Neuropathologic study of resected cerebral tissue from patients with infantile spasms

Human iPS Cell-Derived Neurons Uncover the Impact of Increased Ras Signaling in Costello Syndrome

Increasing evidence implicates abnormal Ras signaling as a major contributor in neurodevelopmental disorders, yet how such signaling causes cortical pathogenesis is unknown. We examined the consequences of aberrant Ras signaling in the developing mouse brain and uncovered several critical phenotypes, including increased production of cortical neurons and morphological deficits. To determine whether these phenotypes are recapitulated in humans, we generated induced pluripotent stem (iPS) cell lines from patients with Costello syndrome (CS), a developmental disorder caused by abnormal Ras signaling and characterized by neurodevelopmental abnormalities, such as cognitive impairment and autism. Directed differentiation toward a neuroectodermal fate revealed an extended progenitor phase and subsequent increased production of cortical neurons. Morphological analysis of mature neurons revealed significantly altered neurite length and soma size in CS patients. This study demonstrates the synergy between mouse and human models and validates the use of iPS cells as a platform to study the underlying cellular pathologies resulting from signaling deficits.

SIGNIFICANCE STATEMENT

Increasing evidence implicates Ras signaling dysfunction as a major contributor in psychiatric and neurodevelopmental disorders, such as cognitive impairment and autism, but the underlying cortical cellular pathogenesis remains unclear. This study is the first to reveal human neuronal pathogenesis resulting from abnormal Ras signaling and provides insights into how these phenotypic abnormalities likely contribute to neurodevelopmental disorders. We also demonstrate the synergy between mouse and human models, thereby validating the use of iPS cells as a platform to study underlying cellular pathologies resulting from signaling deficits. Recapitulating human cellular pathologies in vitro facilitates the future high throughput screening of potential therapeutic agents that may reverse phenotypic and behavioral deficits.

Enhanced GABAergic network and receptor function in pediatric cortical dysplasia Type IIB compared with Tuberous Sclerosis Complex

Tuberous Sclerosis Complex (TSC) and cortical dysplasia Type IIB (CDIIB) share histopathologic features that suggest similar epileptogenic mechanisms. This study compared the morphological and electrophysiological properties of cortical cells in tissue from pediatric TSC (n=20) and CDIIB (n=20) patients using whole-cell patch clamp recordings and biocytin staining. Cell types were normal-appearing and dysmorphic-cytomegalic pyramidal neurons, interneurons, and giant/balloon cells, including intermediate neuronal-glial cells. In the cortical mantle, giant/balloon cells occurred more frequently in TSC than in CDIIB cases, whereas cytomegalic pyramidal neurons were found more frequently in CDIIB. Cell morphology and membrane properties were similar in TSC and CDIIB cases. Except for giant/balloon and intermediate cells, all neuronal cell types fired action potentials and displayed spontaneous postsynaptic currents. However, the frequency of spontaneous glutamatergic postsynaptic currents in normal pyramidal neurons and interneurons was significantly lower in CDIIB compared with TSC cases and the GABAergic activity was higher in all neuronal cell types in CDIIB. Further, acutely dissociated pyramidal neurons displayed higher sensitivity to exogenous application of GABA in CDIIB compared with TSC cases. These results indicate that, in spite of similar histopathologic features and basic cell membrane properties, TSC and CDIIB display differences in the topography of abnormal cells, excitatory and inhibitory synaptic network properties, and GABA(A) receptor sensitivity. These differences support the notion that the mechanisms of epileptogenesis could differ in patients with TSC and CDIIB. Consequently, pharmacologic therapies should take these findings into consideration.

Genetics and function of neocortical GABAergic interneurons in neurodevelopmental disorders

A dysfunction of cortical and limbic GABAergic circuits has been postulated to contribute to multiple neurodevelopmental disorders in humans, including schizophrenia, autism, and epilepsy. In the current paper, I summarize the characteristics that underlie the great diversity of cortical GABAergic interneurons and explore how the multiple roles of these cells in developing and mature circuits might contribute to the aforementioned disorders. Furthermore, I review the tightly controlled genetic cascades that determine the fate of cortical interneurons and summarize how the dysfunction of genes important for the generation, specification, maturation, and function of cortical interneurons might contribute to these disorders.

Comparative study of cellular and synaptic abnormalities in brain tissue samples from pediatric tuberous sclerosis complex and cortical dysplasia type II

Tuberous sclerosis complex (TSC) and severe cortical dysplasia (CD), or CD type II according to Palmini classification, share histopathologic similarities, specifically the presence of cytomegalic neurons and balloon cells. In this study we examined the morphologic and electrophysiologic properties of cells in cortical tissue samples from pediatric patients with TSC and CD type II who underwent surgery for pharmacoresistant epilepsy. Normal-appearing pyramidal neurons from TSC and CD type II cases had similar passive membrane properties. However, the frequency of excitatory postsynaptic currents (EPSCs) was higher in neurons from TSC compared to severe CD cases, particularly the frequency of medium- and large-amplitude synaptic events. In addition, EPSCs rise and decay times were slower in normal cells from TSC compared to severe CD cases. Balloon cells were found more frequently in TSC cases, whereas cytomegalic pyramidal neurons occurred more often in CD type II cases. Both cell types were similar morphologically and electrophysiologically in TSC and severe CD. These results suggest that even though the histopathology in TSC and severe CD is similar, there are subtle differences in spontaneous synaptic activity and topographic distribution of abnormal cells. These differences may contribute to variable mechanisms of epileptogenesis in patients with TSC compared with CD type II.

Neurodevelopmental disorders as a cause of seizures: neuropathologic, genetic, and mechanistic considerations

This review will consider patterns of developmental neuropathologic abnormalities-malformations of cortical development (MCD)--encountered in infants (often with infantile spasms), children, and adults with intractable epilepsy. Treatment of epilepsy associated with some MCD, such as focal cortical dysplasia and tubers of tuberous sclerosis, may include cortical resection performed to remove the "dysplastic" region of cortex. In extreme situations (eg, hemimegalencephaly), hemispherectomy may be carried out on selected patients. Neuropathologic (including immunohistochemical) findings within these lesions will be considered. Other conditions that cause intractable epilepsy and often mental retardation, yet are not necessarily amenable to surgical treatment (eg, lissencephaly, periventricular nodular heterotopia, double cortex syndrome) will be discussed. Over the past 10 years there has been an explosion of information on the genetics of MCD. The genes responsible for many MCD (eg, TSC1, TSC2, LIS-1, DCX, FLN1) have been cloned and permit important mechanistic studies to be carried out with the purpose of understanding how mutations within these genes result in abnormal cortical cytoarchitecture and anomalous neuroglial differentiation. Finally, novel techniques allowing for analysis of patterns of gene expression within single cells, including neurons, is likely to provide answers to the most vexing and important question about these lesions: Why are they epileptogenic?

Co-localization of TSC1 and TSC2 gene products in tubers of patients with tuberous sclerosis

Two genes, mutations in which result in the phenotype of tuberous sclerosis (TSC), have recently been cloned. TSC2 on chromosome 16p13.3 encodes the protein tuberin, which appears to have growth regulating properties. TSC1 on chromosome 9q34 encodes hamartin which, as yet, has no specified cellular functions. Polyclonal antibodies were raised to synthetic peptides representing portions of tuberin and hamartin and used in immunoblots and immunohistochemical studies to localize the proteins in surgically resected neocortical tubers from four TSC patients. On Western blots of autopsy brain specimens, K-562 cell, and NT2 lysates, each antibody labelled a single band at the expected molecular weight. In immunohistochemical protocols on paraffin embedded tissue, antibodies to both tuberin and hamartin prominently labelled atypical and dysmorphic neuroglial cells that are a defining feature of TSC tubers. Some abnormal cells within cortical tuber sections were labelled with both tuberin and hamartin antisera. Our results suggest that tuberin and hamartin are both robustly expressed in similar populations of neuroglial cells of TSC tubers, even in the presence of TSC1 or TSC2 germline mutations. The roles of these gene products in normal and abnormal cortical development, tuber pathogenesis and the generation of seizures remain to be defined.

Aberrant neuronal-glial differentiation in Taylor-type focal cortical dysplasia (type IIA/B)

Focal cortical dysplasia (FCD) type IIA/B (Taylor type) is a malformation of cortical development characterized by laminar disorganization and dysplastic neurons. FCD IIA and FCD IIB denote subtypes in which balloon cells are absent or present, respectively. The etiology of FCD IIA/B is unknown, but previous studies suggest that its pathogenesis may involve aberrant, mixed neuronal-glial differentiation. To investigate whether aberrant differentiation is a consistent phenotype in FCD IIA/B, we studied a panel of neuronal and glial marker antigens in a series of 15 FCD IIB cases, and 2 FCD IIA cases. Double-labeling immunofluorescence and confocal imaging revealed that different combinations of neuronal and glial antigens were co-expressed by individual cells in all cases of FCD IIA/B, but not in control cases of epilepsy due to other causes. Co-expression of neuronal and glial markers was most common in balloon cells, but was also observed in dysplastic neurons. The relative expression of neuronal and glial antigens varied over a broad range. Microtubule-associated protein 1B, an immature neuronal marker, was more frequently co-expressed with glial antigens than were mature neuronal markers, such as neuronal nuclear antigen. Our results indicate that aberrant neuronal-glial differentiation is a consistent and robust phenotype in FCD IIA/B, and support the hypothesis that developmental defects of neuronal and glial fate specification play an important role in its pathogenesis.

Insulin signaling pathways in cortical dysplasia and TSC-tubers: tissue microarray analysis

To evaluate the possible roles of the Akt/PKB-mTOR-p70S6K-S6 and cap-dependent translation (eIF4G) pathways in the pathogenesis of tuberous sclerosis complex (TSC)-associated cortical tubers and focal cortical dysplasia (FCD), we performed qualitative and semiquantitative immunohistochemical evaluation on surgically resected corticectomy specimens to detect phosphorylated molecules as activated downstream targets of the signaling pathways. A tissue microarray paraffin block was constructed from 63 archival specimens of surgically resected TSC tubers, FCDs with balloon cells, cortical dysplasia without balloon cells, and histologically normal-appearing neocortex obtained from cases with Rasmussen encephalitis, cystic-gliotic encephalopathy, and temporal lobe epilepsy. Abnormal neuroglial cells were positive for phospho-S6 and phospho-eIF4G with various staining intensities in FCDs and TSC tubers. Both proteins were much less abundantly expressed in normal-appearing neocortex. Phospho-mTOR expression was observed in neurons in all groups. The expression of phospho-S6 and phospho-eIF4G was associated with dysplastic lesions (p < 0.05), and the cytoplasmic phospho-p70S6K expression was most specific for and abundant in TSC tubers and much less prominent in other groups (p < 0.01). These results suggest that constitutive activation of cytoplasmic p70S6K plays a pivotal role in the pathogenesis of TSC tubers and that FCDs possess a distinct mechanism for activation of S6 and eIF4G.

Malformations of cortical development: molecular pathogenesis and experimental strategies

Malformations of cortical development (MCD) are developmental brain lesions characterized by abnormal formation of the cerebral cortex and a high clinical association with epilepsy in infants, children, and adults. Despite multiple anti-epileptic drugs (AEDs), treatment of epilepsy associated with MCD may require cortical resection performed to remove the cytoarchitecturally abnormal region of cortex. Single genes responsible for distinct MCD including lissencephaly, subcortical band heterotopia, and tuberous sclerosis, have been identified and permit important mechanistic insights into how gene mutations result in abnormal cortical cytoarchitecture. The pathogenesis of MCD such as focal cortical dysplasia, hemimegalencephaly, and polymicrogyria, remains unknown. A variety of new techniques including cDNA array analysis now allow for analysis of gene expression within MCD.

Altered corticogenesis and neuronal morphology in irradiation-induced cortical dysplasia: a Golgi-Cox study

Cortical dysplasia has a strong clinical association with epilepsy and mental retardation, but the relationship between alterations in cortical structure and function in dysplasia-related disorders is poorly understood. The cerebral cortex of irradiated rats, an experimental model of cortical dysplasia, was studied using cresyl violet-stained sections and the Golgi-Cox method. The irradiated cortex is characterized by reductions in size, volume, and number of neurons and fibers reflecting the original lethal injury to neuronal precursors. Consequently, only neurons that survived this injury were able to continue their, albeit altered, development. The result is an altered corticogenesis characterized by neuronal, fiber circuitry, and microvascular alterations. Abnormal aggregates (nodules) of excitatory pyramidal neurons with altered dendritic profiles and functional territories are found between 200 and 400 microm from the pial surface. Their horizontal dendritic profiles and functional territories contrast with the vertical (columnar) dendritic profiles and functional territories of normal pyramidal neurons. This horizontal concentration of spiny dendrites and, hence, of excitatory synaptic contacts suggests a response to the presence of an abnormal horizontal plexus of afferent fibers terminals. Stellate neurons, some morphologically compatible with inhibitory basket cells, are also essential components of these nodules. Some neuronal nodules are characterized by a rich plexus of anastomotic capillaries that contrasts with the sparser vasculature of surrounding gray matter tissue. The presence of well-vascularized aggregates of altered pyramidal and inhibitory neurons suggests a high level of metabolic activity. Well-vascularized deep heterotopias are also found. We propose that the functional activity of well-vascularized neuronal nodules and heterotopias could play a role in the abnormal cortical function in this model.

Treatment considerations: role of surgery

Patients with developmental disabilities, including retardation and global developmental delay, are not ideal candidates for epilepsy surgery. Because they have an increased likelihood of diffuse brain dysfunction and multifocal or generalized epileptogenic zones, there is an increased chance that a focal cortical resection will not confer a major improvement in their seizure frequency and severity. There is also increased concern that cortical resection will lead to increase in the patient's disability. However, by applying the basic principles of epilepsy surgery selection (i.e., convergence of multiple lines of localizing evidence) to this population, patients with a reasonable likelihood of good seizure control can be identified. Various means of localizing seizure onset are reviewed, including history and examination, electroencephalography, magnetic resonance imaging, position emission tomography, single-photon-emission tomography, and magnetoencephalography.

Histopathology of brain tissue from patients with infantile spasms

This chapter reviews the patterns of neuropathologic abnormality encountered in cortical resections performed for the treatment of infantile spasms (ISS) in the broader context of the larger "universe" of neuropathology seen in the central nervous system of infants with this syndrome as well as older children with intractable epilepsy. Although destructive lesions (encephalomalacia), Sturge-Weber-Dimitri syndrome, and even neoplasms can cause ISS, its most common neuropathologic substrate is cortical dysplasia (CD), representing the result of aberrant neuronal migration to the neocortex from the germinal matrix. Ways to recognize CD morphologically and assess its severity are reviewed, as are special stains and immunohistochemical methods that may be useful in confirming the diagnosis. The similarity and relationship between (sporadic) CD and tubers of tuberous sclerosis are discussed. Future potentially fruitful research directions aimed at refining the clinicopathologic analysis of the role of CD in ISS and epilepsies of older children are briefly considered.

Pathophysiology of infantile spasms

Infantile spasms--seen in West's Syndrome--are often associated with cortical abnormalities. The spasms themselves, however, appear to be generated subcortically. Dr. Chugani reviews the clinical data related to the pathophysiology of infantile spasms and proposes a hypothesis which involves both cortical and subcortical mechanisms.

Neuropathology of the limbic system and brainstem in West syndrome

Both West syndrome (WS) and Lennox-Gastaut syndrome (LGS) are associated with various developmental disorders and it has been discussed whether the cerebral cortex or subcortical structures are important in the pathogenesis of both epileptic syndromes. Here we briefly review the literature on the neuropathological findings in WS and LGS, and present our data on immunohistochemical analysis of the brainstem and limbic lesions in autopsy cases of lissencephaly and sequels of hypoxic ischemic encephalopathy (HIE) caused by perinatal asphyxia manifested as both WS and LGS (WS/LGS). Nowadays, the neuroradiological examinations and surgical pathology in WS cases demonstrate dysplastic cerebral lesions more frequently than previously expected. On the other hand, we have delineated the common brainstem lesions such as small size of the tegmentum and spongy state and/or gliosis in the central tegmental tract in a number of WS autopsy cases of various etiologies. Recently, we reported the reduced expression of tyrosine hydroxylase, methionine enkephalin and parvalbumin in the brainstem in autopsy cases of lissencephaly and sequels of HIE manifested as WS/LGS, regardless of the cerebral changes. In the same subjects, we examined the expression of glutamate transporters and calcium-binding proteins in the limbic system by immunohistochemistry. These represent markers of glutamate neurotoxicity and the GABAergic inhibitory neuron system, respectively. The altered expressions of glial glutamate transporters and calcium-binding proteins in the limbic system seemed to reflect temporal lobe sclerosis, irrespective of the past history of WS, and there were no differences in the limbic involvement between the cases manifested as WS/LGS and disease controls of sequels of HIE not manifested as WS/LGS. It is more likely that the brainstem lesions contribute to the pathogenesis of WS and/or LGS more than the heterogeneous limbic lesions in these cases.

Radiologic-pathologic correlation in focal cortical dysplasia and hemimegalencephaly in 18 children

To describe the radiologic-pathologic correlation in children who underwent epilepsy surgery for medically intractable epilepsy with pathologically confirmed focal cortical dysplasia and hemimegalencephaly, we conducted a retrospective review on the magnetic resonance imaging and pathology of 18 children (10 boys and 8 girls). The preoperative MRIs were reviewed by one neuroradiologist who did not know the radiologic diagnosis and the pathology reports. MRI revealed focal cortical dysplasia (10), hemimegalencephaly (3), hamartomas (2), polymicrogyria (1), pial hemosiderosis (1), and no abnormality (1). Pathologic examination revealed focal cortical dysplasia (9), forme fruste of tuberous sclerosis (5), hemimegalencephaly (3), and focal cortical dysplasia with mesial temporal sclerosis (1). MRI was accurate in making the preoperative diagnosis in 16 out of 18 patients. On MRI, 12 patients had abnormal gyral formation and 12 had abnormal cortical thickness. Eleven patients manifested loss of gray-white differentiation, and 11 patients had abnormal signal on T(2)-weighted image. Pathologically, 15 patients had neuronal heterotopia, 12 had misalignment or disorientation of neurons, 11 had large neurons, and 10 had abnormal cortical lamination. The presence of ectopic and large neurons and abnormal cortical lamination may be responsible for the MRI characteristics.

Neuronal hypertrophy in the neocortex of patients with temporal lobe epilepsy

The underlying cause of neocortical involvement in temporal lobe epilepsy (TLE) remains a fundamental and unanswered question. Magnetic resonance imaging has shown a significant loss in temporal lobe volume, and it has been proposed that neocortical circuits are disturbed functionally because neurons are lost. The present study used design-based stereology to estimate the volume and cell number of Brodmann's area 38, a region commonly resected in anterior temporal lobectomy. Studies were conducted on the neocortex of patients with or without hippocampal sclerosis (HS). Results provide the surprising finding that TLE patients have significant atrophy of neocortical gray matter but no loss of neurons. Neurons are also significantly larger, dendritic trees appear sparser, and spine density is noticeably reduced in TLE specimens compared with controls. The increase in neuronal density we found in TLE patients is therefore attributable to large neurons occupying a much smaller volume than in normal brain. Neurons in the underlying white matter are also increased in size but, in contrast to other reports, are not significantly elevated in number or density. Neuronal hypertrophy affects HS and non-HS brains similarly. The reduction in neuropil and its associated elements therefore appears to be a primary feature of TLE, which is not secondary to cell loss. In both gray and white matter, neuronal hypertrophy means more perikaryal surface area is exposed for synaptic contacts and emerges as a hallmark of this disease.

Clinicopathological findings in patients who have undergone epilepsy surgery in the first year of life

Epilepsy presenting early in childhood may be associated with a neurologically devastating clinical course and have significant implications for the child's development. There are limited published data regarding the clinicopathological features of patients who have undergone epilepsy surgery in the first year of life and the role such surgery may have in reducing seizure frequency. This study retrospectively reviews the clinicopathologic features of eight patients from a tertiary care setting who underwent surgery for epilepsy in the first year of life. Eight infants, including seven males and one female, underwent surgery for epilepsy at 3-11 months of age (median 7.5 months). Age at the time of seizure onset ranged from birth to 2 months. Epileptogenic foci were localized by electroencephalographic and radiographic studies to the right side in five patients and left side in three patients. Histopathological findings in excised tissues included cortical dysplasia (n = 7), hemimegalencephaly (n = 3), and Sturge-Weber syndrome (n = 1). Dysplasia was marked by abnormalities in cortical lamination and neuronal orientation (n = 7), neuronal cytomegaly (n = 6), increased molecular layer neurons (n = 5) and balloon cells (n = 2). One patient was known to have epidermal nevus syndrome. Two patients required additional surgery for continued seizures. At last known follow up, all but one patient, who died in the postoperative period, were alive with no or decreased seizures at postoperative intervals of 3-60 months (median 13 months). Surgery can potentially ameliorate epilepsy in patients less than 1 year of age. Most of the patients in this series had cortical dysplasia as the underlying pathology of their epilepsy.

Selective coexpression of NMDAR2A/B and NMDAR1 subunit proteins in dysplastic neurons of human epileptic cortex

NR1 and NR2 are the two gene families for the NMDA receptor. In vitro studies show that while NR2 alone is nonfunctional, NR1 alone produces weak currents to glutamate or NMDA. We previously showed by immunocytochemistry (ICC) that in normal appearing, nonepileptic human cortical neurons, only NR1 and not NR2 proteins were expressed, in contrast to the presence of both NR1 and NR2 in normal rat cortical neurons. We also showed, in dysplastic epileptic cortex, that both NR1 and NR2 were highly expressed using ICC on adjacent 30-microm sections. However, the relative coexpressions of NR1 and NR2 proteins in single neurons in single sections of human epileptic cortex were unknown. In this study, we used double-labeled immunofluorescence and confocal microscopy to examine the distribution and coexpression of subunit proteins for NR1 and NR2A/B in both nondysplastic (control comparison) and dysplastic regions of human brain resected for the treatment of intractable epilepsy (11 patients). In nondysplastic regions, cortical neurons did not have immunoreactivity (ir) for NR2A/B, whereas NR1-ir was abundant. By contrast, dysplastic neurons in the regions with epileptic cortical dysplasia showed intense NR2A/B-ir in the somata and their dendritic processes. These same NR2A/B-ir dysplastic neurons were colabeled by NR1. These results demonstrate directly that dysplastic neurons express both NR2A/B and NR1 proteins, whereas nondysplastic cortical neurons express only NR1 proteins. Selective coexpression of NR2A/B and NR1 in dysplastic neurons suggests that NR2A/B may form heteromeric NR1-NR2 coassemblies and hyperexcitability in dysplastic neurons that could contribute to focal seizure onset.

Spectral properties of EEG fast activity ictal discharges associated with infantile spasms

OBJECTIVE

The aim of this study was to evaluate the characteristics of the ictal EEG event accompanying infantile spasms.

METHODS

Quantitative analysis was used, based on the application of a bivariate autoregressive (AR) parametric model; autospectra, coherence, phase functions and inter-hemispheric time differences were estimated on homologous EEG channels in 18 infants presenting with either cryptogenic or symptomatic West syndrome.

RESULTS

The AR analysis of the 500 ms EEG epochs preceding spasm onset revealed the presence of a short discharge of fast activity restricted to a narrow frequency band in 13 of the 18 cases included in the study. The fast discharge peaked at 17.5+/-2.1 Hz, with rather low inter-hemispheric coherence values (0.52+/-0.17) and asymmetric amplitude on homologous EEG derivations. It persisted briefly after spasm onset, reaching a higher coherence value (0.71+/-0.16). The inter-hemispheric time difference, estimated in those cases with the coherence values significantly different from zero, ranged from 9.1 to 14.3 ms (11.4+/-1.9) in the epoch preceding spasm onset.

CONCLUSION

The data obtained from the analysis of the ictal EEG events, compared with clinical and interictal EEG features, indicate that an asymmetric EEG pattern (mainly consisting of a rhythmic burst of fast activity) consistently preceded both symmetric and asymmetric spasms, thus suggesting a localized cortical origin of the ictal discharge giving rise to the spasms.

Plasma amino acids in childhood epileptic encephalopathies

Abnormalities in plasma amino acid levels have been noted in patients with various epilepsies, and sometimes also in their first degree relatives. We sought to study plasma amino acid levels in children with epileptic encephalopathies and their parents, relating findings to the pattern of cortical glucose metabolism as determined by 18fluorodeoxyglucose (FDG) positron emission tomography (PET). Twenty-eight children with cryptogenic epileptic encephalopathies were studied prospectively. Cortical glucose metabolism was evaluated by FDG PET with combined visual and semiquantitative analysis used to detect focal cortical defects. The plasma concentration of 21 amino acids in the children and their parents was measured by ion exchange chromatography and compared with control values using non-parametric statistical methods. Multivariate analysis was used to assess antiepileptic drug effects. Children were classified as: Lennox-Gastaut syndrome following infantile spasms (six patients); de-novo Lennox-Gastaut syndrome (eight); severe myoclonic epilepsy in infancy (eight) and myoclonic-astatic epilepsy (two). Four patients remained unclassified. Fourteen patients had focal/multifocal abnormalities on PET scans. The plasma level of aspartate was significantly lower in both the children with epileptic encephalopathies and in their parents (P < 0.005). The lowered aspartate levels could not be accounted for by the antiepileptic drug medication taken by the children. Further analysis showed the lowered aspartate levels to be confined to children and their parents who lacked focal PET abnormalities. These findings suggest a possible genetic abnormality in the aspartate neurotransmitter systems in the pathogenesis of seizures in the childhood epileptic encephalopathies.

Tuberous sclerosis complex consensus conference: revised clinical diagnostic criteria

At the recent tuberous sclerosis complex consensus conference, the clinical diagnostic criteria for tuberous sclerosis complex were simplified and revised to reflect both new clinical information about tuberous sclerosis complex and an improved understanding of the disorder derived from molecular genetic studies. Based on this new information, some clinical signs once regarded as pathognomonic for tuberous sclerosis complex are now known to be less specific. No single sign is present in all affected patients, and there is no proof that any single clinical or radiographic sign is absolutely specific for tuberous sclerosis complex. Accordingly, the clinical and radiographic features of tuberous sclerosis complex have now been divided into major and minor categories based on the apparent degree of specificity for tuberous sclerosis complex of each feature. A definitive diagnosis of tuberous sclerosis complex now requires two or more distinct types of lesions, rather than multiple lesions of the same type in the same organ system. Although diagnosis on purely clinical grounds can continue to be difficult in a few patients, there should be little doubt about the diagnosis for those individuals who fulfill these strict criteria. Couples with more than one child with tuberous sclerosis complex, no extended family history, and no clinical features of tuberous sclerosis complex are more likely to have germline mosaicism for tuberous sclerosis than nonexpression of the mutation. Germline mosaicism, while fortunately rare, will not be suspected from either diagnostic criteria or molecular testing until a couple has multiple affected children. Genetic counseling for families with one affected child should include a small (1% to 2%) possibility of recurrence, even for parents who have no evidence of tuberous sclerosis complex after a thorough diagnostic evaluation.

Tuberous sclerosis-related gene expression in normal and dysplastic brain

Cortical dysplasia (CD) broadly defines a complex cerebral malformative lesion associated clinically with intractable, pharmacoresistant epilepsy (including infantile spasms), especially in infants and children. In CD, the spectrum of structural brain abnormalities includes (at a minimum) neuronal dyslamination and (in severe cases) neuronal cytomegaly with cytoskeletal alterations and the presence of gemistocyte-like 'balloon cells'. In some CD variants, the neuropathological features are essentially indistinguishable from those of a tuber of tuberous sclerosis (TSC). Two genes associated with the autosomal dominant, multi-system disorder TSC have recently been cloned: TSC2 (on chromosome 16p13.3) encodes the protein tuberin and TSC1 (on 9q34) encodes hamartin. Tuberin has been immunolocalized to neurons and possibly astrocytes in normal brain and CD/TSC tubers, and is widely expressed in normal viscera; loss of heterozygosity and tissue culture studies suggest it functions as a growth suppressor. The TSC1 gene has been cloned within the last year and hamartin as yet has no well-defined cellular function, though its protein product may also function as a growth suppressor. This article focuses on the cellular pathogenesis of CD and TSC brain lesions and how the two may be biologically related. Studies of how TSC1 and TSC2 function in normal and dysplastic cerebral neocortex may provide a paradigm for understanding the neurobiology of other genes that determine epilepsy-associated cerebral malformations (e.g. lissencephaly, double cortex).

Focal abnormalities detected by 18FDG PET in epileptic encephalopathies

A prospective study of 32 children with epileptic encephalopathies 12 years or younger revealed a high incidence of focal cortical metabolic defects on 18-fluorodeoxyglucose positron emission tomography (PET) not suspected from clinical, EEG, or magnetic resonance imaging findings. PET scans were normal in all five children with typical de novo Lennox-Gastaut syndrome but showed cortical metabolic abnormalities in three out of four with atypical de novo Lennox-Gastaut syndrome, five out of six with Lennox-Gastaut syndrome following infantile spasms, six out of eight with severe myoclonic epilepsy in infancy, one out of two with epilepsy with myoclonic-astatic seizures, and four out of six with an unclassified epileptic encephalopathy. This suggests that some children with epileptic encephalopathies previously thought to have primary generalised seizures or seizures due to multifocal pathology may have unifocal cortical origin for their seizures. Such an origin may be amenable to surgery.

Infantile spasms: III. Prognostic implications of bitemporal hypometabolism on positron emission tomography

Positron emission tomography (PET) of brain glucose utilization is highly sensitive in detecting focal cortical abnormalities in patients with infantile spasms even when the computed tomographic (CT) and magnetic resonance imaging (MRI) scans are normal. Of 110 infants with spasms evaluated for potential surgical intervention during an 8-year period, we encountered 18 infants (7 males, 11 females; age range, 10 mo to 5 yr) with a common metabolic pattern on positron emission tomography (PET) consisting of bilateral hypometabolism in the temporal lobes. CT and MRI scans did not reveal any focal abnormalities in the 18 infants. Video-electroencephalographic monitoring indicated either bilateral or multifocal epileptogenicity, or failed to show any epileptic focus, so that none of the 18 infants were considered candidates for resective surgery. These patients were then enrolled in a prospective study aimed at determining long-term outcome in the presence of bilateral temporal PET hypometabolism. Analysis of outcome in 14 of the 18 subjects (follow-up period, 10 mo to 10 yr 5 mo; mean, 3 yr 11 mo +/- 2 yr 4 mo [SD]) revealed the following: (1) all had severe developmental delay and had failed to gain significant milestones; (2) language development had been minimal or absent; (3) 10 of the 14 met the DSM-IV criteria for autistic disorder. Our findings indicate that patients with infantile spasms and bitemporal glucose hypometabolism on PET comprise a relatively homogeneous group and are typically not candidates for cortical resection. The long-term outcome of these infants is particularly poor and the majority are autistic.

Intractable epilepsy in children

Although most children with epilepsy have a good prognosis, a small but significant minority have seizures that either do not respond to conventional antiepileptic drugs (AEDs) or have significant adverse reactions to AEDs. Many children may benefit from epilepsy surgery. Surgical treatment of epilepsy is becoming a well-established therapy for infants and young children with severe, medically intractable seizures. As in older children and adults, the presurgical evaluations of possible surgical candidates typically consist of a detailed history, neurologic and neuropsychologic examination, and anatomic and functional neuroimaging. The "gold standard" test, however, is the recording of ictal events by using simultaneous EEG and videomonitoring. Although temporal lobe resection is the most commonly performed surgery in older children and adults, nontemporal lobe resection, corpus callosotomy, and hemispherectomy are commonly performed in younger children. Efficacy of surgery in children compares favorably with results from adult patients. In addition, because the immature brain is more plastic than the mature brain, recovery of function is often greater after surgery in children than in adults. Early surgery in children with intractable epilepsy is recommended.

Etiologic classification of infantile spasms in 140 cases: role of positron emission tomography

The classification of infantile spasms into symptomatic, cryptogenic, and idiopathic subgroups depends on clinical examination and available diagnostic technology. Positron emission tomography (PET) of glucose utilization is a powerful tool in detecting brain malformations (particularly cortical dysplasia) in infants with spasms. We analyzed etiologic data from 140 such infants, 78 girls and 62 boys, ages 2 months to 4 years 10 months (mean, 17 months). All had been evaluated extensively in one of two major medical centers. It should be emphasized that our referral population is biased toward infants with intractable spasms who fail to show a structural lesion. Seven patients had neurocutaneous syndromes, two had chromosomal abnormalities, two had inborn errors of metabolism, and one each had craniosynostosis or Menkes syndrome. Computed tomography and/or magnetic resonance imaging detected lesions in another 29 infants (20.7%) who did not have a specific disease or syndrome. Without the benefit of PET, the total number of symptomatic cases was 42 (30.0%). One infant, classified as idiopathic, had normal development and PET. In 97 cryptogenic cases, PET uncovered unifocal abnormalities in 30 and multifocal abnormalities in 62. Diffuse PET abnormalities, which did not provide specific etiologic information, were seen in three infants. Another two infants had normal PET scans. Thus, with the benefit of PET, the number of symptomatic cases rose dramatically from 42 (30.0%) to 134 (95.7%). The majority of unifocal and multifocal abnormalities on PET are believed to represent dysplastic lesions.

Epilepsy in early development: the lesson from surgery for early intractable seizures

This report examines the impact on development and the problems involved in assessing development in very young children with early-onset intractable seizures, particularly infantile spasms. A review of studies on medically and surgically treated children with infantile spasms underscores the relationship between seizure control and developmental outcome. About 50% of children with markedly intractable infantile spasms attained seizure control and significant improvement in the use of nonverbal communication, a developmental measure that has been used in other populations of developmentally delayed children. With the exception of duration of illness, clinical measures of age of onset of infantile spasms, type of surgery, and side of surgery did not appear to be related to the postoperative change in nonverbal communication. The neuropathology findings of surgically treated children with infantile spasms suggest that the underlying pathology occurs early in brain development. In conclusion, the cumulative effect of uncontrolled seizures and the underlying pathology might impact the early development of children with intractable infantile spasms.

Asymmetric hypsarrhythmia: clinical electroencephalographic and radiological findings

Twenty-six children (16 boys and 10 girls) with hypsarrhythmia and infantile spasms (IS) were studied at the University of Michigan EEG Laboratory in a 4-year period. Six (2 boys, 4 girls), had asymmetric hypsarrhythmia with a preponderance of both slowing and epileptiform activity over one hemisphere. All 6 had the symptomatic form of IS, 4 with dysplastic conditions, 1 with porencephaly from a cerebral infarct, and 1 with hypoxicischemic encephalopathy. Five children had focal abnormalities on either physical examination or imaging studies. Four had the highest amplitude slowing and most epileptiform activity ipsilateral to the lesion, in 1, it was contralateral. Asymmetric hypsarrhythmia constituted 23% of cases with hypsarrhythmia examined at our EEG laboratory. The significant success in surgical therapy for some children with IS indicates the importance of identifying focal hemispheric abnormalities even if they are not apparent clinically. EEG may suggest focal changes not detected clinically or radiologically.

West syndrome following deep hypothermic infant cardiac surgery

Postoperative seizures are among the more common complications of cardiac surgery in children. These seizures have traditionally been considered benign, transient phenomena with little, if any, prognostic significance. We report 4 infants with early postoperative seizures following cardiac surgery who later developed the previously unreported complication of West syndrome, with infantile spasms, hypsarrhythmia, and developmental delay. This group constitutes 6% of 67 infant spasms evaluated over a 5-year period at Boston Children's Hospital. The postoperative seizures in these 4 patients were more difficult than usual to control with antiepileptic therapy; otherwise no intra- or perioperative features distinguished these infants who later developed West syndrome from infants with apparently benign "postpump seizures."