Alteration of interneuron migration in a ferret model of cortical dysplasia.
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During cerebral cortical development, gamma-aminobutyric acidergic (GABAergic) interneurons arise from a different site than projection neurons. GABAergic cells are generated in the subpallial ganglionic eminence (GE), while excitatory projection neurons arise from the neocortical ventricular zone. Our laboratory studies a model of cortical dysplasia that displays specific disruption of GABAergic mechanisms and an alteration in the overall balance of excitation in the neocortex. To produce this model, the birth of neurons on a specific gestational day in ferrets (embryonic day 33 [E33]) is interrupted by injection of the antimitotic methylazoxymethanol (MAM). We hypothesized that migration of interneurons might be disrupted in this cortical dysplasia paradigm. We observed that although interneurons migrate into the neocortex in both normal and dysplastic cortex, the migrating cells become disoriented over time after E33 MAM treatment. Coculture experiments using normal GE and MAM-treated cortex (and vice versa) demonstrate that cues dictating proper orientation of migrating interneurons arise from the cortex and are not intrinsic to the migrating cells. As a consequence, interneurons in mature brains of MAM-treated animals are abnormally distributed. We report that GABA(A) receptor activation is crucial to the proper positioning of interneurons migrating into the cortex from the GE in normal and MAM-treated animals. (+info)
Disease-associated mutations affect GPR56 protein trafficking and cell surface expression.
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Bilateral frontoparietal polymicrogyria (BFPP) is a congenital brain malformation resulting in irregularities on the surface of the cortex, where normally convoluted gyri are replaced by numerous (poly) and noticeably smaller (micro) gyri. Individuals with BFPP suffer from epilepsy, mental retardation, language impairment and motor developmental delay. Mutations in the gene-encoding G protein-coupled receptor 56 (GPR56) cause BFPP; however, it remains unclear how these mutations affect GPR56 function. Here, we examine the biochemical properties and protein trafficking of wild-type and mutant GPR56. We demonstrate that GPR56 protein undergoes two major modifications, GPS domain-mediated protein cleavage and N-glycosylation, and that the N-terminal fragment can be released from the cell surface. In contrast to the wild-type protein, disease-associated GPR56 missense mutations in the tip of the N-terminal domain (R38Q, R38W, Y88C and C91S) produce proteins with reduced intracellular trafficking and poor cell surface expression, whereas the two mutations in the GPS domain (C346S and W349S) produce proteins with dramatically impaired cleavage that fail to traffic beyond the endoplasmic reticulum. Cell-trafficking impairments are abrogated in part by pharmacological chaperones that can partially rescue mutant GPR56 cell surface expression. These data demonstrate that some BFPP-associated mutations in GPR56 impair trafficking of the mutant protein to the plasma membrane, thus providing insights into how BFPP-associated mutations affect GPR56 function. (+info)
The clinical spectrum of malformations of cortical development.
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BACKGROUND: Malformations of cortical development (MCD) usually manifest in childhood with epilepsy, developmental delay and focal neurological abnormalities. OBJECTIVE: To evaluate the presentation and severity of epilepsy in the different types of MCD. METHOD: We evaluated the first 100 consecutive patients with a neuroimaging diagnosis of MCD. They were identified among all the high resolution magnetic resonance imaging exams performed at our service between 1997 and 2001. The causes of referral were diverse, according to the routine of the neurology outpatient clinic. After magnetic resonance imaging diagnosis of the subtype of MCD a detailed clinical assessment was performed. RESULTS: There were 55 females and 45 males, with ages ranging from five months to 71 years old (mean=15.2 years). Seventy-seven patients presented with epilepsy. Sixty-one had partial epileptic syndromes, 13 secondary generalized syndromes, and in three, the type of epileptic syndrome could not be established. Epilepsy was less frequent in patients with the MCD subtypes of polymicrogyria and schizencephaly (p<0.001). Patients with schizencephaly and polymicrogyria had their seizures more easily controlled by antiepileptic drugs (p<0.001). CONCLUSION: That the frequency of epilepsy is lower and seizures are more easily controlled in the setting of polymicrogyria and schizencephaly. Patients with MCD frequently present with secondary generalized epilepsy early in childhood. (+info)
Mechanisms of epileptogenesis in tuberous sclerosis complex and related malformations of cortical development with abnormal glioneuronal proliferation.
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Malformations of cortical development (MCDs) are increasingly recognized as causes of medically intractable epilepsy. In order to develop more effective, rational therapies for refractory epilepsy related to MCDs, it is important to achieve a better understanding of the underlying mechanisms of epileptogenesis, but this is complicated by the wide variety of different radiographic, histopathological, and molecular features of these disorders. A subset of MCDs share a number of characteristic cellular and molecular abnormalities due to early defects in neuronal and glial proliferation and differentiation and have a particularly high incidence of epilepsy, suggesting that this category of MCDs with abnormal glioneuronal proliferation may also share a common set of primary mechanisms of epileptogenesis. This review critically analyzes both clinical and basic science evidence for overlapping mechanisms of epileptogenesis in this group of disorders, focusing on tuberous sclerosis complex, focal cortical dysplasia with balloon cells, and gangliogliomas. Specifically, the role of lesional versus perilesional regions, circuit versus cellular/molecular defects, and nonneuronal factors, such as astrocytes, in contributing to epileptogenesis in these MCDs is examined. An improved understanding of these various factors involved in epileptogenesis has direct clinical implications for optimizing current treatments or developing novel therapeutic approaches for epilepsy in these disorders. (+info)
Closed-lip schizencephaly around the central sulcus with intractable epilepsy treated by peri-lesional focus resection.
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A 24-year-old man presented with closed-lip schizencephaly around the right central sulcus manifesting as an 11-year history of intractable epilepsy. Mild motor paresis in the left extremities and mental retardation were observed. Tonic posture with bilateral facial tonic contraction was asymmetrical, predominantly in the left extremities. Magnetic resonance imaging demonstrated closed-lip schizencephaly around the right central sulcus. The epileptogenic zone was determined in the supplementary motor area, and premotor and primary sensorimotor cortices using invasive recordings. As the thickened cortex was considered functional, corticectomy of the supplementary motor area and premotor area was performed, preserving the primary sensorimotor area. Histological examination revealed marked cortico-subcortical gliosis, particularly in the medial part of the resection. Asymmetrical tonic postural seizure disappeared completely after surgery. Medically intractable epilepsy with schizencephaly represents a considerable challenge in epilepsy surgery. Partial corticectomy adjacent to the thickened cortex was effective for seizure control in a patient with closed-lip schizencephaly around the central sulcus. (+info)
Losing their minds: Mena/VASP/EVL triple knockout mice.
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A recent Neuron paper by Kwiatkowski et al. that analyzes the phenotypes of mouse embryos lacking all members of the Ena/VASP family reveals new roles for these molecules in cortical development. (+info)
Proteus syndrome associated with hemimegalencephaly and Ohtahara syndrome: report of two cases.
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The authors report two cases of Brazilian children with most of the common syndromic features of Proteus syndrome, such as asymmetric overgrowth of tissues, skin abnormalities, hypotonia and mental retardation. In both patients, a refractory epilepsy, compatible with Ohtahara syndrome, as well as hemimegalencephaly, with asymmetric distribution of facial fat, were also diagnosed. (+info)
Aberrant midsagittal fiber tracts in patients with hemimegalencephaly.
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