Including Noonan Syndrome Research Articles

Clinical features and molecular genetics of patients with RASopathies: expanding the phenotype with rare genes and novel variants.

In this study, we described rare clinical manifestations and detected three novel variants in NF1, BRAF, and RIT1 genes. We propose that NGS technology enables the detection of variants in rare genes responsible for the etiology of RASopathies. The study, therefore, not only contributes to the existing literature but also expands the spectrum of genotype and phenotype of RASopathies. •RASopathies are a group of disorders caused by germline variants in genes involved in the Ras/mitogen-activated protein kinase (RAS/MAPK) pathway. •These disorders, including Noonan syndrome (NS), Cardiofaciocutaneous syndrome (CFC), Costello syndrome (CS), Legius syndrome, and Neurofibromatosis type 1 (NF1), share overlapping clinical features due to RAS/MAPK dysfunction. Molecular diagnosis of RASopathies is crucial for understanding the genetic basis and guiding clinical management, although the phenotype-genotype relationships remain incompletely defined. •This study provides new insights into the molecular and clinical characteristics of RASopathies by examining 149 patients from 146 families, with a focus on the genetic variants found in 24 RASopathy-related genes. Three novel variants were identified in the RIT1, BRAF, and NF1 genes, expanding the genetic spectrum of RASopathies. •Additionally, rare clinical findings, such as lymphangioma circumscriptum and corpus callosum thickness, were reported in patients with PTPN11 and SOS1 gene variations, respectively. These observations contribute new phenotypic data to the existing body of knowledge.

Irritability in Children with Rasopathies, Insights into Emotional Dysregulation and Social Skills Impairments.

Rasopathies, including Noonan Syndrome (NS) and Neurofibromatosis type 1 (NF1), are developmental disorders caused by germline mutations in genes of the RAS/mitogen-activated protein kinase pathway (RAS-MAPK). This study investigates irritability, a highly prevalent transdiagnostic construct, in children with Rasopathies and the impact of Rasopathy status on the associations between irritability, emotional dysregulation-related disorders, and social skills impairments. The sample comprise 174 children aged 4-17 (age mean = 9.49; 98 females), including 113 children with Rasopathies (NS n = 85, NF1 n = 28) and 61 age-sex-matched typically developed (TD) children. We used parent questionnaires (CBCL, SRS) to assess irritability, symptoms of ADHD, defiance, anxiety/depression, and social skills impairments while controlling for cognitive measures (IQ). Children with Rasopathies exhibited higher irritability than TD children (mean difference = 1.09; p < 0.001). Children with NS showed a weaker association between irritability and ADHD symptoms compared to TD children (p = .032, ηp 2 = .03) and a stronger association between irritability and social skills impairments compared to both TD (p = .033, ηp 2 = .03), and NF1 groups (p = .009, ηp 2 = .06). We present novel and clinically significant findings showing high irritability in children with Rasopathies. Our study provides syndrome-specific results, suggesting differences in the mechanisms involved in irritability, ADHD, and social processes in children with NS and NF1. In essence, children with Rasopathies showed a highly irritable profile associated with ADHD symptoms and social skills impairments, with a significantly stronger association between irritability and social processes in NS. Our results suggest that developing prevention and treatments targeting irritability can distinctly affect the trajectories of neurodevelopmental disorders in children with Rasopathies.

Abstract PR05: The role of the RAS GTPase RIT1 in RASopathies and cancer

Abstract RAS oncoproteins are drivers of tumor initiation and progression and therapies targeting these directly or their downstream pathways have resulted in unprecedented clinical benefit in cancer. However, recent advances in genomic medicine have revealed that many of the known RAS oncoproteins and cancer-associated mutations are also involved in the pathogenesis of a group of congenital disorders termed RASopathies. Our research is aimed at understanding the role of these oncoproteins at the biochemical and signaling level and we develop novel mouse models that allow us to study RAS oncoproteins in the context of cancer and genetic syndromes. Our recent work has focused on the non-classical RAS protein RIT1, a poorly understood GTPase expressed in most tissues. Pathogenic variants in RIT1 are found somatically in some cancers, such as lung and bladder adenocarcinoma, myeloid leukemias, and in the germline of individuals with Noonan syndrome, the most common RASopathy. Our lab recently demonstrated that, in contrast to classical RAS proteins, RIT1 appears to be mostly regulated through proteasomal degradation by interacting with a complex formed by the substrate adaptor protein LZTR1 and the RING E3 Ubiquitin Ligase Cullin3. We found that this complex is conserved in lower organisms and is necessary for the proper regulation of RIT1 protein levels. In addition, we have also found that RIT1 binds directly to the spindle assembly checkpoint protein MAD2 and its dysregulation leads to increased mitotic length and aneuploidy. Taking advantage of genetically-engineered mice, we have also generated models for RIT1-driven disorders, including Noonan syndrome, lung cancer, and leukemia. Finally, we have recently investigated the mechanisms that underlie RIT1-dependent RAF-MEK-ERK activation and proposed novel therapies that could be used for Noonan syndrome and other cancers. Overall, our work provides novel insights into the regulation, function, and pathogenesis of the RAS-like protein RIT1 Citation Format: Pau Castel. The role of the RAS GTPase RIT1 in RASopathies and cancer [abstract]. In: Proceedings of the AACR Special Conference: Targeting RAS; 2023 Mar 5-8; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Res 2023;21(5_Suppl):Abstract nr PR05.

Prenatal Diagnosis of Euploid Increased Nuchal Translucency on Fetal Ultrasound (II): RASopathy Disorders - Prenatal Ultrasound Findings and Genotype-phenotype Correlations.

Prenatal diagnosis of euploid increased nuchal translucency (NT) remains a challenge to obstetricians and genetic counselors, although increased euploid NT at prenatal diagnosis can be associated with a favorable outcome. Prenatal diagnosis of euploid increased NT should include a differential diagnosis of pathogenetic copy number variants and RASopathy disorders (RDs) including Noonan syndrome. Therefore, chromosomal microarray analysis, whole-exome sequencing, RASopathy-disorder testing, and protein-tyrosine phosphatase nonreceptor type 11 gene testing may be necessary under such a circumstance. In this report, a comprehensive review of RDs with its prenatal ultrasound findings and genotype-phenotype correlations is presented.

Modeling (not so) rare developmental disorders associated with mutations in the protein-tyrosine phosphatase SHP2.

Src homology region 2 (SH2)-containing protein tyrosine phosphatase 2 (SHP2) is a highly conserved protein tyrosine phosphatase (PTP), which is encoded by PTPN11 and is indispensable during embryonic development. Mutations in PTPN11 in human patients cause aberrant signaling of SHP2, resulting in multiple rare hereditary diseases, including Noonan Syndrome (NS), Noonan Syndrome with Multiple Lentigines (NSML), Juvenile Myelomonocytic Leukemia (JMML) and Metachondromatosis (MC). Somatic mutations in PTPN11 have been found to cause cancer. Here, we focus on the role of SHP2 variants in rare diseases and advances in the understanding of its pathogenesis using model systems.

OR18-5 A Prospective Clinical Trial of Vosoritide in Selected Genetic Causes of Short Stature

Abstract Objectives Vosoritide is a C-type natriuretic peptide analog which binds its receptor on chondrocytes, leading to increased chondrocyte proliferation and differentiation via its inhibition of the ERK1/2-MAPK pathway. It was recently approved for increasing linear growth in children with achondroplasia. Our study aims to assess the safety and efficacy of vosoritide in children with genetic mutations in 6 categories: hypochondroplasia, Rasopathies (including Noonan syndrome), aggrecan deficiency, carriers of heterozygous NPR2 mutations, CNP deficiency, and SHOX deficiency. Methods This is a prospective, Phase II study with a goal N of 35 subjects. All subjects must have a documented genetic mutation in one of the 6 categories, be prepubertal between the ages of 3 and 11 for boys and 3 and 10 for girls, and have a height &amp;lt; -2.25 SD. Subjects are followed for a 6-month observation period to establish a baseline annualized growth velocity (AGV) and then receive daily subcutaneous vosoritide (15 mcg/kg/day) for 12 months. The primary outcomes are rate of AEs and change in AGV from baseline. Pharmacokinetic studies and pharmacodynamic studies, using cGMP production as a pharmacodynamic marker, are completed at Day 1 and Months 6 and 12. Results To date, 27 subjects have enrolled in the trial (20 hypochondroplasia, 3 Noonan, 2 NPR2, 2 Aggrecan). Median baseline height is -3.1 SD (IQR -3.6, -2.6). 14 subjects have initiated on vosoritide, and 10 completed 6 months of therapy. Median increase in AGV was 3.9 cm/yr (IQR 2.2, 4.6). The two subjects with NPR2 mutations had increased AGVs of 4.4 and 9.2 cm/yr. The two subjects with Noonan syndrome had an increase in AGV of 7.5 and 3.3 cm/yr. One subject with Noonan syndrome, a 4-year-old male, had previously been treated with growth hormone (GH) for 2 years. His AGV was 6.7 cm/yr while on GH, 4.1 cm/yr during the 6-month observation period, and 11.6 cm/year during the first 6 months of vosoritide treatment. There were no serious adverse events related to vosoritide treatment. One subject had a brief episode of syncope with her first injection which self-resolved, and she continued on therapy with no further incidents. PK parameters were similar to previously published parameters for vosoritide in children with achondroplasia. In preliminary data, vosoritide Cmax and AUC correlated strongly with peak increase in cGMP (r=0.70, p=0.01;r=0.84, p&amp;lt;0.01, respectively) but not with increase in AGV (r=0.35, p=0.32). Conclusions This is the first clinical trial of vosoritide for children with genetic short stature who do not have achondroplasia. Vosoritide treatment may work as a precision therapy to improve growth in multiple genetic conditions which interact with the ERK1/2-MAPK pathway. Presentation: Monday, June 13, 2022 12:00 p.m. - 12:15 p.m.

Prenatal Diagnosis of Euploid Increased Nuchal Translucency on Fetal Ultrasound (I): Noonan Syndrome: Prenatal Diagnosis and Genetic Testing.

Prenatal diagnosis of euploid increased nuchal translucency (NT) remains a challenge to obstetricians and genetic counselors although increased euploid NT at prenatal diagnosis can be associated with a favorable outcome. Prenatal diagnosis of euploid increased NT should include a differential diagnosis of pathogenetic copy number variants and RASopathy disorders (RDs) including Noonan syndrome (NS). Therefore, chromosomal microarray analysis, whole-exome sequencing, RD testing, and protein-tyrosine phosphatase, nonreceptor type 11 (PTPN11) gene testing may be necessary under such a circumstance. In this report, a comprehensive review of NS with its prenatal diagnosis and genetic testing is presented.

S3465 Protein-Losing Enteropathy Associated With SHOC2 Gene Mutation in Noonan-Like Syndrome

Introduction: Protein-losing enteropathy (PLE) is the abnormal loss of protein through the gastrointestinal tract and has been associated with many diseases. The group of disorders including Noonan syndrome and Noonan-like syndromes (NS) consist of various dysmorphic features and congenital abnormalities. Multiple gene mutations paired with diverse phenotypic presentations have made identifying relationships between genotype and phenotype challenging, particularly with PLE in NS. In rare cases, PLE has been reported with NS, but few genetic associations have been made. Our case describes a possible connection between PLE and the SHOC2 gene mutation. Case Description/Methods: A 21-year-old female with a history of NS presented to our outpatient clinic with lower extremity edema and diarrhea with four watery bowel movements per day for 3 months. Labs revealed albumin of 2.4 g/dL, creatinine of 0.35 mg/dL, and potassium of 3.1 mEq/L. Acute hepatitis panel and anti-tissue transglutaminase were negative. Stool studies were positive for Clostridioides difficile and she was treated with oral vancomycin. She had an unremarkable esophagogastroduodenoscopy and colonoscopy. Computed tomography enterography suggested altered lymphatic drainage, and a lymphangiogram showed abdominal collateral lymphatics and iliac lymphangiectasia. Overall, these findings were consistent with PLE. A high protein diet and medium-chain triglyceride supplementation were initiated, and she had normalization of serum albumin levels. Genetic analysis showed a SHOC2 gene mutation. Discussion: PLE consists of loss of serum proteins through the digestive tract, which may initially present as hypoalbuminemia in the absence of liver disease. This disorder is important to recognize due to the association between low albumin and increased mortality risk. Lymphatic disease presenting with lymphedema, chylothorax, and lymphangiectasia is well known in NS and may play a role in PLE development. PLE has been tied to the mutation of protein tyrosine phosphatase non-receptor type 11, but to our knowledge, has not been reported with SHOC2 mutation. Because little is understood about PLE in NS, there is no standard treatment. However, supplementation with medium-chain triglycerides and periodic albumin infusions has proven effective. The association between PLE and NS may be more common than acknowledged. This case identifies SHOC2 mutation with PLE and encourages consideration of PLE in NS in hopes of decreasing mortality and increasing quality of life.

Short Stature Syndromes: Case Series from India.

Syndromes causing short stature include Noonan syndrome (NS), Williams syndrome, and Silver-Russell syndrome (SRS). SRS is a primordial dwarfism with genetic heterogeneity. The SRS children present with prenatal growth retardation, neonatal hypoglycemia, feeding difficulties, physical asymmetry, with scoliosis and cardiac defect in some cases. The incidence is up to 1 in 100,000. Uniparental disomy, methylation abnormalities, and variants in some genes have been found underlying such phenotype. Growth hormone therapy has been used to improve the height gain in these patients. NS has genetic heterogeneity and most patients present with short stature with or without cardiac defect. Multiple genetic variants, mostly autosomal dominant, contribute to the phenotype. With the availability of next-generation sequencing, more and more genetic disorders causing short stature are being identified in different ethnic populations like Kabuki syndrome and Nance-Horan syndrome. Here, we present some cases of SRS and other additional syndromes with dysmorphism seen in past 5 years.

Embryonic Expression of NrasG 12 D Leads to Embryonic Lethality and Cardiac Defects.

Ras proteins control a complex intracellular signaling network. Gain-of-function mutations in RAS genes lead to RASopathy disorders in humans, including Noonan syndrome (NS). NS is the second most common syndromic cause of congenital heart disease. Although conditional expression of the NrasG12D/+ mutation in adult hematopoietic system is leukemogenic, its effects on embryonic development remain unclear. Here, we report that pan-embryonic expression of endogenous NrasG12D/+ by Mox2-Cre in mice caused embryonic lethality from embryonic day (E) 15.5 and developmental defects predominantly in the heart. At E13.5, NrasG12D/+; Mox2Cre/+ embryos displayed a moderate expansion of hematopoietic stem and progenitor cells without a significant impact on erythroid differentiation in the fetal liver. Importantly, the mutant embryos exhibited cardiac malformations resembling human congenital cardiac defects seen in NS patients, including ventricular septal defects, double outlet right ventricle, the hypertrabeculation/thin myocardium, and pulmonary valve stenosis. The mutant heart showed dysregulation of ERK, BMP, and Wnt pathways, crucial signaling pathways for cardiac development. Endothelial/endocardial-specific expression of NrasG12D/+ caused the cardiac morphological defects and embryonic lethality as observed in NrasG12D/+; Mox2Cre/+ mutants, but myocardial-specific expression of NrasG12D/+ did not. Thus, oncogenic NrasG12D mutation may not be compatible with embryonic survival.

Ras GEF Mouse Models for the Analysis of Ras Biology and Signaling.

Animal models have become in recent years a crucial tool to understand the physiological and pathological roles of many cellular proteins. They allow analysis of the functional consequences of [1] complete or partial (time- or organ-limited) removal of specific proteins (knockout animals), [2] the exchange of a wild-type allele for a mutant or truncated version found in human illnesses (knock-in), or [3] the effect of overexpression of a given protein in the whole body or in specific organs (transgenic mice). In this regard, the study of phenotypes in Ras GEF animal models has allowed researchers to find specific functions for otherwise very similar proteins, uncovering their role in physiological contexts such as memory formation, lymphopoiesis, photoreception, or body homeostasis. In addition, mouse models have been used to unveil the functional role of Ras GEFs under pathological conditions, including Noonan syndrome, skin tumorigenesis, inflammatory diseases, diabetes, or ischemia among others. In the following sections, we will describe the methodological approaches employed for Ras GEF animal model analyses, as well as the main discoveries made.

The Genetic Epidemiology of Pediatric Pulmonary Arterial Hypertension

To describe the prevalence of pulmonary arterial hypertension (PAH)-associated gene mutations, and other genetic characteristics in a national cohort of children with PAH from the Dutch National registry and to explore genotype-phenotype associations and outcomes. Children (n=70) diagnosed with idiopathic PAH, heritable PAH, PAH associated with congenital heart disease with coincidental shunt (PAH-congenital heart disease group 3), PAH after closure of a cardiac shunt (PAH-congenital heart disease group 4), or PAH associated with other noncardiac conditions were enrolled. Targeted next-generation sequencing was performed on PAH-associated genes (BMPR2, ACVRL1, EIF2AK4, CAV1, ENG, KCNK3, SMAD9, and TBX4). Also, children were tested for specific genetic disorders in case of clinical suspicion. Additionally, children were tested for copy number variations. Nineteen children (27%) had a PAH-associated gene mutation/variant: BMPR2 n=7, TBX4 n=8, ACVRL1 n=1, KCNK3 n=1, and EIF2AK4 n=2. Twelve children (17%) had a genetic disorder with an established association with PAH (including trisomy 21 and cobalamin C deficiency). In another 16 children (23%), genetic disorders without an established association with PAH were identified (including Noonan syndrome, Beals syndrome, and various copy number variations). Survival rates differed between groups and was most favorable in TBX4 variant carriers. Children with PAH show a high prevalence of genetic disorders, not restricted to established PAH-associated genes. Genetic architecture could play a role in risk-stratified care management in pediatric PAH.

RASopathies

RASopathies are a group of disorders characterized by mutations in the RAS-MAPK pathway. RAS-MAP signaling plays a critical role in cell differentiation, proliferation, and survival. Germline mutations can result in distinctive syndromes, including Noonan syndrome, Costello syndrome, and neurofibromatosis type 1. Mosaic RASopathies can present as localized cutaneous lesions like epidermal nevi and nevus sebaceous, or more extensive conditions such as encephalocraniocutaneous lipomatosis. We review the heterogenous presentation of RAS mutations, discuss new targeted therapies, and highlight areas of uncertainty, including carcinogenesis risk and appropriate screening.

Protein loss in the small intestine detected by capsule endoscopy

A 32-year-old woman presented with leg edema and low serum albumin. Although she had experienced intermittent episodes of leg edema since childhood, she had not been examined for this condition. Laboratory data showed hypoproteinemia (3.8 g/dL) and hypoalbuminemia (1.8 g/dL). The result of serology for infectious enteropathy was negative. Gastroduodenoscopy and total colonoscopy showed no abnormal findings. The result of Sudan III staining of the stool was positive. A fecal α-1-antitrypsin clearance test showed abnormal leakage (128 mL/day), and double-balloon enteroscopy showed white villi, white nodules (A), and chylorrhea in the jejunum. Capsule endoscopy showed apparent leakage of white lymphatic fluid from the white villi, where the internal pressure must have been physiologic. It showed leakage of protein from the villi to the intestinal lumen (B). It may be difficult to see a spontaneous leak with double-balloon enteroscopy when the intraluminal pressure is high. Biopsy specimens from the jejunal mucosa demonstrated characteristic lymphangiectasia (C, H&E and D2-40, orig. mag. ×40; D, H&E and D2-40, orig. mag. ×40 D2-40) of the lamina propria. Albumin scintigraphy showed hot spots in the small intestine. These data confirmed a diagnosis of primary intestinal lymphangiectasia and showed that the hypoalbuminemia was secondary to protein-losing enteropathy. The patient was given a low-fat diet with medium-chain triglyceride supplementation, and her clinical condition improved. All authors disclosed no financial relationships. Commentary Primary intestinal lymphangiectasia with protein-losing enteropathy is a disorder wherein ectasia of the enteric lymphatics develops. This can occur at almost any layer of the GI lumen wall. This disorder is usually seen in young patients but can be seen in adults as well (as was the case with this patient). Intestinal lymphangiectasia can be seen in the context of other conditions, including Noonan syndrome, von Recklinghausen syndrome, and Turner syndrome, among others. This patient also had symptoms that suggested this condition had been present for many years. This case illustrates the value of a well-timed capsule endoscopy study, whereby a key finding was detected that allowed elucidation and/or confirmation of a diagnosis for the patient. The findings seen in this study could be intermittent or ongoing, so the capsule findings are both as striking as they are rare. Douglas G. Adler, MD, FASGE, GIE Senior Associate Editor, University of Utah School of Medicine, Salt Lake City, Utah Mohamed O. Othman, MD, Associate Editor for Focal Points

Molecular Genetics of Noonan Syndrome and RASopathies.

The RAS/MAPK signaling pathway plays an essential role in development and tumorigenesis by regulating cell proliferation, differentiation, apoptosis, migration, and metabolism. Therefore, it is not surprising that germline mutations in genes encoding components or regulators of this signaling pathway cause numerous human genetic conditions, including Noonan syndrome and related disorders. The term "RASopathies" has been used to describe these disorders collectively due to their common underlying RAS/MAPK pathway dysregulation and overlapping clinical features. Taken together, the RASopathies represent one of the most common groups of genetic disorders, affecting approximately 1 in 1,000 individuals. This review describes the RAS/MAPK signaling pathway, summarizes multiple molecular genetic approaches used during the last several decades to discover genes responsible for different RASopathies, and finally focuses on several major disease genes associated with Noonan syndrome and related disorders with regard to genomic locations, structure, mutations, and genotype-phenotype correlations.

Pathogenesis of Growth Failure in Rasopathies.

The RASopathies are a group of developmental genetic syndromes that are caused by germline mutations in genes encoding proteins of the Ras-Mitogen-Activated Protein kinase (RAS-MAPK) pathway. RASopathies include Noonan Syndrome (NS), Neurofibromatosis Type 1 (NF1), Noonan syndrome with multiple lentigines (NSML/LEOPARD), Costello syndrome (CS), Cardio-facio-cutaneous syndrome (CFC), capillary malformation-arteriovenous malformation syndrome (CM-AVM) and Legius Syndrome. These syndromes have many overlapping features; however, the most persistent feature common to all is the postnatal growth failure. The mechanism of growth failure in Rasopathies is highly complex and there are many proposed hypotheses including partial growth hormone insensitivity, growth hormone deficiency, neurosecretory dysfunction of growth hormone secretion, delayed puberty, poor feeding and skeletal abnormalities. Amongst these causes, the most widely accepted is partial growth hormone insensitivity due to a post-receptor signaling defect. Growth hormone therapy seems to be effective in improving height velocity in these syndromes, although the long-term effects on final height remain unproven. However, it is important to consider the potential risk of tumors and cardiomyopathy before and during growth hormone therapy.

The ERK MAPK Pathway Is Essential for Skeletal Development and Homeostasis.

Mitogen-activated protein kinases (MAPKs) are a family of protein kinases that function as key signal transducers of a wide spectrum of extracellular stimuli, including growth factors and pro-inflammatory cytokines. Dysregulation of the extracellular signal-regulated kinase (ERK) MAPK pathway is associated with human skeletal abnormalities including Noonan syndrome, neurofibromatosis type 1, and cardiofaciocutaneous syndrome. Here, we demonstrate that ERK activation in osteoprogenitors is required for bone formation during skeletal development and homeostasis. Deletion of Mek1 and Mek2, kinases upstream of ERK MAPK, in osteoprogenitors (Mek1OsxMek2−/−), resulted in severe osteopenia and cleidocranial dysplasia (CCD), similar to that seen in humans and mice with impaired RUNX2 function. Additionally, tamoxifen-induced deletion of Mek1 and Mek2 in osteoprogenitors in adult mice (Mek1Osx-ERTMek2−/−) significantly reduced bone mass. Mechanistically, this corresponded to decreased activation of osteoblast master regulators, including RUNX2, ATF4, and β-catenin. Finally, we identified potential regulators of osteoblast differentiation in the ERK MAPK pathway using unbiased phospho-mass spectrometry. These observations demonstrate essential roles of ERK activation in osteogenesis and bone formation.

Genetic landscape of RASopathies in Chinese: Three decades' experience in Hong Kong.

RASopathies are a group of genetic disorders due to dysregulation of the RAS-MAPK signaling pathway, which is important in regulating cell growth, proliferation, and differentiation. These include Noonan syndrome (NS), Noonan syndrome with multiple lentigines (NSML), cardiofaciocutaneous (CFC) syndrome, and Costello syndrome (CS), clinical manifestations include growth retardation, developmental delay, cardiac defects, and specific dysmorphic features. There were abundant publications describing the genotype and phenotype from the Western populations. However, detailed study of RASopathies in Chinese population is lacking. We present here the largest cohort of RASopathies ever reported in Chinese populations, detailing the mutation spectrum and clinical phenotypes of these patients. The Clinical Genetic Service, Department of Health, and Queen Mary Hospital are tertiary referral centers for genetic disorders in Hong Kong. We retrospectively reviewed all the genetically confirmed cases of RASopathies, including NS, NSML, CFC syndrome, and CS, over the past 29 years (from 1989 to 2017). Analyses of the mutation spectrum and clinical phenotypes were performed. One hundred and ninety-one ethnic Chinese patients with genetically confirmed RASopathies were identified, including 148 patients with NS, 23 NSML, 12 CFC syndrome, and eight CS. We found a lower incidence of hypertrophic cardiomyopathy in individuals with NSML (27.3%), and NS caused by RAF1 mutations (62.5%). Another significant finding was for those NS patients with myeloproliferative disorder, the mutations fall within Exon 3 of PTPN11 but not only restricted to the well-known hotspots, that is, p.Asp61 and p.Thr731, which suggested that re-evaluation of the current tumor surveillance recommendation maybe warranted.

New insight of craniofacial and oral findings of the RASopathies

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), NS with multiple lentigines (NSML), neu-rofibromatosis type 1 (NF1), Costello syndrome (CS), cardio-facio-cutaneous (CFC) syndrome, neurofibromatosis type 1-like syndrome (NFLS) and capillary malformation-arteriovenous malformation syndrome (CM-AVM). These disorders affect multiple systems, including the craniofacial complex. Although the crani-ofacial 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.

Delineation of LZTR1 mutation-positive patients with Noonan syndrome and identification of LZTR1 binding to RAF1-PPP1CB complexes.

RASopathies are a group of developmental disorders caused by mutations in genes that regulate the RAS/MAPK pathway and include Noonan syndrome (NS), Costello syndrome, cardiofaciocutaneous syndrome and other related disorders. Whole exome sequencing studies recently identified LZTR1, PPP1CB and MRAS as new causative genes in RASopathies. However, information on the phenotypes of LZTR1 mutation-positive patients and functional properties of the mutations are limited. To identify variants of LZTR1, PPP1CB, and MRAS, we performed a targeted next-generation sequencing and reexamined previously analyzed exome data in 166 patients with suspected RASopathies. We identified eight LZTR1 variants, including a de novo variant, in seven probands who were suspicious for NS and one known de novo PPP1CB variant in a patient with NS. One of the seven probands had two compound heterozygous LZTR1 variants, suggesting autosomal recessive inheritance. All probands with LZTR1 variants had cardiac defects, including hypertrophic cardiomyopathy and atrial septal defect. Five of the seven probands had short stature or intellectual disabilities. Immunoprecipitation of endogenous LZTR1 followed by western blotting showed that LZTR1 bound to the RAF1-PPP1CB complex. Cells transfected with a small interfering RNA against LZTR1 exhibited decreased levels of RAF1 phosphorylated at Ser259. These are the first results to demonstrate LZTR1 in association with the RAF1-PPP1CB complex as a component of the RAS/MAPK pathway.