Megalencephaly secondary to a novel germline missense variant p.Asp322Tyr in AKT3 associated with growth hormone deficiency and central hypothyroidism: A case report.

Germline gain of function variations in the AKT3 gene cause brain overgrowth syndrome with megalencephaly and diffuse bilateral cortical malformations. Here we report a child with megalencephaly, who is a carrier of a novel heterozygous missense variant in the AKT3 gene NM_005465.7:c.964G>T,p.Asp322Tyr. The phenotype of this patient is associated with pituitary deficiencies diagnosed at 2 years of age: growth hormone (GH) deficiency responsible for growth delay and central hypothyroidism. After 6 months of GH treatment, intracranial hypertension was noted, confirmed by the observation of papilledema and increased intracranial pressure, requiring the initiation of acetazolamide treatment and the discontinuation of GH treatment. This is the second reported patient described with megalencephaly and AKT3 gene variant associated with GH deficiency . Other endocrine disorders have also been reported in few cases with hypothyroidism and hypoglycemia. Pituitary deficiency may be a part of the of megalencephaly phenotype secondary to germline variant in the AKT3 gene. Special attention should be paid to growth in these patients and search for endocrine deficiency is necessary in case of growth retardation or hypoglycemia.

The somatic p.T81dup variant in AKT3 gene underlies a mild cerebral phenotype and expands the spectrum including capillary malformation and lateralized overgrowth.

Heterozygous germline or somatic variants in AKT3 gene can cause isolated malformations of cortical development (MCDs) such as focal cortical dysplasia, megalencephaly (MEG), Hemimegalencephaly (HME), dysplastic megalencephaly, and syndromic forms like megalencephaly-polymicrogyria-polydactyly-hydrocephalus syndrome, and megalencephaly-capillary malformation syndrome. This report describes a new case of HME and capillary malformation caused by a somatic AKT3 variant that differs from the common p.E17K variant described in literature. The patient's skin biopsy from the angiomatous region revealed an heterozygous likely pathogenic variant AKT3:c.241_243dup, p.(T81dup) that may affect the binding domain and downstream pathways. Compared to previously reported cases with a common E17K mosaic variant, the phenotype is milder and patients showed segmental overgrowth, an uncommon characteristic in AKT3 variant cases. These findings suggest that the severity of the disease may be influenced not only by the level of mosaicism but also by the type of variant. This report expands the phenotypic spectrum associated with AKT3 variants and highlights the importance of genomic analysis in patients with capillary malformation and MCDs.

Viral expression of constitutively active AKT3 induces CST axonal sprouting and regeneration, but also promotes seizures.

Increasing the intrinsic growth potential of neurons after injury has repeatedly been shown to promote some level of axonal regeneration in rodent models. One of the most studied pathways involves the activation of the PI3K/AKT/mTOR pathways, primarily by reducing the levels of PTEN, a negative regulator of PI3K. Likewise, activation of signal transducer and activator of transcription 3 (STAT3) has previously been shown to boost axonal regeneration and sprouting within the injured nervous system. Here, we examined the regeneration of the corticospinal tract (CST) after cortical expression of constitutively active (ca) Akt3 and STAT3, both separately and in combination. Overexpression of caAkt3 induced regeneration of CST axons past the injury site independent of caSTAT3 overexpression. STAT3 demonstrated improved axon sprouting compared to controls and contributed to a synergistic improvement in effects when combined with Akt3 but failed to promote axonal regeneration as an individual therapy. Despite showing impressive axonal regeneration, animals expressing Akt3 failed to show any functional improvement and deteriorated with time. During this period, we observed progressive Akt3 dose-dependent increase in behavioral seizures. Histology revealed increased phosphorylation of ribosomal S6 protein within the unilateral cortex, increased neuronal size, microglia activation and hemispheric enlargement (hemimegalencephaly).

A disorder-related variant (E420K) of a PP2A-regulatory subunit (PPP2R5D) causes constitutively active AKT-mTOR signaling and uncoordinated cell growth.

Functional genomic approaches have facilitated the discovery of rare genetic disorders and improved efforts to decipher their underlying etiology. PPP2R5D-related disorder is an early childhood onset condition characterized by intellectual disability, hypotonia, autism-spectrum disorder, macrocephaly, and dysmorphic features. The disorder is caused by de novo single nucleotide changes in PPP2R5D, which generate heterozygous dominant missense variants. PPP2R5D is known to encode a B'-type (B'56δ) regulatory subunit of a PP2A-serine/threonine phosphatase. To help elucidate the molecular mechanisms altered in PPP2R5D-related disorder, we used a CRISPR-single-base editor to generate HEK-293 cells in which a single transition (c.1258G>A) was introduced into one allele, precisely recapitulating a clinically relevant E420K variant. Unbiased quantitative proteomic and phosphoproteomic analyses of endogenously expressed proteins revealed heterozygous-dominant changes in kinase/phosphatase signaling. These data combined with orthogonal validation studies revealed a previously unrecognized interaction of PPP2R5D with AKT in human cells, leading to constitutively active AKT-mTOR signaling, increased cell size, and uncoordinated cellular growth in E420K-variant cells. Rapamycin reduced cell size and dose-dependently reduced RPS6 phosphorylation in E420K-variant cells, suggesting that inhibition of mTOR1 can suppress both the observed RPS6 hyperphosphorylation and increased cell size. Together, our findings provide a deeper understanding of PPP2R5D and insight into how the E420K-variant alters signaling networks influenced by PPP2R5D. Our comprehensive approach, which combines precise genome editing, isobaric tandem mass tag labeling of peptides generated from endogenously expressed proteins, and concurrent liquid chromatography-mass spectrometry (LC-MS3), also provides a roadmap that can be used to rapidly explore the etiologies of additional genetic disorders.

[Megalencephalic leukoencephalopathy with cysts -the clinical importance in the genetic era]. / Leucoencefalopatía megalencefálica con quistes: importancia de la descripción clínica en la era genética.

INTRODUCTION: Megalencephalic leukoencephalopathy with cysts is a leukodystrophy of genetic origin that produces an alteration in the water and ion homeostasis in the brain, generating vacuolar forms and chronic oedema in the white matter with progressive neurological deterioration. It should be suspected in infants who present progressive macrocephaly during the first year of life, motor retardation and characteristic findings in magnetic resonance brain scans. CASE REPORT: We report the case of a girl who was followed up from the age of 9 months due to progressive macrocephaly and delayed psychomotor development and brain MRI findings consistent with megalencephalic leukoencephalopathy with cysts, and the appearance of epilepsy during its development. The usual genetic studies (new generation sequencing and array) were negative, but as the diagnostic criteria were met, a complementary messenger RNA and DNA study was conducted, which confirmed the presence of two pathogenic variants in MLC1. CONCLUSIONS: Megalencephalic leukoencephalopathy with cysts is a rare condition. Progressive macrocephaly in the first year of life, the absence of deterioration or slow deterioration, and the possibility of developing epilepsy, spasticity and ataxia are characteristic signs in its course. It is important for these patients to undergo an imaging test that shows findings that characterise this condition, which, together with the clinical features, makes it possible to differentiate it from other leukodystrophies and to establish a confirmatory diagnosis. Genetic studies can confirm the associated mutation that makes it possible to predict the clinicoradiological phenotype.

TITLE: Leucoencefalopatía megalencefálica con quistes: importancia de la descripción clínica en la era genética.Introducción. La leucoencefalopatía megalencefálica con quistes es una leucodistrofia de origen genético que produce una alteración de la homeostasis del agua e iones en el cerebro, generando formas vacuolares y edema crónico en la sustancia blanca con deterioro neurológico progresivo. Debe sospecharse en los lactantes que presentan macrocefalia progresiva durante el primer año de vida, retraso motor y hallazgos característicos en la resonancia magnética cerebral. Caso clínico. Niña en seguimiento desde los 9 meses por macrocefalia progresiva y retraso del desarrollo psicomotor con presencia en la resonancia magnética cerebral de hallazgos compatibles con leucoencefalopatía megalencefálica con quistes, y aparición de epilepsia en su evolución. Los estudios genéticos habituales (secuenciación de nueva generación y array) fueron negativos, pero, al cumplir los criterios diagnósticos, se procedió al estudio del ARN mensajero y el ADN complementario, que confirmó la presencia de dos variantes patogénicas en MLC1. Conclusiones. La leucoencefalopatía megalencefálica con quistes es una entidad infrecuente. Es característica la macrocefalia progresiva en el primer año de vida, la ausencia de deterioro o deterioro lento, y la posibilidad de desarrollar epilepsia, espasticidad y ataxia en su evolución. Cobra importancia en dichos pacientes la realización de una prueba de imagen que muestre hallazgos propios de la entidad, lo que, junto con la clínica, permite diferenciarla de otras leucodistrofias y establecer un diagnóstico confirmatorio. Los estudios genéticos pueden constatar la mutación asociada que posibilita predecir el fenotipo clinicorradiológico.

Medulloblastoma, macrocephaly, and a pathogenic germline PTEN variant: Cause or coincidence?

BACKGROUND: Medulloblastomas (MBs) are a heterogeneous group of childhood brain tumors with four consensus subgroups, namely MBSHH , MBWNT , MBGroup 3 , and MBGroup 4 , representing the second most common type of pediatric brain cancer after high-grade gliomas. They suffer from a high prevalence of genetic predisposition with up to 20% of MBSHH caused by germline mutations in only six genes. However, the spectrum of germline mutations in MBSHH remains incomplete. METHODS: Comprehensive Next-Generation Sequencing panels of both tumor and patient blood samples were performed as molecular genetic characterization. The panels cover genes that are known to predispose to cancer. RESULTS: Here, we report on a patient with a pathogenic germline PTEN variant resulting in an early stop codon p.(Glu7Argfs*4) (ClinVar ID: 480383). The patient developed macrocephaly and MBSHH , but reached remission with current treatment protocols. CONCLUSIONS: We propose that pathogenic PTEN variants may predispose to medulloblastoma, and show that remission was reached with current treatment protocols. The PTEN gene should be included in the genetic testing provided to patients who develop medulloblastoma at an early age. We recommend brain magnetic resonance imaging upon an unexpected acceleration of growth of head circumference for pediatric patients harboring pathogenic germline PTEN variants.

Primrose syndrome: Characterization of the phenotype in 42 patients.

Primrose syndrome (PS; MIM# 259050) is characterized by intellectual disability (ID), macrocephaly, unusual facial features (frontal bossing, deeply set eyes, down-slanting palpebral fissures), calcified external ears, sparse body hair and distal muscle wasting. The syndrome is caused by de novo heterozygous missense variants in ZBTB20. Most of the 29 published patients are adults as characteristics appear more recognizable with age. We present 13 hitherto unpublished individuals and summarize the clinical and molecular findings in all 42 patients. Several signs and symptoms of PS develop during childhood, but the cardinal features, such as calcification of the external ears, cystic bone lesions, muscle wasting, and contractures typically develop between 10 and 16 years of age. Biochemically, anemia and increased alpha-fetoprotein levels are often present. Two adult males with PS developed a testicular tumor. Although PS should be regarded as a progressive entity, there are no indications that cognition becomes more impaired with age. No obvious genotype-phenotype correlation is present. A subgroup of patients with ZBTB20 variants may be associated with mild, nonspecific ID. Metabolic investigations suggest a disturbed mitochondrial fatty acid oxidation. We suggest a regular surveillance in all adult males with PS until it is clear whether or not there is a truly elevated risk of testicular cancer.

Hotspot Mutations in DICER1 Causing GLOW Syndrome-Associated Macrocephaly via Modulation of Specific microRNA Populations Result in the Activation of PI3K/ATK/mTOR Signaling.

BACKGROUND: We have previously described mosaic mutations in the RNase IIIb domain of DICER1that display global developmental delays, lung cysts, somatic overgrowth, macrocephaly and Wilms tumor. This constellation of phenotypes was classified as GLOW syndrome. Due to the phenotypic overlap between GLOW and syndromes caused by mutations in the PI3K/AKT/mTOR pathway, we hypothesized that alterations in miRNA regulation of this pathway cause its specific constellation of phenotypes. OBJECTIVE: To test the hypothesis that DICER1 "hot spot" mutations associated with GLOW syndrome activate PI3K/AKT/mTOR signaling. METHODS: We developed HEK293T cells with loss of exon 25 in DICER1, a genetic modification that is synonymous with the "hot spot" RNAseIIIb mutations that cause GLOW syndrome. We assayed the cells for activation of the PI3K/AKT/mTOR signaling pathway. RESULTS: We observed activation of the PI3K/AKT/mTOR pathway as demonstrated by increased pS6Kinase, p4EBP1 and pTSC2 levels. Additionally, these cells demonstrate a striking cellular phenotype, with the ability to form spheres when the serum is removed from their growth medium. The cells in these spheres are Oct4 and Sox2 positive and exhibit the property of reversion with the addition of serum. We queried miRNA expression data and identified a population of miRNAs that increase due to these mutations and target negative regulators of the PI3K/AKT/mTOR pathway. CONCLUSION: This work identifies the delicate and essential role for miRNA control of the PI3K/AKT/mTOR pathway. We conclude that the phenotypes observed in the GLOW syndrome are the result of PI3K/AKT/mTOR activation.

Overgrowth syndromes - clinical and molecular aspects and tumour risk.

Overgrowth syndromes are a heterogeneous group of rare disorders characterized by generalized or segmental excessive growth commonly associated with additional features, such as visceromegaly, macrocephaly and a large range of various symptoms. These syndromes are caused by either genetic or epigenetic anomalies affecting factors involved in cell proliferation and/or the regulation of epigenetic markers. Some of these conditions are associated with neurological anomalies, such as cognitive impairment or autism. Overgrowth syndromes are frequently associated with an increased risk of cancer (embryonic tumours during infancy or carcinomas during adulthood), but with a highly variable prevalence. Given this risk, syndrome-specific tumour screening protocols have recently been established for some of these conditions. Certain specific clinical traits make it possible to discriminate between different syndromes and orient molecular explorations to determine which molecular tests to conduct, despite the syndromes having overlapping clinical features. Recent advances in molecular techniques using next-generation sequencing approaches have increased the number of patients with an identified molecular defect (especially patients with segmental overgrowth). This Review discusses the clinical and molecular diagnosis, tumour risk and recommendations for tumour screening for the most prevalent generalized and segmental overgrowth syndromes.

Clinical spectrum of PTEN mutation in pediatric patients. A bicenter experience.

OBJECTIVE OF THE STUDY: To give a full overview of the clinical presentation of PTEN mutations in pediatric patients and to propose a pediatric follow-up protocol. METHODS: Recruitment of 16 PTEN mutated children (age 6 months-11 years) from two pediatric centers in Milan (Italy) between 2006 and 2017. All the patients underwent clinical and neurologic evaluations, cognitive and behavioral tests, and brain MRI; they are currently following an oncologic follow-up. RESULTS: Extreme macrocephaly is present in all the patients (69% HC above +4 SD). Neuropsychiatric issues have high prevalence, with 56% of patients showing developmental delay and 25% showing autism spectrum disorder. Brain MRI reveals in 75% of the patients at least one of the following: enlarged perivascular spaces, white matter anomalies, and/or downward displacement of the cerebellar tonsils through the foramen magnum, resulting in Chiari I malformation in two patients. Vascular malformations have a prevalence of 19%, with further evidence that complex cardiovascular malformations may be related to PTEN mutations; 31% of patients present hamartomas. None of our patients have so far experienced any oncologic complication. CONCLUSIONS: We suggest to screen for PTEN mutations all children presenting macrocephaly and one of the following: neurodevelopmental issues, one of the three major brain MRI anomalies, cutaneous lesions, vascular malformations, family history positive for PTEN related malignancies; or also with macrocephaly alone when exceeding +3 SD. Basing on our cohort results and further recent studies on the condition, we recommend a follow-up protocol that includes annual clinical and dermatological examination, thyroid and abdominal US, and Fecal Occult Blood test plus neurodevelopmental evaluation, heart US (to exclude congenital heart malformations), and brain MRI (to exclude Chiari I malformation) at diagnosis.

PUF60-SCRIB fusion transcript in a patient with 8q24.3 microdeletion and atypical Verheij syndrome.

Expression of the fusion genes is considered to be an important mechanism of tumorigenesis. However it is hardly ever discussed in relation to the neurodevelopmental disorders. Here we report on an 18-years-old female patient with 13.1 kb deletion of 8q24.3 fusing the 5'-portion of SCRIB with the 3'-portion of PUF60 and presenting with borderline intellectual disability, eye coloboma, short stature, scoliosis, heart defects and interestingly postnatal megalencephaly, in contrast to microcephaly, which is usually associated with 8q24.3 deletion (Verheij syndrome). Using next generation sequencing we mapped the breakpoints at nucleotide resolution and showed that the deletion preserved the reading frame. In contrast to the laborious techniques previously used for the precise mapping of deletion breakpoints, our approach identified an accurate interval very rapidly. We demonstrated the expression of the PUF60-SCRIB fusion gene in patient's cells and suggest that the fusion transcript might be a cause of the atypical clinical presentation.

Polymicrogyria in association with hypoglycemia points to mutation in the mTOR pathway.

We report a 16-month-old male with congenital megalencephaly, polymicrogyria and persistent hypoglycemia caused by a mosaic PIK3CA pathogenic variant. Hypoinsulinaemic, hypoketotic hypoglycaemia is a rare complication of pathogenic variants in the PI3K-AKT-mTOR pathway genes including AKT2, AKT3, CCND2, PIK3R2 and PIK3CA, and has been identified in a PIK3CA mutant mouse model. Our case highlights the importance of considering PI3K-AKT-mTOR pathway variants as a cause for megalencephaly and cortical malformation when the phenotype includes hypoglycaemia. Recognizing the association of hypoglycemia with PI3K-AKT-mTOR pathway variants can provide a clue to the genetic basis of the cortical malformation. Patients with megalencephaly and a cortical malformation may be considered at risk of hypoglycaemia and monitored accordingly, at least until a PI3K-AKT-mTOR pathway variant has been excluded.

A mouse model of DEPDC5-related epilepsy: Neuronal loss of Depdc5 causes dysplastic and ectopic neurons, increased mTOR signaling, and seizure susceptibility.

DEPDC5 is a newly identified epilepsy-related gene implicated in focal epilepsy, brain malformations, and Sudden Unexplained Death in Epilepsy (SUDEP). In vitro, DEPDC5 negatively regulates amino acid sensing by the mTOR complex 1 (mTORC1) pathway, but the role of DEPDC5 in neurodevelopment and epilepsy has not been described. No animal model of DEPDC5-related epilepsy has recapitulated the neurological phenotypes seen in patients, and germline knockout rodent models are embryonic lethal. Here, we establish a neuron-specific Depdc5 conditional knockout mouse by cre-recombination under the Synapsin1 promotor. Depdc5flox/flox-Syn1Cre (Depdc5cc+) mice survive to adulthood with a progressive neurologic phenotype that includes motor abnormalities (i.e., hind limb clasping) and reduced survival compared to littermate control mice. Depdc5cc+ mice have larger brains with increased cortical neuron size and dysplastic neurons throughout the cortex, comparable to the abnormal neurons seen in human focal cortical dysplasia specimens. Depdc5 results in constitutive mTORC1 hyperactivation exclusively in neurons as measured by the increased phosphorylation of the downstream ribosomal protein S6. Despite a lack of increased mTORC1 signaling within astrocytes, Depdc5cc+ brains show reactive astrogliosis. We observed two Depdc5cc+ mice to have spontaneous seizures, including a terminal seizure. We demonstrate that as a group Depdc5cc+ mice have lowered seizure thresholds, as evidenced by decreased latency to seizures after chemoconvulsant injection and increased mortality from pentylenetetrazole-induced seizures. In summary, our neuron-specific Depdc5 knockout mouse model recapitulates clinical, pathological, and biochemical features of human DEPDC5-related epilepsy and brain malformations. We thereby present an important model in which to study targeted therapeutic strategies for DEPDC5-related conditions.

From microcephaly to megalencephaly: determinants of brain size.

Expansion of the human brain, and specifically the neocortex, is among the most remarkable evolutionary processes that correlates with cognitive, emotional, and social abilities. Cortical expansion is determined through a tightly orchestrated process of neural stem cell proliferation, migration, and ongoing organization, synaptogenesis, and apoptosis. Perturbations of each of these intricate steps can lead to abnormalities of brain size in humans, whether small (microcephaly) or large (megalencephaly). Abnormalities of brain growth can be clinically isolated or occur as part of complex syndromes associated with other neurodevelopmental problems (eg, epilepsy, autism, intellectual disability), brain malformations, and body growth abnormalities. Thorough review of the genetic literature reveals that human microcephaly and megalencephaly are caused by mutations of a rapidly growing number of genes linked within critical cellular pathways that impact early brain development, with important pathomechanistic links to cancer, body growth, and epilepsy. Given the rapid rate of causal gene identification for microcephaly and megalencephaly understanding the roles and interplay of these important signaling pathways is crucial to further unravel the mechanisms underlying brain growth disorders and, more fundamentally, normal brain growth and development in humans. In this review, we will (a) overview the definitions of microcephaly and megalencephaly, highlighting their classifications in clinical practice; (b) overview the most common genes and pathways underlying microcephaly and megalencephaly based on the fundamental cellular processes that are perturbed during cortical development; and (c) outline general clinical molecular diagnostic workflows for children and adults presenting with microcephaly and megalencephaly.

El crecimiento del cerebro humano, específicamente del neocórtex, está entre los procesos evolutivos más remarcables que se correlacionan con habilidades cognitivas, emocionales y sociales. El crecimiento cortical está determinado por un proceso estrictamente coordinado de la proliferación, migración, organización, sinaptogénesis y apoptosis de las células madre neurales. La alteración de cada una de estas intrincadas etapas puede llevar a anormalidades del tamaño cerebral en los humanos, sea pequeño (microcefalia) o grande (megalencefalia). Las anormalidades del crecimiento cerebral puedan estar clínicamente aisladas o constituir parte de síndromes complejos asociados con otros problemas del neurodesarrollo (como epilepsia, autismo, incapacidad intelectual), malformaciones cerebrales y anormalidades del crecimiento corporal. La revisión de la literatura genética revela que la microcefalia y la megalencefalia son causadas por mutaciones de un número rápidamente creciente de genes relacionados con las vías celulares esenciales que influyen sobre el desarrollo precoz del cerebro, con importantes mecanismos patológicos vinculados con cáncer, crecimiento corporal y epilepsia. Dada la rápida tasa de identificación de genes que causan microcefalia y megalencefalia, la comprensión del papel y de la interacción de estas importantes vías de señalización es crucial para desentrañar los mecanismos subyacentes a los trastornos del crecimiento cerebral y, más fundamentalmente, al crecimiento y desarrollo normal del cerebro en los seres humanos. En esta revisión se presenta: a) una panorámica de las definiciones de microcefalia y megalencefalia, destacando sus clasificaciones en la práctica clínica, b) una panorámica de los genes y vías más comunes que subyacen a la microcefalia y la megalencefalia basada en los procesos celulares fundamentales que están alterados durante el desarrollo cerebral y c) un resumen del plan de trabajo general para el diagnóstico clínico molecular de niños y adultos con microcefalia y megalencefalia.

L'expansion du cerveau humain, et surtout celle du néocortex, est l'un des processus les plus remarquables de l'évolution, corrélé avec les capacités cognitives, émotionnelles et sociales. L'expansion corticale est déterminée au travers d'un processus étroitement orchestré de prolifération, de migration, d'organisation, de synaptogenèse et d'apoptose des cellules souches neurales. Toute perturbation de chacune de ces étapes intriquées peut générer des anomalies de la taille du cerveau humain, qu'elle soit petite (microcéphalie) ou grande (macrocéphalie). Les anomalies de la croissance du cerveau peuvent être isolées cliniquement ou participer à des syndromes complexes associés à d'autres problèmes du neurodéveloppement (par exemple, épilepsie, autisme, déficit intellectuel), à des malformations cérébrales et à des anomalies de la croissance corporelle. Une revue de la littérature génétique montre que la microcéphalie et la macrocéphalie humaines sont dues à des mutations d'un nombre de gènes augmentant rapidement, liées à des voies cellulaires essentielles qui influent sur le développement précoce du cerveau avec des liens mécanistiques pathologiques importants aux cancers, à la croissance corporelle et a l'épilepsie. Compte tenu du taux d'identification rapide de gène causal pour la micro et la macrocéphalie, il est essentiel de comprendre les rôles et l'interaction de ces importantes voies de signalisation pour mieux découvrir les mécanismes sous-tendant les troubles de la croissance cérébrale et, plus fondamentalement, ceux de la croissance cérébrale et du développement normaux chez l'homme. Nous présentons dans cet article 1) une vue d'ensemble des définitions de la micro et de la macrocéphalie, en soulignant leurs classifications en pratique clinique 2) une vue d'ensemble des voies et des gènes les plus courants sous-tendant la micro- et la macrocéphalie d'après les processus cellulaires fondamentaux perturbés au cours du développement cortical et 3) un aperçu des plans de travail généraux du diagnostic clinique moléculaire pour les enfants et les adultes micro- et macrocéphales.

Mutations of AKT3 are associated with a wide spectrum of developmental disorders including extreme megalencephaly.

Mutations of genes within the phosphatidylinositol-3-kinase (PI3K)-AKT-MTOR pathway are well known causes of brain overgrowth (megalencephaly) as well as segmental cortical dysplasia (such as hemimegalencephaly, focal cortical dysplasia and polymicrogyria). Mutations of the AKT3 gene have been reported in a few individuals with brain malformations, to date. Therefore, our understanding regarding the clinical and molecular spectrum associated with mutations of this critical gene is limited, with no clear genotype-phenotype correlations. We sought to further delineate this spectrum, study levels of mosaicism and identify genotype-phenotype correlations of AKT3-related disorders. We performed targeted sequencing of AKT3 on individuals with these phenotypes by molecular inversion probes and/or Sanger sequencing to determine the type and level of mosaicism of mutations. We analysed all clinical and brain imaging data of mutation-positive individuals including neuropathological analysis in one instance. We performed ex vivo kinase assays on AKT3 engineered with the patient mutations and examined the phospholipid binding profile of pleckstrin homology domain localizing mutations. We identified 14 new individuals with AKT3 mutations with several phenotypes dependent on the type of mutation and level of mosaicism. Our comprehensive clinical characterization, and review of all previously published patients, broadly segregates individuals with AKT3 mutations into two groups: patients with highly asymmetric cortical dysplasia caused by the common p.E17K mutation, and patients with constitutional AKT3 mutations exhibiting more variable phenotypes including bilateral cortical malformations, polymicrogyria, periventricular nodular heterotopia and diffuse megalencephaly without cortical dysplasia. All mutations increased kinase activity, and pleckstrin homology domain mutants exhibited enhanced phospholipid binding. Overall, our study shows that activating mutations of the critical AKT3 gene are associated with a wide spectrum of brain involvement ranging from focal or segmental brain malformations (such as hemimegalencephaly and polymicrogyria) predominantly due to mosaic AKT3 mutations, to diffuse bilateral cortical malformations, megalencephaly and heterotopia due to constitutional AKT3 mutations. We also provide the first detailed neuropathological examination of a child with extreme megalencephaly due to a constitutional AKT3 mutation. This child has one of the largest documented paediatric brain sizes, to our knowledge. Finally, our data show that constitutional AKT3 mutations are associated with megalencephaly, with or without autism, similar to PTEN-related disorders. Recognition of this broad clinical and molecular spectrum of AKT3 mutations is important for providing early diagnosis and appropriate management of affected individuals, and will facilitate targeted design of future human clinical trials using PI3K-AKT pathway inhibitors.

Wilms tumor screening in diffuse capillary malformation with overgrowth and macrocephaly-capillary malformation: A retrospective study.

BACKGROUND: CLOVES (congenital lipomatous overgrowth, vascular malformations, epidermal nevi, and skeletal anomalies) syndrome is associated with regional bony and/or soft tissue overgrowth, capillary malformation, and an increased risk for Wilms tumor. OBJECTIVE: To evaluate the frequency of Wilms tumor in patients with 2 similar conditions: diffuse capillary malformation with overgrowth (DCMO) and macrocephaly-capillary malformation (M-CM). METHODS: Culling our Vascular Anomalies Center database, we retrospectively reviewed patients in whom DCMO and M-CM had been diagnosed and who were evaluated between 1998 and 2016 for possible development of Wilms tumor. Patients younger than 8 years of age at their last visit and not seen in more than 2 years were contacted for follow-up. RESULTS: The study comprised 89 patients: 67 with DCMO, 17 with M-CM, and 5 with an indeterminate diagnosis. No case of Wilms tumor was found in these groups. LIMITATIONS: Some patients were younger than 8 years of age at last follow-up visit and the sample size was small. CONCLUSION: Patients with DCMO do not appear to be at increased risk for Wilms tumor. Screening is probably unnecessary in DCMO unless there is associated hemihypertrophy. Although there were no cases in our cohort, there are 2 reports of M-CM associated with Wilms tumor in the literature.

Chd8 Mutation Leads to Autistic-like Behaviors and Impaired Striatal Circuits.

Autism spectrum disorder (ASD) is a heterogeneous disease, but genetically defined models can provide an entry point to studying the molecular underpinnings of this disorder. We generated germline mutant mice with loss-of-function mutations in Chd8, a de novo mutation strongly associated with ASD, and demonstrate that these mice display hallmark ASD behaviors, macrocephaly, and craniofacial abnormalities similar to patient phenotypes. Chd8+/- mice display a broad, brain-region-specific dysregulation of major regulatory and cellular processes, most notably histone and chromatin modification, mRNA and protein processing, Wnt signaling, and cell-cycle regulation. We also find altered synaptic physiology in medium spiny neurons of the nucleus accumbens. Perturbation of Chd8 in adult mice recapitulates improved acquired motor learning behavior found in Chd8+/- animals, suggesting a role for CHD8 in adult striatal circuits. These results support a mechanism linking chromatin modification to striatal dysfunction and the molecular pathology of ASD.

A novel de novo germline mutation Glu40Lys in AKT3 causes megalencephaly with growth hormone deficiency.

Germline or somatic gain-of-function mutations in the v-akt murine thymoma viral oncogene homolog 3 (AKT3) have been reported to cause syndromic megalencephaly. We describe a novel germline mutation, p.Glu40Lys, in AKT3. Phenotypically, the patient presented with megalencephaly with hypotonia, apparent connective tissue laxity, and growth hormone (GH) deficiency. To our knowledge, this is the first instance of a patient with megalencephaly with GH deficiency, harboring a germline de novo mutation in AKT3. © 2017 Wiley Periodicals, Inc.

A Retrospective Analysis of the Utility of Head Computed Tomography and/or Magnetic Resonance Imaging in the Management of Benign Macrocrania.

OBJECTIVE: To assess whether computed tomography (CT), magnetic resonance imaging (MRI), and neurosurgical evaluations altered the diagnosis or management of children diagnosed with benign macrocrania of infancy by ultrasonography (US). STUDY DESIGN: We queried our radiology database to identify patients diagnosed with benign macrocrania of infancy by US between 2006 and 2013. Medical records of those with follow-up CT/MRI were reviewed to determine clinical/neurologic status and whether or not CT/MRI imaging resulted in diagnosis of communicating hydrocephalus or required neurosurgical intervention. RESULTS: Patients with benign macrocrania of infancy (n = 466) were identified (mean age at diagnosis: 6.5 months). Eighty-four patients (18.0%) received subsequent head CT/MRI; of these, 10 patients had neurologic abnormalities before 2 years of age, of which 3 had significant findings on MRI (temporal lobe white matter changes, dysmorphic ventricles, thinned corpus callosum). One patient without neurologic abnormalities had nonspecific white matter signal abnormality (stable over 6 months) but no change in management. None required neurosurgical intervention. Another 9/84 patients had incidental findings including Chiari I (3), small subdural bleeds (2), arachnoid cyst (1), small cavernous malformation (1), frontal bone dermoid (1), and a linear parietal bone fracture after a fall (1). CONCLUSIONS: Children diagnosed with benign macrocrania of infancy on US without focal neurologic findings do not require subsequent brain CT/MRI or neurosurgical evaluation. Decreasing unnecessary imaging would decrease costs, minimize radiation and sedation exposures, and increase clinic availability of neurology and neurosurgery specialists.