RASopathies for Radiologists.

RASopathies are a heterogeneous group of genetic syndromes caused by germline mutations in a group of genes that encode components or regulators of the Ras/mitogen-activated protein kinase (MAPK) signaling pathway. RASopathies include neurofibromatosis type 1, Legius syndrome, Noonan syndrome, Costello syndrome, cardiofaciocutaneous syndrome, central conducting lymphatic anomaly, and capillary malformation-arteriovenous malformation syndrome. These disorders are grouped together as RASopathies based on our current understanding of the Ras/MAPK pathway. Abnormal activation of the Ras/MAPK pathway plays a major role in development of RASopathies. The individual disorders of RASopathies are rare, but collectively they are the most common genetic condition (one in 1000 newborns). Activation or dysregulation of the common Ras/MAPK pathway gives rise to overlapping clinical features of RASopathies, involving the cardiovascular, lymphatic, musculoskeletal, cutaneous, and central nervous systems. At the same time, there is much phenotypic variability in this group of disorders. Benign and malignant tumors are associated with certain disorders. Recently, many institutions have established multidisciplinary RASopathy clinics to address unique therapeutic challenges for patients with RASopathies. Medications developed for Ras/MAPK pathway-related cancer treatment may also control the clinical symptoms due to an abnormal Ras/MAPK pathway in RASopathies. Therefore, radiologists need to be aware of the concept of RASopathies to participate in multidisciplinary care. As with the clinical manifestations, imaging features of RASopathies are overlapping and at the same time diverse. As an introduction to the concept of RASopathies, the authors present major representative RASopathies, with emphasis on their imaging similarities and differences. ©RSNA, 2024 Test Your Knowledge questions for this article are available in the supplemental material.

Prenatal diagnosis of autosomal recessive Noonan syndrome associated with biallelic LZTR1 variants presented with thick nuchal translucency and cardiac abnormalities.

Noonan syndrome (NS) is a common clinical variable disease characterized by a number of features, mainly including congenital heart defects, short stature, and a variable degree of developmental delay. This disorder is transmitted mostly in an autosomal dominant manner and is genetically heterogeneous. We report three prenatal cases of LZTR1-related recessive NS. One case had a recurrent cystic hygroma at 13 weeks gestation and the pregnancy was terminated. Two cases had an increased nuchal translucency at 12 weeks' gestation, but a normal second trimester ultrasound; both presented with hypertrophic cardiomyopathy in the third trimester. The two infants were diagnosed with NS after birth. All of the three cases had invasive genetic investigations during pregnancy, and trio exome sequencing revealed biallelic likely pathogenic or pathogenic LZTR1 variants in the fetuses. All parents were LZTR1 variant carriers. Our report further strengthens the association of LZTR1 with an autosomal recessive form of NS. The affected fetuses are more likely to have cardiac anomalies. Clarification of molecular diagnosis has important implications in these families because they carry a 25% recurrence risk.

Neurological features of Noonan syndrome and related RASopathies: Pain and nerve enlargement characterized by nerve ultrasound.

This study aimed to assess the nature of peripheral nervous system (PNS) involvement in three patients with Noonan syndrome (NS) or NS with multiple lentigines (NSML) as a related RASopathy, presenting primary with intractable neuropathic pain. We studied three unrelated adult patients with severe neuropathic pain and muscle weakness of the limbs. Nerve conduction studies and needle electromyography (EMG) were performed and PNS involvement was assessed by nerve ultrasound imaging, complemented with spinal magnetic resonance imaging (MRI) for the evaluation of proximal nerve segments. Targeted whole-exome sequencing analysis was performed when the diagnosis of NS was suspected. Two patients showed a PTPN11-related dominant and one a LZTR1-related recessive NS or NSML phenotype. The nature of PNS involvement was documented using nerve ultrasound and MRI, showing generalized or multifocal thickening of nerve roots, plexuses and peripheral nerves in all three patients. Nerve imaging using ultrasound and MRI aids in further detailing the nature of neuropathic pain and nerve hypertrophy in patients with NS. This study underlines the relevance of nerve ultrasound in neuropathies and pain syndromes. A NS diagnosis should not be overlooked in longstanding, unexplained neuropathic pain syndromes, with or without muscular weakness. Nerve ultrasound studies can help raise the suspicion for this relatively prevalent inherited multisystem disorder, which is still rather unknown among neurologists, particularly when other potential syndromic features are inconspicuous.

Extending the prenatal Noonan's phenotype by review of ultrasound and autopsy data.

OBJECTIVES: The antenatal phenotypic spectrum of Noonan Syndrome (NS) requires better characterization. METHODS: This multicenter retrospective observational included 16 fetuses with molecularly confirmed NS admitted for fetopathological examination between 2009 and 2016. RESULTS: Among 12 pathogenic variants (PV) in PTPN11 (80%), 5 (42%) fell between position c.179 and c.182. Ultrasound showed increased nuchal translucency (n = 13/16, 93%), increased nuchal fold after 15 weeks of gestation (n = 12/16, 75%), pleural effusions (n = 11/16, 69%), polyhydramnios (n = 9/16, 56%), hydrops (n = 7/16, 44%), cardiovascular (n = 6/16, 38%) and cerebral (n = 4/16, 25%) anomalies. Fetopathological examination found dysmorphic features in all cases, cardiovascular anomalies (n = 12/15, 80%), pulmonary hypoplasia (n = 10/15, 67%), effusions (n = 7/15, 47%) and neuropathological anomalies (n = 5/15, 33%). Hydrops was significantly (p = 0.02) more frequent in the four fetuses with RIT1, NRAS and RAF1 PV versus the 12 fetuses with PTPN11 PV. CONCLUSIONS: Increased nuchal translucency and nuchal fold is common in NS. Noonan Syndrome antenatal phenotype showed high in utero fetal death, hydrops, prenatal pleural effusion and pulmonary hypoplasia, although the inclusion of only deceased fetuses will have selected more severe phenotypes. Non-specific cardiovascular and neurological abnormalities should be added to NS antenatal phenotype. Next generation sequencing will help detect more genotypes, clarifying the prenatal phenotype and identifying genotype-phenotype correlations.

First prenatal case of Noonan syndrome with SOS2 mutation: Implications of early diagnosis for genetic counseling.

RASopathies are a group of syndromes with partially overlapping clinical features caused by germline mutations of the RAS/MAPK signaling pathway genes. The most common disorder is Noonan syndrome (NS; MIM 163950). We report the first prenatal case of NS with SOS2 (NM_006939.4) mutation in a euploid fetus with a severe increase in nuchal translucency (NT > 12 mm). Trio-based custom next-generation sequencing detected a de novo heterozygous missense mutation in the SOS2 gene: c.800 T > A (p.Met267Lys). Owing to the marked variable expressivity of NS and the scarcity of SOS2 mutation-related NS cases reported in the literature, it is difficult to provide appropriate genetic counseling. Several issues such as the best management technique and optimal NT cutoff have been discussed. In addition, in general, the fine balance between the advantages of an early prenatal diagnosis and the challenge of determining if the detected gene variant is pathogenic and, primarily, the stress of the counselees when providing a genetic counseling with limited information on the prenatal phenotype have been discussed. A prenatal path comprising examinations and multidisciplinary counseling is essential to support couples in a shared decision-making process.

The point-of-care use of a facial phenotyping tool in the genetics clinic: Enhancing diagnosis and education with machine learning.

Computer-assisted pattern recognition platforms, such as Face2Gene® (F2G), can facilitate the diagnosis of children with rare genetic syndromes by comparing a patient's features to known genetic diagnoses. Our work designed, implemented, and evaluated an innovative model of care in clinical genetics in a heterogeneous and multicultural patient population that utilized this facial phenotyping software at the point-of-care. We assessed the performance of F2G by comparing the suggested diagnoses to the patient's confirmed molecular diagnosis. Providers' overall experiences with the technology and trainees' educational experiences were assessed with questionnaires. We achieved an overall diagnostic yield of 57%. This increased to 82% when cases diagnosed with syndromes not recognized by F2G were removed. The mean rank of a confirmed diagnosis in the top 10 was 2.3 (CI 1.5-3.2) and the mean gestalt score 37.6%. The most commonly suggested diagnoses were Noonan syndrome, mucopolysaccharidosis, and 22q11.2 deletion syndrome. Our qualitative assessment revealed that clinicians and trainees saw value using the tool in practice. Overall, this work helped to implement an innovative patient care delivery model in clinical genetics that utilizes a facial phenotyping tool at the point-of-care. Our data suggest that F2G has utility in the genetics clinic as a clinical decision support tool in diverse populations, with a majority of patients having their eventual diagnosis listed in the top 10 suggested syndromes based on a photograph alone. It shows promise for further integration into clinical care and medical education, and we advocate for its continued use, adoption and refinement along with transparent and accountable industrial partnerships.

Clinical report of a brain magnetic resonance imaging finding in Noonan syndrome.

Noonan syndrome (NS) is an autosomal dominant disease caused by aberrant up-regulated signaling through RAS GTPase. It is characterized by facial dysmorphisms, short stature, congenital heart defects, malformations of rib cage bones, bleeding problems, learning difficulties, or mild intellectual disability. Additional intracranial findings in NS patients include tumors, midline anomalies, and malformations of cortical development. In this report, we present the case of a young female patient, with a known diagnosis of Noonan syndrome that in complete well being developed two brain lesions, in the right nucleus pallidus and in the left cerebellar hemisphere respectively, whose location and signal on MRI looked similar to neurofibromatosis type 1 unidentified bright objects (UBOs), and whose spectroscopic characteristics excluded neoplasms.

Is there still a role for nuchal translucency measurement in the changing paradigm of first trimester screening?

OBJECTIVES: To give an overview of the genetic and structural abnormalities occurring in fetuses with nuchal translucency (NT) measurement exceeding the 95th percentile at first-trimester screening and to investigate which of these abnormalities would be missed if cell-free fetal DNA (cfDNA) were used as a first-tier screening test for chromosomal abnormalities. METHODS: This is a national study including 1901 pregnancies with NT≥95th percentile referred to seven university hospitals in the Netherlands between 1 January 2010 and 1 January 2016. All cases with unknown pregnancy outcome were excluded. Results of detailed ultrasound examinations, karyotyping, genotyping, pregnancy and neonatal outcomes, investigation by a clinical geneticist and post-mortem investigations were collected. RESULTS: In total, 821 (43%) pregnancies had at least one abnormality. The rate of abnormalities was 21% for fetuses with NT between 95th and 99th percentile and 62% for fetuses with NT≥99th percentile. Prevalence of single-gene disorders, submicroscopic, chromosomal and structural abnormalities was 2%, 2%, 30% and 9%, respectively. CONCLUSION: Although cfDNA is superior to the combined test, especially for the detection of trisomy 21, 34% of the congenital abnormalities occurring in fetuses with increased NT may remain undetected in the first trimester of pregnancy, unless cfDNA is used in combination with fetal sonographic assessment, including NT measurement.

3D Ultrasound Evaluation of the Fetal Outer Ear: Novel Biometry Ratio and Comparison of Different Surface Display Modes.

BACKGROUND: The examination of the fetal ear is a promising but still challenging approach in prenatal diagnosis. OBJECTIVES: This study investigated a novel ear length/width ratio based on anatomical landmarks. Additionally, we compared different 3D ultrasound surface rendering modes regarding their potential to depict detailed structures of the outer ear. METHOD: We measured both the ear length and width of 118 fetal ears from 20 to 40 weeks of gestation to establish a length/width ratio. Additionally, we rendered the volumes in three different surface display modes and one adapted light position. Each image was scored regarding the visibility of distinct structures of the ear relief and indicator scores were evaluated for each mode. RESULTS: The median of the length/width ratio was 1.9 with a slight decline over the gestational period. The overall visibility of the ear structures differed noticeably between the four surface display modes (p < 0.001). The post hoc comparison showed that the display mode "TrueVue" resulted in the highest indicator scores. CONCLUSION: The length/width ratio based on anatomical landmarks of the ear could prospectively be used as a marker in syndrome detection. The study showed a superiority of the surface display mode "TrueVue" for examination of the detailed ear structures.

Testing for Noonan syndrome after increased nuchal translucency.

OBJECTIVE: The aim of this study was to report the prevalence of Noonan syndrome (NS) in a cohort of fetuses that presented with increased nuchal translucency (NT) thickness in the first trimester of pregnancy. METHODS: This is a retrospective chart review. INCLUSION CRITERIA: (1) first trimester NT measurement ≥3 mm, (2) normal karyotype by either a CVS or an amniocentesis procedure, and (3) prenatal molecular genetic testing for NS completed. Results with known pathogenic variants were considered positive, while those with variants of unknown clinical significance, or with no variants, were considered negative. RESULTS: A total of 804 fetuses had an NT measurement of ≥3 mm, with a median NT thickness of 3.6 mm. Of these, 302 had karyotyping by CVS or amniocentesis, 200 (66.23%) with normal results. Of fetuses with a normal karyotype, 39 with a median NT thickness of 4.0 mm had a NS gene sequencing panel done, and 161 fetuses with a mean NT thickness of 4.3 mm were not tested for NS (p = 0.05). Of the 39 fetuses who were tested for NS, four (10.3%) had variants consistent with this diagnosis. CONCLUSION: In euploid fetuses, increased NT is associated with a 10% risk of NS. © 2017 John Wiley & Sons, Ltd.

Retrospective study of prenatal ultrasound findings in newborns with a Noonan spectrum disorder.

OBJECTIVES: Noonan spectrum disorders (NSDs) occur in 1:1000-2500 live births. Currently, there are no guidelines for prenatal molecular genetic testing for NSDs. Recent studies recommend prenatal testing for NSDs when ultrasonography detects two or more associated abnormalities. A stronger association between ultrasound findings and NSDs would enable more informed prenatal genetic testing. METHODS: A total of 212 newborns (0-12 weeks) with prenatal ultrasound findings and a clinical suspicion of a NSD were referred for molecular genetic testing. Of these, 159/212 newborns tested had a single ultrasound abnormality and 53/212 newborns had two or more. Testing was performed by either a microarray-based resequencing assay or next generation sequencing of RAS/MAPK pathway genes associated with NSDs. Prenatal ultrasound findings in positive and negative cases were compared. RESULTS: A disease-causing variant was identified in 21.7% (46/212) of newborns tested. Of these positive cases, 67.4% (31/46) had only one ultrasound abnormality reported. The rate of detecting a disease-causing variant in cases with one ultrasound finding was 19.5% (31/159), which was not significantly different (p-value = 0.36) than that in cases with two or more ultrasound findings (28.3%; 15/53). CONCLUSIONS: Prenatal molecular testing for NSDs should be considered even in the presence of a single associated abnormal ultrasound finding. © 2016 John Wiley & Sons, Ltd.

Development of bilateral coronary artery aneurysms in a child with Noonan syndrome.

Noonan syndrome is a constellation of congenital malformations including heart defects, facial anomalies and short stature. The cardiovascular defects are variable and extensive, with the most common being pulmonary stenosis and hypertrophic cardiomyopathy. Coronary artery anomalies have only been reported in a few cases. We report a child with Noonan syndrome status post pulmonary stenosis and atrial septal defect repair, who developed bilateral coronary artery aneurysms. The aneurysms were diagnosed with both cardiac magnetic resonance imaging and coronary computed tomography angiography. There had been no evidence of them on a cardiac MR exam 5 years previously.

Transnodal lymphangiography and post-CT for protein-losing enteropathy in Noonan syndrome.

Noonan syndrome, which is a multiple congenital disorder, may be associated with lymphatic abnormalities. Protein-losing enteropathy (PLE) developing in Noonan syndrome is rare. We performed transnodal lymphangiography by directly accessing bilateral inguinal nodes under ultrasound guidance in a 17-year-old female with PLE developing in Noonan syndrome to assess detailed anatomical findings regarding lymphatic vessels. There have been no reports on transnodal lymphangiography for Noonan syndrome. Post-lymphangiographic CT images revealed multiple lymphatic abnormalities and lipiodol extravasation into the duodenum and the proximal jejunum. Transnodal lymphangiography was easy and safe for PLE developing in Noonan syndrome, and post-lymphangiographic CT provided invaluable information.

Cervical characteristics of Noonan syndrome.

BACKGROUND/OBJECTIVES A short neck and low posterior hairline are characteristics of Noonan syndrome (NS) and are hallmarks of basilar invagination/impression. However, it is seldom that NS has been directly linked with this symptom. Thus, this study aimed to investigate basilar impression in NS subjects compared with control subjects and individuals exhibiting Turner Syndrome (TS). SUBJECTS/METHODS The degree of basilar impression and vertical positional differences of the third and fourth cervical vertebrae and hyoid bone in NS (n = 9, mean age: 12.1 years), TS (n = 9, mean age: 12.1 years), and control subjects (n = 9, mean age: 12.0 years) were investigated using lateral cephalometric radiographs. Differences between the three groups were compared using the Steel-Dwass test. Vertical positional differences in the anatomical structures within each group were compared using the Wilcoxon signed-rank test accompanied by a Bonferroni-Holm correction. RESULTS The distance by which the odontoid tip extended past McGregor's line in subjects with NS was significantly greater compared with TS and control subjects. The third and fourth cervical vertebrae were positioned significantly superiorly in subjects with NS compared with TS and control subjects and, in NS, were also significantly superior to the hyoid bone. There was no difference in the position of the hyoid bone itself between the groups. CONCLUSION/IMPLICATION These results suggest that basilar impression may be a frequently found symptom of NS.

Cardiac screening in pediatric patients with neurofibromatosis type 1: similarities with Noonan syndrome?

Both Neurofibromatosis type 1 (NF1) and Noonan syndrome (NS) are RASopathies. Characteristic cardiac phenotypes of NS, including specific electrocardiographic changes, pulmonary valve stenosis and hypertrophic cardiomyopathy have not been completely studied in NF1. PURPOSE: The aims of this study were to assess: (1) similarities in the prevalence and types of ECG and conventional echocardiographic findings described in NS in asymptomatic patients with NF1, and (2) the presence of discrete myocardial dysfunction in NF1 patients using myocardial strain imaging. METHODS: Fifty-eight patients with NF1 (ages 0-18 years), and thirty-one age-matched healthy controls underwent cardiac assessment including blood pressure measurements, a 12-lead ECG, and detailed echocardiography. Quantification of cardiac chamber size, mass and function were measured using conventional echocardiography. Myocardial strain parameters were assessed using 2-Dimensional (2D) Speckle tracking echocardiography. RESULTS: Asymptomatic patients with NF1 had normal electrocardiograms, none with the typical ECG patterns described in NS. However, patients with NF1 showed significantly decreased calculated Z scores of the left ventricular internal diameter in diastole and systole, reduced left ventricular mass index and a higher incidence of cardiac abnormal findings, mainly of the mitral valve, in contrast to the frequently described types of cardiac abnormalities in NS. Peak and end systolic global circumferential strain were the only significantly reduced speckle tracking derived myocardial strain parameter. CONCLUSIONS: Children with NF1 demonstrated more dissimilarities than similarities in the prevalence and types of ECG and conventional echocardiographic findings described in NS. The role of the abnormal myocardial strain parameter needs to be explored.

Postnatal phenotype according to prenatal ultrasound features of Noonan syndrome: a retrospective study of 28 cases.

OBJECTIVE: Noonan syndrome is a frequent genetic disorder with autosomal dominant transmission. Classically, it combines postnatal growth restriction with dysmorphic and malformation syndromes that vary widely in expressivity. Lymphatic dysplasia induced during the embryonic stage might interfere with tissue migration. Our hypothesis is that the earlier the edema, the more severe postnatal phenotype. METHOD: This retrospective study analyzed data from all 32 cases of Noonan syndrome diagnosed in the Medical Genetics Department of Hautepierre Hospital in Strasbourg, France, between 1995 and 2011. The postnatal evolution of Noonan syndrome was compared according to the presence of at least one prenatal ultrasound feature of lymphatic dysplasia. RESULTS: The most frequent prenatal ultrasound features found were increased nuchal translucency, cystic hygroma and polyhydramnios; their global prevalence was 46.4%. The presence of these features was not significantly associated with the postnatal phenotype of Noonan syndrome. CONCLUSION: The results of our study indicate that prenatal ultrasound features of lymphatic dysplasia do not predict an unfavorable postnatal prognosis for Noonan syndrome.