Seizures in Adult with Neurofibromatosis Type 1

Neurofibromatosis type 1 (NF1) is an autosomal dominantly inherited disorder, with an estimated prevalence of 1 in 3000–4000 people. Seizures occur 4–7% of individuals with NF1, mostly due to associated brain tumors or cortical malformations. Seizures in NF1 are often relatively easy to control with one or more conventional antiseizure drugs; surgical resection of offending lesions is sometimes pursued. Surgery has been most successful for temporal lobe gliomas. However, if you faced the drug-resistant epilepsy you may consider the cortical malformations, tumors and hippocampal sclerosis. In this chapter, it is aimed to explain the types of seizures, EEG features and the properties of drug therapy in NF1.

The Role of KRAS Mutations in Cortical Malformation and Epilepsy Surgery: A Novel Report of Nevus Sebaceous Syndrome and Review of the Literature

The rare nevus sebaceous (NS) syndrome (NSS) includes cortical malformations and drug-resistant epilepsy. Somatic RAS-pathway genetic variants are pathogenetic in NS, but not yet described within the brain of patients with NSS. We report on a 5-year-old boy with mild psychomotor delay. A brown-yellow linear skin lesion suggestive of NS in the left temporo-occipital area was evident at birth. Epileptic spasms presented at aged six months. EEG showed continuous left temporo-occipital epileptiform abnormalities. Brain MRI revealed a similarly located diffuse cortical malformation with temporal pole volume reduction and a small hippocampus. We performed a left temporo-occipital resection with histopathological diagnosis of focal cortical dysplasia type Ia in the occipital region and hippocampal sclerosis type 1. Three years after surgery, he is seizure-and drug-free (Engel class Ia) and showed cognitive improvement. Genetic examination of brain and skin specimens revealed the c.35G > T (p.Gly12Val) KRAS somatic missense mutation. Literature review suggests epilepsy surgery in patients with NSS is highly efficacious, with 73% probability of seizure freedom. The few histological analyses reported evidenced disorganized cortex, occasionally with cytomegalic neurons. This is the first reported association of a KRAS genetic variant with cortical malformations associated with epilepsy, and suggests a possible genetic substrate for hippocampal sclerosis.

Functional characterization of RELN missense mutations involved in recessive and dominant forms of Neuronal Migration Disorders

RELN is a large secreted glycoprotein that acts at multiple steps of cerebral cortex development, including neuronal migration. Only recessive mutations of the Reelin gene (RELN) have been associated with human cortical malformations and none has been functionally characterized. We identified novel missense RELN mutations in both compound and de novo heterozygous patients exhibiting an array of neuronal migration disorders (NMDs) as diverse as pachygyria, polymicrogyria and heterotopia. Most mutations caused defective RELN secretion in vitro and, when ectopically expressed in the embryonic mouse cortex, affected neuronal aggregation and/or migration in vivo. We determined the de novo heterozygous mutations acted as dominant negative and demonstrated that RELN mutations mediate not only recessive, but also dominant NMDs. This work assesses for the first time the pathogenicity of RELN mutations showing a strong genotype-phenotype correlation. In particular, the behavior of the mutant proteins in vitro and in vivo predicts the severity of cortical malformations and provides valuable insight into the pathogenesis of these disorders.

Neurite Outgrowth Inhibitor (NogoA) Is Upregulated in White Matter Lesions of Complex Cortical Malformations

Complex cortical malformations (CCMs), such as hemimegalencephaly and polymicrogyria, are associated with drug-resistant epilepsy and developmental impairment. They share certain neuropathological characteristics including mammalian target of rapamycin (mTOR) activation and an atypical number of white matter neurons. To get a better understanding of the pathobiology of the lesion architecture, we investigated the role of neurite outgrowth inhibitor A (NogoA), a known regulator of neuronal migration. Epilepsy surgery specimens from 16 CCM patients were analyzed and compared with sections of focal cortical dysplasia IIB (FCD IIB, n = 22), tuberous sclerosis complex (TSC, n = 8) as well as healthy controls (n = 15). Immunohistochemistry was used to characterize NogoA, myelination, and mTOR signaling. Digital slides were evaluated automatically with ImageJ. NogoA staining showed a significantly higher expression within the white matter of CCM and FCD IIB, whereas cortical tubers presented levels similar to controls. Further analysis of possible associations of NogoA with other factors revealed a positive correlation with mTOR and seizure frequency. To identify the main expressing NogoA cell type, double staining revealed dysmorphic neuronal white matter cells. Increased NogoA expression is associated with profound inhibition of neuritic sprouting and therefore contributes to a decrease in neuronal network complexity in CCM patients.

Doublecortin facilitates the elongation of the somatic Golgi apparatus into proximal dendrites

Mutations in the doublecortin ( DCX) gene, which encodes a microtubule-binding protein, cause human cortical malformations, including lissencephaly and subcortical band heterotopia. A deficiency in DCX and doublecortin-like kinase 1 (DCLK1), a functionally redundant and structurally similar cognate of DCX, decreases neurite length and increases the number of primary neurites directly arising from the soma. The underlying mechanism is not completely understood. In this study, the elongation of the somatic Golgi apparatus into proximal dendrites, which have been implicated in dendrite patterning, was significantly decreased in the absence of DCX/DCLK1. Phosphorylation of DCX at S47 or S327 was involved in this process. DCX deficiency shifted the distribution of CLASP2 proteins to the soma from the dendrites. In addition to CLASP2, dynein and its co-factor JIP3 were abnormally distributed in DCX-deficient neurons. The association between JIP3 and dynein was significantly increased in the absence of DCX. Downregulation of CLASP2 or JIP3 expression with specific shRNAs rescued the Golgi phenotype observed in DCX-deficient neurons. We conclude that DCX regulates the elongation of the Golgi apparatus into proximal dendrites through microtubule-associated proteins and motors.

Megalencephaly–Capillary Malformation–Polymicrogyria with Cerebral Venous Thrombosis

Megalencephaly–capillary malformation–polymicrogyria (MCAP) syndrome (OMIM #602501) is characterized by megalencephaly, midline capillary malformations, and cortical malformations. This genetic overgrowth syndrome is associated with mosaic gain-of-function pathogenic PIK3CA variants (OMIM #171834).