem, and cerebellum. Two typical SMA-I patients and a milder case each had 2 copies of the SMN2 gene and more restricted neuropathologic abnormalities. Maturation of acetylcholine receptor subunits was delayed and the neuromuscular junctions were abnormally formed in the SMA-I patients. Thus, the neuropathologic findings in human SMA-I are similar to many findings in animal models; factors other than SMN2 copy number modify disease severity. We present a pathophysiologic model for SMA-I as a protein deficiency disease affecting a neuronal network with variable clinical thresholds. Because new treatment strategies improve survival of infants with SMA-I, a better understanding of these factors will guide future treatments.

Clinical and histopathological outcomes in patients with SCN1A mutations undergoing surgery for epilepsy.

OBJECT: Mutations in the sodium channel alpha 1 subunit gene (SCN1A) have been associated with a wide range of epilepsy phenotypes including Dravet syndrome. There currently exist few histopathological and surgical outcome reports in patients with this disease. In this case series, the authors describe the clinical features, surgical pathology, and outcomes in 6 patients with SCN1A mutations and refractory epilepsy who underwent focal cortical resection prior to uncovering the genetic basis of their epilepsy. METHODS: Medical records of SCN1A mutation-positive children with treatment-resistant epilepsy who had undergone resective epilepsy surgery were reviewed retrospectively. Surgical pathology specimens were reviewed. RESULTS: All 6 patients identified carried diagnoses of intractable epilepsy with mixed seizure types. Age at surgery ranged from 18 months to 20 years. Seizures were refractory to surgery in every case. Surgical histopathology showed evidence of subtle cortical dysplasia in 4 of 6 patients, with more neurons in the molecular layer of the cortex and white matter. CONCLUSIONS: Cortical resection is unlikely to be beneficial in these children due to the genetic defect and the unexpected neuropathological finding of mild diffuse malformations of cortical development. Together, these findings suggest a diffuse pathophysiological mechanism of the patients' epilepsy which will not respond to focal resective surgery.

Abnormal expression of cdk5 in focal cortical dysplasia in humans.

Focal cortical dysplasia (FCD) is an important cause of refractory epilepsy in humans. The origin of its pathognomonic abnormal cell types and the links between abnormal cell morphology and epileptogenicity remain unknown. The developmentally-regulated kinase cdk5 and its neuronal activator p35 are known to be central to a number of key components in neuronal development, cellular morphology, cytoskeletal function, synaptic plasticity and neurodegeneration. Here we examine eight cases of human FCD for expression of cdk5. We show abnormal cdk5 immunoreactivity and aggregation of protein suggesting alterations in cdk5 may also be involved in this important epileptogenic human pathology.

Imaging findings of patients with metastatic neuroblastoma to the brain.

RATIONALE AND OBJECTIVES: Metastatic involvement of brain is rare in neuroblastoma (NB). We retrospectively evaluated conventional and advanced imaging and clinical findings of seven patients with secondary intra-axial brain NB metastases. MATERIALS AND METHODS: Magnetic resonance imaging and computed tomography examinations of patients with metastatic brain NB were reviewed. Recent iodine-123 metaiodobenzylguanidine ((123)I-MIBG) scans were also reviewed. A medical record review was performed for relevant clinical, laboratory, histopathologic, and genetic data. RESULTS: Mean age at the time of primary tumor diagnosis was 35 months, and all were considered high-risk NB at diagnosis. Mean time interval between diagnosis and brain involvement was 23.2 months. Extensive prior extra-central nervous system (CNS) disease was present in all patients, but concomitant extra-CNS disease at the time of brain involvement was absent in three (43%) patients. Various forms of disease, including intraparenchymal, intraventricular, and leptomeningeal lesions were detected. Most intraparenchymal lesions were supratentorial and hemorrhagic; however, hemorrhage was absent in multiple leptomeningeal nodules in one patient. Contrast enhancement of lesions was present on all contrast-enhanced studies. Restricted diffusion of lesions was present in two patients. Arterial spin labeling (ASL) perfusion in two patients also revealed increased cerebral blood flow. Recent (123)I-MIBG scans were available in four patients and showed lesions in two patients with larger metastases but failed to demonstrate lesions in another two patients with smaller lesions. CONCLUSIONS: Brain metastases of NB are often supratentorial and hemorrhagic and demonstrate contrast enhancement. Diffusion-weighted imaging can show restricted diffusion. ASL images may reveal increased perfusion. MIBG scans may not show smaller brain metastases.

Epigenetic genome-wide analysis identifies BEX1 as a candidate tumour suppressor gene in paediatric intracranial ependymoma.

Promoter hypermethylation and transcriptional silencing is a common epigenetic mechanism of gene inactivation in cancer. To identify targets of epigenetic silencing in paediatric intracranial ependymoma, we used a pharmacological unmasking approach through treatment of 3 ependymoma short-term cell cultures with the demethylating agent 5-Aza-2'-deoxycytidine followed by global expression microarray analysis. We identified 55 candidate epigenetically silenced genes, which are involved in the regulation of apoptosis, Wnt signalling, p53 and cell differentiation. The methylation status of 26 of these genes was further determined by combined bisulfite restriction analysis (COBRA) and genomic sequencing in a cohort of 40 ependymoma samples. The most frequently methylated genes were BEX1 (27/40 cases), BAI2 (20/40), CCND2 (18/40), and CDKN2A (14/40). A high correlation between promoter hypermethylation and decreased gene expression levels was established by real-time quantitative PCR, suggesting the involvement of these genes in ependymoma tumourigenesis. Furthermore, ectopic expression of brain-expressed X-linked 1 (BEX1) in paediatric ependymoma short-term cell cultures significantly suppressed cell proliferation and colony formation. These data suggest that promoter hypermethylation contributes to silencing of target genes in paediatric intracranial ependymoma. Epigenetic inactivation of BEX1 supports its role as a candidate tumour suppressor gene in intracranial ependymoma, and a potential target for novel therapies for ependymoma in children.

Diagnostic application of high resolution single nucleotide polymorphism array analysis for children with brain tumors.

Single nucleotide polymorphism (SNP) array analysis is currently used as a first tier test for pediatric brain tumors at The Children's Hospital of Philadelphia. The results from 100 consecutive patients are summarized in the present report. Eighty-seven percent of the tumors had at least one pathogenic copy number alteration. Nineteen of 56 low grade gliomas (LGGs) demonstrated a duplication in 7q34, which resulted in a KIAA1549-BRAF fusion. Chromosome band 7q34 deletions, which resulted in a FAM131B-BRAF fusion, were identified in one pilocytic astrocytoma (PA) and one dysembryoplastic neuroepithelial tumor (DNT). One ganglioglioma (GG) demonstrated a 6q23.3q26 deletion that was predicted to result in a MYB-QKI fusion. Gains of chromosomes 5, 6, 7, 11, and 20 were seen in a subset of LGGs. Monosomy 6, deletion of 9q and 10q, and an i(17)(q10) were each detected in the medulloblastomas (MBs). Deletions and regions of loss of heterozygosity that encompassed TP53, RB1, CDKN2A/B, CHEK2, NF1, and NF2 were identified in a variety of tumors, which led to a recommendation for germline testing. A BRAF p.Thr599dup or p.V600E mutation was identified by Sanger sequencing in one and five gliomas, respectively, and a somatic TP53 mutation was identified in a fibrillary astrocytoma. No TP53 hot-spot mutations were detected in the MBs. SNP array analysis of pediatric brain tumors can be combined with pathologic examination and molecular analyses to further refine diagnoses, offer more accurate prognostic assessments, and identify patients who should be referred for cancer risk assessment.

Brain tumor presenting as somnambulism in an adolescent.

BACKGROUND: Sleepwalking is typically a benign and self-limited non-rapid eye movement parasomnia of childhood. PATIENT: We describe an unusual 15-year-old boy referred to our sleep center for new-onset sleepwalking. RESULTS: An overnight polysomnogram was normal from a respiratory standpoint, but a concurrent extended electroencephalogram montage showed frequent epileptiform discharges from the right parietal-temporal region and two electroclinical seizures arising from the right-frontal-central-temporal region during sleep. Magnetic resonance imaging scan revealed a right parasagittal parietal region lesion consistent with a low-grade neoplasm, and surgical resection of the lesion demonstrated a right parietal dysembryoplastic neuroepithelial tumor. Complex partial seizures and sleepwalking remitted completely with anticonvulsant therapy following surgery. CONCLUSIONS: This patient highlights the differential diagnosis of nocturnal events appearing to be typical parasomnias, especially when they arise abruptly at an older age.

Spontaneous regression of residual low-grade cerebellar pilocytic astrocytomas in children.

BACKGROUND: Cerebellar low-grade astrocytomas (CLGAs) of childhood are benign tumours and are usually curable by surgical resection alone or combined with adjuvant radiotherapy. OBJECTIVE: To undertake a retrospective study of our children with CLGA to determine the optimum schedule for surveillance imaging following initial surgery. In this report we describe the phenomenon of spontaneous regression of residual tumour and discuss its prognostic significance regarding future imaging. MATERIALS AND METHODS: A retrospective review was conducted of children treated for histologically proven CLGA at Great Ormond Street Hospital from 1988 to 1998. RESULTS: Of 83 children with CLGA identified, 13 (15.7%) had incomplete resections. Two children with large residual tumours associated with persistent symptoms underwent additional treatment. Eleven children were followed by surveillance imaging alone for a mean of 6.83 years (range 2-13.25 years). Spontaneous tumour regression was seen in 5 (45.5%) of the 11 children. There were no differences in age, gender, symptomatology, histological grade or Ki-67 fractions between those with spontaneous tumour regression and those with progression. There was a non-significant trend that larger volume residual tumours progressed. CONCLUSIONS: Residual tumour followed by surveillance imaging may either regress or progress. For children with residual disease we recommend surveillance imaging every 6 months for the first 2 years, every year for years 3, 4 and 5, then every second year if residual tumour is still present 5 years after initial surgery. This would detect not only progressive or recurrent disease, but also spontaneous regression which can occur later than disease progression.

Major vault protein, a marker of drug resistance, is upregulated in refractory epilepsy.

PURPOSE: The molecular basis of drug resistance in epilepsy is being explored. Two proteins associated with drug resistance in cancer, P-glycoprotein and multidrug resistance-associated protein 1, are upregulated in human epileptogenic pathologies. Other proteins associated with resistance in cancer include major vault protein (MVP) and breast cancer resistance protein (BCRP). We hypothesized that these proteins would also be upregulated in human epileptogenic pathologies. METHODS: Hippocampal sclerosis (HS), focal cortical dysplasia (FCD), and dysembryoplastic neuroepithelial tumor (DNT) were studied by using immunohistochemistry for MVP and BCRP. Nonepileptogenic control and histologically normal brain adjacent to epileptogenic tissue were used for comparison. RESULTS: MVP and BCRP were expressed ubiquitously in brain capillary endothelium. Ectopic upregulation of MVP was seen in hilar neurons in HS, dysplastic neurons in FCD, and lesional neurons in DNT. Only in HS cases were rare extralesional neurons immunoreactive. Glial upregulation was not seen. There was no qualitative upregulation of BCRP. CONCLUSIONS: These results show that more than one resistance protein may be upregulated in a given epileptogenic pathology and may contribute to drug resistance. Determination of the types, amounts, and distribution of such proteins will be necessary for rational treatment for drug resistance in epilepsy.