Neurodevelopmental Aspects of RASopathies

RAS gene mutations are frequently found in one third of human cancers. Affecting approximately 1 in 1,000 newborns, germline and somatic gain-of-function mutations in the components of RAS/mitogen-activated protein kinase (RAS/MAPK) pathway has been shown to cause developmental disorders, known as RASopathies. Since RAS-MAPK pathway plays essential roles in proliferation, differentiation and migration involving developmental processes, individuals with RASopathies show abnormalities in various organ systems including central nervous system. The frequently seen neurological defects are developmental delay, macrocephaly, seizures, neurocognitive deficits, and structural malformations. Some of the defects stemmed from dysregulation of molecular and cellular processes affecting early neurodevelopmental processes. In this review, we will discuss the implications of RAS-MAPK pathway components in neurodevelopmental processes and pathogenesis of RASopathies.

Costello syndrome: Clinical phenotype, genotype, and management guidelines

Costello syndrome (CS) is a RASopathy caused by activating germline mutations in HRAS. Due to ubiquitous HRAS gene expression, CS affects multiple organ systems and individuals are predisposed to cancer. Individuals with CS may have distinctive craniofacial features, cardiac anomalies, growth and developmental delays, as well as dermatological, orthopedic, ocular, and neurological issues; however, considerable overlap with other RASopathies exists. Medical evaluation requires an understanding of the multifaceted phenotype. Subspecialists may have limited experience in caring for these individuals because of the rarity of CS. Furthermore, the phenotypic presentation may vary with the underlying genotype. These guidelines were developed by an interdisciplinary team of experts in order to encourage timely health care practices and provide medical management guidelines for the primary and specialty care provider, as well as for the families and affected individuals across their lifespan. These guidelines are based on expert opinion and do not represent evidence-based guidelines due to the lack of data for this rare condition.

Severe Noonan syndrome phenotype associated with a germline Q71R MRAS variant: a recurrent substitution in RAS homologs in various cancers

Activation of the RAS pathway through either the activation of genes that accelerate the pathway or the suppression of genes that inhibit the pathway leads to a group of disorders collectively referred to as RASopathies. The key molecules of the RAS pathway are KRAS, HRAS, and NRAS. Mutations in these three RAS homolog genes have been shown to be associated with RASopathies. Recently, two patients with a Noonan syndrome phenotype were shown to carry mutations in the yet another RASopathy gene, MRAS (muscle RAS oncogene homolog). Here, we report a patient with a severe Noonan syndrome phenotype associated with a germline Q71R MRAS variant, which represents a recurrent substitution in RAS homologs in various cancers. The patient's dysmorphic features included relative macrocephaly, a down-slanted palpebral fissure, hypertelorism, a depressed nasal bridge, and low-set ears with thick lobes; these facial features are strongly associated with RASopathy. We confirmed that the MRAS gene represents a causative gene for RASopathy.

RASopathy in Patients With Isolated Sagittal Synostosis

RASopathy is caused by dysfunction in the MAPK pathway, and include syndromes like Noonan syndrome (NS), NS with multiple lentigines (formerly known as Leopard syndrome), cardiofaciocutaneous (CFC), Legius syndrome, capillary malformation–arteriovenous malformation, neurofibromatosis type 1, and Costello syndrome. When counted together, RASopathies affect 1/1000 live births, and are characterized by cardiovascular manifestations, short stature, developmental delay, renal, urogenital, skin/skeletal abnormalities, and dysmorphic appearance. NS—one of the most common RASopathies—occurs in 1/1000 to 1/2500 live births. On the other hand, the frequency of CFC is unknown, but it is one of the rarest RASopathies, with estimates of only a few hundred cases worldwide. However, its phenotype overlaps with that of NS. In this case series, we describe 5 patients with a clinical and genetic diagnosis of RASopathy—either NS or CFC—all of whom were also diagnosed with isolated sagittal synostosis (ISS). Medical records from ophthalmology, cardiology, plastic surgery, medical genetics, cleft craniofacial, and neurosurgery were used to determine patient history. In our cohort, late presentation of ISS was the predominant form of ISS presentation. We hope this report further characterizes the burgeoning relationship between RASopathy and ISS. Furthermore, these findings support including sagittal synostosis among the presenting features in the clinical phenotype of RASopathies. Ethical approval was obtained from the university’s institutional review board.

A Premature Stop Codon in RAF1 Is the Priority Candidate Causative Mutation of the Inherited Chicken Wingless-2 Developmental Syndrome

The chicken wingless-2 (wg-2) mutation is inherited in an autosomal recessive fashion, and the resulting phenotype in mutant (wg-2/wg-2) individuals is a developmental syndrome characterized by absent wings, truncated legs, craniofacial as well as skin and feather defects, and kidney malformations. Mapping and genotyping established that the mutation resides within 227 kilobases (kb) of chromosome 12 in a wg-2 congenic inbred line. A capture array was designed to target and sequence the candidate region along with flanking DNA in 24 birds from the line. Many point mutations and insertions or deletions were identified, and analysis of the linked variants indicated a point mutation predicted to cause a premature stop codon in the RAF1 gene. Expression studies were conducted inclusive of all genes in the candidate region. Interestingly, RAF1 transcription was elevated, yet the protein was absent in the mutants relative to normal individuals. RAF1 encodes a protein integral to the Ras/Raf/MAPK signaling pathway controlling cellular proliferation, and notably, human RASopathies are developmental syndromes caused by germline mutations in genes of this pathway. Our work indicates RAF1 as the priority candidate causative gene for wg-2 and provides a new animal model to study an important signaling pathway implicated in limb development, as well as RASopathies.

Occurrence of high-grade glioma in Noonan syndrome: Report of two cases

Noonan syndrome (NS) is an autosomal dominant disorder commonly caused by PTPN11 germline mutations. Patients are characterized by short stature, congenital heart defects, facial dysmorphism, and increased risk of malignancies including brain tumors. Commonly associated brain tumors are dysembryoplastic neuroepithelial tumor and low-grade glioma. We report two cases of anaplastic astrocytoma with PTPN11-related NS. We conducted a systematic search of medical databases looking for other reported cases of high-grade glioma associated with NS and identified 24 cases of brain tumors, all of which were low-grade glial or glioneuronal tumors except for one case of medulloblastoma.

A YWHAZ Variant Associated With Cardiofaciocutaneous Syndrome Activates the RAF-ERK Pathway

Cardiofaciocutaneous (CFC) syndrome is a genetic disorder characterized by distinctive facial features, congenital heart defects, and skin abnormalities. Several germline gain-of-function mutations in the RAS/RAF/MEK/ERK pathway are associated with the disease, including KRAS, BRAF, MEK1, and MEK2. CFC syndrome thus belongs to a group of disorders known as RASopathies, which are all caused by pathogenic mutations in various genes encoding components of the RAS pathway. We recently identified novel variants in YWHAZ, a 14-3-3 family member, in individuals with a phenotype consistent with CFC that may potentially be deleterious and disease-causing. In the current study, we take advantage of the vertebrate model Xenopus laevis to analyze the functional consequence of a particular YWHAZ variant, S230W, and investigate the molecular mechanisms underlying its activity. We show that compared with wild type YWHAZ, the S230W variant induces severe embryonic defects when ectopically expressed in early Xenopus embryos. The S230W variant also rescues the defects induced by a dominant negative FGF receptor more efficiently and enhances Raf-stimulated Erk phosphorylation to a higher level than wild type YWHAZ. Although neither YWHAZ nor the variant promotes membrane recruitment of Raf proteins, the variant binds to more Raf and escapes phosphorylation by casein kinase 1a. Our data provide strong support to the hypothesis that the S230W variant of YWHAZ is a gain-of-function mutation in the RAS-ERK pathway and may underlie a CFC phenotype.

First International Conference on RASopathies and Neurofibromatoses in Asia: Identification and advances of new therapeutics

The neurofibromatoses, which include neurofibromatosis type I (NF1), neurofibromatosis type II (NF2), and schwannomatosis, are a group of syndromes characterized by tumor growth in the nervous system. The RASopathies are a group of syndromes caused by germline mutations in genes that encode components of the RAS/mitogen-activated protein kinase (MAPK) pathway. The RASopathies include NF1, Noonan syndrome, Noonan syndrome with multiple lentigines, Costello syndrome, cardio-facio-cutaneous syndrome, Legius syndrome, capillary malformation arterio-venous malformation syndrome, and SYNGAP1 autism. Due to their common underlying pathogenetic etiology, all these syndromes have significant phenotypic overlap of which one common feature include a predisposition to tumors, which may be benign or malignant. Together as a group, they represent one of the most common multiple congenital anomaly syndromes estimating to affect approximately one in 1000 individuals worldwide. The subcontinent of India represents one of the largest populations in the world, yet remains underserved from an aspect of clinical genetics services. In an effort to bridge this gap, the First International Conference on RASopathies and Neurofibromatoses in Asia: Identification and Advances of New Therapeutics was held in Kochi, Kerala, India. These proceedings chronicle this timely and topical international symposium directed at discussing the best practices and therapies for individuals with neurofibromatoses and RASopathies.

Non-ossifying fibroma: A RAS-MAPK driven benign bone neoplasm

Non‐ossifying fibroma (NOF) has been an intriguing entity since its first description. It is the most common bone tumour, is usually asymptomatic affecting children and adolescents, is composed of a heterogeneous cell population, and undergoes spontaneous regression after puberty. In a recent article in The Journal of Pathology, Baumhoer and colleagues demonstrate mutations activating the RAS‐MAPK pathway (KRAS, FGFR1 and NF1) in ∼80% of the tumours. Activation of the RAS‐MAPK pathway by somatic mutations is found in a plethora of tumour types, both benign and malignant, while germline mutations cause a wide range of syndromes collectively termed the RASopathies. Their findings indicate that NOF, for long thought to be reactive, should be considered a true neoplasm. Moreover, their data suggest that only a subset of cells in the lesion contain the mutation. A second cell population consisting of histiocytes and osteoclast‐like giant cells appears to be reactive. This intimate relation between WT and mutant cells is also frequently encountered in other benign and locally aggressive bone tumours and seems essential for tumourigenesis. The spontaneous regression remains enigmatic and it is tempting to speculate that pubertal hormonal signalling, especially increased oestrogen levels, affect the balance between mutant and WT cells. © 2019 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Clinical and mutation profile of pediatric patients with RASopathy-associated hypertrophic cardiomyopathy: results from a Chinese cohort

Background

The RASopathies are a class of developmental disorders caused by germline mutations in the RAS-mitogen-activated protein kinase (MAPK) pathway. Hypertrophic cardiomyopathy (HCM) has been frequently described in children with RASopathy, but only a minority of patients have received formal genotyping. The purpose of this study was to evaluate the genetic basis and clinical outcome of pediatric patients with RASopathy-associated HCM.

Methods

We retrospectively reviewed the mutation spectrum and clinical outcome of all the patients with RASopathy derived from 168 pediatric HCM cases referred to our institution between January 2012 and July 2018.

Results

A heterozygous missense mutation in one of known RASopathy genes was identified in 46 unrelated children with HCM. Mutations in the PTPN11 gene were the most prevalent (19/46); this was followed by mutations in RAF1 (11/46), KRAS (5/46), RIT1 (4/46), BRAF (3/46), SOS1 (2/46), HRAS (1/46), and SHOC2 (1/46). Moreover, two compound heterozygous missense mutations in the LZTR1 gene were identified in one patient with the Noonan syndrome phenotype and HCM. The median age at the diagnosis of HCM was 3.0 months (range 0 months to 8.1 years). Twenty-one of the patients had significant left ventricular outflow tract obstruction and 32 had concomitant congenital heart disease. Three patients with a mutation in exon 13 of the PTPN11 gene died of cardiac failure at the ages of 3.0, 3.5, and 6.0 months. The remaining 44 patients were alive after an average follow-up time of 3.9 years (0.5 to 17.1 years, median 2.9 years) from the initial diagnosis of HCM, including 5 patients with spontaneous regression of their cardiac hypertrophy.

Conclusions

RASopathy-associated HCM is a heterogeneous genetic condition characterized by early-onset cardiac hypertrophy and a high prevalence of co-existing congenital heart disease, which is most frequently related to specific mutations in the PTPN11 gene. Rapidly progressive HCM, resulting in an early death, is uncommon in RASopathy patients except those with specific mutations in exon 13 of the PTPN11 gene.

Papular nevus spilus syndrome: old and new aspects of a mosaic RASopathy

The co-existence of papular nevus spilus (PNS) and ipsilateral extracutaneous abnormalities involving peripheral nerves of the skin or muscles was originally described as "speckled lentiginous nevus syndrome". To avoid confusion with macular nevus spilus, the condition was recently re-named "papular nevus spilus syndrome". In addition to 14 published cases, we identified six new cases via a search of the worldwide literature. New diagnostic criteria are suggested: (1) presence of a PNS; (2) presence of a neurological or skeletal abnormality which is usually ipsilateral to the nevus; and (3) absence of a nevus sebaceus. According to current knowledge, PNS syndrome is a rather rarely occurring, sporadic disorder that can be considered to be part of a spectrum of mosaic RASopathies, which includes isolated PNS, isolated nevus sebaceus, PNS syndrome, Schimmelpenning syndrome, and phacomatosis pigmentokeratotica.

Is Schimmelpenning Syndrome Associated with Intracranial Tumors? A Case Report

Schimmelpenning syndrome is a rare, well-defined constellation of clinical phenotypes associated with the presence of nevus sebaceous and multisystem abnormalities most commonly manifested as cerebral, ocular, and skeletal defects [<xref ref-type="bibr" rid="ref1">1</xref>]. A single nucleotide mutation in the HRAS or KRAS genes resulting in genetic mosaicism is responsible for the clinical manifestations of this syndrome in the majority of cases. We report a case of an adolescent boy with Schimmelpenning syndrome with a multifocal pilocytic astrocytoma. No HRAS or KRAS gene mutations were noted in the tumor on genetic sequencing. However, glial tumors have been associated with genetic mutations of RAS upregulation, which may imply a common pathway.

Embryonal rhabdomyosarcoma in a patient with a germline CBL pathogenic variant

Germline pathogenic variants in CBL are associated with an autosomal dominant RASopathy and an increased risk for malignancies, particularly juvenile myelomonocytic leukemia. Herein, we describe a patient with clinical features of a Noonan-spectrum disorder who developed embryonal rhabdomyosarcoma of the bladder at age two years. Tumor analysis using the OncoKids^® cancer panel revealed a CBL pathogenic variant: NM_005188.3:c.1100A>C (p.Gln367Pro). Sanger sequencing of peripheral blood DNA confirmed a de novo heterozygous germline variant. This is the first report of embryonal rhabdomyosarcoma in association with a germline CBL pathogenic variant, further broadening the CBL cancer predisposition spectrum.

Mosaicism in Cutaneous Disorders

Genetic mosaicism arises when a zygote harbors two or more distinct genotypes, typically due to de novo, somatic mutation during embryogenesis. The clinical manifestations largely depend on the differentiation status of the mutated cell; earlier mutations target pluripotent cells and generate more widespread disease affecting multiple organ systems. If gonadal tissue is spared-as in somatic genomic mosaicism-the mutation and its effects are limited to the proband, whereas mosaicism also affecting the gametes, such as germline or gonosomal mosaicism, is transmissible. Mosaicism is easily appreciated in cutaneous disorders, as phenotypically distinct mutant cells often give rise to lesions in patterns determined by the affected cell type. Genetic investigation of cutaneous mosaic disorders has identified pathways central to disease pathogenesis, revealing novel therapeutic targets. In this review, we discuss examples of cutaneous mosaicism, approaches to gene discovery in these disorders, and insights into molecular pathobiology that have potential for clinical translation.

De Novo Missense Variants in TRAF7 Cause Developmental Delay, Congenital Anomalies, and Dysmorphic Features

TRAF7 is a multi-functional protein involved in diverse signaling pathways and cellular processes. The phenotypic consequence of germline TRAF7 variants remains unclear. Here we report missense variants in TRAF7 in seven unrelated individuals referred for clinical exome sequencing. The seven individuals share substantial phenotypic overlap, with developmental delay, congenital heart defects, limb and digital anomalies, and dysmorphic features emerging as key unifying features. The identified variants are de novo in six individuals and comprise four distinct missense changes, including a c.1964G>A (p.Arg655Gln) variant that is recurrent in four individuals. These variants affect evolutionarily conserved amino acids and are located in key functional domains. Gene-specific mutation rate analysis showed that the occurrence of the de novo variants in TRAF7 (p = 2.6 × 10^-3) and the recurrent de novo c.1964G>A (p.Arg655Gln) variant (p = 1.9 × 10^-8) in our exome cohort was unlikely to have occurred by chance. In vitro analyses of the observed TRAF7 mutations showed reduced ERK1/2 phosphorylation. Our findings suggest that missense mutations in TRAF7 are associated with a multisystem disorder and provide evidence of a role for TRAF7 in human development.

A review of craniofacial and dental findings of the RASopathies

OBJECTIVES

The RASopathies are a group of syndromes that have in common germline mutations in genes that encode components of the Ras/mitogen-activated protein kinase (MAPK) pathway and have been a focus of study to understand the role of this pathway in development and disease. These syndromes include Noonan syndrome (NS), Noonan syndrome with multiple lentigines (NSML or LEOPARD syndrome), neurofibromatosis type 1 (NF1), Costello syndrome (CS), cardio-facio-cutaneous (CFC) syndrome, neurofibromatosis type 1-like syndrome (NFLS or Legius syndrome) and capillary malformation-arteriovenous malformation syndrome (CM-AVM). These disorders affect multiple systems, including the craniofacial complex. Although the craniofacial features have been well described and can aid in clinical diagnosis, the dental phenotypes have not been analysed in detail for each of the RASopathies. In this review, we summarize the clinical features of the RASopathies, highlighting the reported craniofacial and dental findings.

METHODS

Review of the literature.

RESULTS

Each of the RASopathies reviewed, caused by mutations in genes that encode different proteins in the Ras pathway, have unique and overlapping craniofacial and dental characteristics.

CONCLUSIONS

Careful description of craniofacial and dental features of the RASopathies can provide information for dental clinicians treating these individuals and can also give insight into the role of Ras signalling in craniofacial development.

MAP2K2 mutation as a cause of cardio-facio-cutaneous syndrome in an infant with a severe and fatal course of the disease

Cardio-facio-cutaneous syndrome (CFCS), a rare congenital disorder of RASopathies, displays high phenotypic variability. Complications during pregnancy and in the perinatal period are commonly reported. Polyhydramnios is observed in over half of pregnancies and might occur with fetal macrocephaly, macrosomia, and/or heart defects. Premature birth is not uncommon and any complications like respiratory insufficiency, edema, and feeding difficulties are present and might delay accurate clinical diagnosis. Besides neonatal complications, CFCS newborns and later infants have distinctive dysmorphic features usually accompanied by neurological (hypotonia with motor delay, neurocognitive delay) findings. Also, heart defects usually present at birth. Herein, we present the case of a female baby born prematurely from a pregnancy complicated with polyhydramnios, presenting at birth with craniofacial features typical for RASopathies, heart defects, neurological abnormalities, and hyperkeratosis unusual for a neonatal period. Due to the presence of a heart defect and other complications related to premature birth, the course of the disease was severe with a fatal outcome at the age of 9 months. The RASopathy, particularly CFCS, clinical diagnosis was confirmed and de novo p.Phe57Ile mutation in MAP2K2 was identified.

NGS testing for cardiomyopathy: Utility of adding RASopathy-associated genes

RASopathies include a group of syndromes caused by pathogenic germline variants in RAS-MAPK pathway genes and typically present with facial dysmorphology, cardiovascular disease, and musculoskeletal anomalies. Recently, variants in RASopathy-associated genes have been reported in individuals with apparently nonsyndromic cardiomyopathy, suggesting that subtle features may be overlooked. To determine the utility and burden of adding RASopathy-associated genes to cardiomyopathy panels, we tested 11 RASopathy-associated genes by next-generation sequencing (NGS), including NGS-based copy number variant assessment, in 1,111 individuals referred for genetic testing for hypertrophic cardiomyopathy (HCM) or dilated cardiomyopathy (DCM). Disease-causing variants were identified in 0.6% (four of 692) of individuals with HCM, including three missense variants in the PTPN11, SOS1, and BRAF genes. Overall, 36 variants of uncertain significance (VUSs) were identified, averaging ∼3VUSs/100 cases. This study demonstrates that adding a subset of the RASopathy-associated genes to cardiomyopathy panels will increase clinical diagnoses without significantly increasing the number of VUSs/case.

Systemic lupus erythematosus in a patient with Noonan syndrome-like disorder with loose anagen hair 1: More than a chance association

Systemic lupus erythematosus (SLE) has been reported among patients with RASopathy. Five patients have been reported: three with SHOC2 variants, one with a PTPN11 variant, and one with a KRAS variant. SHOC2 variant might represent a relatively common predisposing factor for SLE among the RASopathy genes. However, the clinical details were only reported for two patients, while information on the remaining patient appeared only in a tabular format with minimal clinical description. Here, we report a patient with a SHOC2 variant and SLE. The proband was a 28-year-old male patient with intellectual disabilities, a short stature, dysmorphic facial features, and thin hair. He developed hypertrophic cardiomyopathy and afebrile generalized seizures at the ages of 7 and 18 years, respectively. At the age of 24 years, he presented with a 3-day history of intermittent fever accompanied by right chest pain and a malar butterfly rash. He fulfilled both the American College of Rheumatology (ACR) criteria and the Systemic Lupus International Collaborating Clinics (SLICC) criteria for SLE and was successfully treated with prednisolone. Medical exome sequencing identified a de novo SHOC2 variant (c.4A > G, p.S2G). The present report of a second patient who fulfills both the ACR criteria and the SLICC criteria of SLE. We suggest that the association between SHOC2 variant and SLE represents more than a chance association. In the event of fever of unknown origin in patients with constitutional SHOC2 pathogenic variant, SLE should be suspected.

ClinGen's RASopathy Expert Panel consensus methods for variant interpretation

Purpose

Standardized and accurate variant assessment is essential for effective medical care. To that end, Clinical Genome (ClinGen) Resource clinical domain working groups (CDWG) are systematically reviewing disease-associated genes for sufficient evidence to support disease causality and creating disease-specific specifications of ACMG-AMP guidelines for consistent and accurate variant classification.

Methods

The ClinGen RASopathy CDWG established an expert panel (EP) to curate gene information and generate gene and disease-specific specifications to ACMG-AMP variant classification framework. These specifications were tested by classifying 37 exemplar pathogenic variants plus an additional 66 variants in ClinVar distributed across nine RASopathy genes.

Results

RASopathy-related specifications were applied to sixteen ACMG-AMP criteria, with five also having adjustable strength with availability of additional evidence. Another five criteria were deemed not applicable. Key adjustments to minor allele frequency thresholds, multiple de novo occurrence events and/or segregation, and strength adjustments impacted 60% of variant classifications. Unpublished case-level data from participating laboratories impacted 45% of classifications supporting the need for data sharing.

Conclusions

RAS-specific ACMG-AMP specifications optimized the utility of available clinical evidence and Ras/MAPK pathway-specific characteristics to consistently classify RASopathy-associated variants. These specifications highlight how grouping genes by shared features promotes rapid multi-genic variant assessment without sacrificing specificity and accuracy.

Update on Genetic Conditions Affecting the Skin and the Kidneys

Genetic conditions affecting the skin and kidney are clinically and genetically heterogeneous, and target molecular components present in both organs. The molecular pathology involves defects of cell-matrix adhesion, metabolic or signaling pathways, as well as tumor suppressor genes. This article gives a clinically oriented overview of this group of disorders, highlighting entities which have been recently described, as well as the progress made in understanding well-known entities. The genetic bases as well as molecular cell biological mechanisms are described, with therapeutic applications.

A novel patient with an attenuated Costello syndrome phenotype due to an HRAS mutation affecting codon 146-Literature review and update

De novo germline mutations in HRAS cause Costello syndrome, with >95% of the mutations causing Costello syndrome affecting amino acid position 12 (p.Gly12) or 13 (p.Gly13). We report on a patient with de novo missense mutation causing an amino acid change at codon 146 of HRAS, c.436G > C:p.Ala146Pro, who presented with subtle dysmorphic features, failure to thrive, global developmental delay, and hypertrophic obstructive cardiomyopathy. Mutations affecting codon 146 are observed in <1% of patients with Costello syndrome. From literature search, there were only two other patients reported with mutations involving the same location. We summarized and updated their findings, and discussed evidence to show that these patients with less obvious signs of Costello syndrome may not necessarily run a more benign clinical course.

Case report: Left ventricular noncompaction cardiomyopathy and RASopathies

The following is a case report of 6 patients with Noonan syndrome (NS) and/or a related RASsopathy that also have evidence of left ventricular noncompaction cardiomyopathy (LVNC). Noonan syndrome,a type of RASopathy, is an autosomal dominant disorder that is typically associated with congenital heart defects and hypertrophic cardiomyopathy. There have been minimal reports of Noonan syndrome or other RASopathy and the association of LVNC. This report promulgates 6 nonrelated cases of Noonan syndrome or unspecified RASopathy and LVNC.

Craniosynostosis in patients with RASopathies: Accumulating clinical evidence for expanding the phenotype

RASopathies are phenotypically overlapping genetic disorders caused by dysregulation of the RAS/mitogen-activated protein kinase (MAPK) signaling pathway. RASopathies include Noonan syndrome, cardio-facio-cutaneous (CFC) syndrome, Costello syndrome, Neurofibromatosis type 1, Legius syndrome, Noonan syndrome with multiple lentigines, Noonan-like syndrome, hereditary gingival fibromatosis, and capillary malformation/arteriovenous malformation syndrome. Recently, six patients with craniosynostosis and Noonan syndrome involving KRAS mutations were described in a review, and a patient with craniosynostosis and Noonan syndrome involving a SHOC2 mutation has also been reported. Here, we describe patients with craniosynostosis and Noonan syndrome due to de novo mutations in PTPN11 and patients with craniosynostosis and CFC syndrome due to de novo mutations in BRAF or KRAS. All of these patients had cranial deformities in addition to the typical phenotypes of CFC syndrome and Noonan syndrome. In RASopathy, patients with cranial deformities, further assessments may be necessary to look for craniosynostosis. Future studies should attempt to elucidate the pathogenic mechanism responsible for craniosynostosis mediated by the RAS/MAPK signaling pathway.

De novo mutations in CBL causing early-onset paediatric moyamoya angiopathy

BACKGROUND

Moyamoya angiopathy (MMA) is characterised by a progressive stenosis of the terminal part of the internal carotid arteries and the development of abnormal collateral deep vessels. Its pathophysiology is unknown. MMA can be the sole manifestation of the disease (moyamoya disease) or be associated with various conditions (moyamoya syndrome) including some Mendelian diseases. We aimed to investigate the genetic basis of moyamoya using a whole exome sequencing (WES) approach conducted in sporadic cases without any overt symptom suggestive of a known Mendelian moyamoya syndrome.

METHODS

A WES was performed in four unrelated early-onset moyamoya sporadic cases and their parents (trios). Exome data were analysed under dominant de novo, autosomal recessive and X-linked hypotheses. A panel of 17 additional sporadic cases with early-onset moyamoya was available for mutation recurrence analysis.

RESULTS

We identified two germline de novo mutations in CBL in two out of the four trio probands, two girls presenting with an infancy-onset severe MMA. Both mutations were predicted to alter the ubiquitin ligase activity of the CBL protein that acts as a negative regulator of the RAS pathway. These two germline CBL mutations have previously been described in association with a developmental Noonan-like syndrome and susceptibility to juvenile myelomonocytic leukaemia (JMML). Notably, the two mutated girls never developed JMML and presented only subtle signs of RASopathy that did not lead to evoke this diagnosis during follow-up.

CONCLUSIONS

These data suggest that CBL gene screening should be considered in early-onset moyamoya, even in the absence of obvious signs of RASopathy.

Neurofibromatosis type 1 (NF1) gene: Beyond café au lait spots and dermal neurofibromas

Neurofibromatosis 1 (NF1) occurs in 1:2000 births. The main diagnostic signs are visible on the skin, and this opens several interesting aspects for dermatological point of view. The NF1 syndrome is caused by mutations in the NF1 gene which encodes the tumor suppressor protein neurofibromin. Neurofibromin functions as a Ras-GTPase-activating protein (RasGAP), and NF1 mutations lead to overactivation of the Ras signalling pathway. The NF1 gene and neurofibromin have intriguing functions in keratinocytes and melanocytes. Neurofibromin regulates melanin synthesis and keratinocyte differentiation in a currently unknown manner. The NF1 gene has also an important but poorly understood role in tumorigenesis and cancer. Compared to the general population, NF1 patients have a fivefold risk for cancer and a more than 2000-fold risk for neurogenic malignancies. Mutations of the NF1 gene are common in numerous cancer types in patients without NF1, and this suggests a more general role for the NF1 gene in oncogenesis. In melanoma, NF1 mutations seem to drive tumorigenesis and contribute to drug resistance. In this article, we review the literature on neurofibromin with special attention to keratinocytes, melanocytes, NF1-related tumors and melanoma.

Cardiofacio-cutaneous syndrome: Classical presentation of a rare genodermatoses

Cardiofacio-cutaneous syndrome is a rare genodermatoses with multiple congenital anomalies (MCA) and mental retardation. Although various mutations have been described, the diagnosis can be made clinically based on constellation of symptoms. Herein, we report a classical case with typical craniofacial features and atrial septal defect.

Expansion of the RASopathies

The Ras/mitogen activated protein kinase (MAPK) pathway is essential in the regulation of cell cycle, differentiation, growth, cell senescence and apoptosis, all of which are critical to normal development. A class of neurodevelopmental disorders, RASopathies, is caused by germline mutations in genes of the Ras/MAPK pathway. Through the use of whole exome sequencing and targeted sequencing of selected genes in cohorts of panel-negative RASopathy patients, several new genes have been identified. These include: RIT1, SOS2, RASA2, RRAS and SYNGAP1, that likely represent new, albeit rare, causative RASopathy genes. In addition, A2ML1, LZTR1, MYST4, SPRY1 and MAP3K8 may represent new rare genes for RASopathies, but, additional functional studies regarding the mutations are warranted. In addition, recent reports have demonstrated that chromosomal copy number variation in regions encompassing Ras/MAPK pathway genes may be a novel pathogenetic mechanism expanding the RASopathies.

The neurofibromin recruitment factor Spred1 binds to the GAP related domain without affecting Ras inactivation

Neurofibromatosis type 1 (NF1) and Legius syndrome are related diseases with partially overlapping symptoms caused by alterations of the tumor suppressor genes NF1 (encoding the protein neurofibromin) and SPRED1 (encoding sprouty-related, EVH1 domain-containing protein 1, Spred1), respectively. Both proteins are negative regulators of Ras/MAPK signaling with neurofibromin functioning as a Ras-specific GTPase activating protein (GAP) and Spred1 acting on hitherto undefined components of the pathway. Importantly, neurofibromin has been identified as a key protein in the development of cancer, as it is genetically altered in a large number of sporadic human malignancies unrelated to NF1. Spred1 has previously been demonstrated to interact with neurofibromin via its N-terminal Ena/VASP Homology 1 (EVH1) domain and to mediate membrane translocation of its target dependent on its C-terminal Sprouty domain. However, the region of neurofibromin required for the interaction with Spred1 has remained unclear. Here we show that the EVH1 domain of Spred1 binds to the noncatalytic (GAPex) portion of the GAP-related domain (GRD) of neurofibromin. Binding is compatible with simultaneous binding of Ras and does not interfere with GAP activity. Our study points to a potential targeting function of the GAPex subdomain of neurofibromin that is present in all known canonical RasGAPs.

Cell type-specific roles of RAS-MAPK signaling in learning and memory: Implications in neurodevelopmental disorders

The RAS-mitogen-activated protein kinase (MAPK) signaling pathway plays critical roles in brain function, including learning and memory. Mutations of molecules in the RAS-MAPK pathway are associated with a group of disorders called RASopathies, which include Noonan syndrome, neurofibromatosis type 1, Costello syndrome, Noonan syndrome with multiple lentigines, Legius syndrome, and cardio-facio-cutaneous syndrome. RASopathies share certain clinical symptoms, including craniofacial abnormalities, heart defects, delayed growth, and cognitive deficits such as learning disabilities, while each individual syndrome also displays unique phenotypes. Recent studies using mouse models of RASopathies showed that each disorder may have a distinct molecular and cellular etiology depending on the cellular specificity of the mutated molecules. Here, we review the cell-type specific roles of the regulators of the RAS-MAPK pathway in cognitive function (learning and memory) and their contribution to the development of RASopathies. We also discussed recent technical advances in analyzing cell type-specific transcriptomes and proteomes in the nervous system. Understanding specific mechanisms for these similar but distinct disorders would facilitate the development of mechanism-based individualized treatment for RASopathies.

How necessary is to analyze PTPN11 gene in fetuses with first trimester cystic hygroma and normal karyotype?

Cystic hygroma (CH) is a vascular-lymphatic malformation and can occur either as an isolated finding or as a part of a syndrome. The incidence of CH is about 1:1000-1:6000 births. Ultrasonographic diagnosis of CH is usually obtained in the first trimester, and the lesion can appear in septated or non-septated forms. Increased nuchal translucency and CH have been associated with a wide range of structural and genetic abnormalities. Most of CHs are associated with a number of chromosomal abnormalities especially Trisomy 21, 13, 18 and Turner syndrome. Besides, the associations between CH and non-chromosomal syndromes were also reported and Noonan Syndrome (NS) is one of the leading causes. Approximately 50% of NS cases are caused by mutations in the PTPN11 gene. A novel PTPN11 mutation defined in two separate fetuses with CH and associated with NS phenotype is being reported here.

The Fourth International Symposium on Genetic Disorders of the Ras/MAPK pathway

The RASopathies are a group of disorders due to variations of genes associated with the Ras/MAPK pathway. Some of the RASopathies include neurofibromatosis type 1 (NF1), Noonan syndrome, Noonan syndrome with multiple lentigines, cardiofaciocutaneous (CFC) syndrome, Costello syndrome, Legius syndrome, and capillary malformation-arteriovenous malformation (CM-AVM) syndrome. In combination, the RASopathies are a frequent group of genetic disorders. This report summarizes the proceedings of the 4th International Symposium on Genetic Disorders of the Ras/MAPK pathway and highlights gaps in the field. © 2016 Wiley Periodicals, Inc.

Craniosynostosis and Noonan syndrome with KRAS mutations: Expanding the phenotype with a case report and review of the literature

Noonan syndrome (NS) is a multiple congenital anomaly syndrome caused by germline mutations in genes coding for components of the Ras-mitogen-activated protein kinase (RAS-MAPK) pathway. Features include short stature, characteristic facies, congenital heart anomalies, and developmental delay. While there is considerable clinical heterogeneity in NS, craniosynostosis is not a common feature of the condition. Here, we report on a 2 month-old girl with Noonan syndrome associated with a de novo mutation in KRAS (p.P34Q) and premature closure of the sagittal suture. We provide a review of the literature of germline KRAS mutations and find that approximately 10% of published cases have craniosynostosis. Our findings expand on the NS phenotype and suggest that germline mutations in the KRAS gene are causally involved in craniosynostosis, supporting the role of the RAS-MAPK pathway as a mediator of aberrant bone growth in cranial sutures. The inclusion of craniosynostosis as a possible phenotype in KRAS-associated Noonan Syndrome has implications in the differential diagnosis and surgical management of individuals with craniosynostosis.

Mutations in RIT1 cause Noonan syndrome - additional functional evidence and expanding the clinical phenotype

RASopathies are a clinically heterogeneous group of conditions caused by mutations in 1 of 16 proteins in the RAS-mitogen activated protein kinase (RAS-MAPK) pathway. Recently, mutations in RIT1 were identified as a novel cause for Noonan syndrome. Here we provide additional functional evidence for a causal role of RIT1 mutations and expand the associated phenotypic spectrum. We identified two de novo missense variants p.Met90Ile and p.Ala57Gly. Both variants resulted in increased MEK-ERK signaling compared to wild-type, underscoring gain-of-function as the primary functional mechanism. Introduction of p.Met90Ile and p.Ala57Gly into zebrafish embryos reproduced not only aspects of the human phenotype but also revealed abnormalities of eye development, emphasizing the importance of RIT1 for spatial and temporal organization of the growing organism. In addition, we observed severe lymphedema of the lower extremity and genitalia in one patient. We provide additional evidence for a causal relationship between pathogenic mutations in RIT1, increased RAS-MAPK/MEK-ERK signaling and the clinical phenotype. The mutant RIT1 protein may possess reduced GTPase activity or a diminished ability to interact with cellular GTPase activating proteins; however the precise mechanism remains unknown. The phenotypic spectrum is likely to expand and includes lymphedema of the lower extremities in addition to nuchal hygroma.

Fatal congenital hypertrophic cardiomyopathy and a pancreatic nodule morphologically identical to focal lesion of congenital hyperinsulinism in an infant with costello syndrome: case report and review of the literature

Costello syndrome is characterized by constitutional mutations in the proto-oncogene HRAS, causing dysmorphic features, multiple cardiac problems, intellectual disability, and an increased risk of neoplasia. We report a male infant with dysmorphic features, born prematurely at 32 weeks, who, during his 3-month life span, had an unusually severe and ultimately fatal manifestation of hypertrophic cardiomyopathy and hyperinsulinemic hypoglycemia. Molecular studies in this patient demonstrated the uncommon Q22K mutation in the HRAS gene, diagnostic of Costello syndrome. The major autopsy findings revealed hypertrophic cardiomyopathy, congenital myopathy, and a 1.4-cm pancreatic nodule that was positive for insulin expression and morphologically identical to a focal lesion of congenital hyperinsulinism. Sequencing of KCNJ11 and ABCC8, the 2 most commonly mutated genes in focal lesion of congenital hyperinsulinism, revealed no mutations. While hyperinsulinism is a recognized feature of RASopathies, a focal proliferation of endocrine cells similar to a focal lesion of hyperinsulinism is a novel pathologic finding in Costello syndrome.

A germline MTOR mutation in Aboriginal Australian siblings with intellectual disability, dysmorphism, macrocephaly, and small thoraces

We report on three Aboriginal Australian siblings with a unique phenotype which overlaps with known megalencephaly syndromes and RASopathies, including Costello syndrome. A gain-of-function mutation in MTOR was identified and represents the first reported human condition due to a germline, familial MTOR mutation. We describe the findings in this family to highlight that (i) the path to determination of pathogenicity was confounded by the lack of genomic reference data for Australian Aboriginals and that (ii) the disease biology, functional analyses in this family, and studies on the tuberous sclerosis complex support consideration of an mTOR inhibitor as a therapeutic agent.

Rapidly progressive hypertrophic cardiomyopathy in an infant with Noonan syndrome with multiple lentigines: palliative treatment with a rapamycin analog

Noonan syndrome with multiple lentigines (NSML) frequently manifests with hypertrophic cardiomyopathy (HCM). Recently, it was demonstrated that mTOR inhibition reverses HCM in NSML mice. We report for the first time on the effects of treatment with a rapamycin analog in an infant with LS and malignant HCM. In the boy, progressive HCM was diagnosed during the first week of life and a diagnosis of NSML was established at age 20 weeks by showing a heterozygous Q510E mutation in PTPN11. Immunoblotting with antibodies against pERK, pAkt, and pS6RP in fibroblasts demonstrated enhanced Akt/mTOR pathway activity. Because of the patient's critical condition, everolimus therapy was started at age 24 weeks and continued until heart transplantation at age 36 weeks. Prior to surgery, heart failure improved from NYHA stage IV to II and brain natriuretic peptide values decreased from 9,600 to <1,000 pg/ml, but no reversal of cardiac hypertrophy was observed. Examination of the explanted heart revealed severe hypertrophy and myofiber disarray with extensive perivascular fibrosis. These findings provide evidence that Akt/mTOR activity is enhanced in NSML with HCM and suggest that rapamycin treatment could principally be feasible for infantile NSML. The preliminary experiences made in this single patient indicate that therapy should start early to prevent irreversible cardiac remodelling.

Recent developments in neurofibromatoses and RASopathies: management, diagnosis and current and future therapeutic avenues

Neurofibromatosis type 1 (NF1) was the first RASopathy and is now one of many RASopathies that are caused by germline mutations in genes that encode components of the Ras/mitogen-activated protein kinase (MAPK) pathway. Their common underlying pathogenetic etiology causes significant overlap in phenotypic features which includes craniofacial dysmorphology, cardiac, cutaneous, musculoskeletal, GI and ocular abnormalities, and a predisposition to cancer. The proceedings from the symposium "Recent Developments in Neurofibromatoses (NF) and RASopathies: Management, Diagnosis and Current and Future Therapeutic Avenues" chronicle this timely and topical clinical translational research symposium. The overarching goal was to bring together clinicians, basic scientists, physician-scientists, advocate leaders, trainees, students and individuals with Ras pathway syndromes to discuss the most state-of-the-art basic science and clinical issues in an effort to spark collaborations directed towards the best practices and therapies for individuals with RASopathies.

Hydrops, fetal pleural effusions and chylothorax in three patients with CBL mutations

Fetal hydrops, fetal pleural effusions, hydrothorax, and chylothorax, may be associated with various genetic disorders, in particular with the Noonan, cardio-facio-cutaneous and Costello syndromes. These syndromes, collectively called RASopathies, are caused by mutations in the RAS/MAPK pathway, which is known to play a major role in lymphangiogenesis. Recently, germline mutations in the Casitas B-cell lymphoma (CBL) gene were reported in 25 patients and of these, 20 had juvenile myelomonocytic leukemia (JMML). The disorder was named "CBL syndrome" or "Noonan syndrome-like disorder with or without juvenile myelomonocytic leukemia" (NSLL). To date, prenatal abnormalities have not been reported and it is still debated whether the CBL syndrome falls into the category of a RASopathy, or represents a different entity. Here we report on three unrelated patients with CBL mutations manifesting with hydrops fetalis, fetal pleural effusions and/or congenital hydro-/chylothorax. Our findings further connect the CBL syndrome with the RASopathies.

Cardio-facio-cutaneous syndrome: clinical features, diagnosis, and management guidelines

Cardio-facio-cutaneous syndrome (CFC) is one of the RASopathies that bears many clinical features in common with the other syndromes in this group, most notably Noonan syndrome and Costello syndrome. CFC is genetically heterogeneous and caused by gene mutations in the Ras/mitogen-activated protein kinase pathway. The major features of CFC include characteristic craniofacial dysmorphology, congenital heart disease, dermatologic abnormalities, growth retardation, and intellectual disability. It is essential that this condition be differentiated from other RASopathies, as a correct diagnosis is important for appropriate medical management and determining recurrence risk. Children and adults with CFC require multidisciplinary care from specialists, and the need for comprehensive management has been apparent to families and health care professionals caring for affected individuals. To address this need, CFC International, a nonprofit family support organization that provides a forum for information, support, and facilitation of research in basic medical and social issues affecting individuals with CFC, organized a consensus conference. Experts in multiple medical specialties provided clinical management guidelines for pediatricians and other care providers. These guidelines will assist in an accurate diagnosis of individuals with CFC, provide best practice recommendations, and facilitate long-term medical care.

Perinatal features of the RASopathies: Noonan syndrome, cardiofaciocutaneous syndrome and Costello syndrome

The RASopathies are a family of developmental disorders caused by heritable defects of the RAS/MAPK signaling pathway. While the postnatal presentation of this group of disorders is well known, the prenatal and neonatal findings are less widely recognized. We report on the perinatal presentation of 10 patients with Noonan syndrome (NS), nine with Cardiofaciocutaneous syndrome (CFCS) and three with Costello syndrome (CS), in conjunction with the results of a comprehensive literature review. The majority of perinatal findings in NS, CS, and CFCS are shared: polyhydramnios; prematurity; lymphatic dysplasia; macrosomia; relative macrocephaly; respiratory distress; hypotonia, as well as cardiac and renal anomalies. In contrast, fetal arrhythmia and neonatal hypoglycemia are relatively specific to CS. NS, CS, and CFCS should all be considered as a possible diagnosis in pregnancies with a normal karyotype and ultrasound findings of a RASopathy. Recognition of the common perinatal findings of these disorders should facilitate both their prenatal and neonatal diagnosis.

Clinical and Molecular Findings of Tunisian Patients with RASopathies

Noonan syndrome (NS) and related disorders, which are now summarized under the term RASopathies, are caused by germline mutations in genes encoding protein components of the Ras/mitogen-activated protein kinase pathway. In this study, we evaluated the clinical and molecular spectrum of 21 Tunisian patients, recruited by a cardiology unit, for whom RASopathy diagnosis was suspected by clinical geneticists. Overall, 19 patients had a clinical diagnosis of NS and 2 were classified as having Cardiofaciocutaneous (CFC) syndrome. In 52% (n = 11) of patients, a RASopathy has been molecularly confirmed. Mutations in PTPN11 and SOS1 genes were found in patients with diagnosis of NS and BRAF gene mutations in patients with CFC syndrome. As reported from other cohorts, mutations in exons 3 and 8 of the PTPN11 gene predominated in Tunisian NS patients. A very uncommon PTPN11 mutation c.5C>T (p.T2I), the functional consequences of which have so far remained unclear, was identified in one patient. As biased by the mode of recruitment, all patients included in this study had a congenital heart defect, with pulmonary valve stenosis being the most frequent one. Short stature and developmental abnormalities were present in mutation-positive cases. This is the first molecular study in patients from southern Tunisia with RASopathy diagnosis.

Rare copy number variations containing genes involved in RASopathies: deletion of SHOC2 and duplication of PTPN11

BACKGROUND

RASopathies are a group of disorders related to Noonan syndrome that with dysregulated RAS-mitogen-activated protein kinase (MAPK) signaling pathway. Noonan syndrome (NS, OMIM# 163950) is a both phenotypically and genotypically variable disorder. We and other researchers have demonstrated that copy number variations underlie a small percentage of patients with RASopathies.

RESULTS

In a cohort of 12 clinically characterized patients with congenital heart defect (CHD) and features suggestive of Noonan syndrome or Noonan like syndrome without known causative gene mutation, we performed an Illumina SNP-array analysis to identify the pathogenic copy number variations (Human660W-Quad Chip, Beadstation Scanner and GenomeStudio V2011 software). We identifed two rare copy number variations harboring genes involved in RAS- MAPK signaling pathway of RASopathy. One is a 24 Mb duplication of 12q24.1-24.3 containing PTPN11 and the other is a 183 kb deletion of 10q25.2 including SHOC2. The SNP-array results were further validated by quantitative PCR (qPCR). This is might be the first report suggesting that haploinsufficiency of SHOC2 can result in a RASopathy-like phenotype.

CONCLUSIONS

Our findings provide additional support that copy number variations containing disease-causing genes of RAS/MAPK pathway play a minor role in RASopathies or related disorders. We recommend the use of microarrays in Noonan syndrome like patients without identified mutations in the causative genes.

Craniofacial and dental development in Costello syndrome

Costello syndrome (CS) is a RASopathy characterized by a wide range of cardiac, musculoskeletal, dermatological, and developmental abnormalities. The RASopathies are defined as a group of syndromes caused by activated Ras/mitogen-activated protein kinase (MAPK) signaling. Specifically, CS is caused by activating mutations in HRAS. Although receptor tyrosine kinase (RTK) signaling, which is upstream of Ras/MAPK, is known to play a critical role in craniofacial and dental development, the craniofacial and dental features of CS have not been systematically defined in a large group of individuals. In order to address this gap in our understanding and fully characterize the CS phenotype, we evaluated the craniofacial and dental phenotype in a large cohort (n = 41) of CS individuals. We confirmed that the craniofacial features common in CS include macrocephaly, bitemporal narrowing, convex facial profile, full cheeks, and large mouth. Additionally, CS patients have a characteristic dental phenotype that includes malocclusion with anterior open bite and posterior crossbite, enamel hypo-mineralization, delayed tooth development and eruption, gingival hyperplasia, thickening of the alveolar ridge, and high palate. Comparison of the craniofacial and dental phenotype in CS with other RASopathies, such as cardio-facio-cutaneous syndrome (CFC), provides insight into the complexities of Ras/MAPK signaling in human craniofacial and dental development.

Contributions of intrinsic mutation rate and selfish selection to levels of de novo HRAS mutations in the paternal germline

The RAS proto-oncogene Harvey rat sarcoma viral oncogene homolog (HRAS) encodes a small GTPase that transduces signals from cell surface receptors to intracellular effectors to control cellular behavior. Although somatic HRAS mutations have been described in many cancers, germline mutations cause Costello syndrome (CS), a congenital disorder associated with predisposition to malignancy. Based on the epidemiology of CS and the occurrence of HRAS mutations in spermatocytic seminoma, we proposed that activating HRAS mutations become enriched in sperm through a process akin to tumorigenesis, termed selfish spermatogonial selection. To test this hypothesis, we quantified the levels, in blood and sperm samples, of HRAS mutations at the p.G12 codon and compared the results to changes at the p.A11 codon, at which activating mutations do not occur. The data strongly support the role of selection in determining HRAS mutation levels in sperm, and hence the occurrence of CS, but we also found differences from the mutation pattern in tumorigenesis. First, the relative prevalence of mutations in sperm correlates weakly with their in vitro activating properties and occurrence in cancers. Second, specific tandem base substitutions (predominantly GC>TT/AA) occur in sperm but not in cancers; genomewide analysis showed that this same mutation is also overrepresented in constitutional pathogenic and polymorphic variants, suggesting a heightened vulnerability to these mutations in the germline. We developed a statistical model to show how both intrinsic mutation rate and selfish selection contribute to the mutational burden borne by the paternal germline.

Deletion of MAP2K2/MEK2: a novel mechanism for a RASopathy?

RASopathies are a class of genetic syndromes caused by germline mutations in genes encoding Ras/mitogen-activated protein kinase (Ras/MAPK) pathway components. Cardio-facio-cutaneous (CFC) syndrome is a RASopathy characterized by distinctive craniofacial features, skin and hair abnormalities, and congenital heart defects caused by activating mutations of BRAF, MEK1, MEK2, and KRAS. We define the phenotype of seven patients with de novo deletions of chromosome 19p13.3 including MEK2; they present with a distinct phenotype but have overlapping features with CFC syndrome. Phenotypic features of all seven patients include tall forehead, thick nasal tip, underdeveloped cheekbones, long midface, sinuous upper vermilion border, tall chin, angular jaw, and facial asymmetry. Patients also have developmental delay, hypotonia, heart abnormalities, failure to thrive, obstructive sleep apnea, gastroesophageal reflux and integument abnormalities. Analysis of epidermal growth factor-stimulated fibroblasts revealed that P-MEK1/2 was ∼50% less abundant in cells carrying the MEK2 deletion compared to the control. Significant differences in total MEK2 and Sprouty1 abundance were also observed. Our cohort of seven individuals with MEK2 deletions has overlapping features associated with RASopathies. This is the first report suggesting that, in addition to activating mutations, MEK2 haploinsufficiency can lead to dysregulation of the MAPK pathway.