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Noonan syndrome (NS) is a mostly dominantly inherited disorder affecting 1:1000 to 1:2500 live births. The phenotype varies in severity and can involve multiple organ systems over a patient’s lifetime. Diagnosis is based on a combination of features, including typical facial features, short stature, skeletal abnormalities, presence of cardiac defects, mild developmental delay, cryptorchidism, lymphatic dysplasia and a family history of NS. The phenotype varies from oligosymptomatic adults without significant medical issues to severely affected neonates with life-threatening heart disease. Early, accurate diagnosis is important for individualised management and to optimise developmental and long-term outcomes, but mildly affected patients often go undiagnosed for both healthcare provider (HCP)-related and patient-related reasons. Lack of awareness of NS among HCPs means that some do not recognise the condition, particularly in mildly affected patients and families. Some families do not want to receive a diagnosis that medicalises a condition that may account for family traits (eg, distinctive facial features and short stature), particularly when a child’s physical and cognitive development may be satisfactory. As for any condition with lifelong effects on multiple organ systems, a multidisciplinary approach provides the best care. It is proposed that increasing awareness of NS among non-specialist HCPs and other professionals could help direct a parent/carer to seek specialist advice and increase the number of NS diagnoses, with the potential to optimise lifelong patient outcomes. Non-specialists do not need to become experts in either diagnosis or treatment; however, early recognition of NS and referral to an appropriate specialist is important.

Background/Objectives: Neurofibromatosis type 1 (NF1) and Noonan syndrome spectrum disorders (NSSD) are the most common RASopathies, resulting from germline mutations that affect the RAS-MAPK signaling pathway. Both are associated with increased risk for neurodevelopmental and psychiatric conditions, yet few studies have used structured diagnostic interviews to compare their psychiatric comorbidities. Methods: We conducted clinician-administered DSM-5 diagnostic assessments (KSADS) in 123 children with RASopathies (NF1 = 29, NSSD = 94; ages 5–15). Diagnosis prevalence was compared within each group and to population-based estimates. Results: Psychiatric diagnoses were highly prevalent, at 79.3% in NF1 and 76.6% in NSSD, with ADHD (NF1 = 72.4%, NSSD = 51.1%) and anxiety disorders (NF1 = 37.9% and NSSD = 43.6%) being the most common, rates substantially higher than those reported in general population estimates. Behavioral and sleep disorders were identified in approximately 25% of both groups. Notably, social anxiety disorder was identified in 14.9% of NSSD but not in NF1. Full-scale IQ did not significantly differ by diagnosis status. Specific anxiety disorders, elimination disorders, obsessive–compulsive disorder, and post-traumatic stress disorder were characterized, expanding the known psychiatric phenotype of RASopathies. Conclusions: Children with NF1 and NSSD demonstrate similarly high rates of ADHD, anxiety, and behavioral disorders compared to the general population; in addition, we report sleep disorders in NSSD and characterize psychiatric disorders not previously described in RASopathies. The shared psychiatric profiles may reflect the common effect of RAS-MAPK pathway dysregulation on psychiatric outcomes. These findings highlight the need for early, syndrome-informed mental health screening and intervention in the clinical care of individuals with RASopathies.

The RASopathies are a group of genetic rare diseases caused by mutations affecting genes involved in the RAS/MAPK (RAS–mitogen activated protein kinase) pathway. Among them, PTPN11 pathogenic variants are responsible for approximately 50% of Noonan syndrome (NS) cases and, albeit to a lesser extent, of Leopard syndrome (LPRD1), which present a few overlapping clinical features, such as facial dysmorphism, developmental delay, cardiac defects, and skeletal deformities. Motor impairment and decreased muscle strength have been recently reported. The etiology of the muscle involvement in these disorders is still not clear but probably multifactorial, considering the role of the RAS/MAPK pathway in skeletal muscle development and Acetylcholine Receptors (AChR) clustering at the neuromuscular junction (NMJ). We report, herein, four unrelated children carrying three different heterozygous mutations in the PTPN11 gene. Intriguingly, their phenotypic features first led to a clinical suspicion of congenital myasthenic syndrome (CMS), due to exercise-induced fatigability with a variable degree of muscle weakness, and serum proteomic profiling compatible with a NMJ defect. Moreover, muscle fatigue improved after treatment with CMS-specific medication. Although the link between PTPN11 gene and neuromuscular transmission is unconfirmed, an increasing number of patients with RASopathies are affected by muscle weakness and fatigability. Hence, NS or LPDR1 should be considered in children with suspected CMS but negative genetic workup for known CMS genes or additional symptoms indicative of NS, such as facial dysmorphism or intellectual disability.

Background and aimsNeurofibromatosis–Noonan syndrome (NFNS) is an extremely rare genetic entity combining the clinical phenotype of two conditions: neurofibromatosis type 1 syndrome (NF1) and Noonan syndrome (NS). Nevertheless, many inconsistencies reside in our understanding of this condition, mainly its clinical features and genetic background. Through this systematic review, we aim to shed light on the epidemiological features, the broad clinical spectrum, the underlying genetic defects and the associated comorbidities of NFNS.MethodsMedline, Scopus and Google Scholar were searched for publications on the clinical and genetic features of patients with NFNS. Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines were followed and the study protocol was registered in PROSPERO.ResultsOf 951 records screened, 42 were eligible. The mean age at diagnosis was 14.7 years ranging from 0 to 69 years. As for the circumstance of discovery of NFNS, it was dominated by family investigation followed by neurofibromas, facial dysmorphia and short stature (SS). Prematurity was noted in 40.9% of cases. The hallmark features of NFNS at diagnosis were ‘café au lait’ macules, typical facial dysmorphia of NS, postnatal SS, pectus abnormalities, broad neck and lentigines. Macrocephaly, scoliosis and cardiopathies occurred in 26%, 42.4% and 36.9% of cases, respectively. Tumours were found in 18.4% of cases. As for the genetic foundation of NFNS, NF1 gene mutations were depicted in 87.5% of individuals.ConclusionsBased on our findings, we emphasise on the importance of searching for NS features in patients with NF1 since the prognosis, comorbidities and consequently management could be altered.PROSPERO registration number42024522238.

Purpose To characterize the molecular genetics of autosomal recessive Noonan syndrome. Methods Families underwent phenotyping for features of Noonan syndrome in children and their parents. Two multiplex families underwent linkage analysis. Exome, genome, or multigene panel sequencing was used to identify variants. The molecular consequences of observed splice variants were evaluated by reverse-transcription polymerase chain reaction. Results Twelve families with a total of 23 affected children with features of Noonan syndrome were evaluated. The phenotypic range included mildly affected patients, but it was lethal in some, with cardiac disease and leukemia. All of the parents were unaffected. Linkage analysis using a recessive model supported a candidate region in chromosome 22q11, which includes LZTR1 , previously shown to harbor mutations in patients with Noonan syndrome inherited in a dominant pattern. Sequencing analyses of 21 live-born patients and a stillbirth identified biallelic pathogenic variants in LZTR1 , including putative loss-of-function, missense, and canonical and noncanonical splicing variants in the affected children, with heterozygous, clinically unaffected parents and heterozygous or normal genotypes in unaffected siblings. Conclusion These clinical and genetic data confirm the existence of a form of Noonan syndrome that is inherited in an autosomal recessive pattern and identify biallelic mutations in LZTR1 .

Background Infants with Noonan syndrome (NS) are predisposed to developing juvenile myelomonocytic leukaemia (JMML) or JMML-like myeloproliferative disorders (MPD). Whereas sporadic JMML is known to be aggressive, JMML occurring in patients with NS is often considered as benign and transitory. However, little information is available regarding the occurrence and characteristics of JMML in NS. Methods and results Within a large prospective cohort of 641 patients with a germline PTPN11 mutation, we identified MPD features in 36 (5.6%) patients, including 20 patients (3%) who fully met the consensus diagnostic criteria for JMML. Sixty percent of the latter (12/20) had severe neonatal manifestations, and 10/20 died in the first month of life. Almost all (11/12) patients with severe neonatal JMML were males. Two females who survived MPD/JMML subsequently developed another malignancy during childhood. Although the risk of developing MPD/JMML could not be fully predicted by the underlying PTPN11 mutation, some germline PTPN11 mutations were preferentially associated with myeloproliferation: 10/48 patients with NS (20.8%) with a mutation in codon Asp61 developed MPD/JMML in infancy. Patients with a p.Thr73Ile mutation also had more chances of developing MPD/JMML but with a milder clinical course. SNP array and whole exome sequencing in paired tumoral and constitutional samples identified no second acquired somatic mutation to explain the occurrence of myeloproliferation. Conclusions JMML represents the first cause of death in PTPN11-associated NS. Few patients have been reported so far, suggesting that JMML may sometimes be overlooked due to early death, comorbidities or lack of confirmatory tests.

Noonan syndrome belongs to the family of RASopathies, a group of multiple congenital anomaly disorders caused by pathogenic variants in genes encoding components or regulators of the RAS/mitogen-activated protein kinase (MAPK) signalling pathway. Collectively, all these pathogenic variants lead to increased RAS/MAPK activation. The better understanding of the molecular mechanisms underlying the different manifestations of NS and RASopathies has led to the identification of molecular targets for specific pharmacological interventions. Many specific agents (e.g. SHP2 and MEK inhibitors) have already been developed for the treatment of RAS/MAPK-driven malignancies. In addition, other molecules with the property of modulating RAS/MAPK activation are indicated in non-malignant diseases (e.g. C-type natriuretic peptide analogues in achondroplasia or statins in hypercholesterolemia).   Conclusion : Drug repositioning of these molecules represents a challenging approach to treat or prevent medical complications associated with RASopathies. What is Known: • Noonan syndrome and related disorders are caused by pathogenic variants in genes encoding components or regulators of the RAS/mitogen-activated protein kinase (MAPK) signalling pathway, resulting in increased activation of this pathway. • This group of disorders is now known as RASopathies and represents one of the largest groups of multiple congenital anomaly diseases known. What is New: • The identification of pathophysiological mechanisms provides new insights into the development of specific therapeutic strategies, in particular treatment aimed at reducing RAS/MAPK hyperactivation. • Drug repositioning of specific agents already developed for the treatment of malignant (e.g. SHP2 and MEK inhibitors) or non-malignant diseases (e.g. C-type natriuretic peptide analogues in achondroplasia or statins in hypercholesterolaemia) represents a challenging approach to the treatment of RASopathies.

Background Noonan Syndrome (NS) is a rare multisystemic disorder with heterogeneous phenotypic manifestations. The aim of this study was to analyse rates of survival, hospitalisation, surgeries and prescriptions in children born with NS in the first 10 years of life. Methods This is a multi-centre population-based cohort study. Data on 175 liveborn children diagnosed with NS from 11 EUROCAT congenital anomaly registries were linked to healthcare databases. Each registry applied a common data model to standardise data and run common syntax scripts to produce aggregated results which were pooled using random effects meta-analyses. Results Mortality rates were high in the first year of life with 5.4% (95%CI 1.5%-10.1%) of children dying before the age of 1 year with a further 2% dying up to age 5. In the first year, 87.9% (95%CI 75.3%-94.3%) of children were hospitalized and the median Length Of hospital Stay (LOS) was 15.3 days (95%CI 9.3–21.2). After the first year, the proportion of children hospitalized remained higher than 70%, but the LOS decreased to 1.3 days per year. In the first 5 years, 65.2% of children underwent a median of two surgical procedures. The median age at first surgery was 29 weeks. The proportion of children with an antibiotic prescription increased from 53.6% at age 1 to 62.4% yearly until 4 years of age. Conclusions Children with NS have high mortality and morbidity not only in the first year of life but also up to five years of age. This study evaluated the health burden of NS and provided information for clinicians, health-care providers and families.

The RASopathies are a group of disorders caused by a germline mutation in one of the genes encoding a component of the RAS/MAPK pathway. These disorders, including neurofibromatosis type 1, Noonan syndrome, cardiofaciocutaneous syndrome, Costello syndrome and Legius syndrome, among others, have overlapping clinical features due to RAS/MAPK dysfunction. Although several of the RASopathies are very rare, collectively, these disorders are relatively common. In this Review, we discuss the pathogenesis of the RASopathy-associated genetic variants and the knowledge gained about RAS/MAPK signaling that resulted from studying RASopathies. We also describe the cell and animal models of the RASopathies and explore emerging RASopathy genes. Preclinical and clinical experiences with targeted agents as therapeutics for RASopathies are also discussed. Finally, we review how the recently developed drugs targeting RAS/MAPK-driven malignancies, such as inhibitors of RAS activation, direct RAS inhibitors and RAS/MAPK pathway inhibitors, might be leveraged for patients with RASopathies.

Background: Noonan syndrome (NS) is a congenital genetic disorder with a prevalence of 1 in 1000 to 2500 live births, and is characterized by distinctive facial features, short stature, chest deformities, and congenital heart disease. This study aims to evaluate the prevalence of specific genetic mutations and their impact on cardiovascular and other outcomes in NS. Methods: We conducted a retrospective clinical study of 25 pediatric patients diagnosed with NS at two institutions: The Mother and Child Health Care Institute of Serbia and the Clinic for Children Diseases, University Clinical Center of the Republic of Srpska. Patients underwent whole-exome sequencing (WES) to identify genetic mutations. Clinical data, including cardiovascular manifestations, psychomotor development, and stature, were analyzed in relation to mutation types. Results: The cohort comprised 60% male and 40% female patients, with a median age at diagnosis of 7.2 years. Cardiovascular abnormalities were present in 88% of patients. Mutations in PTPN11 were most commonly associated with pulmonary valve stenosis (PVS), while RAF1 mutations were prevalent in patients with hypertrophic cardiomyopathy (HCM). No significant association was found between cardiac disease and delayed psychomotor development (p = 0.755), even though the likelihood ratio showed significance in that regard (p = 0.018). Short stature was observed in 48% of patients but was not significantly correlated with genetic type of disease, presence of cardiac disease, or developmental delay. Conclusions: The study confirms the high prevalence of cardiovascular manifestations in NS and highlights genotype–phenotype correlations. While cardiac abnormalities are common, their impact on psychomotor development and stature is less clear. Further research is needed to explore genetic interactions influencing these outcomes and refine clinical management strategies.