A case of Noonan syndrome with cortical dysplasia

Epilepsy and BRAF Mutations: Phenotypes, Natural History and Genotype-Phenotype Correlations

OBJECTIVE

Cardiofaciocutaneous syndrome (CFCS) is a rare developmental disorder caused by upregulated signaling through the RAS-mitogen-activated protein kinase (MAPK) pathway, mostly resulting from de novo activating BRAF mutations. Children with CFCS are prone to epilepsy, which is a major life-threatening complication. The aim of our study was to define the natural history of epilepsy in this syndrome and exploring genotype-phenotype correlations.

METHODS

We performed an observational study, including 34 patients with molecularly confirmed diagnosis (11 males, mean age: 15.8 years). The mean follow-up period was 9.2 years. For all patients, we performed neurological examination, cognitive assessment when possible, neuroimaging, electrophysiological assessment and systematic assessment of epilepsy features. Correlation analyses were performed, taking into account gender, age of seizure onset, EEG features, degree of cognitive deficits, type of mutation, presence of non-epileptic paroxysmal events and neuroimaging features.

RESULTS

Epilepsy was documented in 64% of cases, a higher prevalence compared to previous reports. Patients were classified into three groups based on their electroclinical features, long-term outcome and response to therapy. A genotype-phenotype correlation linking the presence/severity of epilepsy to the nature of the structural/functional consequences of mutations was observed, providing a stratification based on genotype to improve the clinical management of these patients.

The impact of RASopathy-associated mutations on CNS development in mice and humans

The RAS signaling pathway is involved in the regulation of developmental processes, including cell growth, proliferation, and differentiation, in the central nervous system (CNS). Germline mutations in the RAS signaling pathway genes are associated with a group of neurodevelopmental disorders, collectively called RASopathy, which includes neurofibromatosis type 1, Noonan syndrome, cardio-facio-cutaneous syndrome, and Costello syndrome. Most mutations associated with RASopathies increase the activity of the RAS-ERK signaling pathway, and therefore, most individuals with RASopathies share common phenotypes, such as a short stature, heart defects, facial abnormalities, and cognitive impairments, which are often accompanied by abnormal CNS development. Recent studies using mouse models of RASopathies demonstrated that particular mutations associated with each disorder disrupt CNS development in a mutation-specific manner. Here, we reviewed the recent literatures that investigated the developmental role of RASopathy-associated mutations using mutant mice, which provided insights into the specific contribution of RAS-ERK signaling molecules to CNS development and the subsequent impact on cognitive function in adult mice.

Quantification of perivascular spaces at 7T: A potential MRI biomarker for epilepsy

PURPOSE

7T (7T) magnetic resonance imaging (MRI) facilitates the visualization of the brain with resolution and contrast beyond what is available at conventional clinical field strengths, enabling improved detection and quantification of small structural features such as perivascular spaces (PVSs). The distribution of PVSs, detected in vivo at 7T, may act as a biomarker for the effects of epilepsy. In this work, we systematically quantify the PVSs in the brains of epilepsy patients and compare them to healthy controls.

METHODS

T₂-weighted turbo spin echo images were obtained at 7T on 21 epilepsy patients and 17 healthy controls. For all subjects, PVSs were manually marked on Osirix image analysis software. Marked PVSs with diameter≥0.5mm were then mapped by hemisphere and lobe. The asymmetry index (AI) was calculated for each region and the maximum asymmetry index (|AI_max|) was reported for each subject. The asymmetry in epilepsy subjects was compared to that of controls, and the region with highest asymmetry was compared to the suspected seizure onset zone.

RESULTS

There was a significant difference between the |AI_max| in epilepsy subjects and in controls (p=0.016). In 72% of patients, the region or lobe of the brain showing maximum PVS asymmetry was the same as the region containing the suspected seizure onset zone.

CONCLUSION

These findings suggest that epilepsy may be associated with significantly asymmetric distribution of PVSs in the brain. Furthermore, the region of maximal asymmetry of the PVSs may help provide localization or confirmation of the seizure onset zone.

Seizures and EEG features in 74 patients with genetic-dysmorphic syndromes

Epilepsy is one of the most common findings in chromosome aberrations. Types of seizures and severity may significantly vary both between different conditions and within the same aberration. Hitherto specific seizures and EEG patterns are identified for only few syndromes. We studied 74 patients with defined genetic-dysmorphic syndromes with and without epilepsy in order to assess clinical and electroencephalographic features, to compare our observation with already described electro-clinical phenotypes, and to identify putative electroencephalographic and/or seizure characteristics useful to address the diagnosis. In our population, 10 patients had chromosomal disorders, 19 microdeletion or microduplication syndromes, and 32 monogenic syndromes. In the remaining 13, syndrome diagnosis was assessed on clinical grounds. Our study confirmed the high incidence of epilepsy in genetic-dysmorphic syndromes. Moreover, febrile seizures and neonatal seizures had a higher incidence compared to general population. In addition, more than one third of epileptic patients had drug-resistant epilepsy. EEG study revealed poor background organization in 42 patients, an excess of diffuse rhythmic activities in beta, alpha or theta frequency bands in 34, and epileptiform patterns in 36. EEG was completely normal only in 20 patients. No specific electro-clinical pattern was identified, except for inv-dup15, Angelman, and Rett syndromes. Nevertheless some specific conditions are described in detail, because of notable differences from what previously reported. Regarding the diagnostic role of EEG, we found that--even without any epileptiform pattern--the generation of excessive rhythmic activities in different frequency bandwidths might support the diagnosis of a genetic syndrome.

Cardio-facio-cutaneous syndrome with infantile spasms and delayed myelination

A girl with cardio-facio-cutaneous (CFC) syndrome due to a BRAF gene mutation (c.1454T→C, p.L485S) experienced repetitive epileptic spasms at the corrected age of 4 months. Electroencephalograms revealed hypsarrhythmia, and magnetic resonance imaging identified delayed myelination and a hypoplastic corpus callosum. Various antiepileptic treatments, including adrenocorticotropic hormone therapy, were ineffective, although transient seizure control was achieved by a ketogenic diet and clorazepate dipotassium. However, seizures with epileptic foci at the bilateral posterior temporal areas re-aggravated and remained intractable; severe psychomotor delay persisted. This case indicated that infantile spasms in CFC syndrome can be difficult to control and may be accompanied by severe psychomotor retardation and abnormal myelination.

Control of CNS cell-fate decisions by SHP-2 and its dysregulation in Noonan syndrome

Within the developing mammalian CNS, growth factors direct multipotent precursors to generate neurons versus glia, a process that if perturbed might lead to neural dysfunction. In this regard, genetic mutations resulting in constitutive activation of the protein tyrosine phosphatase SHP-2 cause Noonan Syndrome (NS), which is associated with learning disabilities and mental retardation. Here, we demonstrate that genetic knockdown of SHP-2 in cultured cortical precursors or in the embryonic cortex inhibited basal neurogenesis and caused enhanced and precocious astrocyte formation. Conversely, expression of an NS SHP-2 mutant promoted neurogenesis and inhibited astrogenesis. Neural cell-fate decisions were similarly perturbed in a mouse knockin model that phenocopies human NS. Thus, SHP-2 instructs precursors to make neurons and not astrocytes during the neurogenic period, and perturbations in the relative ratios of these two cell types upon constitutive SHP-2 activation may contribute to the cognitive impairments in NS patients.

Preoperative clinical evaluation and noninvasive electroencephalogram in cortical dysplasia

The preoperative evaluation of patients with suspected cortical dysplasia involves detailed neurologic and neuropsychologic evaluations, electroencephalography, and comprehensive neuroimaging and functional studies. The goal is to identify a focal region of seizure onset and to assess for motor impairments, speech and language difficulties, or developmental delay. Although the electroencephalogram abnormalities in cortical dysplasia are nonspecific, they typically include unusual high-amplitude (slowing and focal) activity. The association of cortical dysplasia with cardiovascular, dermatologic, and other systemic disorders is discussed.