Spectrum of mutations and genotype-phenotype analysis in Noonan syndrome patients with RIT1 mutations

Computer-based facial recognition as an assisting diagnostic tool to identify children with Noonan syndrome

BACKGROUND

Noonan syndrome (NS) is a rare genetic disease, and patients who suffer from it exhibit a facial morphology that is characterized by a high forehead, hypertelorism, ptosis, inner epicanthal folds, down-slanting palpebral fissures, a highly arched palate, a round nasal tip, and posteriorly rotated ears. Facial analysis technology has recently been applied to identify many genetic syndromes (GSs). However, few studies have investigated the identification of NS based on the facial features of the subjects.

OBJECTIVES

This study develops advanced models to enhance the accuracy of diagnosis of NS.

METHODS

A total of 1,892 people were enrolled in this study, including 233 patients with NS, 863 patients with other GSs, and 796 healthy children. We took one to 10 frontal photos of each subject to build a dataset, and then applied the multi-task convolutional neural network (MTCNN) for data pre-processing to generate standardized outputs with five crucial facial landmarks. The ImageNet dataset was used to pre-train the network so that it could capture generalizable features and minimize data wastage. We subsequently constructed seven models for facial identification based on the VGG16, VGG19, VGG16-BN, VGG19-BN, ResNet50, MobileNet-V2, and squeeze-and-excitation network (SENet) architectures. The identification performance of seven models was evaluated and compared with that of six physicians.

RESULTS

All models exhibited a high accuracy, precision, and specificity in recognizing NS patients. The VGG19-BN model delivered the best overall performance, with an accuracy of 93.76%, precision of 91.40%, specificity of 98.73%, and F1 score of 78.34%. The VGG16-BN model achieved the highest AUC value of 0.9787, while all models based on VGG architectures were superior to the others on the whole. The highest scores of six physicians in terms of accuracy, precision, specificity, and the F1 score were 74.00%, 75.00%, 88.33%, and 61.76%, respectively. The performance of each model of facial recognition was superior to that of the best physician on all metrics.

CONCLUSION

Models of computer-assisted facial recognition can improve the rate of diagnosis of NS. The models based on VGG19-BN and VGG16-BN can play an important role in diagnosing NS in clinical practice.

Genetic backgrounds and genotype-phenotype relationships in anthropometric parameters of 116 Japanese individuals with Noonan syndrome

Noonan syndrome (NS) is caused by pathogenic variants in genes encoding components of the RAS/MAPK pathway and presents with a number of symptoms, including characteristic facial features, congenital heart diseases, and short stature. Advances in genetic analyses have contributed to the identification of pathogenic genes in NS as well as genotype-phenotype relationships; however, updated evidence for the detection rate of pathogenic genes with the inclusion of newly identified genes is lacking in Japan. Accordingly, we examined the genetic background of 116 individuals clinically diagnosed with NS and the frequency of short stature. We also investigated genotype-phenotype relationships in the context of body mass index (BMI). Genetic testing revealed the responsible variants in 100 individuals (86%), where PTPN11 variants were the most prevalent (43%) and followed by SOS1 (12%) and RIT1 (9%). The frequency of short stature was the lowest in subjects possessing RIT1 variants. No genotype-phenotype relationships in BMI were observed among the genotypes. In conclusion, this study provides evidence for the detection rate of pathogenic genes and genotype-phenotype relationships in Japanese patients with NS, which will be of clinical importance for accelerating our understanding of the genetic backgrounds of Japanese patients with NS.

RAS-dependent RAF-MAPK hyperactivation by pathogenic RIT1 is a therapeutic target in Noonan syndrome-associated cardiac hypertrophy

RIT1 is a RAS guanosine triphosphatase (GTPase) that regulates different aspects of signal transduction and is mutated in lung cancer, leukemia, and in the germline of individuals with Noonan syndrome. Pathogenic RIT1 proteins promote mitogen-activated protein kinase (MAPK) hyperactivation; however, this mechanism remains poorly understood. Here, we show that RAF kinases are direct effectors of membrane-bound mutant RIT1 necessary for MAPK activation. We identify critical residues in RIT1 that facilitate interaction with membrane lipids and show that these are necessary for association with RAF kinases and MAPK activation. Although mutant RIT1 binds to RAF kinases directly, it fails to activate MAPK signaling in the absence of classical RAS proteins. Consistent with aberrant RAF/MAPK activation as a driver of disease, we show that pathway inhibition alleviates cardiac hypertrophy in a mouse model of RIT1 mutant Noonan syndrome. These data shed light on the function of pathogenic RIT1 and identify avenues for therapeutic intervention.

Dilated coronary arteries in a 2-month-old with RIT1-associated Noonan syndrome: a case report

BACKGROUND

Noonan Syndrome is caused by variants in a variety of genes found in the RAS/MAPK pathway. As more causative genes for Noonan Syndrome have been identified, more phenotype variability has been found, particularly congenital heart defects. Here, we report a case of dilated coronary arteries in a pediatric patient with a RIT1 variant to add to the body of literature around this rare presentation of Noonan Syndrome.  CASE PRESENTATION: A 2-month-old female was admitted due to increasing coronary artery dilation and elevated inflammatory markers. Rapid whole genome sequencing was performed and a likely pathogenic RIT1 variant was detected. This gene has been associated with a rare form of Noonan Syndrome and associated heart defects. Diagnosis of the RIT1 variant also gave reassurance about the patient's cardiac findings and allowed for more timely discharge as she was discharged to home the following day.  CONCLUSIONS: This case highlights the importance of the association between dilated coronary arteries and Noonan syndrome and that careful cardiac screening should be advised in patients diagnosed with Noonan syndrome. In addition, this case emphasizes the importance of involvement of other subspecialities to determine a diagnosis. Through multidisciplinary medicine, the patient was able to return home in a timely manner with a diagnosis and the reassurance that despite her dilated coronary arteries and elevated inflammatory markers there was no immediate concern to her health.

The heart in RASopathies

The cardiovascular phenotype associated with RASopathies has expanded far beyond the original descriptions of pulmonary valve stenosis by Dr Jaqueline Noonan in 1968 and hypertrophic cardiomyopathy by Hirsch et al. in 1975. Because of the common underlying RAS/MAPK pathway dysregulation, RASopathy syndromes usually present with a typical spectrum of overlapping cardiovascular anomalies, although less common cardiac defects can occur. The identification of the causative genetic variants has enabled the recognition of specific correlations between genotype and cardiac phenotype. Characterization and understanding of genotype-phenotype associations is not only important for counseling a family of an infant with a new diagnosis of a RASopathy condition but is also critical for their clinical prognosis with respect to cardiac disease, neurodevelopment and other organ system involvement over the lifetime of the patient. This review will focus on the cardiac manifestations of the most common RASopathy syndromes, the relationship between cardiac defects and causal genetic variation, the contribution of cardiovascular abnormalities to morbidity and mortality and the most relevant follow-up issues for patients affected by RAS/MAPK pathway diseases, with respect to cardiac clinical outcomes and management, in children and in the adult population.

Lymphatic anomalies during lifetime in patients with Noonan syndrome: Retrospective cohort study

Noonan syndrome (NS) has been associated with an increased risk of lymphatic anomalies, with an estimated prevalence of 20%. The prevalence of lymphatic anomalies seems to differ between pathogenic variants. Therefore, this study aims to describe the clinical presentation, prevalence and genotype-phenotype correlations of lymphatic anomalies during life in patients with NS. This retrospective cohort study included patients (n = 115) who were clinically and genetically diagnosed with NS and visited the Noonan expertise Center of the Radboud University Medical Center between January 2015 and March 2021. Data on lymphatic anomalies during lifetime were obtained from medical records. Lymphatic anomalies most often presented as an increased nuchal translucency, chylothorax and/or lymphedema. Prenatal lymphatic anomalies increased the risk of lymphatic anomalies during infancy (OR 4.9, 95% CI 1.7-14.6). The lifetime prevalence of lymphatic anomalies was 37%. Genotype-phenotype correlations showed an especially high prevalence of lymphatic anomalies during infancy and childhood in patients with a pathogenic SOS2 variant (p = 0.03 and p < 0.01, respectively). This study shows that patients with NS have a high predisposition for developing lymphatic anomalies during life. Especially patients with prenatal lymphatic anomalies have an increased risk of lymphatic anomalies during infancy. Genotype-phenotype correlations were found in pathogenic variants in SOS2.

A case of non-immune hydrops fetalis with maternal mirror syndrome diagnosed by trio-based exome sequencing: An autopsy case report and literature review

Non-immune hydrops fetalis (NIHF) indicates the risk for stillbirth. Although the causes vary and most NIHFs have no identifiable cause, recent advances in exome sequencing have increased diagnostic rates. We report a case of NIHF that developed into a giant cystic hygroma complicated by maternal mirror syndrome. Trio-based exome sequencing showed a de novo heterozygous missense variant in the RIT1 (NM_006912: c.246 T > G [p.F82L]). The RIT1 variants are known causative variants of Noonan syndrome (NS; OMIM #163950). The location of the RIT1 variants in the previously reported NS cases with NIHF or/and maternal mirror syndrome was mainly in the switch II region, including the present case. While a further accumulation of cases is needed, exome sequencing, which can identify the variant type in detail, might help predict the phenotype and severity of NIHF.

Molecular and clinical profile of patients referred as Noonan or Noonan-like syndrome in Greece: a cohort of 86 patients

Noonan syndrome (NS) is an autosomal dominant disorder characterized by clinical and genetic heterogeneity. It belongs to a wider group of pathologies, known as Rasopathies, due to the implication of genes encoding components of the Ras/MAPK signalling pathway. Recording the genetic alterations across populations helps assessing specific features to specific genes which is essential for better disease's recognition, prognosis and monitoring. Herein, we report the clinical and molecular data of a Greek cohort comprising of 86 NS or NS-like patients admitted at a single tertiary Centre in Athens, Greece. The analysis was performed using Sanger and next-generation sequencing, comprising 14 different genes. The mutational rates of the confirmed NS-associated genes in the Greek NS population are as follows: PTPN11 32.5%; RIT1 5.8%; SOS1 4.7%; BRAF 1.2%; CBL 1.2%; KRAS 1.2%; MAP2K1 1.2%; RAF1 1.2%; SHOC2 1.2%, corresponding to 50% of positivity in total NS population. The genotype-phenotype analysis showed statistically significant differences in craniofacial dysmorphisms (p = 0.005) and pulmonary valve stenosis (PS) (p < 0.001) frequencies between patients harbouring a pathogenic variant and patients without pathogenic variant in any of the tested genes. Patients with at least a pathogenic variant had 6.71 times greater odds to develop PS compared to pathogenic variant-negative patients (OR = 6.71, 95%; CI = (2.61, 17.27)). PTPN11 positive patients showed higher frequency of epicanthal folds (p = 0.004), ptosis (p = 0.001) and coarseness (p = 0.001) and lower frequency of neurological findings (p = 0.006), compared to patients carrying pathogenic variants in other genes.

CONCLUSION

Craniofacial dysmorphism and PS prevail among pathogenic variant positive compared to pathogenic variant negative NS and NS-like patients while neurological defects are less common in PTPN11-affected NS patients compared to patients harbouring pathogenic variants in other genes. The significant prevalence of the Ras/MAPK pathogenic variants (17.4%), other than PTPN11, in Greek NS patients, highlights the necessity of a wider spectrum of molecular diagnosis.

WHAT IS KNOWN

• Noonan syndrome (NS) has been associated with pathogenic variants in molecules-components of the Ras/MAPK pathway. • Clinical and genetic description of NS patients worldwide helps establishing personalized monitoring.

WHAT IS NEW

• NS and NS-like mutational rate in Greece reaches 50% with pathogenic variants identified mostly in PTPN11 (32.5%), RIT1 (6%) and SOS1 (4.7%) genes. • The risk for pulmonary stenosis increases 6.71-fold in NS patients with a pathogenic variant compared to patients without genetic alterations.

Pathological MAPK activation-mediated lymphatic basement membrane disruption causes lymphangiectasia that is treatable with ravoxertinib

Lymphangiectasia, an anomalous dilation of lymphatic vessels first described in the 17th century, is frequently associated with chylous effusion, respiratory failure, and high mortality in young patients, yet the underlying molecular pathogenesis and effective treatments remain elusive. Here, we identify an unexpected causal link between MAPK activation and defective development of the lymphatic basement membrane that drives lymphangiectasia. Human pathological tissue samples from patients diagnosed with lymphangiectasia revealed sustained MAPK activation within lymphatic endothelial cells. Endothelial KRASG12D-mediated sustained MAPK activation in newborn mice caused severe pulmonary and intercostal lymphangiectasia, accumulation of chyle in the pleural space, and complete lethality. Pathological activation of MAPK in murine vasculature inhibited the Nfatc1-dependent genetic program required for laminin interactions, collagen crosslinking, and anchoring fibril formation, driving defective development of the lymphatic basement membrane. Treatment with ravoxertinib, a pharmacological inhibitor of MAPK, reverses nuclear-to-cytoplasmic localization of Nfatc1, basement membrane development defects, lymphangiectasia, and chyle accumulation, ultimately improving survival of endothelial KRAS mutant neonatal mice. These results reveal defective lymphatic basement membrane assembly and composition as major causes of thoracic lymphangiectasia and provide a potential treatment.

Inside the Noonan "universe": Literature review on growth, GH/IGF axis and rhGH treatment: Facts and concerns

Noonan syndrome (NS) is a disorder characterized by a typical facial gestalt, congenital heart defects, variable cognitive deficits, skeletal defects, and short stature. NS is caused by germline pathogenic variants in genes coding proteins with a role in the RAS/mitogen-activated protein kinase signaling pathway, and it is typically associated with substantial genetic and clinical complexity and variability. Short stature is a cardinal feature in NS, with evidence indicating that growth hormone (GH) deficiency, partial GH insensitivity, and altered response to insulin-like growth factor I (IGF-1) are contributing events for growth failure in these patients. Decreased IGF-I, together with low/normal responses to GH pharmacological provocation tests, indicating a variable presence of GH deficiency/resistance, in particular in subjects with pathogenic PTPN11 variants, are frequently reported. Nonetheless, short- and long-term studies have demonstrated a consistent and significant increase in height velocity (HV) in NS children and adolescents treated with recombinant human GH (rhGH). While the overall experience with rhGH treatment in NS patients with short stature is reassuring, it is difficult to systematically compare published data due to heterogeneous protocols, potential enrolment bias, the small size of cohorts in many studies, different cohort selection criteria and varying durations of therapy. Furthermore, in most studies, the genetic information is lacking. NS is associated with a higher risk of benign and malignant proliferative disorders and hypertrophic cardiomyopathy, and rhGH treatment may further increase risk in these patients, especially as dosages vary widely. Herein we provide an updated review of aspects related to growth, altered function of the GH/IGF axis and cell response to GH/IGF stimulation, rhGH treatment and its possible adverse events. Given the clinical variability and genetic heterogeneity of NS, treatment with rhGH should be personalized and a conservative approach with judicious surveillance is recommended. Depending on the genotype, an individualized follow-up and close monitoring during rhGH treatments, also focusing on screening for neoplasms, should be considered.

Cognitive Phenotype and Psychopathology in Noonan Syndrome Spectrum Disorders through Various Ras/MAPK Pathway Associated Gene Variants

Cognitive difficulties are argued to be common in patients with Noonan syndrome spectrum disorders (NSSDs), but findings are based on studies in which patients with variants in PTPN11 (prevalence ~50%) were overrepresented. The current study, using a structured clinical approach, describes the cognitive phenotype and psychopathology of 100 patients (aged 6 to 61 years) with nine different gene variants in the Ras/MAPK pathway underlying NSSDs (PTPN11n = 61, PTPN11 Noonan syndrome with multiple lentigines n = 3, SOS1n = 14, KRASn = 7, LZTR1n = 5, RAF1n = 4, SHOC2n = 2, CBLn = 2, SOS2n = 2). After weighted assessment and bootstrapping of the results of individual neuropsychological assessments and measures of psychopathology, cognitive performances in most variant groups were within the ranges of expectation. IQs were significantly lower in patients with variants in PTPN11, KRAS, RAF1, and SHOC2, but no specific cognitive impairments were found. The performances of younger participants (<16 years of age) did not differ from those of adults. Alexithymia and internalizing problems were more frequent in patients with variants in PTPN11 and SOS1, while PTPN11 patients also showed higher levels of externalizing problems. These results stress the need to take intelligence into account when interpreting lower cognitive performances in individual neuropsychological assessments, which is crucial for an adequate understanding and guidance of patients with NSSDs.

The added value of the electrocardiogram in Noonan syndrome

Noonan syndrome is a genetic disorder characteried by short stature, typical facial features, developmental delay, and CHD. In this single-centre retrospective study, we analysed typical Noonan syndrome-related electrocardiographic features in 95 patients with clinically and molecularly confirmed Noonan syndrome. Typical Noonan syndrome-related electrocardiographic features are left axis deviation, small left precordial R-waves, large right precordial S-waves, abnormal Q-wave, and abnormal wide QRS complex. In this representative cohort, CHD was found in 59 patients (62.1%) and typical Noonan syndrome-related electrographic features in 60 patients (63.2%). The typical Noonan syndrome-related electrographic features were also increased over baseline in patients without CHD (41.7%). Of all 95 patients, left axis deviation was seen in 46.3%, small left precordial R-waves in 30.5%, large right precordial S-waves in 5.3%, and abnormal Q-wave and wide QRS complex in 2.1%. There was no significant difference in the frequency of the individual-specific electrographic features between the group with CHD and the group without CHD. However, there were significantly more patients with a small left precordial R-wave in the subgroup with pulmonary stenosis compared to patients without pulmonary stenosis. Conclusion: Specific Noonan syndrome-related electrographic features are frequently present in patients with Noonan syndrome, also in the absence of CHD. These results suggest that there may be a continuum of cardiac anomalies from overt CHD to milder abnormalities that are only seen on electrocardiogram.

Prenatal case of RIT1 mutation associated Noonan syndrome by whole exome sequencing (WES) and review of the literature

OBJECTIVE

We aimed to identify the genetic cause of one hydrops fetalis with Noonan syndrome (NS) manifestations including increased nuchal translucency (INT) and ascites through prenatal whole exome sequencing (WES).

CASE REPORT

The case is a gestational age (GA) 18 fetus of two healthy parents with a normal child. We proceeded the genomic DNA from both fetus amniotic cells and parents to WES and identified a RIT1 mutation (c.268A>G) as the pathogenic cause of the hydrops fetalis by automatic prioritization algorithm after array-comparative genomic hybridization results showing negative.

CONCLUSION

Mutations in RIT1 have been reported as the causes for different fetus structural abnormities in the recent years. This case contributes to the summary delineations of the prenatal NS phenotypes related to RIT1 mutation. In addition, the fast WES application, in this case, has demonstrated its advantage in prenatal disorder diagnosis when conventional karyotyping or chromosomal microarray testing result is negative.

Cardiac features of Noonan syndrome in Japanese patients

BACKGROUND

Cardiovascular disease is one of the most important problems in long-term follow-up for Noonan syndrome. We examined cardiovascular issues and clinical manifestations, with a focus on the cardiovascular disease and prognosis of patients with Noonan syndrome.

METHODS

This single-centre study evaluated patients who were clinically and genetically diagnosed with Noonan syndrome.

RESULTS

Forty-three patients diagnosed with Noonan syndrome were analysed. The most prevalent responsible mutation was found in PTPN11 (25/43). The second and third most prevalent causative genes were SOS1 (6/43) and RIT1 (5/43), respectively, and 67.4% of genetically diagnosed patients with Noonan syndrome had structural cardiovascular abnormalities. Pulmonary valve stenosis was prevalent in patients with mutations in PTPN11 (8/25), SOS1 (4/6), and RIT1 (4/5). Hypertrophic cardiomyopathy was found in two of three patients with mutations in RAF1. There was no difference in the cardiovascular events or cardiovascular disease prevalence in patients with or without PTPN11 mutations. The proportion of RIT1 mutation-positive patients who underwent intervention due to cardiovascular disease was significantly higher than that of patients with PTPN11 mutations. Patients who underwent any intervention for pulmonary valve stenosis exhibited significantly higher pulmonary flow velocity than patients who did not undergo intervention, when they visited our hospital for the first time. All patients who underwent intervention for pulmonary valve stenosis had a pulmonary flow velocity of more than 3.0 m/s at first visit.

CONCLUSIONS

These findings suggest that genetic information can provide a clinical prognosis for cardiovascular disease and may be part of genotype-based follow-up in Noonan syndrome.

Disruption of the glomerular basement membrane associated with nutcracker syndrome and double inferior vena cava in Noonan syndrome: a case report

Background

Nutcracker syndrome (NCS) is characterized by compression of the left renal vein (LRV) between the aorta and the superior mesenteric artery. While rare, NCS was reported to be accompanied by double inferior vena cava (IVC). We herein report a case of Noonan syndrome (NS) with double IVC who presented with macrohematuria and proteinuria.

Case presentation

The patient was a 23-year-old man, who had been diagnosed with NS due to RIT1 mutation, after showing foamy macrohematuria 3 weeks previously. A physical examination revealed low-set ears and a webbed neck. A urinalysis showed hematuria and proteinuria, and urinary sediments showed more than 100 isomorphic red blood cells per high-power field. His proteinuria and albuminuria concentrations were 7.1 and 4.5 g/g⋅Cr, respectively. Three-dimensional contrast-enhanced computed tomography (CT) showed double IVC and narrowing of the LRV after interflow of the left IVC. The aortomesenteric angle on a sagittal reconstruction of the CT image was 14.7°. Cystoscopy revealed a flow of macrohematuria from the left ureteral opening. On Doppler ultrasonography, there was scant evidence to raise the suspicion of the nutcracker phenomenon. Since severe albuminuria continued, a left kidney biopsy was performed. Light microscopy showed red blood cells in Bowman’s space and the tubular lumen. Electron microscopy revealed disruption of the glomerular basement membrane (GBM). Vulnerability of the GBM was suspected and a genetic analysis revealed a heterozygous mutation at c.4793 T > G (p.L1598R) in the COL4A3 gene. Screening for coagulation disorders revealed the factor VIII and von Willebrand factor (vWF) values were low, at 47.6 and 23%, respectively. A multimer analysis of vWF showed a normal multimer pattern and he was diagnosed with von Willebrand disease type 1. As the bleeding tendency was mild, replacement of factor VIII was not performed. His macrohematuria and proteinuria improved gradually without treatment, and his urinalysis results have been normal for more than 6 months.

Conclusions

The present case showed macrohematuria and proteinuria due to NCS in NS with double IVC and von Willebrand disease type 1. The macrohematuria and proteinuria originated from glomerular hemorrhage because of vulnerability of the GBM due to COL4A3 mutation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12882-022-02671-4.

Lymphatic Abnormalities in Noonan Syndrome Spectrum Disorders: A Systematic Review

Noonan syndrome spectrum disorders are a group of phenotypically related conditions, resembling Noonan syndrome, caused by germline pathogenic variants in genes within the Ras/mitogen-activated protein kinase (Ras/MAPK) signalling pathway. Lymphatic dysplasia with a clinical lymphatic abnormality is one of the major features. We performed a systematic review to get more insight in (1) the prevalence of clinically lymphatic abnormalities in patients with a genetically proven Noonan syndrome spectrum disorder, (2) if a genotype-lymphatic phenotype relation can be found and describe the clinical presentation and course of the lymphatic abnormality. Most studies report patients with Noonan syndrome. Prenatally, the prevalence of increased nuchal translucency differs from 7% in patients with pathogenic PTPN11 variants to 38% in patients with pathogenic RIT1 variants, and the prevalence of pleural effusions differed from 7% in patients with pathogenic SOS1 to 29% in patients with pathogenic RIT1 variants. Postnatally, the prevalence of lymphedema differs from 16% in patients with pathogenic PTPN11 variants to 44% in patients with pathogenic SOS1 variants, and the prevalence of acquired chylothorax is 4% in patients with pathogenic RIT1 variants. Lymphatic abnormalities do occur in patients with cardiofaciocutaneous syndrome and Costello syndrome. In conclusion, Noonan syndrome spectrum disorders, Noonan syndrome in particular, are associated with lymphatic abnormalities. Combining the available published literature about genetically proven Noonan syndrome spectrum disorders, it appears likely that the lifetime prevalence of these abnormalities in Noonan syndrome is higher than the 20% that were generally accepted so far. This is increasingly important, because the activation of the RAS/MAPK pathway can be inhibited by RAS/MAPK inhibitors, and clinically severe lymphatic abnormalities may improve.

Genetic conditions of short stature: A review of three classic examples

Noonan, Turner, and Prader-Willi syndromes are classical genetic disorders that are marked by short stature. Each disorder has been recognized for several decades and is backed by extensive published literature describing its features, genetic origins, and optimal treatment strategies. These disorders are accompanied by a multitude of comorbidities, including cardiovascular issues, endocrinopathies, and infertility. Diagnostic delays, syndrome-associated comorbidities, and inefficient communication among the members of a patient's health care team can affect a patient's well-being from birth through adulthood. Insufficient information is available to help patients and their multidisciplinary team of providers transition from pediatric to adult health care systems. The aim of this review is to summarize the clinical features and genetics associated with each syndrome, describe best practices for diagnosis and treatment, and emphasize the importance of multidisciplinary teams and appropriate care plans for the pediatric to adult health care transition.

Hypertrophic Cardiomyopathy in RASopathies: Diagnosis, Clinical Characteristics, Prognostic Implications, and Management

RASopathies are multisystemic disorders caused by germline mutations in genes linked to the RAS/mitogen-activated protein kinase pathway. Diagnosis of RASopathy can be triggered by clinical clues ("red flags") which may direct the clinician toward a specific gene test. Compared with sarcomeric hypertrophic cardiomyopathy, hypertrophic cardiomyopathy in RASopathies (R-HCM) is associated with higher prevalence of congestive heart failure and shows increased prevalence and severity of left ventricular outflow tract obstruction. Biventricular involvement and the association with congenital heart disease, mainly pulmonary stenosis, have been commonly described in R-HCM. The aim of this review is to assess the prevalence and unique features of R-HCM and to define the available therapeutic options.

Primary lymphoedema

Lymphoedema is the swelling of one or several parts of the body owing to lymph accumulation in the extracellular space. It is often chronic, worsens if untreated, predisposes to infections and causes an important reduction in quality of life. Primary lymphoedema (PLE) is thought to result from abnormal development and/or functioning of the lymphatic system, can present in isolation or as part of a syndrome, and can be present at birth or develop later in life. Mutations in numerous genes involved in the initial formation of lymphatic vessels (including valves) as well as in the growth and expansion of the lymphatic system and associated pathways have been identified in syndromic and non-syndromic forms of PLE. Thus, the current hypothesis is that most cases of PLE have a genetic origin, although a causative mutation is identified in only about one-third of affected individuals. Diagnosis relies on clinical presentation, imaging of the structure and functionality of the lymphatics, and in genetic analyses. Management aims at reducing or preventing swelling by compression therapy (with manual drainage, exercise and compressive garments) and, in carefully selected cases, by various surgical techniques. Individuals with PLE often have a reduced quality of life owing to the psychosocial and lifelong management burden associated with their chronic condition. Improved understanding of the underlying genetic origins of PLE will translate into more accurate diagnosis and prognosis and personalized treatment.

The RRAS2 pathogenic variant p.Q72L produces severe Noonan syndrome with hydrocephalus: A case report

Noonan syndrome (NS) is the most common disease among RASopathies, characterized by short stature, distinctive facial features, congenital cardiac defects, and variable developmental delay. NS rarely presents with overt neurologic manifestations, in particular hydrocephalus. Recent evidence suggests that pathogenic variants in the gene RRAS2 are a rare cause of NS. Specifically, an RRAS2 pathogenic variant, p.Q72L, may be particularly severe, manifesting with lethal neurologic findings. Here, we report a NS patient with documented p.Q72L variant in RRAS2. The patient was identified in utero to have hydrocephalus and a Dandy Walker malformation. Postnatal examination revealed multiple dysmorphic features, some reminiscent of NS including low-set posteriorly rotated ears, redundant nuchal skin, widely spaced nipples, and cryptorchidism. Despite suspicion of NS, results of a 14-gene Noonan syndrome panel (Invitae) were negative. Follow-up rapid whole exome sequencing revealed a de novo p.Q72L variant in RRAS2, a poorly studied gene recently identified as a cause of NS. The patient herein reported brings to three the total number of cases reported with the RRAS2 p.Q72L pathogenic variant. All three documented patients presented with a particularly fulminant course of NS, which included hydrocephalus. RRAS2, specifically p.Q72L, should be considered in severe NS cases with neurologic manifestations.

Genotype-cardiac phenotype correlations in a large single-center cohort of patients affected by RASopathies: Clinical implications and literature review

Congenital heart disease (CHD) and hypertrophic cardiomyopathy (HCM) are common features in patients affected by RASopathies. The aim of this study was to assess genotype- phenotype correlations, focusing on the cardiac features and outcomes of interventions for cardiac conditions, in a single-center cohort of 116 patients with molecularly confirmed diagnosis of RASopathy, and compare these findings with previously published data. All enrolled patients underwent a comprehensive echocardiographic examination. Relevant information was also retrospectively collected through the analysis of clinical records. As expected, significant associations were found between PTPN11 mutations and pulmonary stenosis (both valvular and supravalvular) and pulmonary valve dysplasia, and between SOS1 mutations and valvular defects. Similarly, HRAS mutations were significantly associated with HCM. Potential associations between less prevalent mutations and cardiac defects were also observed, including RIT1 mutations and HCM, SOS2 mutations and septal defects, and SHOC2 mutations and septal and valve abnormalities. Patients with PTPN11 mutations were the most likely to require both a primary treatment (transcatheter or surgical) and surgical reintervention. Other cardiac anomalies less reported until recently in this population, such as isolated functional and structural mitral valve diseases, as well as a sigmoid-shaped interventricular septum in the absence of HCM, were also reported. In conclusion, our study confirms previous data but also provides new insights on cardiac involvement in RASopathies. Further research concerning genotype/phenotype associations in RASopathies could lead to a more rational approach to surgery and the consideration of drug therapy in patients at higher risk due to age, severity, anatomy, and comorbidities.

Activating MRAS mutations cause Noonan syndrome associated with hypertrophic cardiomyopathy

The RASopathies are a group of genetic syndromes caused by upregulated RAS signaling. Noonan syndrome (NS), the most common entity among the RASopathies, is characterized mainly by short stature, cardiac anomalies and distinctive facial features. Mutations in multiple RAS-MAPK pathway-related genes have been associated with NS and related phenotypes. We describe two unrelated patients presenting with hypertrophic cardiomyopathy (HCM) and dysmorphic features suggestive of NS. One of them died in the neonatal period because of cardiac failure. Targeted sequencing revealed de novo MRAS variants, c.203C > T (p.Thr68Ile) and c.67G > C (p.Gly23Arg) as causative events. MRAS has only recently been related to NS based on the observation of two unrelated affected individuals with de novo variants involving the same codons here found mutated. Gly23 and Thr68 are highly conserved residues, and the corresponding codons are known hotspots for RASopathy-associated mutations in other RAS proteins. Functional analyses documented high level of activation of MRAS mutants due to impaired GTPase activity, which was associated with constitutive plasma membrane targeting, prolonged localization in non-raft microdomains, enhanced binding to PPP1CB and SHOC2 protein, and variably increased MAPK and PI3K-AKT activation. This report provides additional evidence that a narrow spectrum of activating mutations in MRAS represents another rare cause of NS, and that MRAS has to be counted among the RASopathy genes predisposing to HCM. Moreover, our findings further emphasize the relevance of the MRAS-SHOC2-PPP1CB axis in the control of MAPK signaling, and the contribution of both MAPK and PI3K-AKT pathways in MRAS functional upregulation.

Prenatal cases with rare RIT1 variants causing severe fetal hydrops and death

We describe two clinical prenatal cases with rare de novo RIT1 variants, which showed more severe clinical manifestations than other Noonan Syndrome genotypes, resulting in fetal death. Extra attention is recommended when these variants are detected.

The RAS GTPase RIT1 compromises mitotic fidelity through spindle assembly checkpoint suppression

The spindle assembly checkpoint (SAC) functions as a sensor of unattached kinetochores that delays mitotic progression into anaphase until proper chromosome segregation is guaranteed.^1,2 Disruptions to this safety mechanism lead to genomic instability and aneuploidy, which serve as the genetic cause of embryonic demise, congenital birth defects, intellectual disability, and cancer.^3,4 However, despite the understanding of the fundamental mechanisms that control the SAC, it remains unknown how signaling pathways directly interact with and regulate the mitotic checkpoint activity. In response to extracellular stimuli, a diverse network of signaling pathways involved in cell growth, survival, and differentiation are activated, and this process is prominently regulated by the Ras family of small guanosine triphosphatases (GTPases).⁵ Here we show that RIT1, a Ras-related GTPase that regulates cell survival and stress response,⁶ is essential for timely progression through mitosis and proper chromosome segregation. RIT1 dissociates from the plasma membrane (PM) during mitosis and interacts directly with SAC proteins MAD2 and p31^comet in a process that is regulated by cyclin-dependent kinase 1 (CDK1) activity. Furthermore, pathogenic levels of RIT1 silence the SAC and accelerate transit through mitosis by sequestering MAD2 from the mitotic checkpoint complex (MCC). Moreover, SAC suppression by pathogenic RIT1 promotes chromosome segregation errors and aneuploidy. Our results highlight a unique function of RIT1 compared to other Ras GTPases and elucidate a direct link between a signaling pathway and the SAC through a novel regulatory mechanism.

A comprehensive analysis of RAS-effector interactions reveals interaction hotspots and new binding partners

RAS effectors specifically interact with GTP-bound RAS proteins to link extracellular signals to downstream signaling pathways. These interactions rely on two types of domains, called RAS-binding (RB) and RAS association (RA) domains, which share common structural characteristics. Although the molecular nature of RAS-effector interactions is well-studied for some proteins, most of the RA/RB-domain-containing proteins remain largely uncharacterized. Here, we searched through human proteome databases, extracting 41 RA domains in 39 proteins and 16 RB domains in 14 proteins, each of which can specifically select at least one of the 25 members in the RAS family. We next comprehensively investigated the sequence–structure–function relationship between different representatives of the RAS family, including HRAS, RRAS, RALA, RAP1B, RAP2A, RHEB1, and RIT1, with all members of RA domain family proteins (RASSFs) and the RB-domain-containing CRAF. The binding affinity for RAS-effector interactions, determined using fluorescence polarization, broadly ranged between high (0.3 μM) and very low (500 μM) affinities, raising interesting questions about the consequence of these variable binding affinities in the regulation of signaling events. Sequence and structural alignments pointed to two interaction hotspots in the RA/RB domains, consisting of an average of 19 RAS-binding residues. Moreover, we found novel interactions between RRAS1, RIT1, and RALA and RASSF7, RASSF9, and RASSF1, respectively, which were systematically explored in sequence–structure–property relationship analysis, and validated by mutational analysis. These data provide a set of distinct functional properties and putative biological roles that should now be investigated in the cellular context.

The RIT1 C-terminus associates with lipid bilayers via charge complementarity

RIT1 is a member of the Ras superfamily of small GTPases involved in regulation of cellular signaling. Mutations to RIT1 are involved in cancer and developmental disorders. Like many Ras subfamily members, RIT1 is localized to the plasma membrane. However, RIT1 lacks the C-terminal prenylation that helps many other subfamily members adhere to cellular membranes. We used molecular dynamics simulations to examine the mechanisms by which the C-terminal peptide (CTP) of RIT1 associates with lipid bilayers. We show that the CTP is unstructured and that its membrane interactions depend on lipid composition. While a 12-residue region of the CTP binds strongly to anionic bilayers containing phosphatidylserine lipids, the CTP termini fray from the membrane allowing for accommodation of the RIT1 globular domain at the membrane-water interface.

KrasP34R and KrasT58I mutations induce distinct RASopathy phenotypes in mice

Somatic KRAS mutations are highly prevalent in many cancers. In addition, a distinct spectrum of germline KRAS mutations causes developmental disorders called RASopathies. The mutant proteins encoded by these germline KRAS mutations are less biochemically and functionally activated than those in cancer. We generated mice harboring conditional Kras^LSL-P34Rand Kras^LSL-T58I knock-in alleles and characterized the consequences of each mutation in vivo. Embryonic expression of Kras^T58I resulted in craniofacial abnormalities reminiscent of those seen in RASopathy disorders, and these mice exhibited hyperplastic growth of multiple organs, modest alterations in cardiac valvulogenesis, myocardial hypertrophy, and myeloproliferation. By contrast, embryonic Kras^P34R expression resulted in early perinatal lethality from respiratory failure due to defective lung sacculation, which was associated with aberrant ERK activity in lung epithelial cells. Somatic Mx1-Cre–mediated activation in the hematopoietic compartment showed that Kras^P34R and Kras^T58I expression had distinct signaling effects, despite causing a similar spectrum of hematologic diseases. These potentially novel strains are robust models for investigating the consequences of expressing endogenous levels of hyperactive K-Ras in different developing and adult tissues, for comparing how oncogenic and germline K-Ras proteins perturb signaling networks and cell fate decisions, and for performing preclinical therapeutic trials.

Mouse models are developed to accurately recapitulate multiple features of RASopathy disorders caused by germline KRASP34R and KRAST581 mutations.

The molecular functions of RIT1 and its contribution to human disease

RIT1 is a member of the Ras family of GTPases that direct broad cellular physiological responses through tightly controlled signaling networks. The canonical Ras GTPases are well-defined regulators of the RAF/MEK/ERK pathway and mutations in these are pathogenic in cancer and a class of developmental disorders termed RASopathies. Emerging clinical evidences have now demonstrated a role for RIT1 in RASopathies, namely Noonan syndrome, and various cancers including lung adenocarcinoma and myeloid malignancies. While RIT1 has been mostly described in the context of neuronal differentiation and survival, the mechanisms underlying aberrant RIT1-mediated signaling remain elusive. Here, we will review efforts undertaken to characterize the biochemical and functional properties of the RIT1 GTPase at the molecular, cellular, and organismal level, as well as provide a phenotypic overview of different human conditions caused by RIT1 mutations. Deeper understanding of RIT1 biological function and insight to its pathogenic mechanisms are imperative to developing effective therapeutic interventions for patients with RIT1-mutant Noonan syndrome and cancer.

Complicated ventricular arrhythmia and hematologic myeloproliferative disorder in RIT1-associated Noonan syndrome: Expanding the phenotype and review of the literature

Background

Noonan syndrome is an autosomal dominant disorder secondary to RASopathies, which are caused by germ‐line mutations in genes encoding components of the RAS mitogen‐activated protein kinase pathway. RIT1 (OMIM *609591) was recently reported as a disease gene for Noonan syndrome.

Methods and Results

We present a patient with RIT1‐associated Noonan syndrome, who in addition to the congenital heart defect, had monocytosis, myeloproliferative disorder, and accelerated idioventricular rhythm that was associated with severe hemodynamic instability. Noonan syndrome was suspected given the severe pulmonary stenosis, persistent monocytosis, and “left‐shifted” complete blood counts without any evidence of an infectious process. Genetic testing revealed that the patient had a heterozygous c.221 C>G (pAla74Gly) mutation in the RIT1.

Conclusion

We report a case of neonatal Noonan syndrome associated with RIT1 mutation. The clinical suspicion for Noonan syndrome was based only on the congenital heart defect, persistent monocytosis, and myeloproliferative process as the child lacked all other hallmarks characteristics of Noonan syndrome. However, the patient had an unusually malignant ventricular dysrhythmia that lead to his demise. The case highlights the fact that despite its heterogeneous presentation, RIT1‐associated Noonan syndrome can be extremely severe with poor outcome.

Cullin 3 and Its Role in Tumorigenesis

Cullin 3 (Cul3) family of ubiquitin ligases comprises three components, the RING finger protein RBX1, the Cul3 scaffold, and a Bric-a-brac/Tramtrack/Broad complex (BTB) protein. The BTB protein serves as a bridge to connect Cul3 to substrate and is functionally equivalent to the combination of substrate adaptor and linker in other Cullin complexes. Human genome encodes for ~180 BTB proteins, implying a broad spectrum of ubiquitination signals and substrate repertoire. Accordingly, Cul3 ubiquitin ligases are involved in diverse cellular processes, including cell division, differentiation, cytoskeleton remodeling, stress responses, and nerve cell functions. Emerging evidence has pointed to the prominent role of Cul3 ubiquitin ligases in cancer. This chapter will describe recent advances on the roles of Cul3 E3 ligase complexes in regulating various cancer hallmarks and therapeutic responses and the mutation/dysregulation of Cul3 substrate adaptors in cancer. In particular, we will focus on several extensively studied substrate adaptors, such as Keap1, SPOP, KLHL20, and LZTR1, and will also discuss other recently identified Cul3 adaptors with oncogenic or tumor-suppressive functions. We conclude that Cul3 ubiquitin ligases represent master regulators of human malignancies and highlight the importance of developing modulating agents for oncogenic/tumor-suppressive Cul3 E3 ligase complexes to prevent or intervene tumorigenesis.

Cardiac manifestations and gene mutations of patients with RASopathies in Taiwan

RASopathies are developmental diseases caused by mutations in rat sarcoma-mitogen-activated protein kinase pathway genes. These disorders, such as Noonan syndrome (NS) and NS-related disorders (NSRD), including cardio-facio-cutaneous (CFC) syndrome, Costello syndrome (CS), and NS with multiple lentigines (NSML; also known as LEOPARD syndrome), have a similar systemic phenotype. A wide spectrum of congenital heart disease and hypertrophic cardiomyopathy (HCMP) can exhibit major associated characteristics. A retrospective study was conducted at the Mackay Memorial Hospital, National Taiwan University Hospital, Buddhist Tzu-Chi General Hospital, Chang-Gung Memorial Hospital, Taichung Veterans General Hospital, and Chung Shan Medical University Hospital from January 2007 to December 2018. We reviewed the clinical records of 76 patients with a confirmed molecular diagnosis of RASopathies, including NS, CS, CFC syndrome, and NSML. We evaluated the demographic data and medical records with clinical phenotypes of cardiac structural anomalies using cross-sectional and color Doppler echocardiography, electrocardiographic findings, and follow-up data. A total of 47 (61.8%) patients had cardiac abnormalities. The prevalence of cardiac lesions according to each syndrome was 62.7, 50.0, 60.0, and 66.7% in patients with NS, CFC syndrome, CS, and NSML, respectively. An atrial septal defect was usually combined with other cardiac abnormalities, such as pulmonary stenosis (PS), HCMP, ventricular septal defect, or patent ductus arteriosus. Patients with NS most commonly showed PS. In patients with NSRD and cardiac abnormalities, HCMP (29.4%) was the most commonly observed cardiac lesion. PTPN11 was also the most frequently detected mutation in patients with NS and NSRD. Cardiac abnormalities were the most common symptoms observed in patients with RASopathies at the time of their first hospital visit. Performing precise analyses of genotype-cardiac phenotype correlations in a larger cohort will help us accurately diagnose RASopathy as soon as possible.

Genotype-phenotype correlation analysis in Japanese patients with Noonan syndrome

Noonan syndrome (NS) is a heterogeneous disorder with multiple congenital malformations. Recent advances in molecular and genetic approaches have identified a number of responsible genes for NS, most of which are components of the RAS/MAPK signaling pathway, and genotype-phenotype correlation analyses have been extensively performed; however, analysis of Japanese NS patients is limited. Here, we evaluated clinical characteristics in genetically diagnosed NS patients and their relationships to genotypes. A total of 48 clinically diagnosed NS were included, and responsible mutations were identified in 39 patients (81.3%) with PTPN11 mutations being the most prevalent followed by SOS1 mutations. Cardiac anomalies including pulmonary stenosis and hypertrophic cardiomyopathy were most prevalent (87.2%), and the prevalence of hypertrophic cardiomyopathy was greater in patients without PTPN11 mutations than in those with PTPN11 mutations. Short stature was the second-most prevalent (69.2%) characteristic, and present height SD score was significantly associated with height SD score at 1 year old. Patients with SOS1 mutations had greater present height SD score and better growth during infancy. These findings suggest the presence of a genotype-phenotype correlation in Japanese patients with NS, which enables us to use genetic information to predict the clinical course and may allow for genotype-based medical interventions.

Genetic Basis for Congenital Heart Disease: Revisited: A Scientific Statement From the American Heart Association

This review provides an updated summary of the state of our knowledge of the genetic contributions to the pathogenesis of congenital heart disease. Since 2007, when the initial American Heart Association scientific statement on the genetic basis of congenital heart disease was published, new genomic techniques have become widely available that have dramatically changed our understanding of the causes of congenital heart disease and, clinically, have allowed more accurate definition of the pathogeneses of congenital heart disease in patients of all ages and even prenatally. Information is presented on new molecular testing techniques and their application to congenital heart disease, both isolated and associated with other congenital anomalies or syndromes. Recent advances in the understanding of copy number variants, syndromes, RASopathies, and heterotaxy/ciliopathies are provided. Insights into new research with congenital heart disease models, including genetically manipulated animals such as mice, chicks, and zebrafish, as well as human induced pluripotent stem cell-based approaches are provided to allow an understanding of how future research breakthroughs for congenital heart disease are likely to happen. It is anticipated that this review will provide a large range of health care-related personnel, including pediatric cardiologists, pediatricians, adult cardiologists, thoracic surgeons, obstetricians, geneticists, genetic counselors, and other related clinicians, timely information on the genetic aspects of congenital heart disease. The objective is to provide a comprehensive basis for interdisciplinary care for those with congenital heart disease.

[Modern genetic counselling : Practical aspects exemplified by hypertrophic cardiomyopathy]

Genetic counselling and subsequent molecular genetic testing should be performed in patients when an inherited monogenic form of heart disease is suspected. For the individual patient as well as for the (possibly asymptomatic) relatives, molecular diagnostics is important for an early diagnosis, (preventive) therapy and prognosis assessment. Using the example of hypertrophic cardiomyopathy (HCM), the most common monogenic form of structural heart disease, essential aspects of modern genetic counselling are elucidated. Specific examples of one case with a classical form of hypertrophic obstructive cardiomyopathy and one case of congenital HCM with Noonan's syndrome are discussed.

Cardiac transplantation in children with Noonan syndrome

NS and related RAS/MAPK pathway (RASopathy) disorders are the leading genetic cause of HCM presenting in infancy. HCM is a major cause of morbidity and mortality in children with Noonan spectrum disorders, especially in the first year of life. Previously, there have been only isolated reports of heart transplantation as a treatment for heart failure in NS. We report on 18 patients with NS disorders who underwent heart transplantation at seven US pediatric heart transplant centers. All patients carried a NS diagnosis: 15 were diagnosed with NS and three with NSML. Sixteen of eighteen patients had comprehensive molecular genetic testing for RAS pathway mutations, with 15 having confirmed pathogenic mutations in PTPN11, RAF1, and RIT1 genes. Medical aspects of transplantation are reported as well as NS-specific medical issues. Twelve of eighteen patients described in this series were surviving at the time of data collection. Three patients died following transplantation prior to discharge from the hospital, and another three died post-discharge. Heart transplantation in NS may be a more frequent occurrence than is evident from the literature or registry data. A mortality rate of 33% is consistent with previous reports of patients with HCM transplanted in infancy and early childhood. Specific considerations may be important in evaluation of this population for heart transplant, including a potentially increased risk for malignancies as well as lymphatic, bleeding, and coagulopathy complications.

SOS1 mutations in Noonan syndrome: Cardiomyopathies and not only congenital heart defects! Report of six patients including two novel variants and literature review

Noonan syndrome (NS) is caused by mutations in more than 10 genes, mainly PTPN11, SOS1, RAF1, and RIT1. Congenital heart defects and cardiomyopathy (CMP) are associated with significant morbidity and mortality in NS. Although hypertrophic CMP has "classically" been reported in association to RAF1, RIT1, and PTPN11 variants, SOS1 appears to be poorly related to CMP. Patients with NS attending our Center from January 2013 to June 2018 were eligible for inclusion if they carried SOS1 variants and presented with-or developed-CMP. Literature review describing the co-existence of SOS1 mutation and CMP was also performed. We identified six patients with SOS1 variants and CMP (male to female ratio 2:1) including two novel variants. CMP spectrum encompassed: (a) dilated CMP, (b) nonobstructive hypertrophic CMPs, and (c) obstructive hypertrophic CMPs. Survival is 100%. Literature review included 16 SOS1 mutated in CMP. CMP, mainly hypertrophic, has been often reported in association to RAF1, RIT1, and PTPN11 variants. Differently from previous reports, due to the frequent association of SOS1 variants and CMP in our single center experience, we suggest potential underestimated proportion of SOS1 in pediatric CMPs.

The Ras Superfamily of Small GTPases in Non-neoplastic Cerebral Diseases

The small GTPases from the Ras superfamily play crucial roles in basic cellular processes during practically the entire process of neurodevelopment, including neurogenesis, differentiation, gene expression, membrane and protein traffic, vesicular trafficking, and synaptic plasticity. Small GTPases are key signal transducing enzymes that link extracellular cues to the neuronal responses required for the construction of neuronal networks, as well as for synaptic function and plasticity. Different subfamilies of small GTPases have been linked to a number of non-neoplastic cerebral diseases such as Alzheimer’s disease (AD), Parkinson’s disease (PD), intellectual disability, epilepsy, drug addiction, Huntington’s disease (HD), amyotrophic lateral sclerosis (ALS) and a large number of idiopathic cerebral diseases. Here, we attempted to make a clearer illustration of the relationship between Ras superfamily GTPases and non-neoplastic cerebral diseases, as well as their roles in the neural system. In future studies, potential treatments for non-neoplastic cerebral diseases which are based on small GTPase related signaling pathways should be explored further. In this paper, we review all the available literature in support of this possibility.

Williams-Beuren syndrome in diverse populations

Williams-Beuren syndrome (WBS) is a common microdeletion syndrome characterized by a 1.5Mb deletion in 7q11.23. The phenotype of WBS has been well described in populations of European descent with not as much attention given to other ethnicities. In this study, individuals with WBS from diverse populations were assessed clinically and by facial analysis technology. Clinical data and images from 137 individuals with WBS were found in 19 countries with an average age of 11 years and female gender of 45%. The most common clinical phenotype elements were periorbital fullness and intellectual disability which were present in greater than 90% of our cohort. Additionally, 75% or greater of all individuals with WBS had malar flattening, long philtrum, wide mouth, and small jaw. Using facial analysis technology, we compared 286 Asian, African, Caucasian, and Latin American individuals with WBS with 286 gender and age matched controls and found that the accuracy to discriminate between WBS and controls was 0.90 when the entire cohort was evaluated concurrently. The test accuracy of the facial recognition technology increased significantly when the cohort was analyzed by specific ethnic population (P-value < 0.001 for all comparisons), with accuracies for Caucasian, African, Asian, and Latin American groups of 0.92, 0.96, 0.92, and 0.93, respectively. In summary, we present consistent clinical findings from global populations with WBS and demonstrate how facial analysis technology can support clinicians in making accurate WBS diagnoses.

New Noonan syndrome model mice with RIT1 mutation exhibit cardiac hypertrophy and susceptibility to β-adrenergic stimulation-induced cardiac fibrosis

BACKGROUND

Noonan syndrome (NS) is a genetic disorder characterized by short stature, a distinctive facial appearance, and heart defects. We recently discovered a novel NS gene, RIT1, which is a member of the RAS subfamily of small GTPases. NS patients with RIT1 mutations have a high incidence of hypertrophic cardiomyopathy and edematous phenotype, but the specific role of RIT1 remains unclear.

METHODS

To investigate how germline RIT1 mutations cause NS, we generated knock-in mice that carried a NS-associated Rit1 A57G mutation (Rit1^A57G/+). We investigated the phenotypes of Rit1^A57G/+ mice in fetal and adult stages as well as the effects of isoproterenol on cardiac function in Rit1^A57G/+ mice.

FINDINGS

Rit1^A57G/+ embryos exhibited decreased viability, edema, subcutaneous hemorrhage and AKT activation. Surviving Rit1^A57G/+ mice had a short stature, craniofacial abnormalities and splenomegaly. Cardiac hypertrophy and cardiac fibrosis with increased expression of S100A4, vimentin and periostin were observed in Rit1^A57G/+ mice compared to Rit1^+/+ mice. Upon isoproterenol stimulation, cardiac fibrosis was drastically increased in Rit1^A57G/+ mice. Phosphorylated (at Thr308) AKT levels were also elevated in isoproterenol-treated Rit1^A57G/+ hearts.

INTERPRETATION

The A57G mutation in Rit1 causes cardiac hypertrophy, fibrosis and other NS-associated features. Biochemical analysis indicates that the AKT signaling pathway might be related to downstream signaling in the RIT1 A57G mutant at a developmental stage and under β-adrenergic stimulation in the heart. FUND: The Grants-in-Aid were provided by the Practical Research Project for Rare/Intractable Diseases from the Japan Agency for Medical Research and Development, the Japan Society for the Promotion of Science KAKENHI Grant.

RIT1 oncoproteins escape LZTR1-mediated proteolysis

RIT1 oncoproteins have emerged as an etiologic factor in Noonan syndrome and cancer. Despite the resemblance of RIT1 to other members of the Ras small guanosine triphosphatases (GTPases), mutations affecting RIT1 are not found in the classic hotspots but rather in a region near the switch II domain of the protein. We used an isogenic germline knock-in mouse model to study the effects of RIT1 mutation at the organismal level, which resulted in a phenotype resembling Noonan syndrome. By mass spectrometry, we detected a RIT1 interactor, leucine zipper-like transcription regulator 1 (LZTR1), that acts as an adaptor for protein degradation. Pathogenic mutations affecting either RIT1 or LZTR1 resulted in incomplete degradation of RIT1. This led to RIT1 accumulation and dysregulated growth factor signaling responses. Our results highlight a mechanism of pathogenesis that relies on impaired protein degradation of the Ras GTPase RIT1.

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.

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.

Cardiovascular disease in Noonan syndrome

PURPOSE OF REVIEW

To provide information on the scope of cardiac disease in Noonan syndrome.

RECENT FINDINGS

Noonan syndrome is a common autosomal dominant RASopathy disorder characterized by clinical findings of facial dysmorphism, congenital heart disease, and short stature. The degree of genetic heterogeneity has recently become evident in that Noonan syndrome is now known to be caused by mutations in a large variety of genes which produce dysregulation of the RAS-MAPK (mitogen-activated protein kinase) signaling pathway. The scope of cardiac disease in Noonan syndrome is quite variable depending on the gene mutation, with some mutations usually associated with a high incidence of congenital heart defects (PTPN11, KRAS, and others) while those with predominantly hypertrophic cardiomyopathy (HCM) have higher risk and morbidity profiles (RAF1, RIT1, and those associated with multiple lentigines).

SUMMARY

Cardiac disease in Noonan syndrome varies according to the type of gene mutation. The most common forms of cardiac disease include pulmonary stenosis, HCM, and atrial septal defect. HCM in general is associated with increased risk, mortality, and morbidity. New concepts for potential treatments are discussed.

The RASopathy Family: Consequences of Germline Activation of the RAS/MAPK Pathway

Noonan syndrome [NS; Mendelian Inheritance in Men (MIM) #163950] and related syndromes [Noonan syndrome with multiple lentigines (formerly called LEOPARD syndrome; MIM #151100), Noonan-like syndrome with loose anagen hair (MIM #607721), Costello syndrome (MIM #218040), cardio-facio-cutaneous syndrome (MIM #115150), type I neurofibromatosis (MIM #162200), and Legius syndrome (MIM #611431)] are a group of related genetic disorders associated with distinctive facial features, cardiopathies, growth and skeletal abnormalities, developmental delay/mental retardation, and tumor predisposition. NS was clinically described more than 50 years ago, and disease genes have been identified throughout the last 3 decades, providing a molecular basis to better understand their physiopathology and identify targets for therapeutic strategies. Most of these genes encode proteins belonging to or regulating the so-called RAS/MAPK signaling pathway, so these syndromes have been gathered under the name RASopathies. In this review, we provide a clinical overview of RASopathies and an update on their genetics. We then focus on the functional and pathophysiological effects of RASopathy-causing mutations and discuss therapeutic perspectives and future directions.

Diagnosis and outcome in nonhydropic fetal pleural effusions

OBJECTIVE

To determine the outcome of all pregnancies with nonhydropic fetal pleural effusions in the Wessex region.

METHOD

Data were extracted from the Wessex congenital anomaly database for the years 1994-2015 inclusive.

RESULTS

Sixty-two fetuses and babies were identified giving a total prevalence of 1:9500. Eight fetuses had bilateral effusions with additional, nonhydrops anomalies, and 54 had isolated effusions. Of the isolated cases, 36 presented before 24-week gestation: 12 were unilateral and 24 bilateral. All of the unilateral effusions resolved before or soon after birth with no other diagnosis but of the bilateral cases, four (17%) had a trisomy and three (13%) a genetic or syndrome diagnosis. Eighteen isolated cases presented after 24-week gestation, six were unilateral of which one had trisomy 21 (17%), and three (50%) Noonan's or another lymphoedema syndrome. Twelve were bilateral: One had trisomy 21, one an unbalanced translocation (17%), three had Noonan's or another lymphoedema syndrome, and two an unspecified syndrome (42%) at birth.

CONCLUSION

These data suggest that a chromosomal microarray should be offered to all fetuses presenting with a pleural effusion in the absence of hydrops, and Noonan's syndrome testing should be considered for those that develop after 24 weeks.

AIM

To determine the outcome of all pregnancies with nonhydropic fetal pleural effusions in the Wessex region from 1994-2015.