Cerebral organoids to unravel the mechanisms underlying malformations of human cortical development.

Genetic studies identified multiple mutations associated with malformations of cortical development (MCD) in humans. When analyzing the underlying mechanisms in non-human experimental models it became increasingly evident, that these mutations accumulate in genes, which functions evolutionary progressed from rodents to humans resulting in an incomplete reflection of the molecular and cellular alterations in these models. Human brain organoids derived from human pluripotent stem cells resemble early aspects of human brain development to a remarkable extent making them an attractive model to investigate MCD. Here we review how human brain organoids enable the generation of fundamental new insight about the underlying pathomechanisms of MCD. We show how phenotypic features of these diseases are reflected in human brain organoids and discuss challenges and future considerations but also limitations for the use of human brain organoids to model human brain development and associated disorders.

KCl-induced cortical spreading depression waves more heterogeneously propagate than optogenetically-induced waves in lissencephalic brain: an analysis with optical flow tools.

Although cortical spreading depolarizations (CSD) were originally assumed to be homogeneously and concentrically propagating waves, evidence obtained first in gyrencephalic brains and later in lissencephalic brains suggested a rather non-uniform propagation, shaped heterogeneously by factors like cortical region differences, vascular anatomy, wave recurrences and refractory periods. Understanding this heterogeneity is important to better evaluate the experimental models on the mechanistics of CSD and to make appropriate clinical estimations on neurological disorders like migraine, stroke, and traumatic brain injury. This study demonstrates the application of optical flow analysis tools for systematic and objective evaluation of spatiotemporal CSD propagation patterns in anesthetized mice and compares the propagation profile in different CSD induction models. Our findings confirm the asymmetric angular CSD propagation in lissencephalic brains and suggest a strong dependency on induction-method, such that continuous potassium chloride application leads to significantly higher angular propagation variability compared to optogenetically-induced CSDs.

New insights into the mechanism of dynein motor regulation by lissencephaly-1.

Lissencephaly ('smooth brain') is a severe brain disease associated with numerous symptoms, including cognitive impairment, and shortened lifespan. The main causative gene of this disease - lissencephaly-1 (LIS1) - has been a focus of intense scrutiny since its first identification almost 30 years ago. LIS1 is a critical regulator of the microtubule motor cytoplasmic dynein, which transports numerous cargoes throughout the cell, and is a key effector of nuclear and neuronal transport during brain development. Here, we review the role of LIS1 in cellular dynein function and discuss recent key findings that have revealed a new mechanism by which this molecule influences dynein-mediated transport. In addition to reconciling prior observations with this new model for LIS1 function, we also discuss phylogenetic data that suggest that LIS1 may have coevolved with an autoinhibitory mode of cytoplasmic dynein regulation.

Neuronal migration genes and a familial translocation t (3;17): candidate genes implicated in the phenotype.

BACKGROUND: While Miller-Dieker syndrome critical region deletions are well known delineated anomalies, submicroscopic duplications in this region have recently emerged as a new distinctive syndrome. So far, only few cases have been described overlapping 17p13.3 duplications. METHODS: In this study, we report on clinical and cytogenetic characterization of two new cases involving 17p13.3 and 3p26 chromosomal regions in two sisters with familial history of lissencephaly. Fluorescent In Situ Hybridization and array Comparative Genomic Hybridization were performed. RESULTS: A deletion including the critical region of the Miller-Dieker syndrome of at least 2,9 Mb and a duplication of at least 3,6 Mb on the short arm of chromosome 3 were highlighted in one case. The opposite rearrangements, 17p13.3 duplication and 3p deletion, were observed in the second case. This double chromosomal aberration is the result of an adjacent 1:1 meiotic segregation of a maternal reciprocal translocation t(3,17)(p26.2;p13.3). CONCLUSIONS: 17p13.3 and 3p26 deletions have a clear range of phenotypic features while duplications still have an uncertain clinical significance. However, we could suggest that regardless of the type of the rearrangement, the gene dosage and interactions of CNTN4, CNTN6 and CHL1 in the 3p26 and PAFAH1B1, YWHAE in 17p13.3 could result in different clinical spectrums.

Mutations in TBR1 gene leads to cortical malformations and intellectual disability.

The advent of next generation sequencing has improved gene discovery in neurodevelopmental disorders. A greater understanding of the genetic basis of these disorders has expanded the spectrum of pathogenic genes, thus enhancing diagnosis and therapeutic management. Genetic overlap between distinct neurodevelopmental disorders has also been revealed, which can make determining a strict genotype-phenotype correlation more difficult. Intellectual disability and cortical malformations are two neurodevelopmental disorders particularly confronted by this difficulty. Indeed, for a given pathogenic gene, intellectual disability can be associated, or not, with cortical malformations. Here, we report for the first time, two individuals with the same de novo mutation in TBR1, leading to a frameshift starting at codon Thr532, and resulting in a premature stop codon 143 amino acids downstream (c.1588_1594dup, p.(Thr532Argfs*144)). These individuals presented with a developmental encephalopathy characterized by frontal pachygyria and severe intellectual disability. Remarkably, 11 TBR1 gene mutations were previously reported in intellectual disability and autism spectrum disorders. Our study supports the observation that TBR1-related disorders range from intellectual disability to frontal pachygyria. We also highlight the need for first-line, good quality neuroimaging for patients with intellectual disability.

Analysis of 17 genes detects mutations in 81% of 811 patients with lissencephaly.

PURPOSE: To estimate diagnostic yield and genotype-phenotype correlations in a cohort of 811 patients with lissencephaly or subcortical band heterotopia. METHODS: We collected DNA from 756 children with lissencephaly over 30 years. Many were tested for deletion 17p13.3 and mutations of LIS1, DCX, and ARX, but few other genes. Among those tested, 216 remained unsolved and were tested by a targeted panel of 17 genes (ACTB, ACTG1, ARX, CRADD, DCX, LIS1, TUBA1A, TUBA8, TUBB2B, TUBB, TUBB3, TUBG1, KIF2A, KIF5C, DYNC1H1, RELN, and VLDLR) or by whole-exome sequencing. Fifty-five patients studied at another institution were added as a validation cohort. RESULTS: The overall mutation frequency in the entire cohort was 81%. LIS1 accounted for 40% of patients, followed by DCX (23%), TUBA1A (5%), and DYNC1H1 (3%). Other genes accounted for 1% or less of patients. Nineteen percent remained unsolved, which suggests that several additional genes remain to be discovered. The majority of unsolved patients had posterior pachygyria, subcortical band heterotopia, or mild frontal pachygyria. CONCLUSION: The brain-imaging pattern correlates with mutations in single lissencephaly-associated genes, as well as in biological pathways. We propose the first LIS classification system based on the underlying molecular mechanisms.

An in vitro model of lissencephaly: expanding the role of DCX during neurogenesis.

Lissencephaly comprises a spectrum of brain malformations due to impaired neuronal migration in the developing cerebral cortex. Classical lissencephaly is characterized by smooth cerebral surface and cortical thickening that result in seizures, severe neurological impairment and developmental delay. Mutations in the X-chromosomal gene DCX, encoding doublecortin, is the main cause of classical lissencephaly. Much of our knowledge about DCX-associated lissencephaly comes from post-mortem analyses of patient's brains, mainly since animal models with DCX mutations do not mimic the disease. In the absence of relevant animal models and patient brain specimens, we took advantage of induced pluripotent stem cell (iPSC) technology to model the disease. We established human iPSCs from two males with mutated DCX and classical lissencephaly including smooth brain and abnormal cortical morphology. The disease was recapitulated by differentiation of iPSC into neural cells followed by expression profiling and dissection of DCX-associated functions. Here we show that neural stem cells, with absent or reduced DCX protein expression, exhibit impaired migration, delayed differentiation and deficient neurite formation. Hence, the patient-derived iPSCs and neural stem cells provide a system to further unravel the functions of DCX in normal development and disease.

Homozygous null variant in CRADD, encoding an adaptor protein that mediates apoptosis, is associated with lissencephaly.

Lissencephaly is a severe malformation of cortical development, most often attributed to abnormalities in neuronal migration. It is associated with a severe prognosis including developmental delay, intellectual disability, and seizures. Lissencephaly can be reliably diagnosed during late gestation by neurosonography or fetal magnetic resonance imaging (MRI). We report two sibling male fetuses who were diagnosed with delayed cortical sulcation highly suggestive of lissencephaly during late pregnancy. After receiving genetic counseling, the parents elected to terminate the pregnancies based on the neuroradiological findings and the associated severe prognosis. Whole exome sequencing (WES) of an affected fetus, and subsequent Sanger sequencing of the second fetus, revealed a homozygous frameshift variant in CRADD, which encodes an adaptor protein that interacts with PIDD and caspase-2 to initiate apoptosis. Biallelic variants in this gene have been recently reported to cause "thin" lissencephaly and intellectual disability. Interestingly, the allegedly healthy father was also found to be homozygous for the variant, prompting evaluation by brain MRI which revealed hypogyration. This study underscores the phenotypic variability of pathogenic variants in CRADD and the challenges of prenatal genetic counseling.

Visualization of migration of human cortical neurons generated from induced pluripotent stem cells.

BACKGROUND: Neuronal migration is considered a key process in human brain development. However, direct observation of migrating human cortical neurons in the fetal brain is accompanied by ethical concerns and is a major obstacle in investigating human cortical neuronal migration. NEW METHOD: We established a novel system that enables direct visualization of migrating cortical neurons generated from human induced pluripotent stem cells (hiPSCs). RESULTS: We observed the migration of cortical neurons generated from hiPSCs derived from a control and from a patient with lissencephaly. METHODS: Our system needs no viable brain tissue, which is usually used in slice culture. Migratory behavior of human cortical neuron can be observed more easily and more vividly by its fluorescence and glial scaffold than that by earlier methods. CONCLUSIONS: Our in vitro experimental system provides a new platform for investigating development of the human central nervous system and brain malformation.

Lissencephaly: Expanded imaging and clinical classification.

Lissencephaly ("smooth brain," LIS) is a malformation of cortical development associated with deficient neuronal migration and abnormal formation of cerebral convolutions or gyri. The LIS spectrum includes agyria, pachygyria, and subcortical band heterotopia. Our first classification of LIS and subcortical band heterotopia (SBH) was developed to distinguish between the first two genetic causes of LIS-LIS1 (PAFAH1B1) and DCX. However, progress in molecular genetics has led to identification of 19 LIS-associated genes, leaving the existing classification system insufficient to distinguish the increasingly diverse patterns of LIS. To address this challenge, we reviewed clinical, imaging and molecular data on 188 patients with LIS-SBH ascertained during the last 5 years, and reviewed selected archival data on another ∼1,400 patients. Using these data plus published reports, we constructed a new imaging based classification system with 21 recognizable patterns that reliably predict the most likely causative genes. These patterns do not correlate consistently with the clinical outcome, leading us to also develop a new scale useful for predicting clinical severity and outcome. Taken together, our work provides new tools that should prove useful for clinical management and genetic counselling of patients with LIS-SBH (imaging and severity based classifications), and guidance for prioritizing and interpreting genetic testing results (imaging based- classification).

Familial pachygyria in both genders related to a DCX mutation.

Doublecortin (DCX) and tubulin play critical roles in neuronal migration. DCX mutations usually cause anterior dominant lissencephaly in males and subcortical band heterotopia (SBH) in females. We used whole-exome sequencing to investigate causative gene variants in a large family with late-childhood-onset focal epilepsy and anterior dominant pachygyria without SBH in both genders. Two potential variants were found for the genes encoding DCX and beta tubulin isotype 1 (TUBB1). The novel DCX mutation (p.D90G, NP_000546.2) appeared to be a major causative variant, whereas the novel mutation of TUBB1 (p.R62fsX, NP_110400.1) was found only in patients with more-severe intellectual disability after gender matching. We report an unusual DCX-related disorder exhibiting familial pachygyria without SBH in both genders.

Efficacy of long term weekly ACTH therapy for intractable epilepsy.

BACKGROUND: Adrenocorticotropic hormone (ACTH) therapy is the first-line therapy for infantile spasms, and is effective for many other intractable epilepsies. While spasms may respond to ACTH for weeks, a substantial proportion of patients develop recurrent seizures over a yearly period. To maintain efficacy, we treated two children with intractable epilepsy with weekly ACTH therapy for 1 year and described the changes in clinical seizures, electroencephalograms, developmental assessments and side effects. SUBJECTS AND METHODS: A girl with infantile spasms due to lissencephaly and a boy with atypical absence seizures were studied. In both cases, seizures were frequent and resistant to antiepileptic drugs; electroencephalograms showed continuous epileptiform activities, and the patients' development was delayed and stagnant prior to ACTH treatment. The initial ACTH therapy (daily 0.015 mg/kg for 2 weeks, 0.015 mg/kg every 2 days for 1 week, 0.0075 mg/kg every 2 days for 1 week), was transiently effective in both cases. The second-round ACTH therapy consisted of the initial ACTH therapy protocol followed by weekly ACTH injections (0.015 mg/kg or 0.0075 mg/kg) for 1 year. Both cases were followed for at least 1 year after therapy. RESULTS: In both patients, clinical seizures were completely controlled during and 1 year after the second-round AHCH therapy. Continuous epileptiform discharges disappeared, while intermittent interictal epileptiform discharges remained. Both patients showed some developmental gains after achieving seizure control. No serious side effects were recorded. CONCLUSION: Further studies are warranted to determine if a long-term weekly ACTH is a safe and effective treatment for intractable epilepsy.

Fine-tuning of neurogenesis is essential for the evolutionary expansion of the cerebral cortex.

We used several animal models to study global and regional cortical surface expansion: The lissencephalic mouse, gyrencephalic normal ferrets, in which the parietal cortex expands more than the temporal cortex, and moderately lissencephalic ferrets, showing a similar degree of temporal and parietal expansion. We found that overall cortical surface expansion is achieved when specific events occur prior to surpragranular layer formation. (1) The subventricular zone (SVZ) shows substantial growth, (2) the inner SVZ contains an increased number of outer radial glia and intermediate progenitor cells expressing Pax6, and (3) the outer SVZ contains a progenitor cell composition similar to the combined VZ and inner SVZ. A greater parietal expansion is also achieved by eliminating the latero-dorsal neurogenic gradient, so that neurogenesis displays a similar developmental degree between parietal and temporal regions. In contrast, mice or lissencephalic ferrets show more advanced neurogenesis in the temporal region. In conclusion, we propose that global and regional cortical surface expansion rely on similar strategies consisting in altering the timing of neurogenic events prior to the surpragranular layer formation, so that more progenitor cells, and ultimately more neurons, are produced. This hypothesis is supported by findings from a ferret model of lissencephaly obtained by transiently blocking neurogenesis during the formation of layer IV.

Identification of DCX gene mutation in lissencephaly spectrum with subcortical band heterotopia using whole exome sequencing.

Malformations of cortical development include a wide range of brain developmental anomalies that commonly lead to developmental delay and epilepsy. Lissencephaly and subcortical band heterotopia are major malformations of cortical development due to abnormal neuronal migration and several genes have been identified including ARX, DCX, LIS1, RELN, TUBA1A, and VLDLR. Traditionally, genetic testing for lissencephaly and subcortical band heterotopia has been done in the order of the probability of detection of mutation according to the radiologic features, but the success rate could be variable with this time-consuming approach. In this study we used whole-exome sequencing to identify mutations in a 5-year-old girl with lissencephaly spectrum with subcortical band heterotopia. After excluding lissencephaly-related genes, one deleterious mutation (NM_178153.2:c.665C > T, p.Thr222Ile) in the DCX gene was identified. Further Sanger sequencing validated the variant in the patient but not in both parents indicating a de novo mutation. The present report demonstrates that whole-exome sequencing may be a useful tool for the identification of mutations in patients with lissencephaly and subcortical band heterotopias as well as malformations of cortical development.

Post-natal treatment by a blood-brain-barrier permeable calpain inhibitor, SNJ1945 rescued defective function in lissencephaly.

Toward a therapeutic intervention of lissencephaly, we applied a novel calpain inhibitor, SNJ1945. Peri-natal or post-natal treatment with SNJ1945 rescued defective neuronal migration in Lis1⁺/⁻ mice, impaired behavioral performance and improvement of ¹8F-FDG uptake. Furthermore, SNJ1945 improved the neural circuit formation and retrograde transport of NFG in Lis1⁺/⁻ mice. Thus, SNJ1945 is a potential drug for the treatment of human lissencephaly patients.

EEG and neuroimaging correlations in children with lissencephaly.

PURPOSE: To study the usefulness of EEG in the diagnosis of lissencephaly, a rare cortical developmental disorder associated with abnormal cellular proliferation. Currently, the clinical emphasis is placed on the radiological and genetic aspects for the diagnosis of lissencephaly. METHODS: This is a retrospective review of consecutive EEG recordings and imaging data from 14 children, with the diagnosis of lissencephaly, who were admitted from January 1998 to January 2010. All EEG recordings were performed with the 10-20 system of electrode placement, in both awake and sleep states. All EEG recordings were reviewed using anterior-posterior bipolar and transverse montages and then they were interpreted blindly, with respect to the imaging and genetic investigations for each patient. RESULTS: All children showed one of the three characteristic EEG patterns reported in the literature of lissencephaly. The EEG pattern I, showed an anterior posterior gradient that corresponded to the severity of the imaging study abnormality. All patients were on two or more AEDs and reported to continue having active epilepsy. CONCLUSION: In a child with clinical characteristics of lissencephaly, one of these three reported EEG patterns can prove useful in making the diagnosis very probable, preceding imaging and genetic testing.

ALLN rescues an in vitro excitatory synaptic transmission deficit in Lis1 mutant mice.

LIS1 gene mutations lead to a rare neurological disorder, classical lissencephaly, characterized by brain malformations, mental retardation, seizures, and premature death. Mice heterozygous for Lis1 (Lis1(+/-)) exhibit cortical malformations, defects in neuronal migration, increased glutamate-mediated synaptic transmission, and spontaneous electrographic seizures. Recent work demonstrated that in utero treatment of Lis1(+/-) mutant dams with ALLN, a calpain inhibitor, partially rescues neuronal migration defects in the offspring. Given the challenges of in utero drug administration, we examined the therapeutic potential of ALLN on postnatal lissencephalic cells. Voltage- and current-clamp studies were performed with acute hippocampal slices obtained from Lis1 mutant mice and age-matched littermate control mice. Specifically, we determined whether postnatal ALLN treatment can reverse excitatory synaptic transmission deficits, namely, an increase in spontaneous and miniature excitatory postsynaptic current (EPSC) frequency, on CA1 pyramidal neurons observed in tissue slices from Lis1(+/-) mice. We found that acute application of ALLN restored spontaneous and miniature EPSC frequencies to wild-type levels without affecting inhibitory postsynaptic synaptic current. Furthermore, Western blot analysis of protein expression, including proteins involved in excitatory synaptic transmission, demonstrated that ALLN blocks the cleavage of the calpain substrate αII-spectrin but does not rescue Lis1 protein levels in Lis1(+/-) mutants.

Does subtle disturbance of neuronal migration contribute to schizophrenia and other neurodevelopmental disorders? Potential genetic mechanisms with possible treatment implications.

Pathways associated with genes that regulate neuronal migration by influencing the function of microtubules in the developing fetal brain may be interfered with as part of the "first-hit" of schizophrenia. In the fully-developed brain, these same pathways that impact microtubule function mediate at least some aspects of experience-dependent plasticity, which may also be impaired in schizophrenia. Whereas severe presentations of "lissencephaly" are associated with mutations and deletions of DISC1, LIS1 and the gene for the very low-density lipoprotein receptor, genetic variations of these loci are good candidate schizophrenia genes. Importantly, in the fully-developed brain, there is a possibility that at least some of the consequences of these disturbed genetic pathways that adversely affect microtubule function may be "bypassed" or mitigated.