Band Heterotopia Research Articles

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.

New insights into genotype–phenotype correlations for the doublecortin-related lissencephaly spectrum

X-linked isolated lissencephaly sequence and subcortical band heterotopia are allelic human disorders associated with mutations of doublecortin (DCX), giving both familial and sporadic forms. DCX encodes a microtubule-associated protein involved in neuronal migration during brain development. Structural data show that mutations can fall either in surface residues, likely to impair partner interactions, or in buried residues, likely to impair protein stability. Despite the progress in understanding the molecular basis of these disorders, the prognosis value of the location and impact of individual DCX mutations has largely remained unclear. To clarify this point, we investigated a cohort of 180 patients who were referred with the agyria-pachygyria subcortical band heterotopia spectrum. DCX mutations were identified in 136 individuals. Analysis of the parents' DNA revealed the de novo occurrence of DCX mutations in 76 cases [62 of 70 females screened (88.5%) and 14 of 60 males screened (23%)], whereas in the remaining cases, mutations were inherited from asymptomatic (n = 14) or symptomatic mothers (n = 11). This represents 100% of families screened. Female patients with DCX mutation demonstrated three degrees of clinical-radiological severity: a severe form with a thick band (n = 54), a milder form (n = 24) with either an anterior thin or an intermediate thickness band and asymptomatic carrier females (n = 14) with normal magnetic resonance imaging results. A higher proportion of nonsense and frameshift mutations were identified in patients with de novo mutations. An analysis of predicted effects of missense mutations showed that those destabilizing the structure of the protein were often associated with more severe phenotypes. We identified several severe- and mild-effect mutations affecting surface residues and observed that the substituted amino acid is also critical in determining severity. Recurrent mutations representing 34.5% of all DCX mutations often lead to similar phenotypes, for example, either severe in sporadic subcortical band heterotopia owing to Arg186 mutations or milder in familial cases owing to Arg196 mutations. Taken as a whole, these observations demonstrate that DCX-related disorders are clinically heterogeneous, with severe sporadic and milder familial subcortical band heterotopia, each associated with specific DCX mutations. There is a clear influence of the individual mutated residue and the substituted amino acid in determining phenotype severity.

′Double cortex′ sign on FDG-PET/CT in diffuse band heterotopia

F-18 Fluorodeoxyglucose (FDG) Positron emission tomography/Computed Tomography (PET/CT) has come to play an increasingly important role for the pre-surgical evaluation of drug resistant epilepsy and complements Magnetic Resonance Imaging (MRI) in the evaluation of grey matter heterotopias. This case illustrates the characteristic pattern of metabolic abnormality in diffuse band heterotopia (DBH) which is otherwise called double cortex syndrome. The presence of metabolic activity in the heterotopic inner cortical band and in the overlying true cortex gives rise to the ‘double cortex’ sign on FDG-PET, concurrent CT provides a good anato-metabolic coregistration.

前頭葉起源の両側同期性発射の関与が疑われる失立発作を呈した皮質下帯状異所性灰白質の一例

前頭葉起源の両側同期性発射の関与が疑われる失立発作を呈した皮質下帯状異所性灰白質の一例

A male case of subcortical band heterotopia with somatic mosaicism of DCX mutation

A male case of subcortical band heterotopia with somatic mosaicism of <i>DCX</i> mutation

Mosaic DCX deletion causes subcortical band heterotopia in males

Subcortical band heterotopia (SBH) is a neuronal migration disorder usually described in females carrying heterozygous mutations in the X-linked doublecortin (DCX) gene. Hemizygous DCX mutations in males result in lissencephaly. Recently, exonic deletions of DCX resulting in a severer form of agyria have been reported. Nevertheless, rare male patients with SBH have been described with somatic mosaicism of point mutations. Here, we identified a somatic mosaicism for a deletion of exon 4 in the DCX gene in a male patient with SBH detected prenatally. This finding points to the possible implication of mosaic deletions in the DCX gene in unexplained forms of SBH and may allow for detection of SBH prenatally.

Doublecortin Recognizes the 13-Protofilament Microtubule Cooperatively and Tracks Microtubule Ends

Neurons, like all cells, face the problem that tubulin forms microtubules with too many or too few protofilaments (pfs). Cells overcome this heterogeneity with the γ-tubulin ring complex, which provides a nucleation template for 13-pf microtubules. Doublecortin (DCX), a protein that stabilizes microtubules in developing neurons, also nucleates 13-pf microtubules invitro. Using fluorescence microscopy assays, we show that the binding of DCX to microtubules is optimized for the lateral curvature of the 13-pf lattice. This sensitivity depends on a cooperative interaction wherein DCX molecules decrease the dissociation rate of their neighbors. Mutations in DCX found in patients with subcortical band heterotopia weaken these cooperative interactions. Using assays with dynamic microtubules, we discovered that DCX binds to polymerization intermediates at growing microtubule ends. These results support a mechanism for stabilizing 13-pf microtubules that allows DCX to template new 13-pf microtubules through associations with the sides of the microtubule lattice.

Subcortical Band Heterotopia without Detectable DCX or LIS1 Gene Mutations (PD3.002)

Objective: To study twenty patients with epilepsy and subcortical band heterotopia without LIS1/DCX mutations. Background Subcortical band heterotopia (SBH), also called double cortex syndrome, is a malformation of cortical development due to deficient neuronal migration. Anterior and posterior SBH are associated with DCX and LIS1 gene mutations, respectively. Design/Methods: Review of our database of adult epilepsy patients with SBH for which no DCX or LIS1 mutation was found; perform karyotype and CGH array in these patients. Results: Twenty-eight patients presenting with various degrees of epilepsy, with or without associated cognitive delay, had an SBH. All were sporadic. They were evaluated with DCX and/or LIS1 sequencing and MLPA analysis. In twenty patients, no DCX or LIS1 mutation was identified. Karyotype and/or array CGH were then carried out in a number of patients. In one woman, the karyotype showed a rearrangement of chromosome 9, suggesting a paracentric inversion of the q13-q22.3 region. Karyotype analysis in both parents was normal, indicating a de novo chromosomal rearrangement in the proband. This patient had a history of infantile spasms, morning myoclonic seizures and pervasive developmental delay. She presented a thick and diffuse SBH. DCX and LIS1 sequencing and deletion/duplication analysis were negative. A CGH microarray (with 135,000 oligonucleotides) was added and did not reveal any deletion or duplication. A higher resolution CGH microarray is planned in order to detect a possible microdeletion/duplication. Conclusions: Genetic evaluation of SBH deserves DCX and/or LIS1 sequencing and deletion/duplication analysis, but does not always reveal the genetic cause of this brain malformation. Karyotype analysis and/or array CGH may still be of interest in these unsolved cases. Careful analysis of other sporadic SBH patients, as well as familial cases, negative for DCX/LIS1 evaluation, is mandatory in order to elucidate their genetic cause and improve genetic counselling. Disclosure: Dr. Andermann has nothing to disclose. Dr. Amrom has nothing to disclose. Dr. D9Agostino has nothing to disclose. Dr. Dubeau has nothing to disclose. Dr. Andermann has nothing to disclose. Dr. Dobyns has nothing to disclose.

Lissencephaly and Band Heterotopia: LIS1, TUBA1A, and DCX Mutations in Hungary

The spectrum of lissencephaly ranges from absent (agyria) or decreased (pachygyria) convolutions to less severe malformation known as subcortical band heterotopia. Mutations involving LIS1 and TUBA1A result in the classic form of lissencephaly, whereas mutations of the DCX gene cause lissencephaly in males and subcortical band heterotopia in females. This report describes the clinical manifestations and imaging and genetic findings in 2 boys with lissencephaly and a girl with subcortical band heterotopia. An ovel mutation (c.83_84delAT, p.Tyr28Phefs*31) was identified in LIS1 in 1 of the boys with lissencephaly and another novel mutation (c.200delG, p.Ile68Leufs*87) was found in DCX in the girl with subcortical band heterotopia. The mutations appeared in the first half of the genes and are predicted to result in truncated proteins. A mutation was found in the TUBA1A gene (c.1205G>A, p.Arg402His) in the other boy. This mutation affects the folding of tubulin heterodimers, changing the interactions with proteins that bind microtubules.

A Radial Glia-Specific Role of RhoA in Double Cortex Formation

The positioning of neurons in the cerebral cortex is of crucial importance for its function as highlighted by the severe consequences of migrational disorders in patients. Here we show that genetic deletion of the small GTPase RhoA in the developing cerebral cortex results in two migrational disorders: subcortical band heterotopia (SBH), a heterotopic cortex underlying the normotopic cortex, and cobblestone lissencephaly, in which neurons protrude beyond layer I at the pial surface of the brain. Surprisingly, RhoA(-/-) neurons migrated normally when transplanted into wild-type cerebral cortex, whereas the converse was not the case. Alterations in the radial glia scaffold are demonstrated to cause these migrational defects through destabilization of both the actin and the microtubules cytoskeleton. These data not only demonstrate that RhoA is largely dispensable for migration in neurons but also showed that defects in radial glial cells, rather than neurons, can be sufficient to produce SBH.

Sudden Death in a 61-Year-Old Woman with Subcortical Band Heterotopia

Subcortical band heterotopia (SBH), also known as double cortex syndrome, is a rare congenital abnormality seen almost exclusively in women. Affected individuals present with seizures, decreased cognitive ability, and behavioral problems, all of which may be expressed with variable severity. The diagnosis is considered with the characteristic MRI findings coupled with the neurologic features and appropriate family history. The rarity of this disorder combined with the typically early presentation with seizures and the characteristic imaging findings make initial diagnosis in a forensic setting unlikely. Therefore, to our knowledge, SBH has not been described in the forensic literature. This case demonstrates a case of sudden death in a woman with known epilepsy, without further clinical history available at the time of autopsy.

Cellular anatomy, physiology and epileptiform activity in the CA3 region of Dcx knockout mice: a neuronal lamination defect and its consequences

We report data on the neuronal form, synaptic connectivity, neuronal excitability and epileptiform population activities generated by the hippocampus of animals with an inactivated doublecortin gene. The protein product of this gene affects neuronal migration during development. Human doublecortin (DCX) mutations are associated with lissencephaly, subcortical band heterotopia, and syndromes of intellectual disability and epilepsy. In Dcx(-/Y) mice, CA3 hippocampal pyramidal cells are abnormally laminated. The lamination defect was quantified by measuring the extent of the double, dispersed or single pyramidal cell layer in the CA3 region of Dcx(-/Y) mice. We investigated how this abnormal lamination affected two groups of synapses that normally innervate defined regions of the CA3 pyramidal cell membrane. Numbers of parvalbumin (PV)-containing interneurons, which contact peri-somatic sites, were not reduced in Dcx(-/Y) animals. Pyramidal cells in double, dispersed or single layers received PV-containing terminals. Excitatory mossy fibres which normally target proximal CA3 pyramidal cell apical dendrites apparently contact CA3 cells of both layers in Dcx(-/Y) animals but sometimes on basilar rather than apical dendrites. The dendritic form of pyramidal cells in Dcx(-/Y) animals was altered and pyramidal cells of both layers were more excitable than their counterparts in wild-type animals. Unitary inhibitory field events occurred at higher frequency in Dcx(-/Y) animals. These differences may contribute to a susceptibility to epileptiform activity: a modest increase in excitability induced both interictal and ictal-like discharges more effectively in tissue from Dcx(-/Y) mice than from wild-type animals.

Fiber tractography assessment in double cortex syndrome

Subcortical band heterotopia (SBH) or double cortex syndrome is a malformation of cortical development that may be related to intractable epilepsy and severe mental retardation or to mild epilepsy and slight mental delay or normal cognitive functions. Several studies have been performed using neuroradiological or neurophysiological techniques, like SPECT, PET, MRS, fMRI, and MEG, in attempt to better characterize this neuronal migration disorder. Recently, also diffusion tensor imaging (DTI) and fiber tracking (FT) have been used to investigate on white matter anomalies in SBH, adding more information about such gray matter anomaly. We report on three cases of SBH, evaluated with MRI, DTI, and FT. The data gathered from DTI and TF allow us to hypothesize a new functional role for heterotopic gray matter.

Mutations in WDR62, encoding a centrosomal and nuclear protein, in Indian primary microcephaly families with cortical malformations

Primary microcephaly is an autosomal recessive disorder characterized by smaller than normal brain size and mental retardation. It is genetically heterogeneous with seven loci: MCPH1-MCPH7. We have previously reported genetic analysis of 35 families, including the identification of the MCPH7 gene STIL. Of the 35 families, three families showed linkage to the MCPH2 locus. Recent whole-exome sequencing studies have shown that the WDR62 gene, located in the MCPH2 candidate region, is mutated in patients with severe brain malformations. We therefore sequenced the WDR62 gene in our MCPH2 families and identified two novel homozygous protein truncating mutations in two families. Affected individuals in the two families had pachygyria, microlissencephaly, band heterotopias, gyral thickening, and dysplastic cortex. Using immunofluorescence study, we showed that, as with other MCPH proteins, WDR62 localizes to centrosomes in A549, HepG2, and HaCaT cells. In addition, WDR62 was also localized to nucleoli. Bioinformatics analysis predicted two overlapping nuclear localization signals and multiple WD-40 repeats in WDR62. Two other groups have also recently identified WDR62 mutations in MCPH2 families. Our results therefore add further evidence that WDR62 is the MCPH2 gene. The present findings will be helpful in genetic diagnosis of patients linked to the MCPH2 locus.

Molecular Genetics of Neuronal Migration Disorders

Cortical malformations associated with defects in neuronal migration result in severe developmental consequences including intractable epilepsy and intellectual disability. Genetic causes of migration defects have been identified with the advent and widespread use of high-resolution MRI and genetic techniques. Thus, the full phenotypic range of these genetic disorders is becoming apparent. Genes that cause lissencephaly, pachygyria, subcortical band heterotopia, and periventricular nodular heterotopias have been defined. Many of these genes are involved in cytoskeletal regulation including the function of microtubules (LIS1, TUBA1A,TUBB3, and DCX) and of actin (FilaminA). Thus, the molecular pathways regulating neuronal migration including the cytoskeletal pathways appear to be defined by human mutation syndromes. Basic science, including cell biology and animal models of these disorders, has informed our understanding of the pathogenesis of neuronal migration disorders and further progress depends on the continued integration of the clinical and basic sciences.

Double Inversion Recovery Magnetic Resonance Imaging of Subcortical Band Heterotopia

We report 2 cases of subcortical band heterotopia (SBH) with emphasis on double inversion recovery (DIR) magnetic resonance imaging (MRI). The heterotopic gray matter demonstrated homogeneous high signal intensity and the delineation between the SBH and white matter was distinctly depicted on DIR MRI. Double inversion recovery is a useful adjunct to conventional MRI for the diagnosis of SBH.

Disturbances in the positioning, proliferation and apoptosis of neural progenitors contribute to subcortical band heterotopia formation

Cortical malformations are commonly associated with intractable epilepsy and other developmental disorders. Our studies utilize the tish rat, a spontaneously occurring genetic model of subcortical band heterotopia (SBH) associated with epilepsy, to evaluate the developmental events underlying SBH formation in the neocortex. Our results demonstrate that Pax6+ and Tbr2+ progenitors are mislocalized in tish+/− and tish−/−- neocortex throughout neurogenesis. In addition, mislocalized tish−/− progenitors possess a longer cell cycle than wild type or normally-positioned tish−/− progenitors, owing to a lengthened G2+M+G1 time. This mislocalization is not associated with adherens junction breakdown or loss of radial glial polarity in the ventricular zone (VZ), as assessed by immunohistochemistry against phalloidin (to identify F-actin), aPKC-λ and Par3. However, vimentin immunohistochemistry indicates that the radial glial scaffold is disrupted in the region of the tish−/− heterotopia. Moreover, lineage tracing experiments using in utero electroporation in tish−/− neocortex demonstrate that mislocalized progenitors do not retain contact with the ventricular surface and that ventricular/subventricular zone (SVZ) progenitors produce neurons that migrate into both the heterotopia and cortical plate (CP). Taken together, these findings define a series of developmental errors contributing to SBH formation that differs fundamentally from a primary error in neuronal migration.

Congenital Infiltrating Lipomatosis of the Face with Ipsilateral Hemimegalencephaly, Band Heterotopia, and Hypertrophy of Brainstem and Cerebellum

The simultaneous appearance of congenital infiltrating lipomatosis of the face that causes facial hemihypertrophy and ipsilateral hemimegalencephaly is extremely rare. We report a 4-year-old boy with congenital facial asymmetry and infantile-onset epilepsy. Magnetic resonance imaging (MRI) results led to the diagnosis of infiltrating lipomatosis of the face; the diagnosis was confirmed on the basis of the results of pathological examinations. Additionally, brain MRI revealed ipsilateral hemimegalencephaly, associated with band heterotopia and the hemihypertrophy of the ipsilateral brainstem and cerebellum. He had no nevi or other skin abnormalities suggesting neurocutaneous syndrome. His seizures were so intractable that they necessitated functional hemispherectomy. The lipomatous lesion was successfully resected without relapse. Psychomotor delay and left hemiplegia were observed at the last follow-up.

The Doublecortin Gene Family and Disorders of Neuronal Structure

The doublecortin gene family is associated with subcortical band heterotopia, lissencephaly, epilepsy, developmental dyslexia and retinitis pigmentosa. At least 11 genes homologous to the doublecortin gene exist in humans and mice. Cellular processes regulated by different members of the doublecortin family involve neuronal migration, neurogenesis and eye receptor development. Underlying mechanisms include regulation of cytoskeletal structure and microtubule-based transport. Through their doublecortin-domains, doublecortin proteins can bind microtubules and regulate microtubule-dependent processes. However, this regulation is complex and involves many interacting proteins. Moreover, different spatiotemporal expression patterns and the generation of splice variants further contribute to this complexity. The doublecortin-like kinase 1 gene in particular, produces splice variants with different protein domains such as doublecortin-domains, a serine, threonine and proline-rich domain and a serine/threonine kinase-domain. Here, we review our current knowledge on the doublecortin gene family with an emphasis on proteins interacting with doublecortin domains and other domains. In addition, to generate new hypotheses for further research, we analyzed the serine, threonine and proline-rich domain for predicted protein interactions.

The clinical patterns and molecular genetics of lissencephaly and subcortical band heterotopia

The clinical patterns and molecular genetics of lissencephaly and subcortical band heterotopia