MYCN in human development and diseases.

Somatic mutations in MYCN have been identified across various tumors, playing pivotal roles in tumorigenesis, tumor progression, and unfavorable prognoses. Despite its established notoriety as an oncogenic driver, there is a growing interest in exploring the involvement of MYCN in human development. While MYCN variants have traditionally been associated with Feingold syndrome type 1, recent discoveries highlight gain-of-function variants, specifically p.(Thr58Met) and p.(Pro60Leu), as the cause for megalencephaly-polydactyly syndrome. The elucidation of cellular and murine analytical data from both loss-of-function (Feingold syndrome model) and gain-of-function models (megalencephaly-polydactyly syndrome model) is significantly contributing to a comprehensive understanding of the physiological role of MYCN in human development and pathogenesis. This review discusses the MYCN's functional implications for human development by reviewing the clinical characteristics of these distinct syndromes, Feingold syndrome, and megalencephaly-polydactyly syndrome, providing valuable insights into the understanding of pathophysiological backgrounds of other syndromes associated with the MYCN pathway and the overall comprehension of MYCN's role in human development.

A de novo Mutation (p.Gln277X) of Cyclin D2 is Responsible for a Child with Megalencephaly-Polymicrogyria-Polydactyly-Hydrocephalus Syndrome.

Megalencephaly-polymicrogyria-polydactyly-hydrocephalus syndrome (MPPH), a type of overgrowth syndrome, is characterized by progressive megalencephaly, cortical brain malformations, and distal limb anomalies. Previous studies have revealed that the overactivity of the phosphatidylinositol 3-kinase-Protein kinase B pathway and the increased cyclin D2 (CCND2) expression were the main factors contributing to this disease. Here, we present the case of a patient who exhibited megalencephaly, polymicrogyria, abnormal neuronal migration, and developmental delay. Serum tandem mass spectrometry and chromosome examination did not detect any metabolic abnormalities or copy number variants. However, whole-exome sequencing and Sanger sequencing revealed a de novo nonsense mutation (NM_001759.3: c.829C>T; p.Gln277X) in the CCND2 gene of the patient. Bioinformatics analysis predicted that this mutation may disrupt the structure and surface charge of the CCND2 protein. This disruption could potentially prevent polyubiquitination of CCND2, leading to its resistance against degradation. Consequently, this could drive cell division and growth by altering the activity of key cell cycle regulatory nodes, ultimately contributing to the development of MPPH. This study not only presents a new case of MPPH and expands the mutation spectrum of CCND2 but also enhances our understanding of the mechanisms connecting CCND2 with overgrowth syndromes.

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.

Syndrome of megalencephaly, mega corpus callosum, and complete lack of motor development: an unusual case and a literature review.

The syndrome of megalencephaly, mega corpus callosum (MEG-MegaCC) accompanied by complete lack of motor development is a rare condition with only few sporadic cases having been reported in the literature. In this paper, we describe a child from non-consanguineous parents presenting with MegaCC, psychomotor retardation, and language impairment linked to MEG-MegaCC syndrome. Genetic analysis, radiological findings, and detailed neurological phenotype of MEG-MegaCC syndrome with its overlapping syndromes would allow for a better classification of the disease spectrum.

Prenatal Ultrasound Diagnosis of Megalencephaly-Polymicrogyria-Polydactyly-Hydrocephalus Syndrome with Persistent Hyperplastic Primary Vitreous: A Case Report.

INTRODUCTION: Megalencephaly-polymicrogyria-polydactyly-hydrocephalus (MPPH) syndrome is a rare autosomal dominant disorder characterized by megalencephaly (i.e., overgrowth of the brain), polymicrogyria, focal hypoplasia of the cerebral cortex, and polydactyly. Persistent hyperplastic primary vitreous (PHPV) involves a spectrum of congenital ocular abnormalities that are characterized by the presence of a vascular membrane behind the lens. CASE PRESENTATION: Here, we present a case of foetal MPPH with PHPV that was diagnosed using prenatal ultrasound. Ultrasound revealed the presence of megalencephaly, multiple cerebellar gyri, and hydrocephalus. Whole-exome sequencing confirmed the mutation of the AKT3 gene, which led to the consideration of MPPH syndrome. Moreover, an echogenic band with an irregular surface was observed between the lens and the posterior wall of the left eye; therefore, MPPH with PHPV was suspected. CONCLUSION: MPPH syndrome with PHPV can be diagnosed prenatally.

Case report: Progressive pulmonary artery hypertension in a case of megalencephaly-capillary malformation syndrome.

Megalencephaly-capillary malformation syndrome (MCAP, OMIM # 602501) is caused by hyperactivity of the thephosphoinositide-3-kinase (PI3K)-Vakt murine thymoma viral oncogene homolog (AKT)-mammalian target of rapamycin (mTOR) pathway, which results in megalencephaly, capillary malformations, asymmetrical overgrowth, and connective tissue dysplasia. Herein, we report the case of a 7-month-old girl with MCAP due to a PIK3CA somatic mosaic variant who presented with atrial tachycardia, finally diagnosed as pulmonary arterial hypertension (PAH). Oxygen therapy and sildenafil decreased pulmonary blood pressure and improved atrial tachycardia. Previous studies reported an association between the PI3K/AKT/mTOR pathway and abnormal pulmonary arterial smooth muscle cell proliferation, which may be associated with PAH. PAH should be considered a potentially lethal complication in MCAP patients, even when no structural cardiac abnormalities are identified in the neonatal period.

Variants in PTEN Are Associated With a Diverse Spectrum of Cortical Dysplasia.

BACKGROUND: Inactivating mutations in PTEN are among the most common causes of megalencephaly. Activating mutations in other nodes of the PI3K/AKT/MTOR signaling pathway are recognized as a frequent cause of cortical brain malformations. Only recently has PTEN been associated with cortical malformations, and analyses of their prognostic significance have been limited. METHODS: Retrospective neuroimaging analysis and detailed chart review were conducted on 20 participants identified with pathogenic or likely pathogenic mutations in PTEN and a cortical brain malformation present on brain magnetic resonance imaging. RESULTS: Neuroimaging analysis revealed four main cerebral phenotypes-hemimegalencephaly, focal cortical dysplasia, polymicrogyria (PMG), and a less severe category, termed "macrocephaly with complicated gyral pattern" (MCG). Although a high proportion of participants (90%) had neurodevelopmental findings on presentation, outcomes varied and were favorable in over half of participants. Consistent with prior work, 39% of participants had autism spectrum disorder and 19% of participants with either pure-PMG or pure-MCG phenotypes had epilepsy. Megalencephaly and systemic overgrowth were common, but other systemic features of PTEN-hamartoma tumor syndrome were absent in over one-third of participants. CONCLUSIONS: A spectrum of cortical dysplasias is present in individuals with inactivating mutations in PTEN. Future studies are needed to clarify the prognostic significance of each cerebral phenotype, but overall, we conclude that despite a high burden of neurodevelopmental disease, long-term outcomes may be favorable. Germline testing for PTEN mutations should be considered in cases of megalencephaly and cortical brain malformations even in the absence of other findings, including cognitive impairment.

mTOR pathway: Insights into an established pathway for brain mosaicism in epilepsy.

The mechanistic target of rapamycin (mTOR) signaling pathway is an essential regulator of numerous cellular activities such as metabolism, growth, proliferation, and survival. The mTOR cascade recently emerged as a critical player in the pathogenesis of focal epilepsies and cortical malformations. The 'mTORopathies' comprise a spectrum of cortical malformations that range from whole brain (megalencephaly) and hemispheric (hemimegalencephaly) abnormalities to focal abnormalities, such as focal cortical dysplasia type II (FCDII), which manifest with drug-resistant epilepsies. The spectrum of cortical dysplasia results from somatic brain mutations in the mTOR pathway activators AKT3, MTOR, PIK3CA, and RHEB and from germline and somatic mutations in mTOR pathway repressors, DEPDC5, NPRL2, NPRL3, TSC1 and TSC2. The mTORopathies are characterized by excessive mTOR pathway activation, leading to a broad range of structural and functional impairments. Here, we provide a comprehensive literature review of somatic mTOR-activating mutations linked to epilepsy and cortical malformations in 292 patients and discuss the perspectives of targeted therapeutics for personalized medicine.

Canavan's spongiform leukodystrophy (Aspartoacylase deficiency) with emphasis on sonographic features in infancy: description of a case report and review of the literature.

Canavan disease (CD; MIM 271,900) or spongy degeneration of the central nervous system (CNS) is a lethal, rare autosomal recessive leukodystrophy, first described in 1931 (Canavan in Arch Neurol Psychiatry 25: 299-308, 1931). The clinical presentation includes severe neurologic impairment and macrocephaly with onset of symptoms at the age of 3-5 months. Biochemical and genetic fundamentals of the disease are elucidated. Imaging diagnosis is principally based on MRI with important role of MR spectroscopy. We report the cerebral sonographic findings in a severely affected infant with CD: Diffuse hyperechogenicity and small multicystic changes of white matter as well as an inverted pattern of echogenicity between cortical gray and subcortical white matter. These findings are compared to to the few cases found in literature and to normal ultrasound examples. Finally, ultrasound and MRI imaging findings are correlated.

Cochlear implantation in a profoundly deaf child with cystic leukoencephalopathy without megalencephaly.

BACKGROUND: Cochlear implantation candidacy criteria have continued to evolve over the years, and cochlear implantation is possible with many inner-ear and brain anomalies with good hearing and linguistic outcomes. Cystic leukoencephalopathy without megalencephaly is a rare disease in children, with only 30 cases reported in the literature, but it is associated with hearing loss in only three cases. Radiological investigations can help in diagnosing this rare entity before proceeding with cochlear implantation. CASE REPORT: A four-year-old female child born out of consanguinity with normal psychomotor development, bilateral sensorineural hearing loss and an incidental magnetic resonance imaging finding of cystic leukoencephalopathy without megalencephaly underwent successful cochlear implantation. Her post-operative period was uneventful with successful mapping of the cochlear implant. CONCLUSION: This is the first reported case of cystic leukoencephalopathy without megalencephaly and with sensorineural hearing loss in which cochlear implantation was performed successfully. White matter and temporal lobe abnormalities should not deter paediatric cochlear implantation.

Hemimegalencephaly: Evolution From an Atypical Focal Early Appearance on Fetal MRI to More Conventional MR Findings.

Hemimegalencephaly, or unilateral megalencephaly, is a sporadic congenital brain malformation characterized by enlargement of a cerebral hemisphere due to an abnormal proliferation of neurons or glial cells. Hemimegalencephaly is part of a spectrum of disorders, increasingly referred to as mTORopathies, which arise as a result of dysregulation or hyperactivation of the mammalian target of rapamycin (mTOR)-signaling cascade resulting in less restricted cell growth and survival. The resultant cortical disorganization and enhanced neuronal excitability often manifest clinically in the form of seizures. Ultrasound and magnetic resonance imaging (MRI) are often used to characterize hemimegalencephaly. Typical imaging findings seen include diffuse unilateral enlargement of a cerebral hemisphere with overlying cortical malformation and ipsilateral dilation of the lateral ventricle. This paper will review an unusual case of focal hemimegalencephaly diagnosed on prenatal imaging. Initial in utero MRI revealed a mass-like lesion in the frontal lobe without associated perilesional cerebral edema. Keying in on abnormalities within the overlying cortex was crucial in suggesting focal hemimegalencephaly as a leading diagnosis and distinguishing it from alternative diagnoses such as a neoplasm. Follow-up fetal MRI demonstrated the evolution of the cerebral abnormality and confirmed the diagnosis. Early diagnosis facilitated appropriate counseling of the parents and guided postnatal imaging and management.

Imaging of Macrocephaly.

Macrocephaly is a common diagnosis in the pediatric population, particularly in the infantile time period. There is a wide range of causes of macrocephaly, from benign to malignant, for which imaging plays a key role in the diagnosis and clinical guidance. Our aim is to review the distinct and prevalent neuroimaging findings in the evaluation of the macrocephalic infant.

Brain Abnormalities in PIK3CA-Related Overgrowth Spectrum: Physician, Patient, and Caregiver Experiences.

PIK3CA-related overgrowth spectrum (PROS) disorders are caused by somatic, gain-of-function mutations in PIK3CA (phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha) that result in hyperactivation of the phosphatidylinositol-3-kinase (PI3K) signaling pathway. PROS encompasses a broad spectrum of overlapping phenotypes that vary considerably in their severity and tissue distribution, leading to different and complex experiences for affected children and their families. The parent of a child with the PROS disorder megalencephaly-capillary malformation (MCAP) coauthored this article. MCAP is characterized by significant neurological involvement, and she describes personal experiences with this condition, including delays associated with obtaining a correct diagnosis, finding an experienced care team, challenges with schooling, medical complications, and the ongoing emotional and financial impacts on their lives. A physician perspective, which reinforces the challenges faced by the young child and his family, is provided by a clinician and researcher specializing in PROS disorders with central nervous system involvement. The physician reviews the mechanism of disease, some of the challenges in accurately diagnosing PROS conditions, disease-related complications, current treatment options and their limitations, and emerging therapeutic options including ongoing clinical trials. Our objective is to share these experiences and insights to benefit patients with PROS disorders, their families, and health care professionals involved with caring for patients with PROS.

Clinical and Molecular Spectrum of Sporadic Vascular Malformations: A Single-Center Study.

Sporadic vascular malformations (VMs) are a large group of disorders of the blood and lymphatic vessels caused by somatic mutations in several genes-mainly regulating the RAS/MAPK/ERK and PI3K/AKT/mTOR pathways. We performed a cross-sectional study of 43 patients affected with sporadic VMs, who had received molecular diagnosis by high-depth targeted next-generation sequencing in our center. Clinical and imaging features were correlated with the sequence variants identified in lesional tissues. Six of nine patients with capillary malformation and overgrowth (CMO) carried the recurrent GNAQ somatic mutation p.Arg183Gln, while two had PIK3CA mutations. Unexpectedly, 8 of 11 cases of diffuse CM with overgrowth (DCMO) carried known PIK3CA mutations, and the remaining 3 had pathogenic GNA11 variants. Recurrent PIK3CA mutations were identified in the patients with megalencephaly-CM-polymicrogyria (MCAP), CLOVES, and Klippel-Trenaunay syndrome. Interestingly, PIK3CA somatic mutations were associated with hand/foot anomalies not only in MCAP and CLOVES, but also in CMO and DCMO. Two patients with blue rubber bleb nevus syndrome carried double somatic TEK mutations, two of which were previously undescribed. In addition, a novel sporadic case of Parkes Weber syndrome (PWS) due to an RASA1 mosaic pathogenic variant was described. Finally, a girl with a mild PWS and another diagnosed with CMO carried pathogenic KRAS somatic variants, showing the variability of phenotypic features associated with KRAS mutations. Overall, our findings expand the clinical and molecular spectrum of sporadic VMs, and show the relevance of genetic testing for accurate diagnosis and emerging targeted therapies.

Brain overgrowth associated with megalencephaly-capillary malformation syndrome causing progressive Chiari and syringomyelia.

Background: Megalencephaly-capillary malformation (M-CM) syndrome is a rare overgrowth syndrome characterized by macrocephaly, port-wine stains, asymmetric brain growth, hydrocephalus, and developmental delay. Cerebellar tonsil herniation is often seen, but rarely with syringomyelia. Case Description: A newborn with M-CM syndrome developed a progressive Chiari malformation type I (CM-I) with syringomyelia. At 4 months, he was treated for subdural hematomas, while at 10 months, he required a shunt for hydrocephalus. At 16 years of age, he newly presented a left hemiparesis and ataxia. Notably, successive volumetric measurements of the posterior fossa/cerebellum showed disproportionate cerebellar growth over time that correlated with the appearance of a CM-I. Following a suboccipital craniectomy with C1-laminectomy and duraplasty, he neurologically improved. Conclusion: M-CM with CM-I and syringomyelia rarely present together. Here, we treated an infant with M-CM who developed a progressive CM-I malformation and syringomyelia reflecting disproportionate growth of the cerebellum/posterior fossa over a 16-year period.

Megalencephaly-Capillary Malformation-Polymicrogyria Syndrome (MCAP): A Rare Dynamic Genetic Disorder.

Megalencephaly-capillary malformation-polymicrogyria syndrome (MCAP) is an uncommon malformation syndrome, characterized by primary megalencephaly, capillary malformations of the midline face and body, or distal limb anomalies such as syndactyly and polymicrogyria. Herein, we report a young male child, who presented with complaints of increasing head size, delay in speech, and one episode of focal seizure with distinctive morphological and neuroradiological manifestations which led to the diagnosis of MCAP. We have also reviewed recently published literature and the various diagnostic criteria proposed by authors to achieve the early clinical diagnosis of these patients in the outpatient department.

PIK3CA-related overgrowth with an uncommon phenotype: case report.

BACKGROUND: Megalencephaly-capillary malformation syndrome is a rare multiple-malformation syndrome secondary to somatic activating mutations in the PI3K-AKT-MTOR pathway. This is included in a heterogeneous group of disorders, now defined "PIK3CA-related overgrowth spectrum". CASE PRESENTATION: We report a 22-months-old female presenting an uncommon phenotype associated with a genetic mosaicism in the PIK3CA gene, detected on DNA extracted from blood peripheral and tissue biopsy. CONCLUSIONS: NGS is the preferred method for molecular diagnosis of PROS on affected skin and overgrown tissues as primary samples. The wide phenotypic variability is based on the distribution of mosaicism, in fact the same mutation can cause different PIK3CA related disorders. Continuous understanding of the clinical spectrum and of molecular basis of PROS and their overlap will lead to improve diagnosis, management and new treatment strategies.

The non-essential TSC complex component TBC1D7 restricts tissue mTORC1 signaling and brain and neuron growth.

The tuberous sclerosis complex (TSC) 1 and 2 proteins associate with TBC1D7 to form the TSC complex, which is an essential suppressor of mTOR complex 1 (mTORC1), a ubiquitous driver of cell and tissue growth. Loss-of-function mutations in TSC1 or TSC2, but not TBC1D7, give rise to TSC, a pleiotropic disorder with aberrant activation of mTORC1 in various tissues. Here, we characterize mice with genetic deletion of Tbc1d7, which are viable with normal growth and development. Consistent with partial loss of function of the TSC complex, Tbc1d7 knockout (KO) mice display variable increases in tissue mTORC1 signaling with increased muscle fiber size but with strength and motor defects. Their most pronounced phenotype is brain overgrowth due to thickening of the cerebral cortex, with enhanced neuron-intrinsic mTORC1 signaling and growth. Thus, TBC1D7 is required for full TSC complex function in tissues, and the brain is particularly sensitive to its growth-suppressing activities.

Clinical Conundrum: Polyhydramnios as a Marker for a Fetal Genetic Syndrome in the Canadian Old Order Mennonite Population.

A 35-year-old woman was referred to genetics for 2 soft markers but was also found to have polyhydramnios. The couple were Old Order Mennonite, and carrier testing allowed for targeted investigation of syndromes associated with polyhydramnios in this population. Both parents were carriers of a 7304 bp deletion in the STRADA (LYK5) gene, causing an autosomal recessive syndrome of polyhydramnios, megalencephaly, and symptomatic epilepsy. This led to early recognition and treatment of neonatal seizures. Targeted testing can significantly shorten the diagnostic odyssey and decrease the cost of investigations, an especially important consideration for families who do not accept health insurance.

[How I explore... macrocephaly]. / Comment j'explore. Une macrocéphalie.

Macrocephaly is a frequent reason for seeking advice in a pediatric neurology consultation. It is a non-specific neurological sign that can be isolated, be the sign of a serious acquired pathology or be part of a syndromic picture. Clinical history, physical examination and imaging are key elements of the diagnostic strategy. Signs of intracranial hypertension require an emergency work-up. Genetics, exome in particular, has enabled the characterization of various syndromes associating macrocephaly and neurodevelopmental delay. In this article, we propose an update of practices based on clinical signs.

La macrocéphalie est un motif fréquent de demande d'avis en consultation de neuropédiatrie. Il s'agit d'un signe somatique peu spécifique et pouvant être isolé, être le signe d'une pathologie acquise grave ou faire partie d'un tableau syndromique. L'anamnèse, l'examen clinique et l'imagerie sont des éléments clés de la stratégie diagnostique. La découverte de signes d'hypertension intracrânienne implique une mise au point en urgence. La génétique, notamment la réalisation de l'exome, a permis la caractérisation de différents syndromes associant la macrocéphalie et des troubles du neurodéveloppement. Compte tenu des évolutions technologiques, une mise à jour des pratiques, basée sur la clinique, est proposée dans cet article.