Showing papers by "Christopher A. Walsh published in 2006"

Molecular approaches to brain asymmetry and handedness

Abstract: The human left and right hemispheres have distinct functions. Sun and Walsh discuss recent genetic, imaging and neurological studies in an attempt to unravel the molecular mechanisms of brain asymmetry and handedness and to understand their evolutionary underpinning.

Periventricular heterotopia: phenotypic heterogeneity and correlation with Filamin A mutations

Abstract: Periventricular heterotopia (PH) occurs when collections of neurons lay along the lateral ventricles or just beneath. Human Filamin A gene (FLNA) mutations are associated with classical X-linked bilateral periventricular nodular heterotopia (PNH), featuring contiguous heterotopic nodules, mega cisterna magna, cardiovascular malformations and epilepsy. FLNA encodes an F-actin-binding cytoplasmic phosphoprotein and is involved in early brain neurogenesis and neuronal migration. A rare, recessive form of bilateral PNH with microcephaly and severe delay is associated with mutations of the ADP-ribosylation factor guanine nucleotide-exchange factor-2 (ARFGEF2) gene, required for vesicle and membrane trafficking from the trans-Golgi. However, PH is a heterogeneous disorder. We studied clinical and brain MRI of 182 patients with PH and, based on its anatomic distribution and associated birth defects, identified 15 subtypes. Classical bilateral PNH represented the largest group (98 patients: 54%). The 14 additional phenotypes (84 patients: 46%) included PNH with Ehlers-Danlos syndrome (EDS), temporo-occipital PNH with hippocampal malformation and cerebellar hypoplasia, PNH with fronto-perisylvian or temporo-occipital polymicrogyria, posterior PNH with hydrocephalus, PNH with microcephaly, PNH with frontonasal dysplasia, PNH with limb abnormalities, PNH with fragile-X syndrome, PNH with ambiguous genitalia, micronodular PH, unilateral PNH, laminar ribbon-like and linear PH. We performed mutation analysis of FLNA in 120 patients, of whom 72 (60%) had classical bilateral PNH and 48 (40%) other PH phenotypes, and identified 25 mutations in 40 individuals. Sixteen mutations had not been reported previously. Mutations were found in 35 patients with classical bilateral PNH, in three with PNH with EDS and in two with unilateral PNH. Twenty one mutations were nonsense and frame-shift and four missense. The high prevalence of mutations causing protein truncations confirms that loss of function is the major cause of the disorder. FLNA mutations were found in 100% of familial cases with X-linked PNH (10 families: 8 with classical bilateral PNH, 1 with EDS and 1 with unilateral PH) and in 26% of sporadic patients with classical bilateral PNH. Overall, mutations occurred in 49% of individuals with classical bilateral PNH irrespective of their being familial or sporadic. However, the chances of finding a mutation were exceedingly gender biased with 93% of mutations occurring in females and 7% in males. The probability of finding FLNA mutations in other phenotypes was 4% but was limited to the minor variants of PNH with EDS and unilateral PNH. Statistical analysis considering all 42 mutations described so far identifies a hotspot region for PNH in the actin-binding domain (P < 0.05).

Filamin A (FLNA) is required for cell–cell contact in vascular development and cardiac morphogenesis

Abstract: Mutations in the human Filamin A (FLNA) gene disrupt neuronal migration to the cerebral cortex and cause cardiovascular defects. Complete loss of Flna in mice results in embryonic lethality with severe cardiac structural defects involving ventricles, atria, and outflow tracts, as well as widespread aberrant vascular patterning. Despite these widespread developmental defects, migration and motility of many cell types does not appear to be affected. Instead, Flna-null embryos display abnormal epithelial and endothelial organization and aberrant adherens junctions in developing blood vessels, heart, brain, and other tissues. Essential roles for FLNA in intercellular junctions provide a mechanism for the diverse developmental defects seen in patients with FLNA mutations.

Impaired neuronal positioning and dendritogenesis in the neocortex after cell-autonomous Dab1 suppression.

Abstract: Reelin and Disabled 1 (Dab1) are essential for positioning migrating neurons in the developing neocortex. Cell-autonomous RNA interference-mediated suppression of Dab1 in migrating neurons destined for layer 2/3 shifted the median position of these cells to deeper positions within the cortex. At the time of migration arrest [embryonic day 20 (E20) to E21], Dab1-suppressed cells were underrepresented in the upper ∼40 μm of the cortex compared with controls, suggesting that Dab1 is essential for somal translocation through the cell-dense cortical plate. Closer examination of the morphology of Dab1-suppressed neurons at E20 revealed simplified leading processes that are less likely to contact the marginal zone (MZ), in which high levels of Reelin are expressed. Examination of Dab1-suppressed cells 3 d later (postnatal day 2) revealed simplified dendrites that are also less likely to contact the MZ. These data reveal a cell-autonomous role of Dab1 in dendritogenesis in the neocortex and suggest that remodeling of the leading process of a migrating neuron into a nascent dendrite by Reelin/Dab1 signaling plays an important role in cell positioning.

Mutated nup62 causes autosomal recessive infantile bilateral striatal necrosis.

Abstract: Objective: The objective of this study was to identify the gene causing autosomal recessive infantile bilateral striatal necrosis. Methods: We have mapped the disease gene in the candidate region to approximately 230kb on 19q13.33 in 8 interrelated families including a total of 12 patients and 39 unaffected individuals. Results: Sequencing of the nup62 gene showed a missense mutation causing a change from glutamine to proline (Q391P) in all the patients, producing a substitution from a polar, hydrophilic residue to a nonpolar, neutral residue. All the other 12 candidate genes were sequenced, and no pathogenic sequence changes were found. Comparisons of p62 protein sequences from diverse species indicate that glutamine at position 391 is highly conserved. Five prenatal diagnoses were performed in three at-risk families. Interpretation: This is the second example of a nuclear pore complex protein causing mendelian disease in humans (the first one is triple A syndrome). Our findings suggest that p62 has a cell type–specific role and is important in the degeneration of the basal ganglia in humans. Ann Neurol 2006;60:214 –222

Genomic and Evolutionary Analyses of Asymmetrically Expressed Genes in Human Fetal Left and Right Cerebral Cortex

Abstract: In the human brain, the left and right hemispheres are anatomically asymmetric and have distinctive cognitive function, although the molecular basis for this asymmetry has not yet been characterized. We compared gene expression levels in the perisylvian regions of human left--right cortex at fetal weeks 12, 14, and 19 using serial analysis of gene expression (SAGE). We identified dozens of genes with evidence of differential expression by SAGE and confirmed these by quantitative reverse transcriptase--polymerase chain reaction. Most genes with differential levels of expression in the left and right hemispheres function in signal transduction and gene expression regulation during early cortical development. By comparing genes differentially expressed in left and right fetal brains with those previously reported to be differently expressed in human versus chimpanzee adult brains, we identified a subset of genes that shows evidence of asymmetric expression in humans and altered expression levels between chimps and humans. We also compared the coding sequences of genes differentially expressed between left and right hemispheres and found genes that show both asymmetric expression and evidence of positive evolutionary selection in the primate lineage leading to humans. Our results identify candidate genes involved in the evolution of human cerebral cortical asymmetry.

Periventricular nodular heterotopia and Williams syndrome

Abstract: We report here on the first case of a child with bilateral periventricular nodular heterotopia (PNH) and Williams syndrome. Fluorescent in situ hybridization (FISH) analyses demonstrated a deletion of the elastin gene in the Williams syndrome critical region (WSCR). Further mapping by loss of heterozygosity analysis both by microsatellite marker and SNP profiling demonstrated a 1.5 Mb deletion beyond the telomeric end of the typical WSCR. No mutations were identified in the X-linked filamin-A gene (the most common cause of PNH). These findings suggest another dominant PNH disorder along chromosome 7q11.23.

A familial syndrome of unilateral polymicrogyria affecting the right hemisphere

Abstract: A number of familial syndromes of bilateral polymicrogyria (PMG) have been described, but reported unilateral PMG cases have generally been sporadic. The authors identified four families in which unilateral right-sided PMG on MRI was present in more than one individual, with pathologic confirmation in one. Core clinical features included contralateral hemiparesis, developmental delay, and focal seizures. The authors' findings suggest that unilateral PMG exists in a familial syndrome of probable germline genetic origin.

Deletion of chromosome 1p36 is associated with periventricular nodular heterotopia

Abstract: Periventricular heterotopia (PH) is a malformation of cortical development characterized by the ectopic localization of neuronal nodules along the lateral ventricle. Mutations in X-linked filamin A gene are the most common cause of PH, although a rarer autosomal recessive form of PH with microcephaly due to ARFGEF2 mutations has been described [Sheen et al., 2001]. Affected individuals generally are of normal intelligence and most often present with adolescent onset seizures. The 1p36 deletion syndrome is associated with multiple congenital anomalies caused by haploinsufficiency of numerous contiguous genes. This deletion produces specific physical characteristics such as distinctive facial anomalies (pointed chin, flat nose, low set ears) and cardiovascular malformations (atrial septal defect, patent ductus arteriosus, tetralogy of Fallot). Central nervous system (CNS) defects include mental retardation, cranial nerve abnormalities (VI nerve palsies, optic disc anomalies, sensorineural hearing loss), neonatal hypotonia, cortical dysplasia, and seizures [Heilstedt et al., 2003; Kurosawa et al., 2005; Battaglia, 2005]. A reduction in the KCNAB2 potassium channel betasubunit has been hypothesized to be responsible for the seizures [Hirose et al., 2002]. Affected individuals can display outbursts, tendencies to strike people, and self-injurious behavior, as well as autistic-like behaviors [Slavotinek et al., 1999]. Previous neuroimaging and postmortem studies on individuals with 1p36 deletions have revealed mild CNS structural abnormalities. Deletions involving the most distal p-terminus (D1S508, 1p36.23-> 1pter) have only been associated with microcephaly, mild ventricular asymmetry, and ventricular enlargement [Kurosawa et al., 2005; Slavotinek et al., 1999]. An interstitial deletion (1p36.1->1p36.2) was suggested as causal for the development of neuroblastoma in a single case report [Keppler-Noreuil et al., 1995]. Finally, a series of three patients harboring 1p36.22->1pter deletions was reported to have hydrocephalus by cranial ultrasound but no mention of PH [Keppler-Noreuil et al., 1995]. To date, there have been no reported associations of PH with chromosome 1p36 deletions. Here, we describe the first case describing PH in an individual with a 1p36.22-> 1pter deletion. This study was approved by the IRB at the respective institutions in accordance with NIH. Informed consent was obtained from the participating subject’s parents. Genomic DNA was extracted from peripheral whole blood lymphocytes using standard blood DNA isolation techniques (Qiagen Inc., Valencia, CA). Metaphase chromosome analysis of lymphocytes was performed according to standard protocols. Initial routine karyotyping on the child was read as normal, although deletions on 1p36 are commonly missed due to the Giemsa-negative/poor staining in this region. Given the numerous clinical features seen in this subject, FISH analysis utilizing 41 subtelomere probes was performed (Genzyme laboratories (Hawthorne, NY), using Vysis probes (Downers Grove, IL). Results were confirmed with a chromosome 1p subtelomere probe (1pSUBTEL; Vysis) and the D1Z2 midi-satellite probe with repeats in band 1p36 (Oncor). The D1Z2 probe is used for confirmationof a commondeletion interval (1p36.3). A chromosome 1 centromere probe (D1Z5; Vysis)

Impaired proliferation and migration in human Miller-Dieker neural precursors.

Abstract: Objective Miller-Dieker syndrome (MDS) is a malformation of cortical development that results in lissencephaly (meaning smooth brain). This disorder is caused by heterozygous deletions on chromosome 17p13.3, including the lissencephaly 1 (LIS1) gene. Various mouse models have been used as an experimental paradigm in understanding human lissencephaly, but clear limitations exist in these studies, particularly because mice are naturally lissencephalic. Thus, the objective of this article was to establish human neural precursor cell lines from postmortem MDS tissue and to characterize the pathological cellular processes that contribute to the human lissencephalic phenotype. Methods Human neural precursors were isolated and expanded from the frontal cortices of a 33-week postmortem fetus with MDS and an age-matched control subject. Relative rates of proliferation and cell death were assessed in vitro, whereas the migration of precursors was examined after transplantation in vivo. Results Precursors showed haploinsufficiency of the LIS1 gene and a reduction in LIS1 protein. Precursors could also differentiate into both neurons and glia. MDS precursors demonstrated impairments in neuronal migration, diminished rates of cell proliferation, and increased cell death. Interpretation These results suggest that, in addition to migration, disruption in cell proliferation could play a more important role in the development of lissencephaly than previously suspected. Ann Neurol 2006

Mutation in filamin A causes periventricular heterotopia, developmental regression, and West syndrome in males.

Abstract: Summary: Purpose: Familial periventricular heterotopia (PH) represents a disorder of neuronal migration resulting in multiple gray-matter nodules along the lateral ventricular walls. Prior studies have shown that mutations in the filamin A (FLNA) gene can cause PH through an X-linked dominant pattern. Heterozygotic female patients usually remain asymptomatic until the second or third decade of life, when they may have predominantly focal seizures, whereas hemizygotic male fetuses typically die in utero. Recent studies have also reported mutations in FLNA in male patients with PH who are cognitively normal. We describe PH in three male siblings with PH due to FLNA ,s evere developmental regression, and West syndrome. Methods: The study includes the three affected brothers and their parents. Video-EEG recordings and magnetic resonance image (MRI) scanning were performed on all individuals. Mutations for FLNA were detected by using polymerase chain reaction (PCR) on genomic DNA followed by single-stranded conformational polymorphism (SSCP) analysis or sequencing. Results: Tw oo fthe siblings are monozygotic twins, and all had West syndrome with hypsarrthymia on EEG. MRI of the brain revealed periventricular nodules of cerebral gray-matter intensity, typical for PH. Mutational analyses demonstrated a cytosine-to-thymidine missense mutation (c. C1286T), resulting in a threonine-to-methionine amino acid substitution in exon 9 of the FLNA gene. Conclusions: The association between PH and West syndrome, to our knowledge, has not been previously reported. Males with PH have been known to harbor FLNA mutations, although uniformly, they either show early lethality or survive and have a normal intellect. The current studies show that FLNA mutations can cause periventricular heterotopia, developmental regression, and West syndrome in male patients, suggesting that this type of FLNA mutation may contribute to severe neurologic deficits. Ke yW ords: Subependymal heterotopia— Periventricular heterotopia—Familial—West syndrome—Male.

Bilateral periventricular heterotopias in an X-linked dominant transmission in a family with two affected males†

Abstract: We report on the case of dizygotic twin boys, born prematurely to an asymptomatic mother. Bilateral periventricular heterotopias with enlarged ventricles were discovered at birth in both twins. One of the twins died prematurely of bronchopulmonary complications, and was shown to have several neuropathological anomalies (microgyria, thin corpus callosum, and reduced white matter). The surviving twin had mental retardation, without epilepsy. MRI of the mother showed asymptomatic periventricular heterotopias without ventricular enlargement. She had two affected daughters also with asymptomatic periventricular heterotopias. A point mutation in the last coding exon 48 of the Filamin A (FLNA) gene (7922c > t) was discovered on sequencing and segregated with the affected individuals. This family has a classical X-linked dominant BPNH pathology, with greater severity in males than females. The location of the FLNA mutation is discussed in light of the neuropathological anomalies and mental retardation in male patients.

An autosomal recessive form of spastic cerebral palsy (CP) with microcephaly and mental retardation.

Abstract: Cerebral palsy (CP) is defined as any nonprogressive motor deficits resulting from cerebral abnormalities that occur in the prenatal or perinatal period. Symptoms become apparent during the first year of life. Genetic forms of CP account for about 2% in European populations but are thought to cause a substantial proportion in consanguineous families. We have identified a large consanguineous family from Oman with spastic diplegia, microcephaly, and mental retardation. Additional manifestations include hyperreflexia, clumsiness, unstable gait, drooling, and dysarthria. There was phenotypic variability among different individuals, but spastic diplegia, microcephaly, and mental retardation were three constant traits present in all affected individuals.

Neocortical neuronal arrangement in Miller Dieker syndrome.

Abstract: Miller Dieker syndrome (MDS, type I lissencephaly) is a neuronal migration disorder, which is caused by deletions along the short arm of chromosome 17 (17p13.3). Recent studies would suggest that the cortical lamination in MDS is inverted, based on morphological criteria. The present neuropathological study examines the cerebral cortex from a 33-week old fetus with MDS using both neuronal and laminar-specific markers. These expression studies demonstrate a relatively preserved cortex and cortical lamination, overlying a layer of immature neurons in MDS brain. The findings are consistent with both a migratory and proliferative defect, giving rise to lissencephaly. Moreover, characterization of such rare human malformations of cortical development by immunohistochemical techniques will provide a greater understanding of the underlying mechanisms.

Cerebellar ataxia with progressive improvement.

Abstract: Background Nonprogressive cerebellar ataxias are characterized by a persistent, nonprogressive ataxia associated with cognitive impairment. Cerebellar hypoplasia on imaging is variable but is not predictive of the degree of ataxia or cognitive impairment. Objective To describe a family with a nonprogressive cerebellar ataxia associated with cognitive and motor impairments that improve with age. Design Genetic study in a family with nonprogressive cerebellar ataxia. Clinical and imaging features are also described. Setting Community hospital. Patients Both parents and 3 children from an affected family. Main Outcome Measures Clinical features, magnetic resonance imaging findings, and genetic findings. Results A genome-wide single nucleotide polymorphism screen did not show clear linkage to known spinocerebellar ataxia loci, in particular spinocerebellar ataxia type 15. Repeat spinocerebellar ataxia loci expansions were excluded. Magnetic resonance images of all affected individuals demonstrated cerebellar vermian abnormalities. Conclusions These findings suggest that nonprogressive cerebellar ataxia is genetically heterogeneous and, when associated with gradual improvement in cognition and motor skills, likely represents a separate, distinct clinical entity.

The Genetic Basis of Human Cerebral Cortical Malformations

Abstract: Malformations of cortical development occur when the normal process of brain development is disrupted. With the widespread use of high-resolution neuroimaging, brain malformations are increasingly being recognized as a relatively common cause orefractory epilepsy, mental retardation, and other neurological disorders. The molecular and genetic bases of many cortical malformations have been elucidated in recent years, both expanding our understanding of the underlying biological processes in brain development and informing our approach to these disorders in clinical practice. This chapter highlights some of these malformations, including disorders of microcephaly, gray matter hetero-topia, lissencephaly syndromes, and polymicrogyria.

Periventricular heterotopia with complete agenesis of the corpus callosum : a case report.

Abstract: Sirs: Periventricular heterotopia (PH) is an absence of or incomplete neuronal migration characterized by ectopically placed neurons along the lateral ventricle and beneath an otherwise normal appearing cortex. A single case report has previously described an association between PH and complete agenesis of the corpus callosum (ACC). The affected individual had a balanced translocation involving two zinc-finger transcripts KIAA1803 and ASXL2[1]. Here we report the second reported case of a child with PH and complete ACC. The baby girl was born by an elective caesarean section at 39 weeks gestational age (GA) to a 27-year-old gravida 2, para 2 mother. The Apgar scores were 9 and 9, the birth weight was 2608g, and the head circumference was 32.5 cm. The prenatal course was notable for cold infections and a history of alcohol use in the mother. An alpha-fetal protein level was elevated at 14 weeks GA but the amniocentesis at 18 weeks GA revealed a normal female karyotype. An ultrasound at 35 weeks GA demonstrated unexpected agenesis of the corpus callosum with ventriculomegaly. On general examination, the newborn baby appeared entirely normal with no dysmorphic features and no neurocutaneous stigmata. On neurologic examination the baby had normal truncal and upper and lower extremity tone. She had good hand and foot grasps and a normal and symmetric Moro sign. Rooting and suckling reflexes were intact. She had good strength throughout. She was able to fix briefly on the face and tracked intermittently. No chorioretinal lesions or retinal colobomas were identified by ophthalmological examination. A skeletal survey was normal without costovertebral abnormalities. Brain MRI revealed complete ACC, bilateral PH and ventriculomegaly along the posterior aspect of the lateral ventricles, which were indistinguishable from the previously reported case [1] (Fig. 1). Exonic and exon/intron boundary sequencing by PCR was performed on genomic DNA using primers generated for the exons of ASXL2 and KIAA1803 and followed previously published methods [2]. Consensus genomic sequences for ASXL2 and KIAA1803 were obtained through the NCBI and UC Santa Cruz databases and primers were designed using the Primer 3 software program. Over 95% of the amplified exons from the patient DNA were compared with the genomic sequence for each gene. Exonic sequencing of the two genes associated with PH and complete agenesis of the corpus callosum (ASXL2 and KIAA1803) failed to detect any mutations in the coding sequence. Thus, no balanced translocation was seen on karyotyping and no intragenicmutations were appreciated on sequencing. The genetic causes underlying PH with ACC are not known. While ACC is associated with over 50 human congenital syndromes [3], very few of these disorders are characterized by complete ACC (Aicardi, acrocallosal, Andermann and Shapiro syndromes). Moreover, these disorders are uniformly associated with other clinical findings. In this same context, PH can be viewed as a relatively rare malformation of cortical development, caused by mutations in two genes filamin A (FLNA) and ARFGEF2 (4, 5). The X-linked dominant form of PH due to FLNA can be associated with thinning of the corpus callosum, but has never been seen with complete ACC and posterior ventriculomegaly[4]. The autosomal recessive form of PH due to ARFGEF2 is associated with microcephaly and shows no changes in the corpus callosum [5]. Collectively, the radiographic findings of both PH and complete ACC have only been reported in a single case J. Neal, BS Æ A. Bodell Æ K. Apse C.A. Walsh, MD, PhD V.L. Sheen, MD, PhD (&) Department of Neurology Beth Israel Deaconess Medical Center Harvard Medical School Boston, MA, USA

Filamin A, periventricular nodular heterotopia, and west syndrome. Commentary and Authors' reply

Abstract: To the Editor: Masruha et al. (1) recently reported the association between a phenotype of periventricular nodular heterotopia, developmental regression, and West syndrome in males and a missense mutation in the X-linked gene FLNA. The described mutation, 1286C>T, found in exon 9, predicts the substitution T429M. The mutation was present in three male sibs and also in their clinically normal mother, who was assigned as a presumptive mosaic on account of her nonpenetrance for the trait. This finding was unusual because mutations in this gene are usually not associated with cognitive impairment and only exceptionally with survivorship in males. In our comprehensive screening of FLNA in individuals with otopalatodigital (OPD) spectrum disorder phenotypes (2), conditions that are allelic to X-linked PH, we have observed this sequence variant in six individuals, including segregation in one family. None of these individuals (four female, two male patients) with the sequence variant had PH, and all were intellectually normal. Two of these individuals (both female subjects) had other de novo mutations in FLNA to account for their phenotype. One of the two healthy men with the 1286C>T variant transmitted it to both his daughters, only one of whom had frontometaphyseal dysplasia, an OPD spectrum disorder, in this case accounted for by a de novo mutation in exon 46. These observations are also in keeping with a previous report of the 1286C>T variant in a female patient with incontinentia pigmenti (3). Here this sequence variant was ascribed the status of polymorphism on account of the relative nonconservation of the substituted threonine between human filamin paralogues and in cross-species sequence comparisons. Subsequent to that report, the causative gene for this condition was identified as IKBKG (4) . Together these observations make it likely that the 1286C>T variant is a low-frequency polymorphism and not casually related to PH and West syndrome, its rarity explaining its nonappearance on SNP databases and in the control panel of 100 chromosomes examined by Masruha et al. (1). The genetic basis for the phenotype they report still remains to be identified.

Clinical Report Periventricular Nodular Heterotopia and Williams Syndrome

Abstract: We report here on the first case of a child with bilateralperiventricular nodular heterotopia (PNH) and Williamssyndrome. Fluorescent in situ hybridization (FISH) analysesdemonstrated a deletion of the elastin gene in the Williamssyndromecriticalregion(WSCR).Furthermappingbylossofheterozygosity analysis both by microsatellite marker andSNP profiling demonstrated a 1.5 Mb deletion beyond thetelomeric end of the typical WSCR. No mutations wereidentified in the X-linked filamin-A gene (the most commoncause of PNH). These findings suggest another dominantPNH disorder along chromosome 7q11.23.