Lissencephaly

Comprehensive genotype-phenotype correlation in lissencephaly

Malformations of cortical development (MCD) are a heterogenous group of disorders with diverse genotypic and phenotypic variations. Lissencephaly is a subtype of MCD caused by defect in neuronal migration, which occurs between 12 and 24 weeks of gestation. The continuous advancement in the field of molecular genetics in the last decade has led to identification of at least 19 lissencephaly-related genes, most of which are related to microtubule structural proteins (tubulin) or microtubule-associated proteins (MAPs). The aim of this review article is to bring together current knowledge of gene mutations associated with lissencephaly and to provide a comprehensive genotype-phenotype correlation. Illustrative cases will be presented to facilitate the understanding of the described genotype-phenotype correlation.

Rare ACTG1 variants in fetal microlissencephaly

Heterozygous ACTG1 mutations are responsible for Baraitser-Winter cerebrofrontofacial syndrome which cortical malformation is characterized by pachygyria with frontal to occipital gradient of severity. We identified by whole exome sequencing in a cohort of 12 patients with prenatally diagnosed microlissencephaly, 2 foetal cases with missense mutations in the ACTG1 gene and in one case of living patient with typical Baraitser-Winter syndrome. Both foetuses and child exhibited microcephaly and facial dysmorphism consisting of microretrognatism, hypertelorism and low-set ears. Brain malformations included lissencephaly with an immature cortical plate, dysmorphic (2/3) or absent corpus callosum and vermian hypoplasia (2/3). Our results highlight the powerful diagnostic value of exome sequencing for patients with microlissencephaly, that may expand the malformation spectrum of ACTG1-related Baraitser-Winter cerebrofrontofacial syndrome and may suggest that ACTG1 could be added to the list of genes for assessing microlissencephaly.

What next-generation sequencing (NGS) technology has enabled us to learn about primary autosomal recessive microcephaly (MCPH)

The impact that next-generation sequencing technology (NGS) is having on many aspects of molecular and cell biology, is becoming increasingly apparent. One of the most noticeable outcomes of the new technology in human genetics, has been the accelerated rate of identification of disease-causing genes. Especially for rare, heterogeneous disorders, such as autosomal recessive primary microcephaly (MCPH), the handful of genes previously known to harbour disease-causing mutations, has grown at an unprecedented rate within a few years. Knowledge of new genes mutated in MCPH over the last four years has contributed to our understanding of the disorder at both the clinical and cellular levels. The functions of proteins such as WDR62, CASC5, PHC1, CDK6, CENP-E, CENP-F, CEP63, ZNF335, PLK4 and TUBGPC, have been added to the complex network of critical cellular processes known to be involved in brain growth and size. In addition to the importance of mitotic spindle assembly and structure, centrosome and centriole function and DNA repair and damage response, new mechanisms involving kinetochore-associated proteins and chromatin remodelling complexes have been elucidated. Two of the major contributions to our clinical knowledge are the realisation that primary microcephaly caused by mutations in genes at the MCPH loci is seldom an isolated clinical feature and is often accompanied either by additional cortical malformations or primordial dwarfism. Gene-phenotype correlations are being revisited, with a new dimension of locus heterogeneity and phenotypic variability being revealed.

Cenpj/CPAP regulates progenitor divisions and neuronal migration in the cerebral cortex downstream of Ascl1

The proneural factor Ascl1 controls multiple steps of neurogenesis in the embryonic brain, including progenitor division and neuronal migration. Here we show that Cenpj, also known as CPAP, a microcephaly gene, is a transcriptional target of Ascl1 in the embryonic cerebral cortex. We have characterized the role of Cenpj during cortical development by in utero electroporation knockdown and found that silencing Cenpj in the ventricular zone disrupts centrosome biogenesis and randomizes the cleavage plane orientation of radial glia progenitors. Moreover, we show that downregulation of Cenpj in post-mitotic neurons increases stable microtubules and leads to slower neuronal migration, abnormal centrosome position and aberrant neuronal morphology. Moreover, rescue experiments shows that Cenpj mediates the role of Ascl1 in centrosome biogenesis in progenitor cells and in microtubule dynamics in migrating neurons. These data provide insights into genetic pathways controlling cortical development and primary microcephaly observed in humans with mutations in Cenpj.

The proneural factor Ascl1/Mash1 is an important regulator of embryonic neurogenesis. Here the authors identify that the microcephaly protein Cenpj/CPAP is essential for several microtubule-dependent steps in the neurogenic program driven by Ascl1 in the developing cerebral cortex.

The wide spectrum of tubulinopathies: what are the key features for the diagnosis?

Complex cortical malformations associated with mutations in tubulin genes: TUBA1A, TUBA8, TUBB2B, TUBB3, TUBB5 and TUBG1 commonly referred to as tubulinopathies, are a heterogeneous group of conditions with a wide spectrum of clinical severity. Among the 106 patients selected as having complex cortical malformations, 45 were found to carry mutations in TUBA1A (42.5%), 18 in TUBB2B (16.9%), 11 in TUBB3 (10.4%), three in TUBB5 (2.8%), and three in TUBG1 (2.8%). No mutations were identified in TUBA8. Systematic review of patients' neuroimaging and neuropathological data allowed us to distinguish at least five cortical malformation syndromes: (i) microlissencephaly (n = 12); (ii) lissencephaly (n = 19); (iii) central pachygyria and polymicrogyria-like cortical dysplasia (n = 24); (iv) generalized polymicrogyria-like cortical dysplasia (n = 6); and (v) a 'simplified' gyral pattern with area of focal polymicrogyria (n = 19). Dysmorphic basal ganglia are the hallmark of tubulinopathies (found in 75% of cases) and are present in 100% of central pachygyria and polymicrogyria-like cortical dysplasia and simplified gyral malformation syndromes. Tubulinopathies are also characterized by a high prevalence of corpus callosum agenesis (32/80; 40%), and mild to severe cerebellar hypoplasia and dysplasia (63/80; 78.7%). Foetal cases (n = 25) represent the severe end of the spectrum and show specific abnormalities that provide insights into the underlying pathophysiology. The overall complexity of tubulinopathies reflects the pleiotropic effects of tubulins and their specific spatio-temporal profiles of expression. In line with previous reports, this large cohort further clarifies overlapping phenotypes between tubulinopathies and although current structural data do not allow prediction of mutation-related phenotypes, within each mutated gene there is an associated predominant pattern of cortical dysgenesis allowing some phenotype-genotype correlation. The core phenotype of TUBA1A and TUBG1 tubulinopathies are lissencephalies and microlissencephalies, whereas TUBB2B tubulinopathies show in the majority, centrally predominant polymicrogyria-like cortical dysplasia. By contrast, TUBB3 and TUBB5 mutations cause milder malformations with focal or multifocal polymicrogyria-like cortical dysplasia with abnormal and simplified gyral pattern.

Mutations in tubulin genes are frequent causes of various foetal malformations of cortical development including microlissencephaly

Complex cortical malformations associated with mutations in tubulin genes are commonly referred to as “Tubulinopathies”. To further characterize the mutation frequency and phenotypes associated with tubulin mutations, we studied a cohort of 60 foetal cases. Twenty-six tubulin mutations were identified, of which TUBA1A mutations were the most prevalent (19 cases), followed by TUBB2B (6 cases) and TUBB3 (one case). Three subtypes clearly emerged. The most frequent (n = 13) was microlissencephaly with corpus callosum agenesis, severely hypoplastic brainstem and cerebellum. The cortical plate was either absent (6/13), with a 2–3 layered pattern (5/13) or less frequently thickened (2/13), often associated with neuroglial overmigration (4/13). All cases had voluminous germinal zones and ganglionic eminences. The second subtype was lissencephaly (n = 7), either classical (4/7) or associated with cerebellar hypoplasia (3/7) with corpus callosum agenesis (6/7). All foetuses with lissencephaly and cerebellar hypoplasia carried distinct TUBA1A mutations, while those with classical lissencephaly harbored recurrent mutations in TUBA1A (3 cases) or TUBB2B (1 case). The third group was polymicrogyria-like cortical dysplasia (n = 6), consisting of asymmetric multifocal or generalized polymicrogyria with inconstant corpus callosum agenesis (4/6) and hypoplastic brainstem and cerebellum (3/6). Polymicrogyria was either unlayered or 4-layered with neuronal heterotopias (5/6) and occasional focal neuroglial overmigration (2/6). Three had TUBA1A mutations and 3 TUBB2B mutations. Foetal TUBA1A tubulinopathies most often consist in microlissencephaly or classical lissencephaly with corpus callosum agenesis, but polymicrogyria may also occur. Conversely, TUBB2B mutations are responsible for either polymicrogyria (4/6) or microlissencephaly (2/6).

Human mutations in NDE1 cause extreme microcephaly with lissencephaly [corrected]

Genes disrupted in human microcephaly (meaning "small brain") define key regulators of neural progenitor proliferation and cell-fate specification. In comparison, genes mutated in human lissencephaly (lissos means smooth and cephalos means brain) highlight critical regulators of neuronal migration. Here, we report two families with extreme microcephaly and grossly simplified cortical gyral structure, a condition referred to as microlissencephaly, and show that they carry homozygous frameshift mutations in NDE1, which encodes a multidomain protein that localizes to the centrosome and mitotic spindle poles. Both human mutations in NDE1 truncate the C-terminal NDE1domains, which are essential for interactions with cytoplasmic dynein and thus for regulation of cytoskeletal dynamics in mitosis and for cell-cycle-dependent phosphorylation of NDE1 by Cdk1. We show that the patient NDE1 proteins are unstable, cannot bind cytoplasmic dynein, and do not localize properly to the centrosome. Additionally, we show that CDK1 phosphorylation at T246, which is within the C-terminal region disrupted by the mutations, is required for cell-cycle progression from the G2 to the M phase. The role of NDE1 in cell-cycle progression probably contributes to the profound neuronal proliferation defects evident in Nde1-null mice and patients with NDE1 mutations, demonstrating the essential role of NDE1 in human cerebral cortical neurogenesis.

Norman-Roberts syndrome: characterization of the phenotype in early fetal life

PURPOSE

Our purpose is to describe the prenatal manifestation of Norman-Roberts syndrome and to expand the knowledge of the fetal phenotype of this rare condition. The recurrence in two sibs might contribute to the hypothesis of a recessive condition.

METHODS

Three cases are presented in which the diagnosis was suggested by a prenatal ultrasound examination and confirmed by pathology of the fetuses, after termination of pregnancy. The major sign was the ultrasound detection of microcephaly at the 22nd and 23rd week of gestation. Fetal Magnetic Nuclear Resonance, the pathological examination with histological studies, was applied to arrive at the diagnosis of Norman-Roberts syndrome.

CONCLUSION

To the best of our knowledge, this is the second description of prenatal cases of Norman-Roberts syndrome. The combined clinical and pathological data is a contribution that might help to increase the identification of this rare condition and to correctly define the risk of its recurrence.

Autosomal recessive type I lissencephaly

Lissencephaly (LIS) is a brain malformation manifested by a smooth cerebral surface, thickened cortical mantle and microscopic evidence of incomplete neuronal migration, excluding polymicrogyria and other cortical dysplasias. It is important to consider LIS in the diagnosis of developmental delay as many patients may be diagnosed as cerebral palsy. It may have familial occurrence and can occur in sibs of same family often leading to a diagnostic problem. Several lissencephaly syndromes have been described. Here a familial syndrome of lissencephaly is reported. Autosomal recessive inheritance is suggested by recurrence in sibs within the same family, but germ cell mosaicism for a dominant mutation cannot be excluded.

Genetics of disorders of cortical development

Since the advent of MR imaging, cortical malformations have become an increasingly recognized cause of epilepsy and neurologic impairment. Improved radiographic characterization of cortical malformations has been requisite to defining their genetics, and a large portion of these disorders are now known to have a genetic basis. Uncovering genetic etiologies has provided insight into phenotypic diversity, revealed the importance of de novo mutations, and resulted in improved radiographic-genetic correlation. This article provides an overview of major cerebral cortical malformations and focuses on the genetic mechanisms of their causation.

Cortical dysplasia and epilepsy: animal models

Cortical dysplasia syndromes--those conditions of abnormal brain structure/organization that arise during aberrant brain development--frequently involve epileptic seizures. Neuropathological and neuroradiological analyses have provided descriptions and categorizations based on gross anatomical and cellular histological features (e.g., lissencephaly, heterotopia, giant cells), as well as on the developmental mechanisms likely to be involved in the abnormality (e.g., cell proliferation, migration). Recently, the genes responsible for several cortical dysplastic conditions have been identified and the underlying molecular processes investigated. However, it is still unclear how the various structural abnormalities associated with cortical dysplasia are related to (i.e., "cause") chronic seizures. To elucidate these relationships, a number of animal models of cortical dysplasia have been developed in rats and mice. Some models are based on laboratory manipulations that injure the brain (e.g., freeze, undercut, irradiation, teratogen exposure) of immature animals; others are based on spontaneous genetic mutations or on gene manipulations (knockouts/transgenics) that give rise to abnormal cortical structures. Such models of cortical dysplasia provide a means by which investigators can not only study the developmental mechanisms that give rise to these brain lesions, but also examine the cause-effect relationships between structural abnormalities and epileptogenesis.

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.

Malformations of cortical development and epilepsy

Although once thought to be rare, malformations of cortical development are being increasingly recognized as the underlying cause of developmental delay in children and of epilepsy in children and young adults. Advances in neuroimaging and developmental neurobiology have created the tools by which these important malformations have been investigated. Through a symbiotic type of relationship, these investigations, and the search for a better understanding of these malformations, have led to advances in neuroimaging techniques and better understanding of both normal and abnormal brain development. In this review, the most common malformations or cortical development associated with epilepsy are discussed in regard to their clinical manifestations, classification, imaging appearance and basic neurobiology.

Cortical malformations and epilepsy

Brain malformations, resulting from aberrant patterns of brain development, are highly correlated with childhood seizure syndromes, as well as with cognitive disabilities and other neurological disorders. The structural malformations, often referred to as cortical dysplasia, are extremely varied, reflecting diverse underlying processes and critical timing of the developmental aberration. Recent studies have revealed a genetic basis for many forms of dysplasia. Gene mutations responsible for such common forms of dysplasia as lissencephaly and tuberous sclerosis have been identified, and investigators are beginning to understand how these gene mutations interrupt and/or misdirect the normal developmental pattern. Laboratory investigations, using animal models of cortical dysplasia, are beginning to elucidate how these structural malformations give rise to epilepsy and other functional pathologies.

Human cytomegalovirus DNA in cerebrospinal fluid

To determine the involvement of human cytomegalovirus (CMV) in conditions of neurological impairment, detection of CMV DNA was attempted in cerebrospinal fluid obtained from 45 neurologically affected children aged from 1 month to 17 years by means of the polymerase chain reaction. Four patients (congenital CMV encephalopathy with West's syndrome, acute encephalitis, chronic epileptic encephalopathy, and lissencephaly) had CMV DNA in their cerebrospinal fluid. CMV DNA was absent in the cerebrospinal fluid of 11 neurologically unaffected controls aged from 1 month to 11 years. Three patients with acute CMV hepatitis had no CMV DNA in their cerebrospinal fluid. Among the four patients who had CMV DNA in their cerebrospinal fluid, two did not excrete CMV DNA or CMV antigen in the urine. The possible pathogenetic significance of CMV DNA in the cerebrospinal fluid is discussed. By applying the polymerase chain reaction to cerebrospinal fluid, the mode of brain invasion by CMV can be clarified further.

Prenatal events and genetic factors in epileptic patients with neuronal migration disorders

Because disorders of neuronal migration to cerebral cortex in humans are believed to occur in the first half of gestation, prenatal events or genetic factors are suspected to have a pathogenetic role. We evaluated this by comparing the frequency of potentially harmful prenatal events and of genetic factors in a series of 40 patients (38 with epilepsy) with neuronal migration disorders (NMD) and in 40 epileptic controls, using a predetermined standardized questionnaire to minimize interviewer bias. Potentially harmful prenatal events (significant maternal physical trauma, ingestion of medications, exposure to roentgenograms, infections, uterine or metabolic abnormalities) were reported in the pregnancy histories of 58% of patients with NMD but in only 15% of epileptic controls (p = 0.0002). In contrast, peri- and postnatal potentially relevant etiologic factors were reported in the histories of only 22% of patients with NMD but in 50% of the epileptic controls (p = 0.01). Genetic factors (a family history of epilepsy, mental retardation, or congenital malformations of the CNS) were noted in 13 and 20% of the families, respectively. Stillbirths occurred only in the group with NMD, accounting for 3.06% of sibling pregnancies. The findings suggest that prenatal potentially harmful environmental events play a central role in the pathogenesis of NMD in humans.

The place of neuronal migration abnormalities in child neurology

With the development of modern imaging techniques, disturbances of neuronal migration appear to be a major cause of epilepsy, mental retardation and chronic neurological disability in childhood. Sixty-nine cases are presented, including 46 of diffuse migration abnormalities and 23 of localized dysplasia. Patients with diffuse migration disorders presented with mental retardation, gross motor impairment and severe seizure disorders whereas in those with focal anomalies, epilepsy was the chief complaint. Magnetic resonance imaging, although usually diagnostic of migration disorders often does not allow definition of the pathologic type. Some EEG patterns, such as high amplitude fast rhythms or the theta-delta pattern are highly suggestive. Most cases of abnormal migration are sporadic and probably acquired. Some are due to chromosomal anomalies, especially of chromosome 17p where a gene for lissencephaly has been mapped. Familial cases occur with both recessive and possibly dominant inheritance. Epilepsy due to migration abnormalities is often intractable. Resection of dysplastic cortex may be effective for localized disease and callosotomy has been proposed for diffuse anomalies.

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)

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.

Norman-Roberts syndrome: clinical and molecular studies

We report on a 7-year-old boy with microcephaly, bitemporal hollowing, low sloping forehead, slightly prominent occiput, widely set eyes, broad and prominent nasal bridge, and severe postnatal growth deficiency. Hypertonia, hyperreflexia, seizures, and profound mental retardation were also present. Brain MRI documented partial agyric cortex with patchy pachygyria, colpocephaly, and hypoplasia of corpus callosum and brain stem, which is consistent with the diagnosis of lissencephaly type I grade 2. On the basis of his phenotypic appearance the patient is considered to have the Norman-Roberts syndrome. Molecular studies, performed by means of in situ hybridization and DNA probe analysis, did not demonstrate deletion in the Miller-Dieker/isolated Lissencephaly critical region on the short arm of chromosome 17.

Miller-Dieker syndrome with ring chromosome 17

A girl presented at 6 weeks of age with failure to thrive and arching of the back. She had various dysmorphic features, hepatosplenomegaly, and developmental delay. The electroencephalogram and cranial ultrasound were abnormal, and a computed tomogram showed lissencephaly and apparent agenesis of the corpus callosum. Because of frequent aspiration she became oxygen dependent. She later developed intractable convulsions and died at the age of 9 months.

Lissencephaly-pachygyria associated with congenital cytomegalovirus infection

We report the presence of major cerebral migrational defects in five severely, multiply handicapped children with congenital cytomegalovirus (CMV) infection. These patients had both computed tomographic (CT) scan and magnetic resonance imaging (MRI) evidence of marked migrational central nervous system defects consistent anatomically with the spectrum of lissencephaly-pachygyria, a disorder commonly idiopathic or associated with chromosomal abnormalities or with unknown early gestational insults. Neuroradiologic features included broad, flat gyri, shallow sulci, incomplete opercularization, ventriculomegaly, periventricular calcifications, and white-matter hypodensity on CT scans or increased signal intensity on long-TR MRI scans. Evidence for congenital CMV infection included prenatal onset of microcephaly, periventricular calcifications, neonatal jaundice, hepatomegaly, elevated CMV-specific immunoglobulin M, or viral isolation from urine. Previous reports of the neurologic sequelae of CMV have emphasized varying degrees of psychomotor retardation, cerebral palsy and epilepsy due to polymicrogyria, periventricular calcification, microcephaly, or rarely, hydrocephalus. Our patients appear to represent extremely severe examples of the effects of CMV on neurologic growth, maturation, and development. Recognition of these severe migrational abnormalities was improved by use of MRI, a technique that affords superior definition of the nature and extent of gyral and white-matter abnormalities. We suggest that these abnormalities may be more common than has previously been recognized.

Diagnostic features and clinical signs of 21 patients with lissencephaly type 1

Lissencephaly type I has been described as either the cerebral expression of a complex malformation syndrome such as Miller-Dieker syndrome (MDS), or as isolated lissencephaly sequence (ILS). In a nation-wide study in The Netherlands, of 21 patients with lissecephaly type I, four were found to have MDS and 17 ILS. New clinical aspects were as follows: the mean life-span of the entire group was longer than previously reported; patients with lissencephaly grades 3 or 4 (mixture of agyria and pachygyria, or complete pachygyria) developed seizures later than those with grades 1 and 2 (complete and almost complete agyria); microcephaly was not always present in patients with grades 3 and 4 lissencephaly; and patients with lissencephaly grades 1 and 2 had hardly any psychomotor development, while those with grades 3 and 4 were severely retarded.

Isolated lissencephaly: report of four patients from two unrelated families

Lissencephaly is a brain malformation manifested by a smooth cerebral surface and caused by incomplete neuronal migration. Clinical sequellae include minor craniofacial changes (bitemporal hollowing, small jaw), severe mental retardation, and other neurological abnormalities. Patients with classical or type I lissencephaly and its sequellae but no other significant anomalies are classified as having isolated lissencephaly sequence. Possible causes of isolated lissencephaly sequence include ischemia or viral infection during the time of neuronal migration, microdeletion within the Miller-Dieker syndrome critical region in chromosome band 17p13.3, and Mendelian inheritance. The last is based on a report of a single family with three affected children in 1933. We report four patients with isolated lissencephaly sequence from two unrelated families who provide further support for autosomal (or possibly X-linked) recessive inheritance. In the first family, three brothers were affected. In the second, the parents are first cousins.

Agyria--pachygyria and Miller-Dieker syndrome: clinical, genetic and chromosome studies

Twelve cases of lissencephaly are reported. A high resolution chromosome study was performed on each in order to detect small chromosomal anomalies, undetectable with routine techniques. Only one case was shown to have an unbalanced karyotype with a microdeletion of the short arm of chromosome 17 (del 17p). This child also had symptoms of the Miller-Dieker syndrome, consisting of lissencephaly, characteristic facies, pre- and post-natal growth retardation and other birth defects. As proposed by Dobyns, it seems justifiable to classify lissencephalies into four different groups, according to other clinical manifestations and results of chromosome studies.

Shaking rat Kawasaki (SRK): a new neurological mutant rat in the Wistar strain

Shaking rat Kawasaki (SRK), a newly discovered neurological mutant rat in the Wistar strain, is described. The abnormalities of SRK rats are transmitted as an autosomal recessive trait. The neurological signs are shaking of the body and an ataxic-paretic gait from day 10 postnatal. The affected rats survive for about 1 month. Macroscopically, the cerebellum is small and frequently the vermis and paraflocculus lacking. The most conspicuous histological finding in the central nervous system is malposition of the neurons in the cerebral cortex, hippocampus and cerebellum. Myelination and synapse formation are intact. Abnormal myelinated fibers are present in the molecular layer of the cerebral cortex and in the central gray matter of the spinal cord. These morphological abnormalities resemble those reported in the reeler mutant mouse. SRK rats are another good animal model of human congenital malformations with neuronal migration disorders.

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.

Disorders of neuronal migration

Neuronal migration constitutes one of the major processes by which the central nervous system takes shape. Detailed knowledge about this important process now exists for different brain regions in rodent and monkey models as well as in the human. In the human, distinct genetic, chromosomal and environmental causes are known that affect neuronal migration, often in a morphologically distinct pattern, but the underlying pathological mechanisms are largely unknown. This review is intended to integrate our basic knowledge of the field with the accumulated intelligence on a large number of disorders and syndromes that represent the human part of the story.

Cortical dysplasia associated with massive ectopia of neurons and glial cells within the subarachnoid space

A detailed neuropathological study of the brain of a 31-day-old premature newborn infant revealed the presence of massive ectopia of neurons and glial cells within the subarachnoid space. The extrusion of neural tissue into the subarachnoid space appeared to have taken place through multiple pial-glial bridges. The laminar cortical pattern was also severely disturbed at these sites. Narrow strips of normal and dysplastic cortex alternated in direct relationship to the presence or absence of the pial-glial gaps. Migration of postmitotic neurons and the final positioning of postmigratory neurons appear to take place within highly specified and restricted pathways entrained in a radial direction. Our findings suggest that the pial-glial barrier plays an important role in the control of neuronal migration, and that its disruption may lead to the development of neuronal and glial cell ectopias in the subarachnoid space. The crucial role played by radial glia, the glia limitans and the basal lamina during cortical neurogenesis is emphasized.

A syndrome with intracranial calcification and microcephaly in two sibs, resembling intrauterine infection

We report two children, the products of a consanguineous union, who died in infancy. Both children had severe microcephaly intracranial calcification, lissencephaly and polymicrogyria.

Disorders of neuronal migration: sonographic features

The cranial ultrasound features of two neonates with neuronal migration disorders are described. One infant had lissencephaly and the other polymicrogyria in conjunction with the Pena-Shokeir syndrome type 1. A third infant is described who was born extremely prematurely and with Down's syndrome, who had similar ultrasound features. By two weeks of age, however, the scan of this third infant had become normal, which illustrates the need for caution in diagnosing migrational disorders in very preterm babies and those with Down's syndrome. The disorders of neuronal migration are discussed.

Further comments on the lissencephaly syndromes

Detailed clinical, pathological, and cytogenetic investigations of patients with lissencephaly over the past several years have demonstrated the existence of at least eight distinct conditions with variable genetic implications. In several of these disorders, especially chromosomally normal MDS, ILS, and CCL, too few patients have been reported to permit citation of accurate recurrence risk figures. Accordingly, we wish to begin a registry of patients with lissencephaly of all types for the purpose of developing such risk figures and request that any available information be sent to one of us (W.B.D. or J.M.O.).

New chromosomal syndrome: Miller-Dieker syndrome and monosomy 17p13

The Miller-Dieker Syndrome (MDS) consists of lissencephaly, characteristic facies, pre- and postnatal growth retardation, plus various other birth defects. Autosomal recessive inheritance has been presumed based on four reported families with two or more affected siblings. We present substantial evidence that monosomy 17p13.3 causes the MDS phenotype. This includes two patients with ring chromosome 17, one patient with a de novo 17p13 deletion, and one patient with monosomy 17p due to an unbalanced 7p; 17p translocation. We report the first prenatal diagnosis of MDS in a 20-week fetus from this latter family. Additionally, we report a balanced translocation between chromosome 17 and different autosomes (8, 12, and 15) in three of the four familial cases of lissencephaly. The finding of a chromosomal basis for this presumed autosomal recessive disorder significantly alters genetic counseling and makes prenatal diagnosis possible in some families.

Syndromes with lissencephaly. I: Miller-Dieker and Norman-Roberts syndromes and isolated lissencephaly

Lissencephaly (smooth-brain) is an abnormality of brain development characterized by incomplete neuronal migration and a smooth cerebral surface. At least 2, and possibly more, distinct pathological types occur, each associated with several distinct syndromes. In this paper, the manifestations of 3 disorders associated with type I (classical) lissencephaly are discussed, including the Miller-Dieker syndrome with or without deficiency of 17p13, Norman-Roberts syndrome, and isolated lissencephaly sequence.

A spectrum of gyral anomalies in Miller-Dieker (lissencephaly) syndrome

Four unrelated patients who had the clinical appearance of Miller-Dieker syndrome, also called lissencephaly syndrome, were studied. All four had a typical clinical course with failure to thrive, severe psychomotor retardation, opisthotonos, seizures, and death early in life. None of these children had lissencephaly, the anticipated central feature of this disorder. One of the four had pachygyria, one had polymicrogyria, and two had both pachygyria and polymicrogyria. The brain weights were normal to decreased. The ventricles were dilated in all cases. The cerebral cortex was thickened in each, with decreased white matter and diminution or distortion of the cellular layers, and there were neuroglial heterotopias. The corpus callosum was partially absent in one and thinned in three. The neuropathy found in these children with Miller-Dieker syndrome suggests a spectrum of gyral anomalies resulting from a single type of embryonic error.

Miller-Dieker syndrome: lissencephaly and monosomy 17p

Miller-Dieker syndrome, which includes lissencephaly and a characteristic phenotypic appearance, has been reported to have an autosomal recessive pattern of inheritance. However, we have found abnormalities of chromosome 17 in two of three unrelated patients with this syndrome, one with a ring chromosome 17 and the other with an unbalanced translocation resulting in partial monosomy of 17p13. A review of the literature revealed five additional patients in three families, who had Miller-Dieker syndrome and an abnormality of 17p. Thus, we propose that monosomy of distal 17p may be the cause of Miller-Dieker syndrome in some patients.

Lissencephaly: two distinct clinico-pathological types

The present study is a review of four new cases of lissencephaly and two others previously reported. This study demonstrates that lissencephaly is a gross feature of the brain occurring in two different groups of cortical malformations. The first group, the classic agyria syndrome extensively analyzed by Jellinger and Rett [8] includes two types of abnormal cortical organization. They may be found in familial syndromes and also can appear sporadically. The second group includes smooth brains with the internal features of polymicrogyria and a more severely disorganized cortex. This type appears in familial lissencephaly in the cerebro-oculo-muscular syndrome, belonging to the same group as Fukuyama congenital-cerebro-muscular dystrophy. The other incidences of this type of cortical malformation require further investigation. The clinico-pathological differential diagnosis of two types of lissencephaly are also discussed.

Familial lissencephaly with extreme neopallial hypoplasia

Two siblings, male and female, with identical lethal brain malformation are described. Their anomaly is characterized by very low brain weight, lissencephaly, wide ventricles and thin neopallium (colpocephaly) varying in thickness between 0.2 and 3 mm. The neocortex is four layered as in classic lissencephaly. Brainstem and cerebellar anomalies are more extensive than in cases hitherto described in detail. No extracranial malformation is found. The parental karyotypes are normal. The relationship to previously reported familial cases of lissencephaly and several inherited syndromes featuring lissencephaly is discussed. The present family may represent a severe expression of previously described autosomal recessive lissencephaly without extracranial anomaly or may represent a new genetic lissencephaly syndrome.

Neurological and neuropathological findings in ring chromosome 4

Despite the fact that mental retardation, microcephaly, seizures, and hyperactivity are common in patients with ring chromosome 4, little has been written about the underlying neuropathology. We describe a 6-year-old girl whose neuropathological findings included low brain weight, abnormal gyral development, and heterotopic neurons. The significance of these findings in regard to other retardation syndromes is discussed.

The evolution of electroencephalographic features in lissencephaly syndrome

The electroencephalographic features and their evolutional changes with age were described in three cases of lissencephaly syndrome diagnosed by CT scan. The case with more severe lissencephaly displayed very similar EEG findings. In early or middle infancy when infantile spasms began, EEG showed very high amplitude (more than 400 microV) slow waves mixed with sharp theta-waves. In their clinical course, they showed extreme spindles and in late infancy, the EEG revealed a tendency towards bilaterally synchronous discharges of high amplitude sharp and slow waves. On the other hand, milder forms of lissencephaly showed hypsarrhythmia in early infancy. In the late infancy the EEG showed bisynchronous sharp and slow waves of more than 200 microV. The anomaly ranging from agyria to pachygyria seems to be closely associated with varying EEG abnormalities from extremely high voltage hypsarrhythmia to focal spikes. The very high voltage of hypsarrhythmic patterns and the very low frequency of sharp wave discharges seem to be typical in the most severe lissencephaly or agyria