Lissencephaly: two distinct clinico-pathological types

Ecotomografia delle malformazioni congenite del sistema nervoso centrale

In questo lavoro, sulla base della nuova classificazione di Van der Knapp e Valk, sono state trattate le malformazioni congenite del Sistema Nervoso Centrale diagnosticabili nel feto e nel neonato con l'ecotomografia. Particolare attenzione è stata rivolta alla precisa caratterizzazione semeiologica di ciascuna malformazione nel tentativo di puntualizzare gli elementi necessari per una corretta diagnosi differenziale ecotomografica.

Malformations of cortical development and epilepsy

Malformations of cortical development (MCDs) are an important cause of epilepsy and an extremely interesting group of disorders from the perspective of brain development and its perturbations. Many new MCDs have been described in recent years as a result of improvements in imaging, genetic testing, and understanding of the effects of mutations on the ability of their protein products to correctly function within the molecular pathways by which the brain functions. In this review, most of the major MCDs are reviewed from a clinical, embryological, and genetic perspective. The most recent literature regarding clinical diagnosis, mechanisms of development, and future paths of research are discussed.

Malformations of cortical development

Structural abnormalities of the brain are increasingly recognized in patients that suffer from pharmacoresistant focal epilepsies by applying high-resolution imaging techniques. In many of these patients, epilepsy surgery results in control of seizures. Neuropathologically, a broad spectrum of malformations of cortical development (MCD) is observed in respective surgical brain samples. These samples provide a unique basis to further understand underlying pathomechanisms by molecular approaches and develop improved diagnostics and entirely new therapeutic perspectives. Here we provide a comprehensive description of neuropathological findings, available classification systems as well as molecular mechanisms of MCDs. We emphasize the recently published ILEA classification system for focal cortical dysplasias (FCDs), which are now histopathologically distinguished as types I to III. However, this revised classification system represents a major challenge for molecular neuropathologists, as the underlying pathomechanisms in virtually all FCD entities will need to be specified in detail. The fact that only recently, the mammalian target of rapamycin (mTOR)-antagonist Everolimus has been introduced as a treatment of epilepsies in the context of tuberous sclerosis-associated brain lesions is a striking example of a successful translational "bedside to bench and back" approach. Hopefully, the exciting clinico-pathological developments in the field of MCDs will in short term foster further therapeutic breakthroughs for the frequently associated medically refractory epilepsies.

Cobblestone lissencephaly: neuropathological subtypes and correlations with genes of dystroglycanopathies

Cobblestone lissencephaly represents a peculiar brain malformation with characteristic radiological anomalies, defined as cortical dysplasia combined with dysmyelination, dysplastic cerebellum with cysts and brainstem hypoplasia. Cortical dysplasia results from neuroglial overmigration into the arachnoid space, forming an extracortical layer, responsible for agyria and/or 'cobblestone' brain surface and ventricular enlargement. The underlying mechanism is a disruption of the glia limitans, the outermost layer of the brain. Cobblestone lissencephaly is pathognomonic of a continuum of autosomal recessive diseases with cerebral, ocular and muscular deficits, Walker-Warburg syndrome, muscle-eye-brain and Fukuyama muscular dystrophy. Mutations in POMT1, POMT2, POMGNT1, LARGE, FKTN and FKRP genes attributed these diseases to α-dystroglycanopathies. However, studies have not been able to identify causal mutations in the majority of patients and to establish a clear phenotype/genotype correlation. Therefore, we decided to perform a detailed neuropathological survey and molecular screenings in 65 foetal cases selected on the basis of histopathological criteria. After sequencing the six genes of α-dystroglycanopathies, a causal mutation was observed in 66% of cases. On the basis of a ratio of severity, three subtypes clearly emerged. The most severe, which we called cobblestone lissencephaly A, was linked to mutations in POMT1 (34%), POMT2 (8%) and FKRP (1.5%). The least severe, cobblestone lissencephaly C, was linked to POMGNT1 mutations (18%). An intermediary type, cobblestone lissencephaly B, was linked to LARGE mutations (4.5%) identified for the first time in foetuses. We conclude that cobblestone lissencephaly encompasses three distinct subtypes of cortical malformations with different degrees of neuroglial ectopia into the arachnoid space and cortical plate disorganization regardless of gestational age. In the cerebellum, histopathological changes support the novel hypothesis that abnormal lamination arises from a deficiency in granule cells. Our studies demonstrate the positive impact of histoneuropathology on the identification of α-dystroglycanopathies found in 66% of cases, while with neuroimaging criteria and biological values, mutations are found in 32-50% of patients. Interestingly, our morphological classification was central in the orientation of genetic screening of POMT1, POMT2, POMGNT1, LARGE and FKRP. Despite intensive research, one-third of our cases remained unexplained; suggesting that other genes and/or pathways may be involved. This material offers a rich resource for studies on the affected neurodevelopmental processes of cobblestone lissencephaly and on the identification of other responsible gene(s)/pathway(s).

Malformations of cortical development and epilepsy

Malformations of cortical development (MCDs) are macroscopic or microscopic abnormalities of the cerebral cortex that arise as a consequence of an interruption to the normal steps of formation of the cortical plate. The human cortex develops its basic structure during the first two trimesters of pregnancy as a series of overlapping steps, beginning with proliferation and differentiation of neurons, which then migrate before finally organizing themselves in the developing cortex. Abnormalities at any of these stages, be they environmental or genetic in origin, may cause disruption of neuronal circuitry and predispose to a variety of clinical consequences, the most common of which is epileptic seizures, A large number of MCDs have now been described, each with characteristic pathological, clinical, and imaging features. The causes of many of these MCDs have been determined through the study of affected individuals, with many MCDs now established as being secondary to mutations in cortical development genes. This review will highlight the best-known of the human cortical malformations associated with epilepsy. The pathological, clinical, imaging, and etioiogic features of each MCD will be summarized, with representative magnetic resonance imaging (MRI) images shown for each MCD, The malformations tuberous sclerosis, focal cortical dysplasia, hemimegalencephaiy, classical iissencephaly, subcortical band heterotopia, periventricular nodular heterotopia, polymicrogyria, and schizencephaly will be presented.

Neocortical neuronal arrangement in LIS1 and DCX lissencephaly may be different

In type I or classical lissencephaly, two genetic causes, namely the LIS1 gene mapping at 17p13.3 and the DCX (doublecortin on X) gene mapping at Xq22.3 are involved. These are considered to act during corticogenesis on radial migratory pathways. The prevailing view is that heterozygous mutations in the LIS1 gene and hemizygous mutations in the DCX gene produce similar histological pattern. The present detailed neuropathological study in two unrelated fetuses with respectively a mutation in the LIS1 and the DCX genes do not confirm this view. In LIS1 mutation, the cortical ribbon displays a characteristic inverted organization, also called "four layered cortex" while in DCX mutation, the cortex displays a roughly ordered "six layered" lamination. Our hypothesis is that mutations of the LIS1 and DCX genes, may not affect the same neuronal arrangement in the neocortex. Because the pathology of proven XLIS is rarely documented, further detailed neuropathological analysis in other cases identified through molecular study would be of a great help in the recognition of neuronal population involved in these migrational disorders and their underlying molecular mechanism.

Anaesthesia for a child with Walker-Warburg syndrome

Walker-Warburg syndrome (WWS) is a rare lethal autosomal recessive disorder manifested by characteristic central nervous system and eye malformations. We have not come across reports of general anaesthesia in a child with WWS in the English literature. We report a case of general anaesthesia in a 12-month-old male child with WWS. The child also had bilateral cleft lip, cleft palate, urogenital malformation and hydronephrosis. Despite many potential anaesthesia concerns, anaesthesia was uneventful in this child.

The role of Glial-Pial barrier lesions and impaired vascularization in anomalous formation of cortical convolutions

The abnormal patterns of cerebral convolutions range from severe to small anomalies restricted to tertiary gyri and sulci. Lesions within Glial-Pial barrier were found in examined cases with cortical developmental abnormalities. Anomalies and impaired function of vessels penetrating the cortex from meningeal plexus coexisted often with Glial-Pial barrier lesions. We are able to say that our cases constitute a group of graded changes demonstrating that both observed developmental lesions vascular and/or Glial-Pial barrier damage may result in cortical anomalies. Their formation and character depend on the stage of cortical maturation when analyzed lesions occur.

Walker-Warburg syndrome: neurologic features and muscle membrane structure

Walker-Warburg syndrome is an autosomal-recessive genetic disorder characterized by congenital muscular dystrophy in association with complex developmental abnormalities of the central nervous system and the eyes. Two patients with Walker-Warburg syndrome are presented to demonstrate clinical variability. Previously unreported pathologic findings involving heart, muscle, spinal cord, and gall bladder are described, and the literature is reviewed. Histopathologic studies of the muscle membrane protein network in both Walker-Warburg syndrome patients reveal a decreased immunostaining for laminin alpha2 and beta-dystroglycan. The clinical, histologic, and biochemical variability in Walker-Warburg patients may reflect heterogeneity.

Neuroimaging in lissencephalies

Based on the published literature and on our own experiences in the imaging of lissencephalies with ultrasound (US), computed tomography (CT) and magnetic resonance imaging (MRI) we propose a strategy for the use of the different methods depending on the clinical symptoms and the age of the patient. In newborns and babies with suspected lissencephaly ultrasound should be used as the first method. If there is a cortical malformation and a more thorough examination seems necessary, CT can be used in type I lissencephaly. However, due to its excellent grey-white matter contrast MRI is the best method for imaging of lissencephalies. Especially in the diagnosis of type II lissencephaly, MRI is definitely superior to CT and US, and so it should be used in all patients with Walker-Warburg syndrome and other congenital muscular dystrophies as well as in all doubtful cases. It must always be remembered that the extent of the cortical dysplasias is quite variable, as is the presence of further malformations.

Neuropathology of lissencephalies

The neuropathological findings at autopsy in four cases of type I and three of type II lissencephaly are presented. Type I lissencephaly is characterized by agyriapachygyria with a markedly thickened cerebral cortex with four coarse histological layers. The normally myelinated white matter, often with neuronal heterotopias, is very narrow, and the gray-to-white matter ratio is inverted (about 4:1); there are no white-gray interdigitations. Claustrum and capsula extrema are absent. Ventricular dilatation is present, especially of the occipital horns. In the hypoplastic brain stem large olivary heterotopias can often be observed. Severe cerebellar malformations, obstructive hydrocephalus, severe eye abnormalities, and congenital muscular dystrophy are not seen. Clinically, type I lissencephaly presents as "isolated lissencephaly sequence" or as "Miller-Dieker syndrome" with characteristic facial dysmorphism. The long survival of 20 years achieved by one of our patients is very uncommon. Type II lissencephaly is characterized by widespread agyria. Usually, obstructive hydrocephalus is present with a thin cerebral mantle showing a slightly thickened cortex and a narrow, hypomyelinated white matter often with neuronal heterotopias (gray-to-white matter ratio about 1:1). The border between gray and white matter is blurred. Claustrum and capsula extrema are absent. Histologically, the cortex appears disorganized without layering; widespread leptomeningeal gliomesenchymal proliferations and glioneuronal heterotopias are present.(ABSTRACT TRUNCATED AT 250 WORDS)

Lissencephaly syndromes: clinical aspects

We report clinical and neurophysiological findings in six children (three female, three male) with type I lissencephaly and three children (all female) with type II lissencephaly (Walker-Warburg syndrome). In type I lissencephaly the diagnosis is based only on electroencephalographic (EEG) signs, whereas in type II lissencephaly the diagnosis rests on clinical signs. In type I lissencephaly the EEG typically shows high alpha-beta activity, which is not seen in type II lissencephaly.

Genetic factors in lissencephaly syndromes: a review

Lissencephaly is a sign of various genetic and non-genetic conditions and a constant feature in the so-called lissencephaly syndromes. Type I lissencephaly in the Miller-Dieker syndrome (MDS) and the isolated lissencephaly sequence (ILS) is differentiated from type II lissencephaly in the Walker-Warburg (hydrocephalus, agyria, retinal dysplasia with or without encephalocele, HARD +/- E) syndrome and related conditions (e.g. muscle-eye-brain syndrome). In about 90% of patients with MDS structural defects have been confirmed in the short arm of chromosome 17 (p13.3), detectable by classical cytogenetic methods, fluorescence in situ hybridisation (FISH), or molecular genetic techniques. The identification of unbalanced inversions and translocations is of particular importance because of the risk of their recurrence, while deletions and ring chromosomes are mainly sporadic. Recently, submicroscopic deletions have also been reported in ILS, providing evidence that lissencephaly in MDS and ILS is caused by deletions of the same gene(s) in 17p13.3 and that MDS may be considered to be a "contiguous gene syndrome." Syndromes featuring lissencephaly type II (HARD +/- E and related conditions) are most probably autosomal-recessively inherited. Neither the location of the genes involved nor the nature of the mutations are known at present. It is also unknown whether HARD +/- E and muscle-eye-brain syndrome are allelic.

Somatosensory evoked potentials in hemimegalencephaly and lissencephaly: anatomo-functional correlations

Four patients with hemimegalencephaly and four with lissencephaly were studied by median nerve somatosensory evoked potentials. The peripheral conduction velocity and the conduction time between the brachial plexus (Erb's point) and cervical cord were normal in both malformations. In hemimegalencephaly, the cortical components were absent on the malformed hemisphere but normal on the healthy side, whereas in lissencephaly an abnormal, prolonged N20 wave was recorded bilaterally. The difference presumably relates to the absence of normal cortical lamination in hemimegalencephaly and to the presence of a 'four-layered' cortex in lissencephaly.

Development of the cortical dysplasia of type II lissencephaly

A detailed neuropathological study of five immature brains with type II lissencephaly is reported. The cases described include two pairs of siblings. One infant survived for 2 months after birth, the others died at 18, 20, 20 and 32 weeks of gestation. This series of cases demonstrates the sequence in which the malformation develops from mid-gestation to post-natal life and shows that type II lissencephaly is not an intracortical malformation but is the result of massive glial and neuronal ectopia in the leptomeninges. This results from a failure of arrest of neuronal migration due to defects in the integrity of the pial/glial barrier.

Congenital muscular dystrophy, brain and eye abnormalities: one or more clinical entities?

Four children with congenital muscular dystrophy (CMD), eye and brain abnormalities are described. Their clinical and neuroradiological features are compatible with a diagnosis of Walker-Warburg syndrome (WWS), according to the criteria proposed by Dobyns et al. (i.e., presence of type II lissencephaly, typical cerebellar and retinal malformations, CMD), who also conclude that WWS is indistinguishable from the muscle-eye-brain disease (MEBD) described by Santavuori. On the basis of our own experience and two recently published series, we emphasize certain features that are different in patients with WWS and patients with MEBD, which make their inclusion in the same syndrome dubious.

Intrauterine-onset myoclonic encephalopathy associated with cerebral cortical dysgenesis

The intrauterine onset of convulsive syndromes has been documented only rarely, and previous reports have lacked detailed neuropathologic description. This report details a case of severe, intractable myoclonic encephalopathy, which, on the basis of severely abnormal paroxysmal fetal movement patterns confirmed by antenatal ultrasound, appears to have been of antenatal onset. The infant suffered an early demise and at autopsy showed features of a severe brain dysgenesis with polymicrogyria and superadded encephaloclastic features. Despite an extensive evaluation, the etiology of this condition remains elusive in our case. This case demonstrates that closer analysis of the qualitative features of fetal movements by, for instance, real-time ultrasound could aid in the antenatal diagnosis of neurologic, particularly convulsive, syndromes.

Lissencephaly (agyria-pachygyria): clinical findings and serial EEG studies

Fifteen cases of lissencephaly were studied and the literature reviewed. The authors conclude that the clinical findings of lissencephaly in infancy are non-specific, consisting of developmental delay and hypotonia. While the CT scan establishes the diagnosis, it may also be strongly suggested by an EEG showing 'major fast dysrhythmia', characterized by abnormally rapid, very high-voltage activity, predominantly in the alpha and beta frequency bands. Some possible mechanisms for this highly suggestive EEG pattern are proposed.

Clinicopathological findings associated with agenesis of the corpus callosum

Seven hundred five cases of agenesis of the corpus callosum (ACC) are reviewed from the literature (n = 660) and from our own observations (n = 45). The diagnosis was made or confirmed using neuroradiological techniques (n = 519) and necropsy or surgery (n = 231). Association with abnormalities often of chromosomes 8, 11, 13-15 and 18 suggests their involvement in abnormal corpus callosum (CC) morphogenesis. Four syndromes (e.g. Aicardi, acrocallosal, Andermann and Shapiro) are characterized by ACC, while others are only sporadically associated (e.g. fetal alcohol syndrome, Dandy-Walker syndrome, Leigh disease, Arnold-Chiari II syndrome). In non-Aicardi patients, the male-to-female ratio was 3:2 and X-linked recessive inheritance is postulated to play a role in some cases. Common abnormalities in acallosal patients included: mental retardation (MR), 73% [corrected]; seizures, 42%; ocular anomalies, 42%; gyral abnormalities, 32%; hydrocephalus, 23%; other central nervous system (CNS) lesions, 29%; costovertebral defects, 24%. Developmental disabilities are not attributable to absence of the CC per se, but due to other CNS malformation or dysfunction, which may be genetic or non-genetic. Future research using recombinant DNA techniques will enable isolation and identification of specific chromosomal defects in those cases with a genetic abnormality.

Congenital muscular dystrophy and cerebral CT scan anomalies. Results of a collaborative study of the Société de Neurologie Infantile

We present the results of a collaborative study on the association of congenital muscular dystrophy with central nervous system anomalies revealed by CT scan investigation of 10 patients. In seven children, an abnormal hypodensity of the cerebral white matter is found; in four of these patients, this radiological anomaly is either isolated, or associated with a moderate intellectual impairment; in one case, severe mental retardation and ocular changes had occurred; in the other two cases, the muscular disease was progressing slowly, in association with microcephaly, epilepsy, and moderate mental retardation. Three children were afflicted with a severe early encephalopathy and congenital muscular dystrophy, and presented signs of cortical and subcortical atrophy on CT scan. Two of these patients corresponded to different types of cerebro-ocular dysplasia-muscular dystrophy syndromes, and the third patient of Fukuyama's congenital muscular dystrophy. These observations are discussed and compared with those reported in the literature. The authors emphasize the need to investigate possible cerebral CT scan anomalies in congenital muscular dystrophies, and to look for muscular changes in some prenatal encephalopathies.

Syndromes with lissencephaly. II: Walker-Warburg and cerebro-oculo-muscular syndromes and a new syndrome with type II lissencephaly

Lissencephaly (smooth brain) is an abnormality of brain development characterized by incomplete neuronal migration and a smooth cerebral surface. At least two distinct pathological types occur, each associated with several recognized syndromes. In this paper, we report on the clinical and pathologic manifestations of four additional patients and classify and delineate three separate disorders with type II lissencephaly. We also report on a previously undescribed abnormality in one of the four patients--dilated rough endoplasmic reticulum cisternae containing an unknown osmiophilic secretory product, probably a glycoprotein.

Agyria (lissencephaly) with anomalous pyramidal crossing. Case report and review of literature

A case of agyria (lissencephaly) with a highly unusual course of the corticospinal tract at the crossing and in the spinal cord is described. Published cases of agyria (lissencephaly) are reviewed with special attention to the cortical fiber system and organization of the necortex, and their implications for possible pathogenetic mechanisms. The problem of nomenclature is discussed.

Congenital hydrocephalus and eye abnormalities with severe developmental brain defects: Warburg's syndrome

Five patients are reported with Warburg's syndrome, characterized by: (1) congenital hydrocephalus, (2) severe neonatal neurological dysfunction, (3) abnormalities of the anterior and posterior chambers of the eyes, (4) absence of known cause, and (5) severe developmental abnormalities of cortical gyration and architectonics. Fourteen similar published cases are reviewed. The syndrome can be diagnosed during life on the conjunction of the first four features listed. Evidence is adduced that this syndrome is a genetically determined condition with an autosomal recessive mode of inheritance and with a 25% recurrence risk for offspring of the parents of an affected infant.

Congenital muscular dystrophy with cerebral white matter spongiosis

Two siblings affected with a slowly progressive congenital myopathy presented mental retardation, epilepsy and craniofacial dysmorphy. The cerebral necropsic study of one of these patients showed severe anomalies of the white matter, with spongiosis, astrogliosis and vascular hyperplasia, whereas a diffuse and marked hypodensity of white matter was observed at cerebral CT scan in the other patient. There were any lesion of cerebellar grey matter, heterotopy, micropolygyria or neuronal destruction. This syndrome seems to be an original variant of congenital neuromyopathy.