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Nonmuscle myosin II complexes are master regulators of actin dynamics that play essential roles during embryogenesis with vertebrates possessing 3 nonmuscle myosin II heavy chain genes, MYH9, MYH10, and MYH14. As opposed to MYH9and MYH14, no recognizable disorder has been associated with MYH10. We sought to define the clinical characteristics and molecular mechanism of a novel autosomal dominant disorder related to MYH10.

BackgroundHigh-impact pathogenic variants in more than a thousand genes are involved in Mendelian forms of neurodevelopmental disorders (NDD).MethodsThis study describes the molecular and clinical characterisation of 28 probands with NDD harbouring heterozygous AGO1coding variants, occurring de novo for all those whose transmission could have been verified (26/28).ResultsA total of 15 unique variants leading to amino acid changes or deletions were identified: 12 missense variants, two in-frame deletions of one codon, and one canonical splice variant leading to a deletion of two amino acid residues. Recurrently identified variants were present in several unrelated individuals: p.(Phe180del), p.(Leu190Pro), p.(Leu190Arg), p.(Gly199Ser), p.(Val254Ile) and p.(Glu376del). AGO1encodes the Argonaute 1 protein, which functions in gene-silencing pathways mediated by small non-coding RNAs. Three-dimensional protein structure predictions suggest that these variants might alter the flexibility of the AGO1 linker domains, which likely would impair its function in mRNA processing. Affected individuals present with intellectual disability of varying severity, as well as speech and motor delay, autistic behaviour and additional behavioural manifestations.ConclusionOur study establishes that de novo coding variants in AGO1are involved in a novel monogenic form of NDD, highly similar to the recently reported AGO2-related NDD.

The human neonatal cerebellum is one-fourth of its adult size yet contains the blueprint required to integrate environmental cues with developing motor, cognitive and emotional skills into adulthood. Although mature cerebellar neuroanatomy is well studied, understanding of its developmental origins is limited. In this study, we systematically mapped the molecular, cellular and spatial composition of human fetal cerebellum by combining laser capture microscopy and SPLiT-seq single-nucleus transcriptomics. We profiled functionally distinct regions and gene expression dynamics within cell types and across development. The resulting cell atlas demonstrates that the molecular organization of the cerebellar anlage recapitulates cytoarchitecturally distinct regions and developmentally transient cell types that are distinct from the mouse cerebellum. By mapping genes dominant for pediatric and adult neurological disorders onto our dataset, we identify relevant cell types underlying disease mechanisms. These data provide a resource for probing the cellular basis of human cerebellar development and disease.

We describe a novel neurobehavioral phenotype of autism spectrum disorder (ASD), intellectual disability, and/or attention-deficit/hyperactivity disorder (ADHD) associated with de novo or inherited deleterious variants in members of the RFXfamily of genes. RFXgenes are evolutionarily conserved transcription factors that act as master regulators of central nervous system development and ciliogenesis.

BackgroundVariants in genes belonging to the tubulin superfamily account for a heterogeneous spectrum of brain malformations referred to as tubulinopathies. Variants in TUBB2Ahave been reported in 10 patients with a broad spectrum of brain imaging features, ranging from a normal cortex to polymicrogyria, while one patient has been reported with progressive atrophy of the cerebellar vermis.MethodsIn order to further refine the phenotypical spectrum associated with TUBB2A, clinical and imaging features of 12 patients with pathogenic TUBB2Avariants, recruited via the international network of the authors, were reviewed.ResultsWe report 12 patients with eight novel and one recurrent variants spread throughout the TUBB2Agene but encoding for amino acids clustering at the protein surface. Eleven patients (91.7%) developed seizures in early life. All patients suffered from intellectual disability, and 11 patients had severe motor developmental delay, with 4 patients (36.4 %) being non-ambulatory. The cerebral cortex was normal in five individuals and showed dysgyria of variable severity in seven patients. Associated brain malformations were less frequent in TUBB2Apatients compared with other tubulinopathies. None of the patients had progressive cerebellar atrophy.ConclusionThe imaging phenotype associated with pathogenic variants in TUBB2Ais highly variable, ranging from a normal cortex to extensive dysgyria with associated brain malformations. For recurrent variants, no clear genotype–phenotype correlations could be established, suggesting the role of additional modifiers.

Vascular malformations (VM) are primarily caused by somatic activating pathogenic variants in oncogenes. Targeted pharmacotherapies are emerging but require molecular diagnosis. Since variants are currently only detected in malformation tissue, patients may be ineligible for clinical trials prior to surgery. We hypothesized that cell-free DNA (cfDNA) could provide molecular diagnoses for patients with isolated VM.

Malformations of cortical development (MCDs) are neurodevelopmental disorders that result from abnormal development of the cerebral cortex in utero. MCDs place a substantial burden on affected individuals, their families and societies worldwide, as these individuals can experience lifelong drug-resistant epilepsy, cerebral palsy, feeding difficulties, intellectual disability and other neurological and behavioural anomalies. The diagnostic pathway for MCDs is complex owing to wide variations in presentation and aetiology, thereby hampering timely and adequate management. In this article, the international MCD network Neuro-MIG provides consensus recommendations to aid both expert and non-expert clinicians in the diagnostic work-up of MCDs with the aim of improving patient management worldwide. We reviewed the literature on clinical presentation, aetiology and diagnostic approaches for the main MCD subtypes and collected data on current practices and recommendations from clinicians and diagnostic laboratories within Neuro-MIG. We reached consensus by 42 professionals from 20 countries, using expert discussions and a Delphi consensus process. We present a diagnostic workflow that can be applied to any individual with MCD and a comprehensive list of MCD-related genes with their associated phenotypes. The workflow is designed to maximize the diagnostic yield and increase the number of patients receiving personalized care and counselling on prognosis and recurrence risk.

Congenital muscular dystrophy type 1A (MDC1A) is caused by recessive variants in laminin α2(LAMA2). Patients have been found to have white matter signal abnormalities on magnetic resonance imaging (MRI) but rarely structural brain abnormalities. We describe the autopsy neuropathology in a 17-year-old with white matter signal abnormalities on brain MRI. Dystrophic pathology was observed in skeletal muscle, and the sural nerve manifested a mild degree of segmental demyelination and remyelination. A diffuse, bilateral cobblestone appearance, and numerous points of fusion between adjacent gyri were apparent on gross examination of the cerebrum. Brain histopathology included focal disruptions of the glia limitans associated with abnormal cerebral cortical lamination or arrested cerebellar granule cell migration. Subcortical nodular heterotopia was present within the cerebellar hemispheres. Sampling of the centrum semiovale revealed no light microscopic evidence of leukoencephalopathy. Three additional MDC1A patients were diagnosed with cobblestone malformation on brain MRI. Unlike the autopsied patient whose brain had a symmetric distribution of cobblestone pathology, the latter patients had asymmetric involvement, most severe in the occipital lobes. These cases demonstrate that cobblestone malformation may be an important manifestation of the brain pathology in MDC1A and can be present even when patients have a structurally normal brain MRI.

TBR1, a T-box transcription factor expressed in the cerebral cortex, regulates the expression of several candidate genes for autism spectrum disorders (ASD). Although TBR1has been reported as a high-confidence risk gene for ASD and intellectual disability (ID) in functional and clinical reports since 2011, TBR1has only recently been recorded as a human disease gene in the OMIM database. Currently, the neurodevelopmental disorders and structural brain anomalies associated with TBR1variants are not well characterized. Through international data sharing, we collected data from 25 unreported individuals and compared them with data from the literature. We evaluated structural brain anomalies in seven individuals by analysis of MRI images, and compared these with anomalies observed in TBR1mutant mice. The phenotype included ID in all individuals, associated to autistic traits in 76% of them. No recognizable facial phenotype could be identified. MRI analysis revealed a reduction of the anterior commissure and suggested new features including dysplastic hippocampus and subtle neocortical dysgenesis. This report supports the role of TBR1in ID associated with autistic traits and suggests new structural brain malformations in humans. We hope this work will help geneticists to interpret TBR1variants and diagnose ASD probands.

Megalencephaly (MEG) is a developmental abnormality of brain growth characterized by early onset, often progressive, brain overgrowth. Focal forms of megalencephaly associated with cortical dysplasia, such as hemimegalencephaly and focal cortical dysplasia, are common causes of focal intractable epilepsy in children. The increasing use of high throughput sequencing methods, including high depth sequencing to more accurately detect and quantify mosaic mutations, has allowed us to identify the molecular etiologies of many MEG syndromes, including most notably the PI3K‐AKT‐MTOR related MEG disorders. Thorough molecular and clinical characterization of affected individuals further allow us to derive preliminary genotype–phenotype correlations depending on the gene, mutation, level of mosaicism, and tissue distribution. Our review of published data on these disorders so far shows that mildly activating variants (that are typically constitutional or germline) are associated with diffuse megalencephaly with intellectual disability and/or autism spectrum disorder; moderately activating variants (that are typically high‐level mosaic) are associated with megalencephaly with pigmentary abnormalities of the skin; and strongly activating variants (that are usually very low‐level mosaic) are associated with focal brain malformations including hemimegalencephaly and focal cortical dysplasia. Accurate molecular diagnosis of these disorders is undoubtedly crucial to more optimally treat children with these disorders using PI3K‐AKT–MTOR pathway inhibitors.

The common genes responsible for overgrowth syndromes play key roles in regulating transcription through histone modification and chromatin modeling. The SETD2gene encoding a H3K36 trimethyltransferase is implicated in Sotos‐like syndrome. This syndrome is characterized by postnatal overgrowth, macrocephaly, obesity, speech delay, and advanced carpal ossification. We report four new patients with constitutional SETD2mutations and review nine earlier reported patients. Almost all patients presented with macrocephaly associated with advanced stature and obesity in half of the cases. In addition to these principal manifestations, neurodevelopmental disorders are common such as intellectual disability (83%), autism spectrum disorders (89%), and behavioral difficulties (100%) with aggressive outbursts (83%). A variety of features such as joint hypermobility (29%), hirsutism (33%), and naevi (50%) were also reported. Constitutional SETD2mutations are intragenic loss‐of‐function variants with truncating (69%) and missense (31%) mutations. Functional studies are necessary to improve understanding of the pathogenicity of some missense SETD2mutations.

Hypopigmentation along Blaschko’s lines is a hallmark of a poorly defined group of mosaic syndromes whose genetic causes are unknown. Here we show that postzygotic inactivating mutations of RHOAcause a neuroectodermal syndrome combining linear hypopigmentation, alopecia, apparently asymptomatic leukoencephalopathy, and facial, ocular, dental and acral anomalies. Our findings pave the way toward elucidating the etiology of pigmentary mosaicism and highlight the role of RHOAin human development and disease.

Oculocerebrocutaneous syndrome (OCCS) is a rare disorder characterized primarily by congenital skin, eye, and brain anomalies. The most distinctive findings are hypoplastic or aplastic skin defects; pedunculated, typically hamartomatous, or nodular skin appendages; cystic microphthalmia; and a combination of forebrain anomalies and a specific mid‐hindbrain malformation. Based on a review of 40 patients with OCCS, existing clinical criteria have been revised. Because of the asymmetric and patchy distribution of features, lack of recurrence in families, male preponderance and completely skewed X‐inactivation in one female, OCCS is hypothesized to result from postzygotic mosaic variants in an X‐linked gene. Whole exome and genome sequencing on blood DNA in two patients failed to identify pathogenic variants so far. In view of the overlapping features, in particular of the brain, of OCCS and Aicardi syndrome, both may be pathogenetically related or even result from different variants in the same gene. For the elucidation of the cause of OCCS, exome or genome sequencing on multiple lesional tissues is the primary goal.

Rhombencephalosynapsis (RES) is a unique cerebellar malformation characterized by fusion of the cerebellar hemispheres with partial or complete absence of a recognizable cerebellar vermis. Subsets of patients also have other brain malformations such as midbrain fusion with aqueductal stenosis, characteristic craniofacial features (prominent forehead, flat midface, hypertelorism, ear abnormalities), and somatic malformations (heart, kidney, spine, and limb defects). Similar to known genetic brain malformations, the RES cerebellar malformation is highly stereotyped, yet no genetic causes have been identified. Here, we outline our current understanding of the genetic basis for RES, discuss limitations, and outline future approaches to identifying the causes of this fascinating brain malformation.

Dominant variants in the retinoic acid receptor beta (RARB) gene underlie a syndromic form of microphthalmia, known as MCOPS12, which is associated with other birth anomalies and global developmental delay with spasticity and/or dystonia. Here, we report 25 affected individuals with 17 novel pathogenic or likely pathogenic variants in RARB. This study aims to characterize the functional impact of these variants and describe the clinical spectrum of MCOPS12.

Neuronal migration defects, including pachygyria, are among the most severe developmental brain defects in humans. Here, we identify biallelic truncating mutations in CTNNA2, encoding αN-catenin, in patients with a distinct recessive form of pachygyria. CTNNA2was expressed in human cerebral cortex, and its loss in neurons led to defects in neurite stability and migration. The αN-catenin paralog, αE-catenin, acts as a switch regulating the balance between β-catenin and Arp2/3 actin filament activities1. Loss of αN-catenin did not affect β-catenin signaling, but recombinant αN-catenin interacted with purified actin and repressed ARP2/3 actin-branching activity. The actin-binding domain of αN-catenin or ARP2/3 inhibitors rescued the neuronal phenotype associated with CTNNA2loss, suggesting ARP2/3 de-repression as a potential disease mechanism. Our findings identify CTNNA2as the first catenin family member with biallelic mutations in humans, causing a new pachygyria syndrome linked to actin regulation, and uncover a key factor involved in ARP2/3 repression in neurons.

Zika virus infection of pregnant nonhuman primates results in the loss of fetal neuronal progenitor cells, even in the absence of overt microcephaly.

In this study, Liu et al. investigated the molecular mechanisms regulating the proper organization and orderly mitosis of radial glial progenitors (RGPs), which drive the formation of a laminated mammalian cortex in the correct size. They show that RGP behavior and cortical development are controlled by partitioning-defective 3 (PARD3) in concert with dynamic HIPPO and NOTCH signaling regulation, thus providing new insights into mammalian cortical development.

IMPORTANCE: Early-life epilepsies are often a consequence of numerous neurodevelopmental disorders, most of which are proving to have genetic origins. The role of genetic testing in the initial evaluation of these epilepsies is not established. OBJECTIVE: To provide a contemporary account of the patterns of use and diagnostic yield of genetic testing for early-life epilepsies. DESIGN, SETTING, AND PARTICIPANTS: In this prospective cohort, children with newly diagnosed epilepsy with an onset at less than 3 years of age were recruited from March 1, 2012, to April 30, 2015, from 17 US pediatric hospitals and followed up for 1 year. Of 795 families approached, 775 agreed to participate. Clinical diagnosis of the etiology of epilepsy were characterized based on information available before genetic testing was performed. Added contributions of cytogenetic and gene sequencing investigations were determined. EXPOSURES: Genetic diagnostic testing. MAIN OUTCOMES AND MEASURES: Laboratory-confirmed pathogenic variant. RESULTS: Of the 775 patients in the study (367 girls and 408 boys; median age of onset, 7.5 months [interquartile range, 4.2-16.5 months]), 95 (12.3%) had acquired brain injuries. Of the remaining 680 patients, 327 (48.1%) underwent various forms of genetic testing, which identified pathogenic variants in 132 of 327 children (40.4%; 95% CI, 37%-44%): 26 of 59 (44.1%) with karyotyping, 32 of 188 (17.0%) with microarrays, 31 of 114 (27.2%) with epilepsy panels, 11 of 33 (33.3%) with whole exomes, 4 of 20 (20.0%) with mitochondrial panels, and 28 of 94 (29.8%) with other tests. Forty-four variants were identified before initial epilepsy presentation. Apart from dysmorphic syndromes, pathogenic yields were highest for children with tuberous sclerosis complex (9 of 11 [81.8%]), metabolic diseases (11 of 14 [78.6%]), and brain malformations (20 of 61 [32.8%]). A total of 180 of 446 children (40.4%), whose etiology would have remained unknown without genetic testing, underwent some testing. Pathogenic variants were identified in 48 of 180 children (26.7%; 95% CI, 18%-34%). Diagnostic yields were greater than 15% regardless of delay, spasms, and young age. Yields were greater for epilepsy panels (28 of 96 [29.2%]; P < .001) and whole exomes (5 of 18 [27.8%]; P = .02) than for chromosomal microarray (8 of 101 [7.9%]). CONCLUSIONS AND RELEVANCE: Genetic investigations, particularly broad sequencing methods, have high diagnostic yields in newly diagnosed early-life epilepsies regardless of key clinical features. Thorough genetic investigation emphasizing sequencing tests should be incorporated into the initial evaluation of newly presenting early-life epilepsies and not just reserved for those with severe presentations and poor outcomes.

Deadenylases are best known for degrading the poly(A) tail during mRNA decay. The deadenylase family has expanded throughout evolution and, in mammals, consists of 12 Mg2+-dependent 3′-end RNases with substrate specificity that is mostly unknown. Pontocerebellar hypoplasia type 7 (PCH7) is a unique recessive syndrome characterized by neurodegeneration and ambiguous genitalia. We studied 12 human families with PCH7, uncovering biallelic, loss-of-function mutations in TOE1, which encodes an unconventional deadenylase. toe1-morphant zebrafish displayed midbrain and hindbrain degeneration, modeling PCH-like structural defects in vivo. Surprisingly, we found that TOE1 associated with small nuclear RNAs (snRNAs) incompletely processed spliceosomal. These pre-snRNAs contained 3′ genome-encoded tails often followed by post-transcriptionally added adenosines. Human cells with reduced levels of TOE1 accumulated 3′-end-extended pre-snRNAs, and the immunoisolated TOE1 complex was sufficient for 3′-end maturation of snRNAs. Our findings identify the cause of a neurodegenerative syndrome linked to snRNA maturation and uncover a key factor involved in the processing of snRNA 3′ ends.

IMPORTANCE: Zika virus infection can be prenatally passed from a pregnant woman to her fetus. There is sufficient evidence to conclude that intrauterine Zika virus infection is a cause of microcephaly and serious brain anomalies, but the full spectrum of anomalies has not been delineated. To inform pediatric clinicians who may be called on to evaluate and treat affected infants and children, we review the most recent evidence to better characterize congenital Zika syndrome. OBSERVATIONS: We reviewed published reports of congenital anomalies occurring in fetuses or infants with presumed or laboratory-confirmed intrauterine Zika virus infection. We conducted a comprehensive search of the English literature using Medline and EMBASE for Zika from inception through September 30, 2016. Congenital anomalies were considered in the context of the presumed pathogenetic mechanism related to the neurotropic properties of the virus. We conclude that congenital Zika syndrome is a recognizable pattern of structural anomalies and functional disabilities secondary to central and, perhaps, peripheral nervous system damage. Although many of the components of this syndrome, such as cognitive, sensory, and motor disabilities, are shared by other congenital infections, there are 5 features that are rarely seen with other congenital infections or are unique to congenital Zika virus infection: (1) severe microcephaly with partially collapsed skull; (2) thin cerebral cortices with subcortical calcifications; (3) macular scarring and focal pigmentary retinal mottling; (4) congenital contractures; and (5) marked early hypertonia and symptoms of extrapyramidal involvement. CONCLUSIONS AND RELEVANCE: Although the full spectrum of adverse reproductive outcomes caused by Zika virus infection is not yet determined, a distinctive phenotype—the congenital Zika syndrome—has emerged. Recognition of this phenotype by clinicians for infants and children can help ensure appropriate etiologic evaluation and comprehensive clinical investigation to define the range of anomalies in an affected infant as well as determine essential follow-up and ongoing care.

BackgroundWe aimed for a comprehensive delineation of genetic, functional and phenotypic aspects of GRIN2Bencephalopathy and explored potential prospects of personalised medicine.MethodsData of 48 individuals with de novo GRIN2Bvariants were collected from several diagnostic and research cohorts, as well as from 43 patients from the literature. Functional consequences and response to memantine treatment were investigated in vitro and eventually translated into patient care.ResultsOverall, de novo variants in 86 patients were classified as pathogenic/likely pathogenic. Patients presented with neurodevelopmental disorders and a spectrum of hypotonia, movement disorder, cortical visual impairment, cerebral volume loss and epilepsy. Six patients presented with a consistent malformation of cortical development (MCD) intermediate between tubulinopathies and polymicrogyria. Missense variants cluster in transmembrane segments and ligand-binding sites. Functional consequences of variants were diverse, revealing various potential gain-of-function and loss-of-function mechanisms and a retained sensitivity to the use-dependent blocker memantine. However, an objectifiable beneficial treatment response in the respective patients still remains to be demonstrated.ConclusionsIn addition to previously known features of intellectual disability, epilepsy and autism, we found evidence that GRIN2Bencephalopathy is also frequently associated with movement disorder, cortical visual impairment and MCD revealing novel phenotypic consequences of channelopathies.

New animal models of Zika virus (ZIKV) infection are imperative to accelerating efforts to treat or prevent disease in humans. Adams Waldorf et al. now report that ZIKV infection of a pregnant female pigtailed macaque caused brain lesions in the developing fetus, suggesting that this model may be useful for understanding ZIKV-associated congenital abnormalities in humans.

The corpus callosum is the major axon tract that connects and integrates neural activity between the two cerebral hemispheres. Although ∼1:4,000 children are born with developmental absence of the corpus callosum, the primary etiology of this condition remains unknown. Here, we demonstrate that midline crossing of callosal axons is dependent upon the prior remodeling and degradation of the intervening interhemispheric fissure. This remodeling event is initiated by astroglia on either side of the interhemispheric fissure, which intercalate with one another and degrade the intervening leptomeninges. Callosal axons then preferentially extend over these specialized astroglial cells to cross the midline. A key regulatory step in interhemispheric remodeling is the differentiation of these astroglia from radial glia, which is initiated by Fgf8 signaling to downstream Nfi transcription factors. Crucially, our findings from human neuroimaging studies reveal that developmental defects in interhemispheric remodeling are likely to be a primary etiology underlying human callosal agenesis.

Guillain-Barr syndrome is a neurological condition characterized by paralysis, which becomes progressively worse. Although its cause is unknown, the condition usually becomes manifest after a viral infection, surgery, cancer and vaccination. Three children developed Guillain-Barr syndrome after routine Haemophilus influenzae vaccination. A 19-month-old girl with difficulty walking had a polyribosylribitol phosphate linked to diphtheria toxoid (PRP-D) vaccine, the vaccine given to prevent Haemophilus influenzae type b infections, at a well-child care visit. Although she had received other vaccines without incident, her inability to walk a few steps was investigated further. Examination of the patient's brain by computerized tomography (CT), the use of detailed cross-sectional X-rays used to visualize internal structures, yielded nothing unusual. Electromyography, recording the electrical activity in the muscle, revealed abnormal nerve functioning. The patient was discharged after three treatments with plasmapheresis, a process of removing the plasma portion of blood and replacing it with other fresh or frozen plasma, which improved nerve functioning somewhat. In a second case, a 20-month-old girl had a well-child visit, received routine vaccination, and several days later developed progressive muscle incoordination, and had episodes of screaming during sleep, coughing, gagging and difficulty swallowing. Test results were normal, but difficulty walking and swallowing continued. Two months later she was able to walk and run. In a third case report, a 33-month-old girl with leg weakness and uncoordinated muscle movements reported unusual crying during sleep after routine PRP- D vaccination. Two months later neurological evaluation was normal. The association between the PRP-D vaccine and Guillain- Barr syndrome has not been clearly established in this study and results should be conservatively interpreted. The incidence is assumed to be rare given the large number of vaccinations currently administered.

Malformations of cortical development (MCD) represent a major cause of developmental disabilities, severe epilepsy, and reproductive disadvantage. Genes that have been associated to MCD are mainly involved in cell proliferation and specification, neuronal migration, and late cortical organization. Lissencephaly-pachygyria-severe band heterotopia are diffuse neuronal migration disorders causing severe global neurological impairment. Abnormalities of the LIS1, DCX, ARX, RELN, VLDLR, ACTB, ACTG1, TUBG1, KIF5C, KIF2A, andCDK5genes have been associated with these malformations. More recent studies have also established a relationship between lissencephaly, with or without associated microcephaly, corpus callosum dysgenesis as well as cerebellar hypoplasia, and at times, a morphological pattern consistent with polymicrogyria with mutations of several genes (TUBA1A, TUBA8, TUBB, TUBB2B, TUBB3, andDYNC1H1), regulating the synthesis and function of microtubule and centrosome key components and hence defined as tubulinopathies. MCD only affecting subsets of neurons, such as mild subcortical band heterotopia and periventricular heterotopia, have been associated with abnormalities of the DCX, FLN1A, and ARFGEF2genes and cause neurological and cognitive impairment that vary from severe to mild deficits. Polymicrogyria results from abnormal late cortical organization and is inconstantly associated with abnormal neuronal migration. Localized polymicrogyria has been associated with anatomo-specific deficits, including disorders of language and higher cognition. Polymicrogyria is genetically heterogeneous, and only in a small minority of patients, a definite genetic cause has been identified. Megalencephaly with normal cortex or polymicrogyria by MRI imaging, hemimegalencephaly and focal cortical dysplasia can all result from mutations in genes of the PI3K-AKT-mTOR pathway. Postzygotic mutations have been described for most MCD and can be limited to the dysplastic tissue in the less diffuse forms.

IMPORTANCE: Focal cortical dysplasia (FCD), hemimegalencephaly, and megalencephaly constitute a spectrum of malformations of cortical development with shared neuropathologic features. These disorders are associated with significant childhood morbidity and mortality. OBJECTIVE: To identify the underlying molecular cause of FCD, hemimegalencephaly, and diffuse megalencephaly. DESIGN, SETTING, AND PARTICIPANTS: Patients with FCD, hemimegalencephaly, or megalencephaly (mean age, 11.7 years; range, 2-32 years) were recruited from Pediatric Hospital A. Meyer, the University of Hong Kong, and Seattle Children’s Research Institute from June 2012 to June 2014. Whole-exome sequencing (WES) was performed on 8 children with FCD or hemimegalencephaly using standard-depth (50-60X) sequencing in peripheral samples (blood, saliva, or skin) from the affected child and their parents and deep (150-180X) sequencing in affected brain tissue. Targeted sequencing and WES were used to screen 93 children with molecularly unexplained diffuse or focal brain overgrowth. Histopathologic and functional assays of phosphatidylinositol 3-kinase–AKT (serine/threonine kinase)–mammalian target of rapamycin (mTOR) pathway activity in resected brain tissue and cultured neurons were performed to validate mutations. MAIN OUTCOMES AND MEASURES: Whole-exome sequencing and targeted sequencing identified variants associated with this spectrum of developmental brain disorders. RESULTS: Low-level mosaic mutations of MTOR were identified in brain tissue in 4 children with FCD type 2a with alternative allele fractions ranging from 0.012 to 0.086. Intermediate-level mosaic mutation of MTOR (p.Thr1977Ile) was also identified in 3 unrelated children with diffuse megalencephaly and pigmentary mosaicism in skin. Finally, a constitutional de novo mutation of MTOR (p.Glu1799Lys) was identified in 3 unrelated children with diffuse megalencephaly and intellectual disability. Molecular and functional analysis in 2 children with FCD2a from whom multiple affected brain tissue samples were available revealed a mutation gradient with an epicenter in the most epileptogenic area. When expressed in cultured neurons, all MTOR mutations identified here drive constitutive activation of mTOR complex 1 and enlarged neuronal size. CONCLUSIONS AND RELEVANCE: In this study, mutations of MTOR were associated with a spectrum of brain overgrowth phenotypes extending from FCD type 2a to diffuse megalencephaly, distinguished by different mutations and levels of mosaicism. These mutations may be sufficient to cause cellular hypertrophy in cultured neurons and may provide a demonstration of the pattern of mosaicism in brain and substantiate the link between mosaic mutations of MTOR and pigmentary mosaicism in skin.

To describe a homogeneous subtype of periventricular nodular heterotopia (PNH) as part of a newly defined malformation complex.

Hereditary hemihypotrophy hemiparesis hemiathetosis syndrome (HHHH; OMIM 306960) was first reported in a family with congenital left hemiplegia in two males and moderately affected females. We describe a family with three males demonstrating congenital right hemiplegia with porencephalic lesions of the left internal capsule and putamen, or the periventricular white matter just above the internal capsule. Clinical findings within each family are limited to the same side, though sidedness differed between families. Both pedigrees were most consistent with X‐linked inheritance. Genome‐wide linkage analysis in our family further supports a locus for HHHH on chromosome X. © 2010 Wiley‐Liss, Inc.

Hydrocephalus is a clinically and genetically heterogeneous condition. Individuals with posterior fossa abnormalities have an increased risk of developing hydrocephalus. The Dandy–Walker malformation, Dandy–Walker variant, and mega‐cisterna magna (MCM) seem to represent a continuum of developmental anomalies of the posterior fossa. Here we describe the natural clinical history and the radiological features of a family with autosomal or X‐linked dominant inheritance of MCM and hydrocephalus of variable severity. The affected family members demonstrate similar structural brain abnormalities including midline cyst, colpocephaly, MCM with a large posterior fossa and minimal vermian hypoplasia. The cognitive development of the affected individuals is normal. L1CAMand FOXC1gene involvement in the pathogenesis of the disease in this family was excluded. The rare possibility of autosomal dominant or X‐linked dominant inheritance and variable penetrance and expressivity must always be considered in genetic counseling of families with hereditary hydrocephalus. © 2010 Wiley‐Liss, Inc.

The pontocerebellar hypoplasias PCH are a group of earlyonset, autosomal recessive disorders resulting in abnormal growth and function of the brainstem and cerebellum. PCH type 2 PCH2 is characterized by respiratory and feeding difficulties at birth, extrapyramidal dyskinesia, severe developmental impairment, progressive microcephaly and frequent death in childhood. Neuropathologic findings include diffuse cerebral gliosis with white matter changes, hypoplastic pons with depletion of neurons in the pontine nuclei, hypoplastic cerebellar hemispheres due to short cerebellar folia with poor branching, segmental loss of dentate, inferior olivary, and ventral pontine nuclei, and near absence of transverse pontine fibers with preservation of long fiber tracts and spinal anterior horn cells. On brain imaging, the cerebellar hemispheres appear very flat, and are more severely involved than the vermis. Most patients with PCH2 have mutations in TSEN54, with occasional mutations found in TSEN34or TSEN2, genes that encode subunits of tRNA splicing endonuclease. Although this is a congenital disorder of pontocerebellar dysgenesis with fetal onset of neurodegeneration and symptoms at birth, prenatal imaging is unreliable in diagnosing this disorder in utero. We report on IVF dizygous twins with detailed prenatal imaging that failed to reveal any cerebellar abnormalities. Direct sequence analysis of TSEN54showed homozygosity for c.919G>T, the common founder mutation in most PCH2 patients, and both parents were heterozygous for this mutation. We found no evidence of cerebellar dysgenesis on prenatal ultrasounds, but MRI tractography showed absence of pontine crossing fibers, a unique feature that might be useful for prenatal diagnosis of this condition. © 2010 WileyLiss, Inc.

Agenesis of the corpus callosum ACC is a common brain malformation of variable clinical expression that is seen in many syndromes of various etiologies. Although ACC is predominantly genetic, few genes have as yet been identified. We have constructed and analyzed a comprehensive map of ACC loci across the human genome using data generated from 374 patients with ACC and structural chromosome rearrangements, most having heterozygous loss or gain of genomic sequence and a few carrying apparently balanced rearrangements hypothesized to disrupt key functional genes. This cohort includes more than 100 previously unpublished patients. The subjects were ascertained from several large research databases as well as the published literature over the last 35 years. We identified 12 genomic loci that are consistently associated with ACC, and at least 30 other recurrent loci that may also contain genes that cause or contribute to ACC. Our data also support the hypothesis that many ACC loci confer susceptibility to other brain malformations as well as ACC, such as cerebellar hypoplasia, microcephaly, and polymicrogyria. The database presented here provides a valuable resource for diagnosis and management of individuals with ACC and individuals with chromosome rearrangements in whom ACC should be suspected, and of course for identifying ACC causal and contributory genes. Welldefined diagnostic criteria, improved scanning techniques, and increased recognition of associated abnormalities will further facilitate gene mapping and allow definition of distinct syndromes within this heterogeneous group of patients. © 2010 WileyLiss, Inc.

Six subtypes of autosomal recessive pontocerebellar hypoplasia PCH have been identified and the genetic basis of four of these PCH1, PCH2, PCH4, and PCH6 is known. PCH6 is associated with cerebral atrophy and multiple but variable respiratory chain defects in muscle and has been reported in one consanguineous Sephardic Jewish family. It is caused by mutations in the RARS2gene which encodes mitochondrial argininetransfer RNA synthetase. Here we describe a female patient born to nonconsanguineous British parents. She presented in the neonatal period with increased respiratory rate, poor feeding and transiently elevated blood and CSF lactate levels. She went on to manifest profound developmental delay and severe microcephaly. Edema of the hands, feet, and face were suggestive of a PEHOlike condition progressive encephalopathy, edema, hypsarrhythmia and optic atrophy, although optic atrophy and hypsarrhythmia were absent. Cranial MRI at age 14 months showed generalized cerebral atrophy, thinning of the pons and gross atrophy and flattening of the cerebellar hemispheres. Muscle biopsies on two occasions were normal with normal respiratory chain studies. Despite the absence of respiratory chain defects, the phenotype was felt to be consistent with PCH6 and indeed two novel pathogenic RARS2mutations were identified. Ours is the second report of PCH6 due to RARS2mutations and demonstrates that respiratory chain abnormalities are not obligatory, whereas some features of PEHO might be present. © 2010 WileyLiss, Inc.

We present double first cousins, a girl and a boy, with the uncommon association of agenesis of the corpus callosum and congenital lymphedema. Other features shared by both include oligohydramnios, similar facial dysmorphism, sacral dimple, developmental delay, and sociable personality. While some of these findings overlap with FG syndrome and Hennekam syndrome, the findings in our patients are sufficiently different to exclude these diagnoses. We propose that this is a new syndrome with presumed autosomal recessive inheritance. © 2010 WileyLiss, Inc.

The combination of megalencephaly, perisylvian polymicrogyria, polydactyly and hydrocephalus MPPH is a rare syndrome of unknown cause. We observed two first cousins affected by an MPPHlike phenotype with a submicroscopic chromosome 5q35 deletion as a result of an unbalanced der5t5;20q35.2;q13.3 translocation, including the NSD1Sotos syndrome locus. We describe the phenotype and the deletion breakpoints of the two MPPHlike patients and compare these with five unrelated MPPH and Sotos patients harboring a 5q35 microdeletion. Mapping of the breakpoints in the two cousins was performed by MLPA, FISH, high density SNParrays and QPCR for the 5q35 deletion and 20q13 duplication. The 5q35 deletion area of the two cousins almost completely overlaps with earlier described patients with an atypical Sotos microdeletion, except for the DRD1gene. The five unrelated MPPH patients neither showed submicroscopic chromosomal aberrations nor DRD1mutations. We reviewed the brain MRI of 10 Sotos patients and did not detect polymicrogyria in any of them. In our two cousins, the MPPHlike phenotype is probably caused by the contribution of genes on both chromosome 5q35 and 20q13. Some patients with MPPH may harbor a submicroscopic chromosomal aberration and therefore highresolution array analysis should be part of the diagnostic workup. © 2010 WileyLiss, Inc.

Costello syndrome is a rasopathy caused by germline mutations in the protooncogene HRAS. Its presentation includes failuretothrive with macrocephaly, characteristic facial features, hypertrophic cardiomyopathy, papillomata, malignant tumors, and cognitive impairment. In a systematic review we found absolute or relative macrocephaly 100, ventriculomegaly 50, and other abnormalities on brain and spinal cord imaging studies in 2728 individuals. Posterior fossa crowding with cerebellar tonsillar herniation CBTH was noted in 2728 96, and in 1017 59 with serial studies posterior fossa crowding progressed. Sequelae of posterior fossa crowding and CBTH included hydrocephalus requiring shunt or ventriculostomy 25, Chiari 1 malformation 32, and syrinx formation 25. Our data reveal macrocephaly with progressive frontal bossing and CBTH, documenting an ongoing process rather than a static congenital anomaly. Comparison of images obtained in young infants to subsequent studies demonstrated postnatal development of posterior fossa crowding. This process of evolving megalencephaly and cerebellar enlargement is in keeping with mouse model data, delineating abnormal genesis of neurons and glia, resulting in an increased number of astrocytes and enlarged brain volume. In Costello syndrome and macrocephalycapillary malformation syndrome disproportionate brain growth is the main factor resulting in postnatal CBTH and Chiari 1 malformation. © 2010 WileyLiss, Inc.

To make evidence-based recommendations concerning the evaluation of the child with microcephaly.

Holoprosencephaly is the most common structural malformation of the forebrain in humans and has a complex etiology including chromosomal aberrations, single gene mutations and environmental components. Here we present the pertinent clinical findings among members of an unusually large kindred ascertained over 15 years ago following the evaluation and subsequent genetic work‐up of a female infant with congenital anomalies. A genome‐wide scan and linkage analysis showed only suggestive evidence of linkage to markers on chromosome 2 among the most likely of several pedigree interpretations. We now report that a novel missense mutation in the SIX3holoprosencephaly gene is the likely cause in this family. Molecular genetic analysis and/or clinical characterization now show that at least 15 members of this family are presumed SIX3mutation gene carriers, with clinical manifestations ranging from phenotypically normal adults (non‐penetrance) to alobar holoprosencephaly incompatible with postnatal life. This particular family represents a seminal example of the variable manifestations of gene mutations in holoprosencephaly and difficulties encountered in their elucidation. Published 2009 Wiley‐Liss, Inc.

We report on three patients with macrocephaly and polymicrogyria, and additional anomalies seen in megalencephaly polymicrogyria‐polydactyly hydrocephalus (MPPH) and macrocephaly capillary malformation (MCM) syndromes. Based on their characteristic brain malformations they were originally diagnosed with MPPH. In one patient the phenotype evolved during early infancy, and ultimately resulted in a diagnosis of MCM. A second was prenatally diagnosed with MPPH, but postnatally visualized capillary malformations led to a diagnosis of MCM. In a third, the original MPPH diagnosis was reconsidered after a critical review revealed additional subtle findings suggestive of MCM. Characteristic brain malformations are thought to distinguish between MPPH with perisylvian polymicrogyria, and MCM with megalencephaly with Chiari 1 malformation. However, polymicrogyria was reported in a significant number of patients with MCM. Conversely, upon review of imaging studies of patients with MPPH, we noted progressive crowding of the posterior fossa and acquired tonsillar herniation, a process deemed characteristic for MCM. Thus, neither polymicrogyria nor acquired tonsillar herniation are distinguishing features, and occur in both disorders. In addition to brain abnormalities, shared findings include cognitive impairment, coarse facial features and postaxial polydactyly. Facial nevus flammeus and cutis marmorata are most noticeable in infancy, and ligamentous laxity and redundant soft tissue are somewhat subjective findings. While asymmetric overgrowth is considered typical for MCM, it is not universally present. These variable and subtle findings can be identified in patients with MPPH. We propose that MPPH and MCM may not represent distinct entities and that the term MPPH‐CM syndrome be used to describe this spectrum. © 2009 Wiley‐Liss, Inc.

Two interrelated Omani families are described with eight children manifesting a genetic disorder with widespread brain calcifications. Brain imaging showed extensive scattered calcifications of basal ganglia and cortex, suggesting possible Aicardi–Goutieres syndrome AGS or Coats Plus syndrome. However, the clinical features in the present families diverge substantially from these two conditions. Growth delay, mild developmental delay, and poor school performance were present in all affected individuals, but progressive deterioration of neurological function was not apparent, nor were there significant cortical whitematter disease or retinopathy. Genomewide linkage and finemapping analyses of the extended family members and affected individuals indicate a genetic locus for this disorder on Chromosome 2 with a LOD score of 6.17. The Chromosome 2 locus is novel and the clinical presentation displays features distinguishing the condition from either Coats or AGS, making this a new variant or possibly a new disorder of inherited brain calcification. © 2009 WileyLiss, Inc.

Polymicrogyria is a malformation of cortical development characterized by loss of the normal gyral pattern, which is replaced by many small and infolded gyri separated by shallow, partly fused sulci, and loss of middle cortical layers. The pathogenesis is unknown, yet emerging data supports the existence of several loci in the human genome. We report on the clinical and brain imaging features, and results of cytogenetic and molecular genetic studies in 29 patients with polymicrogyria associated with structural chromosome rearrangements. Our data map new polymicrogyria loci in chromosomes 1p36.3, 2p16.1–p23, 4q21.21–q22.1, 6q26–q27, and 21q21.3–q22.1, and possible loci in 1q44 and 18p as well. Most and possibly all of these loci demonstrate incomplete penetrance and variable expressivity. We anticipate that these data will serve as the basis for ongoing efforts to identify the causal genes located in these regions. © 2008 WileyLiss, Inc.

Schizencephaly SCH is a rare disorder of cerebral cortical development, characterized by full thickness clefts spanning the wall of the cerebral hemispheres that are lined and surrounded by polymicrogyric cortex. Based on pathological analysis, SCH was originally considered to have multiple causes including infectious and vascular injuries, and toxic agents. However, a few reports of familial SCH have suggested a possible genetic etiology. Ten years ago two articles identified EMX2as the first causative gene for human SCH in 13 of 18 patients, although for several putative mutations no pathogenic role was demonstrated. Here, we reinterpret the original articles as showing a significantly lower mutational rate 17 than originally reported 72, and provide results of EMX2sequencing in 39 new SCH patients, detecting no pathogenic mutations. We conclude that the reported association between SCH and EMX2mutations is not adequately supported by current data, and that diagnostic testing of EMX2is not justified, as any results would be uninterpretable. © 2008 WileyLiss, Inc.

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

Encephalocraniocutaneous lipomatosis (ECCL) is a sporadically occurring neurocutaneous disorder characterized by ocular anomalies, skin lesions, and CNS anomalies. We report on four new patients with this syndrome. Additionally, we reviewed (i) the brain imaging studies and clinical data of these new cases of ECCL and six other previously published ECCL patients, and (ii) the literature on 42 other patients who had undergone some form of neuroimaging, including three cases with probable or uncertain ECCL diagnoses. Thirty‐three of 52 patients showed intracranial lipomas, frequently of cerebello‐pontine location, and/or spinal lipomatosis. The latter has been found in 12/13 patients who had imaging studies of the spine. Other frequent findings included congenital anomalies of the meninges, in particular arachnoid cysts, and remarkably asymmetric anomalies caused by putative focal vascular defects, such as (partial) atrophy of one hemisphere or thin cerebral mantle, porencephalic cysts and calcifications. Vessel anomalies were found in nine patients. No correlation between the brain anomalies and the degree of retardation or epilepsy could be established. These data provide evidence that the brain anomalies in ECCL are not primary brain malformations but arise secondary to a mesenchymal defect affecting mostly neural crest derivatives. © 2007 Wiley‐Liss, Inc.

Here, we report the neuroimaging findings and neurological changes in 17 unpublished patients with Macrocephaly–Capillary Malformation (M–CM). This syndrome has been traditionally known as Macrocephaly–Cutis Marmorata Telangiectatica Congenita (M–CMTC), but we explain why M–CM is a more accurate term for this overgrowth syndrome. We analyzed the 17 patients with available brain MRI or CT scans and compared their findings with features identified by a comprehensive review of published cases. White matter irregularities with increased signal on T2‐weighted images were commonly observed findings. A distinctive feature in more than half the patients was cerebellar tonsillar herniation associated with rapid brain growth and progressive crowding of the posterior fossa during infancy. In four such cases, we confirmed that the tonsillar herniation was an acquired event. Concurrently, with the development of these findings, ventriculomegaly (frequently obstructive) and dilated dural venous sinuses were observed in conjunction with prominent Virchow–Robin spaces in many of those in whom cerebellar tonsil herniation had developed. We postulate that this constellation of unusual features suggests a dynamic process of mechanical compromise in the posterior fossa, perhaps initiated by a rapidly growing cerebellum, which leads to congestion of the venous drainage with subsequently compromised cerebrospinal fluid reabsorption, all of which increases the posterior fossa pressure and leads to acquired tonsillar herniation. We make a distinction between congenital Chiari I malformation and acquired cerebellar tonsil herniation in this syndrome. We also observed numerous examples of abnormal cortical morphogenesis, including focal cortical dysplasia, polymicrogyria which primarily involved the perisylvian and insular regions, and cerebral and/or cerebellar asymmetric overgrowth. Other findings included a high frequency of cavum septum pellucidum or vergae, thickened corpus callosum, prominent optic nerve sheaths and a single case of venous sinus thrombosis. One patient was found to have a frontal perifalcine mass resembling a meningioma at age 5 years. This is the second apparent occurrence of this specific tumor in M–CM. © 2007 Wiley‐Liss, Inc.

Two siblings from a consanguineous Egyptian marriage showed an identical phenotype of cortical lissencephaly with cerebellar hypoplasia, severe epilepsy, and mental retardation. Examination of karyotype revealed 46, t(7;12)(q22;p13)mat (7;12)(q22;p13)pat in both affected children, suggesting a homozygous reciprocal balanced translocation. Each healthy parent was a carrier of the balanced translocation in the heterozygous state, suggesting homozygous disruption of a gene involved in brain development. There were early spontaneous abortions in this family, as would be expected from transmission of an unbalanced chromosome. A disruption of RELN at 7q22.1 with absence of encoded protein was identified. This is the first demonstration that such rare homozygous translocations can be used to identify recessive disease gene mutations. © 2007 Wiley‐Liss, Inc.

Several brain malformations have been described in rare patients with the deletion 22q11.2 syndrome (DEL22q11) including agenesis of the corpus callosum, pachygyria or polymicrogyria (PMG), cerebellar anomalies and meningomyelocele, with PMG reported most frequently. In view of our interest in the causes of PMG, we reviewed clinical data including brain‐imaging studies on 21 patients with PMG associated with deletion 22q11.2 and another 11 from the literature. We found that the cortical malformation consists of perisylvian PMG of variable severity and frequent asymmetry with a striking predisposition for the right hemisphere (P = 0.008). This and other observations suggest that the PMG may be a sequela of abnormal embryonic vascular development rather than a primary brain malformation. We also noted mild cerebellar hypoplasia or mega‐cisterna magna in 8 of 24 patients. Although this was not the focus of the present study, mild cerebellar anomalies are probably the most common brain malformation associated with DEL22q11. © 2006 Wiley‐Liss, Inc.