Noonan, Costello and cardio–facio–cutaneous syndromes: dysregulation of the Ras–MAPK pathway

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.

Non-Mammalian Models for Understanding Neurological Defects in RASopathies

RASopathies, a group of neurodevelopmental congenital disorders stemming from mutations in the RAS/MAPK pathway, present a unique opportunity to delve into the intricacies of complex neurological disorders. Afflicting approximately one in a thousand newborns, RASopathies manifest as abnormalities across multiple organ systems, with a pronounced impact on the central and peripheral nervous system. In the pursuit of understanding RASopathies' neurobiology and establishing phenotype-genotype relationships, in vivo non-mammalian models have emerged as indispensable tools. Species such as Danio rerio, Drosophila melanogaster, Caenorhabditis elegans, Xenopus species and Gallus gallus embryos have proven to be invaluable in shedding light on the intricate pathways implicated in RASopathies. Despite some inherent weaknesses, these genetic models offer distinct advantages over traditional rodent models, providing a holistic perspective on complex genetics, multi-organ involvement, and the interplay among various pathway components, offering insights into the pathophysiological aspects of mutations-driven symptoms. This review underscores the value of investigating the genetic basis of RASopathies for unraveling the underlying mechanisms contributing to broader neurological complexities. It also emphasizes the pivotal role of non-mammalian models in serving as a crucial preliminary step for the development of innovative therapeutic strategies.

BRAF - a tumour-agnostic drug target with lineage-specific dependencies

In June 2022, the FDA granted Accelerated Approval to the BRAF inhibitor dabrafenib in combination with the MEK inhibitor trametinib for the treatment of adult and paediatric patients (≥6 years of age) with unresectable or metastatic BRAFV600E-mutant solid tumours, except for BRAFV600E-mutant colorectal cancers. The histology-agnostic approval of dabrafenib plus trametinib marks the culmination of two decades of research into the landscape of BRAF mutations in human cancers, the biochemical mechanisms underlying BRAF-mediated tumorigenesis, and the clinical development of selective RAF and MEK inhibitors. Although the majority of patients with BRAFV600E-mutant tumours derive clinical benefit from BRAF inhibitor-based combinations, resistance to treatment develops in most. In this Review, we describe the biochemical basis for oncogenic BRAF-induced activation of MAPK signalling and pan-cancer and lineage-specific mechanisms of intrinsic, adaptive and acquired resistance to BRAF inhibitors. We also discuss novel RAF inhibitors and drug combinations designed to delay the emergence of treatment resistance and/or expand the population of patients with BRAF-mutant cancers who benefit from molecularly targeted therapies.

In-Depth Genomic Analysis: The New Challenge in Congenital Heart Disease

The use of next-generation sequencing has provided new insights into the causes and mechanisms of congenital heart disease (CHD). Examinations of the whole exome sequence have detected detrimental gene variations modifying single or contiguous nucleotides, which are characterised as pathogenic based on statistical assessments of families and correlations with congenital heart disease, elevated expression during heart development, and reductions in harmful protein-coding mutations in the general population. Patients with CHD and extracardiac abnormalities are enriched for gene classes meeting these criteria, supporting a common set of pathways in the organogenesis of CHDs. Single-cell transcriptomics data have revealed the expression of genes associated with CHD in specific cell types, and emerging evidence suggests that genetic mutations disrupt multicellular genes essential for cardiogenesis. Metrics and units are being tracked in whole-genome sequencing studies.

An Assessment of the Therapeutic Landscape for the Treatment of Heart Disease in the RASopathies

The RAS/mitogen-activated protein kinase (MAPK) pathway controls a plethora of developmental and post-developmental processes. It is now clear that mutations in the RAS-MAPK pathway cause developmental diseases collectively referred to as the RASopathies. The RASopathies include Noonan syndrome, Noonan syndrome with multiple lentigines, cardiofaciocutaneous syndrome, neurofibromatosis type 1, and Costello syndrome. RASopathy patients exhibit a wide spectrum of congenital heart defects (CHD), such as valvular abnormalities and hypertrophic cardiomyopathy (HCM). Since the cardiovascular defects are the most serious and recurrent cause of mortality in RASopathy patients, it is critical to understand the pathological signaling mechanisms that drive the disease. Therapies for the treatment of HCM and other RASopathy-associated comorbidities have yet to be fully realized. Recent developments have shown promise for the use of repurposed antineoplastic drugs that target the RAS-MAPK pathway for the treatment of RASopathy-associated HCM. However, given the impact of the RAS-MAPK pathway in post-developmental physiology, establishing safety and evaluating risk when treating children will be paramount. As such insight provided by preclinical and clinical information will be critical. This review will highlight the cardiovascular manifestations caused by the RASopathies and will discuss the emerging therapies for treatment.

Molecular and phenotypic spectrum of cardio-facio-cutaneous syndrome in Chinese patients

BACKGROUND

Cardio-facio-cutaneous (CFC) syndrome is a RASopathy subtype that presents with unique craniofacial dysmorphology, congenital heart disease, dermatologic abnormalities, growth retardation, and intellectual disability. This study describes the phenotypic spectrum of CFC in China and its association with CFC syndrome gene variants.

RESULTS

Twenty Chinese CFC patients, aged 0.6-9.5 years old, were included in this study and their clinical phenotypic spectrum was compared with that of 186 patients with CFC from non-Chinese ethnicities. All 20 Chinese patients with CFC carried de novo heterozygous BRAF, MAP2K1, and MAP2K2 variants. Two novel variants were detected and consistently predicted to be deleterious using bioinformatic tools. The clinical features of CFC in the Chinese patients included hypertrophic cardiomyopathy (2/20, 10%), pulmonary valve stenosis (2/20, 10%), curly or sparse hair (7/20, 35%), epilepsy (1/20, 5%), and hypotonia (10/20, 50%); these features were less frequently observed in Chinese patients than non-Chinese patients (p < 0.05). In contrast, feeding difficulties (19/20, 95%) were more frequently observed in the Chinese patients. Absent eyebrows and severe short stature were more common in patients with BRAF variants than in those with MAP2K1/2 variants. Facial recognition software was used to recognize most CFC patients using artificial intelligence.

CONCLUSION

This study identified novel and common variants in our cohort of 20 Chinese patients with CFC. We uncovered differences in clinical features between Chinese and non-Chinese patients and detected genotype-phenotype correlations among the BRAF and MAP2K1/2 variant subgroups. This is the largest cohort of Chinese CFC patients to our knowledge, providing new insights into a subtype of RASopathy.

Central Precocious Puberty in an Infant with Sotos Syndrome and Response to Treatment

Sotos syndrome (SS) is characterized by overgrowth, distinctive facial appearance, and learning disability. It is caused by heterozygous mutations, including deletions of NSD1 located at chromosome 5q35. While advanced bone age can occur in some cases, precocious puberty (PP) has only been reported in three cases previously. Here, we reported a case of SS diagnosed in the infancy period with central PP. The discovery of potential factors that trigger puberty is one of the central mysteries of pubertal biology. Depot gonadotropin-releasing hormone analogs constitute the first-line therapy in central PP (CPP), which has proven to be both effective and safe. In our cases, leuprolide acetate at maximum dose was not successful in controlling pubertal progression, and cyproterone acetate (CPA) was added to therapy, with successful control of pubertal progression. In some specific syndromes with PP, such as SS, treatment can be challenging. CPA may be an asset for effective treatment.

Epilepsy in a cohort of children with Noonan syndrome and related disorders

Noonan syndrome (NS) and related disorders encompass a phenotypically heterogeneous group of conditions due to mutations in the Ras/Mitogen-activated protein kinase pathway. The main objective of this study was to assess the presence and characteristics of epilepsy in children and adolescents affected by NS and related disorders. The study included all the patients aged 5-21 years who had been diagnosed with NS or of one of three Noonan-like syndromes (i.e., cardio-facio-cutaneous syndrome, Noonan syndrome with multiple lentigines, and Noonan-like syndrome with loose anagen hair) at a university pediatric hospital. Clinical, EEGs, brain MRIs, and genotype data were extracted from the medical records, and follow-up telephone interviews were conducted to obtain updated information about epilepsy and its course. Out of a total of 75 patients (38 [50.7%] males, median age at assessment 12.0 years [q1 9.0-q3 17.0]; 61 [81.3%] with NS; and 14 [18.7%] with a Noonan-like syndrome), 13 (17.3%) had epilepsy, with median age at onset of 4.0 years (q1 2.0-q3 8.0, min 0.1-max 17.0). Epilepsy was more common among Noonan-like patients (50.0%) than in NS (9.8%, p < 0.001), and its presence was associated with neurodevelopmental delay (p < 0.001, OR 14.6 95% CI 3.6-59.4), cognitive impairment (p = 0.002, OR 11.2 95% CI 2.5-51.0), need for educational support (p < 0.001, OR 21.8, 95% CI 2.6-179.1), and lower adaptive functioning (median [q1-q3]: 54.0 [q1 40.0-q3 77.5] vs 97.0 [q1 76.5-q3 107.0] of the non-epileptic subgroup, p = 0.004). In 10 out of 13 cases (76.9%), the epilepsy outcome was good (i.e., seizure-free for more than 12 months with or without anti-seizure medication).

CONCLUSION

Epilepsy was more common in NS than reported in the general population, with a significantly higher rate in Noonan-like syndromes. Epilepsy was associated with neurodevelopmental delay, cognitive impairment, and lower adaptive functioning.

WHAT IS KNOWN

• Neurological abnormalities have been reported in NS and related disorders. • There is evidence of a phenotype-genotype relationship for neurological abnormalities.

WHAT IS NEW

• Epilepsy was found to be more common in NS and related disorders than typically reported in the general population and associated with neurodevelopmental delay, cognitive, and functional impairment. • The Noonan-like phenotype had a higher frequency of epilepsy than typical NS.

Differences in severity of cardiovascular anomalies in children with Noonan syndrome based on the causative gene

BACKGROUND

Noonan syndrome (NS) is a genetic syndrome, characterized by various dysmorphic features, cardiac anomalies, short stature, and developmental delay. NS is a leading cause of cardiovascular anomalies. The syndrome results from dysregulation in the RAS-MAPK pathway and is related to the RASopathy family syndromes. Pathogenic variants in more than 20 related genes have been identified in association with NS, and several genotype-phenotype correlations were suggested. The specific severity of the same cardiovascular anomalies has not been described as linked to a specific causative gene.

METHODS

For this retrospective, single-center study, data retrieved from medical charts of a multidisciplinary NS clinic included genetic diagnosis, cardiac malformations, the need for intervention, demographics, and prenatal diagnosis. We analyzed molecular genetics and the severity of cardiac malformations.

RESULTS

The cohort comprised 74 children with NS. Consistent with previous studies, pathogenic variants in PTPN11 were the most common (62%). Cardiovascular anomalies presented in 57%; pulmonary stenosis (PS) was the most common (about 79% of anomalies). In children with pathogenic variants in PTPN11, PS tended to be more severe and required intervention in 53%, compared to 25% of children with PS and a variant in other genes.

CONCLUSION

This first Israeli cohort of NS showed similar rates of cardiac malformations and genetic breakdown as previously published. Variants in PTPN11 were prone to a higher risk for severe PS that requires intervention. This finding may assist in genetic counseling and cardiac treatment decisions, and stresses the importance of genetic in addition to clinical diagnosis of NS.

Updated Approach to Patients with Multiple Café au Lait Macules

Café au lait macules (CALMs) are a normal and frequent finding in the general population, but multiple CALMs raise the possibility of an underlying neurocutaneous disease like neurofibromatosis type I. Certain features of CALMs like number, size, shape, and distribution are important in identifying children at higher risk of having a neurocutaneous disorder or another genetic disorder. Genetic testing can be especially helpful in establishing a diagnosis in atypical presentations, or when the child is young and other features of the disease aside from CALMs have not manifested.

Dermatologic manifestations of pediatric cardiovascular diseases: Skin as a reflection of the heart

Cutaneous disease can often be an initial clue of an underlying cardiovascular disease. Many congenital conditions (ie, Noonan syndrome with multiple lentigines, Carney complex, and Fabry disease) and acquired conditions may present initially with specific cutaneous features that should prompt clinicians to conduct a full cardiac workup. Given the extensive number of conditions with both cardiovascular and cutaneous findings, this review will focus on diseases with cardiocutaneous pathology with hopes of raising clinician awareness of these associations to decrease morbidity and mortality, as several of these diseases often result in fatal outcomes.

Regulation of the Small GTPase Ras and Its Relevance to Human Disease

Ras research has experienced a considerable boost in recent years, not least prompted by the Ras initiative launched by the NCI in 2013 ( https://www.cancer.gov/research/key-initiatives/ras ), accompanied and conditioned by a strongly reinvigorated determination within the Ras community to develop therapeutics attacking directly the Ras oncoproteins. As a member of the small G-protein superfamily, function and transforming activity of Ras all revolve about its GDP/GTP loading status. For one thing, the extent of GTP loading will determine the proportion of active Ras in the cell, with implications for intensity and quality of downstream signaling. But also the rate of nucleotide exchange, i.e., the Ras-GDP/GTP cycling rate, can have a major impact on Ras function, as illustrated perhaps most impressively by newly discovered fast-cycling oncogenic mutants of the Ras-related GTPase Rac1. Thus, while the last years have witnessed memorable new findings and technical developments in the Ras field, leading to an improved insight into many aspects of Ras biology, they have not jolted at the basics, but rather deepened our view of the fundamental regulatory principles of Ras activity control. In this brief review, we revisit the role and mechanisms of Ras nucleotide loading and its implications for cancer in the light of recent findings.

Chiari I malformation in patients with RASopathies

PURPOSE

Chiari I malformation (CIM) is a common pediatric neurologic anomaly which could be associated with a variety of genetic disorders. However, it is not always clear whether the observed associations between CIM and RASopathies are real or random. The knowledge of the real association could provide useful guidance to clinicians. Furthermore, it could help to better understand the still unknown genetic etiology of CIM.

METHOD AND RESULTS

We reviewed the current knowledge of CIM and RASopathies in the paper. Here, we describe one patient with CIM and Noonan syndrome and three patients with CIM and neurofibromatosis type 1. Three of the four patients underwent standard surgical therapy of Chiari decompression and had a straightforward recovery without further complications from surgery.

CONCLUSION

In RASopathy, imaging of the nervous system may be necessary. With the increase in availability of magnetic resonance imaging, we believe that there will be a growing body of evidence to suggest that CIM is more commonly seen in RASopathy. Future studies should attempt to elucidate the pathogenic mechanism responsible for CIM mediated by the RAS/MAPK signaling pathway.

Personality and Psychopathology in Adults with Noonan Syndrome

This is the first controlled study regarding personality and psychopathology in adults with Noonan syndrome (NS). Anxiety, depression, alexithymia and symptoms of Attention Deficit-Hyperactivity Disorder and Autism Spectrum Disorder, have been previously described in NS. More information regarding personality and psychopathology in NS could improve mental health care for this population. Therefore, scores on the Minnesota Multiphasic Personality Inventory-2-Restructured Form (MMPI-2-RF), a widely used self-report questionnaire of personality and psychopathology, were compared between patients with NS (n = 18) and matched, healthy controls (n = 18). Furthermore, correlations between MMPI-2-RF scores and alexithymia, measured by the Toronto Alexithymia Scale-20, were investigated. Patients with NS showed significantly higher scores, with medium effect sizes, on MMPI-2-RF scales reflecting infrequent responses (F-r), somatic and cognitive complaints (FBS-r and RBS-r), internalizing problems (EID), demoralization (RCd) and introversion (INTR-r), although the overall profile in both groups was within the non-clinical range. Alexithymia correlated with internalizing problems and negative emotionality in the patient group. In conclusion, patients with NS showed higher levels of introversion, which may predispose them to internalizing problems. These problems were indeed more frequent in patients with NS, especially higher levels of demoralization. Patients may benefit from psychological interventions aimed to decrease internalizing problems, introversion and alexithymia.

Cardiofaciocutaneous syndrome - a longitudinal study of a case over 33 years: case report and review of the literature

Cardiofaciocutaneous (CFC) syndrome [Online Mendelian Inheritance in Man (OMIM) #115150] is characterized by craniofacial dysmorphism, heart malformation, ectodermal abnormalities, neuromotor delay and intellectual disability. It is not a frequent disease, about 300 cases have been reported in the medical literature. We describe the case of a 34-year-old patient presenting with CFC syndrome phenotype, monitored since the age of 1 1/2 years. Clinical findings included craniofacial dysmorphism, development delay, heart malformation and severe intellectual disability. The evolution was with progressive intellectual disability, hypogonadism, hypertrophic cardiomyopathy, wrinkled palms and soles. Molecular analysis showed a heterozygous variant in the B-Raf proto-oncogene, serine/threonine kinase (BRAF) gene (7q34): NM_001354609.2:c.1502A>G, with pathogenic significance. We report this case, observed along a period of 33 years, for illustration of clinical evolutive particularities, and for difficulties in establishing the positive diagnosis.

SHP2 mutations induce precocious gliogenesis of Noonan syndrome-derived iPSCs during neural development in vitro

Background

Noonan syndrome (NS) is a developmental disorder caused by mutations of Src homology 2 domain-containing protein tyrosine phosphatase 2 (SHP2). Although NS patients have diverse neurological manifestations, the mechanisms underlying the involvement of SHP2 mutations in neurological dysfunction remain elusive.

Methods

Induced pluripotent stem cells generated from dermal fibroblasts of three NS-patients (NS-iPSCs) differentiated to the neural cells by using two different culture systems, 2D- and 3D-cultured systems in vitro.

Results

Here we represent that SHP2 mutations cause aberrant neural development. The NS-iPSCs exhibited impaired development of EBs in which BMP and TGF-β signalings were activated. Defective early neuroectodermal development of NS-iPSCs recovered by inhibition of both signalings and further differentiated into NPCs. Intriguingly, neural cells developed from NS-NPCs exhibited abundancy of the glial cells, neurites of neuronal cells, and low electrophysiological property. Those aberrant phenotypes were also detected in NS-cerebral organoids. SHP2 inhibition in the NS-NPCs and NS-cerebral organoids ameliorated those anomalies such as biased glial differentiation and low neural activity.

Conclusion

Our findings demonstrate that SHP2 mutations contribute to precocious gliogenesis in NS-iPSCs during neural development in vitro.

GTP hydrolysis is modulated by Arg34 in the RASopathy-associated KRASP34R

RAS proteins are commonly mutated in cancerous tumors, but germline RAS mutations are also found in RASopathy syndromes such as Noonan syndrome (NS) and cardiofaciocutaneous (CFC) syndrome. Activating RAS mutations can be subclassified based on their activating mechanisms. Understanding the structural basis for these mechanisms may provide clues for how to manage associated health conditions. We determined high-resolution X-ray structures of the RASopathy mutant KRASP34R seen in NS and CFCS. GTP and GDP-bound KRASP34R crystallized in multiple forms, with each lattice consisting of multiple protein conformations. In all GTP-bound conformations, the switch regions are not compatible with GAP binding, suggesting a structural mechanism for the GAP insensitivity of this RAS mutant. However, GTP-bound conformations are compatible with intrinsic nucleotide hydrolysis, including one that places R34 in a position analogous to the GAP arginine finger or intrinsic arginine finger found in heterotrimeric G proteins, which may support intrinsic GTP hydrolysis. We also note that the affinity between KRASP34R and RAF-RBD is decreased, suggesting another possible mechanism for dampening of RAS signaling. These results may provide a foothold for development of new mutation-specific strategies to address KRASP34R -driven diseases.

NRAS associated RASopathy and embryonal rhabdomyosarcoma

RASopathies are a group of phenotypically overlapping disorders that arise from dysregulation of the RAS/MAPK pathway. These disorders include Noonan syndrome, Costello syndrome, cardiofaciocutaneous syndrome, and neurofibromatosis-Type 1. While somatic mutations in the three human Ras genes (KRAS, HRAS, and NRAS) are a common finding in a variety of cancers, germline mutations in each of the these genes cause developmental RASopathy phenotypes with mutations in specific genes typically correlating with specific phenotypes. We present the case of a germline heterozygous NRAS mutation producing a severe phenotype involving embryonal rhabdomyosarcoma, severe intellectual disability, and numerous melanocytic nevi in addition to more typical manifestations of Noonan syndrome. Additionally, the specific p.G12R NRAS mutation in this case is a common somatic mutation in cancer cells, and analysis of previously reported NRAS-RASopathy cases suggests that mutations at traditionally oncogenic codons are associated with elevated cancer risk not present with mutations at other sites.

Narrowing the wingless-2 mutation to a 227 kb candidate region on chicken chromosome 12

Wingless-2 (wg-2) is an autosomal recessive mutation in chicken that results in an embryonic lethal condition. Affected individuals exhibit a multisystem syndrome characterized by absent wings, truncated legs, and craniofacial, kidney, and feather malformations. Previously, work focused on phenotype description, establishing the autosomal recessive pattern of Mendelian inheritance and placing the mutation on an inbred genetic background to create the congenic line UCD Wingless-2.331. The research described in this paper employed the complementary tools of breeding, genetics, and genomics to map the chromosomal location of the mutation and successively narrow the size of the region for analysis of the causative element. Specifically, the wg-2 mutation was initially mapped to a 7 Mb region of chromosome 12 using an Illumina 3 K SNP array. Subsequent SNP genotyping and exon sequencing combined with analysis from improved genome assemblies narrowed the region of interest to a maximum size of 227 kb. Within this region, 3 validated and 3 predicted candidate genes are found, and these are described. The wg-2 mutation is a valuable resource to contribute to an improved understanding of the developmental pathways involved in chicken and avian limb development as well as serving as a model for human development, as the resulting syndrome shares features with human congenital disorders.

RAS signalling in energy metabolism and rare human diseases

The RAS pathway is a highly conserved cascade of protein-protein interactions and phosphorylation that is at the heart of signalling networks that govern proliferation, differentiation and cell survival. Recent findings indicate that the RAS pathway plays a role in the regulation of energy metabolism via the control of mitochondrial form and function but little is known on the participation of this effect in RAS-related rare human genetic diseases. Germline mutations that hyperactivate the RAS pathway have been discovered and linked to human developmental disorders that are known as RASopathies. Individuals with RASopathies, which are estimated to affect approximately 1/1000 human birth, share many overlapping characteristics, including cardiac malformations, short stature, neurocognitive impairment, craniofacial dysmorphy, cutaneous, musculoskeletal, and ocular abnormalities, hypotonia and a predisposition to developing cancer. Since the identification of the first RASopathy, type 1 neurofibromatosis (NF1), which is caused by the inactivation of neurofibromin 1, several other syndromes have been associated with mutations in the core components of the RAS-MAPK pathway. These syndromes include Noonan syndrome (NS), Noonan syndrome with multiple lentigines (NSML), which was formerly called LEOPARD syndrome, Costello syndrome (CS), cardio-facio-cutaneous syndrome (CFC), Legius syndrome (LS) and capillary malformation-arteriovenous malformation syndrome (CM-AVM). Here, we review current knowledge about the bioenergetics of the RASopathies and discuss the molecular control of energy homeostasis and mitochondrial physiology by the RAS pathway.

In vivo efficacy of the AKT inhibitor ARQ 092 in Noonan Syndrome with multiple lentigines-associated hypertrophic cardiomyopathy

Noonan Syndrome with Multiple Lentigines (NSML, formerly LEOPARD syndrome) is an autosomal dominant "RASopathy" disorder manifesting in congenital heart disease. Most cases of NSML are caused by catalytically inactivating mutations in the protein tyrosine phosphatase (PTP), non-receptor type 11 (PTPN11), encoding the SH2 domain-containing PTP-2 (SHP2) protein. We previously generated knock-in mice harboring the PTPN11 mutation Y279C, one of the most common NSML alleles; these now-termed SHP2Y279C/+ mice recapitulate the human disorder and develop hypertrophic cardiomyopathy (HCM) by 12 weeks of age. Functionally, heart and/or cardiomyocyte lysates from SHP2Y279C/+ mice exhibit increased basal and agonist-induced AKT and mTOR activities. Here, we sought to determine whether we could reverse the hypertrophy in SHP2Y279C/+ mice using ARQ 092, an oral and selective allosteric AKT inhibitor currently in clinical trials for patients with PI3K/AKT-driven tumors or Proteus syndrome. We obtained echocardiographs of SHP2Y279C/+ and wildtype (SHP2+/+) littermates, either in the presence or absence of ARQ 092 at 12, 14, and 16 weeks of age. While SHP2Y279C/+ mice developed significant left ventricular hypertrophy by 12 weeks, as indicated by decreased chamber dimension and increased posterior wall thickness, treatment of SHP2Y279C/+ mice with ARQ 092 normalized the hypertrophy in as early as 2 weeks following treatment, with hearts comparable in size to those in wildtype (SHP2+/+) mice. In addition, we observed an increase in fractional shortening (FS%) in SHP2Y279C/+ mice, an effect of increased compensatory hypertrophy, which was not apparent in SHP2Y279C/+ mice treated with ARQ 092, suggesting functional improvement of HCM upon treatment with the AKT inhibitor. Finally, we found that ARQ 092 specifically inhibited AKT activity, as well as its downstream effectors, PRAS and S6RP in NSML mice. Taken together, these data suggest ARQ 092 may be a promising novel therapy for treatment of hypertrophy in NSML patients.

Cutaneous skeletal hypophosphatemia syndrome (CSHS) is a multilineage somatic mosaic RASopathy

BACKGROUND

We recently demonstrated multilineage somatic mosaicism in cutaneous skeletal hypophosphatemia syndrome (CSHS), which features epidermal or melanocytic nevi, elevated fibroblast growth factor (FGF)-23, and hypophosphatemia, finding identical RAS mutations in affected skin and bone.

OBJECTIVE

We sought to: (1) provide an updated overview of CSHS; (2) review its pathobiology; (3) present a new patient with CSHS; and (4) discuss treatment modalities.

METHODS

We searched PubMed for "nevus AND rickets," and "nevus AND hypophosphatemia," identifying cases of nevi with hypophosphatemic rickets or elevated serum FGF-23. For our additional patient with CSHS, we performed histopathologic and radiographic surveys of skin and skeletal lesions, respectively. Sequencing was performed for HRAS, KRAS, and NRAS to determine causative mutations.

RESULTS

Our new case harbored somatic activating HRAS p.G13 R mutation in affected tissue, consistent with previous findings. Although the mechanism of FGF-23 dysregulation is unknown in CSHS, interaction between FGF and MAPK pathways may provide insight into pathobiology. Anti-FGF-23 antibody KRN-23 may be useful in managing CSHS.

LIMITATIONS

Multilineage RAS mutation in CSHS was recently identified; further studies on mechanism are unavailable.

CONCLUSION

Patients with nevi in association with skeletal disease should be evaluated for serum phosphate and FGF-23. Further studies investigating the role of RAS in FGF-23 regulation are needed.

RASopathies Are Associated With Delayed Puberty; Are They Associated With Precocious Puberty Too?

RASopathies, such as Noonan, Costello, and cardio-facio-cutaneous syndromes, are developmental disorders caused by mutations in rat sarcoma-mitogen-activated protein kinase pathway genes. Mutations that cause Noonan syndrome have been associated with delayed puberty. Here we report 4 patients with either Costello or cardio-facio-cutaneous syndrome who developed precocious puberty, suggesting complex regulation of the hypothalamic-pituitary-gonadal axis and the timing of puberty by the rat sarcoma-mitogen-activated protein kinase pathway. Additional study of the timing of puberty among patients with RASopathies is warranted to ascertain the incidence of delayed and precocious puberty in these conditions and to examine genotype-phenotype correlations, which may provide insight into pathways that regulate the timing of puberty.

Molecular screening strategies for NF1-like syndromes with café-au-lait macules (Review)

Multiple café-au-lait macules (CALM) are usually associated with neurofibromatosis type 1 (NF1), one of the most common hereditary disorders. However, a group of genetic disorders presenting with CALM have mutations that are involved in human skin pigmentation regulation signaling pathways, including KIT ligand/KIT proto‑oncogene receptor tyrosine kinase and Ras/mitogen‑activated protein kinase. These disorders, which include Legius syndrome, Noonan syndrome with multiple lentigines or LEOPARD syndrome, and familial progressive hyperpigmentation) are difficult to distinguish from NF1 at early stages, using skin appearance alone. Furthermore, certain syndromes are clinically overlapping and molecular testing is a vital diagnostic method. The present review aims to provide an overview of these 'NF1‑like' inherited diseases and recommend a cost‑effective strategy for making a clear diagnosis among these diseases with an ambiguous borderline.

P2A-Fluorophore Tagging of BRAF Tightly Links Expression to Fluorescence In Vivo

The Braf proto-oncogene is a key component of the mitogen-activated protein kinase signaling cascade and is a critical regulator of both normal development and tumorigenesis in a variety of tissues. In order to elucidate BRAF's differing roles in varying cell types, it is important to understand both the pattern and timing of BRAF expression. Here we report the production of a mouse model that links the expression of Braf with the bright red fluorescent protein, tdTomato. We have utilized a P2A knock-in strategy, ensuring that BRAF and the fluorophore are expressed from the same endogenous promoter and from the same bicistronic mRNA transcript. This mouse model (BrafTOM) shows bright red fluorescence in organs and cell types known to be sensitive to BRAF perturbation. We further show that on a cell-by-cell basis, fluorescence correlates with BRAF protein levels. Finally, we extend the utility of this mouse by demonstrating that the remnant P2A fragment attached to BRAF acts as a suitable epitope for immunoprecipitation and biochemical characterization of BRAF in vivo.

The function of Shoc2: A scaffold and beyond

The extracellular signal-regulated kinase (ERK1/2) cascade regulates a myriad of functions in multicellular organisms. Scaffold proteins provide critical spatial and temporal control over the specificity of signaling. Shoc2 is a scaffold that accelerates activity of the ERK1/2 pathway. Loss of Shoc2 expression in mice results in embryonic lethality, thus highlighting the essential role of Shoc2 in embryogenesis. In agreement, patients carrying mutated Shoc2 suffer from a wide spectrum of developmental deficiencies. Efforts to understand the mechanisms by which Shoc2 controls ERK1/2 activity revealed the intricate machinery that governs the ability of Shoc2 to transduce signals of the ERK1/2 pathway. Understanding the mechanisms by which Shoc2 contributes to a high degree of specificity of ERK1/2 signaling as well as deciphering the biological functions of Shoc2 in development and human disorders are major unresolved questions.

Enhanced SMAD1 Signaling Contributes to Impairments of Early Development in CFC-iPSCs

Cardio-facio-cutaneous (CFC) syndrome is a developmental disorder caused by constitutively active ERK signaling manifesting mainly from BRAF mutations. Little is known about the role of elevated ERK signaling in CFC syndrome during early development. Here, we show that both SMAD1 and ERK signaling pathways may contribute to the developmental defects in CFC syndrome. Induced pluripotent stem cells (iPSCs) derived from dermal fibroblasts of a CFC syndrome patient (CFC-iPSCs) revealed early developmental defects in embryoid body (EB) development, β-catenin localization, and neuronal differentiation. Both SMAD1 and ERK signalings were significantly activated in CFC-iPSCs during EB formation. Most of the β-catenin was dissociated from the membrane and preferentially localized into the nucleus in CFC-EBs. Furthermore, activation of SMAD1 signaling recapitulated early developmental defects in wild-type iPSCs. Intriguingly, inhibition of SMAD1 signaling in CFC-iPSCs rescued aberrant EB morphology, impaired neuronal differentiation, and altered β-catenin localization. These results suggest that SMAD1 signaling may be a key pathway contributing the pathogenesis of CFC syndrome during early development.

Haploinsufficiency and triploinsensitivity of the same 6p25.1p24.3 region in a family

Background

Chromosome 6pter-p24 deletion syndrome (OMIM #612582) is a recognized chromosomal disorder. Most of the individuals with this syndrome carry a terminal deletion of the short arm of chromosome 6 (6p) with a breakpoint within the 6p25.3p23 region. An approximately 2.1 Mb terminal region has been reported to be responsible for some major features of the syndrome. The phenotypic contributions of other deleted regions are unknown. Interstitial deletions of the region are uncommon, and reciprocal interstitial duplication in this region is extremely rare.

Case presentation

We present a family carrying an interstitial deletion and its reciprocal duplication within the 6p25.1p24.3 region. The deletion is 5.6 Mb in size and was detected by array comparative genomic hybridization (aCGH) in a 26-month-old female proband who presented speech delay and mild growth delay, bilateral conductive hearing loss and dysmorphic features. Array CGH studies of her family members detected an apparently mosaic deletion of the same region in the proband’s mildly affected mother, but a reciprocal interstitial duplication in her phenotypically normal brother. Further chromosomal and fluorescence in situ hybridization (FISH) analyses revealed that instead of a simple mosaic deletion of 6p25.1p24.3, the mother actually carries three cell populations in her peripheral blood, including a deletion (~70 %), a duplication (~8 %) and a normal (~22 %) populations. Therefore, both the deletion and duplication seen in the siblings were apparently inherited from the mother.

Conclusions

Interstitial deletion within the 6p25.1p24.3 region and its reciprocal duplication may co-exist in the same individual and/or family due to mitotic unequal sister chromatid exchange. While the deletion causes phenotypes reportedly associated with the chromosome 6pter-p24 deletion syndrome, the reciprocal duplication may have no or minimal phenotypic effect, suggesting possible triploinsensitivity of the same region. In addition, the cells with the duplication may compensate the phenotypic effect of the cells with the deletion in the same individual as implied by the maternal karyotype and her mild phenotype. Chromosomal and FISH analyses are essential to verify abnormal cytogenomic array findings.

The impact of the genetic background in the Noonan syndrome phenotype induced by K-Ras(V14I)

Noonan syndrome (NS) is an autosomal dominant genetic disorder characterized by short stature, craniofacial dysmorphism, and congenital heart defects. A significant fraction of NS-patients also develop myeloproliferative disorders. The penetrance of these defects varies considerably among patients. In this study, we have examined the effect of 2 genetic backgrounds (C57BL/6J.OlaHsd and 129S2/SvPasCrl) on the phenotypes displayed by a mouse model of NS induced by germline expression of the mutated K-Ras^V14I allele, one of the most frequent NS-KRAS mutations. Our results suggest the presence of genetic modifiers associated to the genetic background that are essential for heart development and function at early stages of postnatal life as well as in the severity of the haematopoietic alterations.

Management of laryngomalacia in children with congenital syndrome: the role of supraglottoplasty

BACKGROUND/IMPORTANCE

Supraglottoplasty is the surgical procedure of choice for severe laryngomalacia and has shown to be successful in most cases; however, patients with medical comorbidities present a higher rate of failure. To date, the best management of laryngomalacia in children with congenital syndrome remains unclear.

PURPOSE

To study the outcome of supraglottoplasty in children with severe laryngomalacia, and to analyze the management and outcome in infants with a congenital syndrome.

METHODS

Retrospective medical records review from January 2003 to October 2012 of all patients who underwent laser supraglottoplasty for severe laryngomalacia at the University Children's Hospital Zurich, Switzerland.

RESULTS

Thirty-one patients were included; median age at time of surgery was 3.5 months. Three patients (10%) had a genetically proven congenital syndrome with associated neurologic anomalies. Overall success rate was 87%. Failures were observed in four (13%) of 31 cases; including all three patients presenting a congenital syndrome.

CONCLUSIONS

Supraglottoplasty is an effective and safe treatment for laryngomalacia in otherwise healthy children. Signs of a possible underlying predominant neurologic origin and discrepancy between the clinical presentation and the endoscopic findings have to be taken into account, as in children with congenital syndrome with neurologic anomalies the risk of failure is higher.

Recurrent duplication mutation in HRAS causing mild Costello syndrome in a Chinese patient

Costello syndrome (CS; OMIM 218040) is caused by heterozygous germline mutations of HRAS (OMIM 190020).We report on a patient with sporadic CS presenting with characteristic craniofacial dysmorphism, congenital cardiopulmonary disorders, intellectual impairment, and skin abnormalities manifesting as loose redundant skin of the hands and feet, acanthosis nigricans, multiple naevi and hypotrichosis. Using Sanger sequencing for the case-parents trio, we detected a de novo insertion mutation (c.187_207dup) in HRAS, which was predicted to result in duplication of amino acids 63-69 (p.E63_D69dup). This mutation was recently described in a mild case of CS, with hyperactivation of HRAS and disrupted capacity to respond to incoming signals. Our study delineates the detailed clinical features associated with this noncanonical HRAS mutation and further expands the phenotypic spectrum of CS.

Facial dysmorphology and odontogenic tumor development associated with inborn errors of metabolism: a case report

PURPOSE

Inborn errors of metabolism (IEMs) are genetic disorders that alter normal physiologic functioning. Deficiency of 3-methylcrotonyl-coenzyme A carboxylase is one such IEM that can lead to major episodes of metabolic dysfunction. Certain IEMs are associated with characteristic congenital dysmorphic facial features. This can be problematic, because these dysmorphisms can mask underlying tumor growth. Literature is lacking on a causal relation between IEM and odontogenic tumor development.

MATERIALS AND METHODS

This case was explained in detail and a review of the literature was undertaken. PubMed was used to search for articles involving surgical management of odontogenic myxoma (OM) and associations between odontogenic tumors and IEM.

RESULTS

It was determined that the development of odontogenic tumors, specifically OM, is associated with IEMs. These tumors can easily be overlooked as a common dysmorphic feature of an IEM.

CONCLUSION

IEMs lead to major metabolic disturbances and, thus, can alter the cellular microenvironment. Hypothetically, these alterations can lead to the development of odontogenic tumors. With the diagnosis of IEM becoming more common owing to improved newborn screening, careful attention should be given to these patients because of the possibility that dysmorphologic facial features could be masking underlying tumor growth.

Syndrome in question. Costello syndrome

Costello syndrome (CS) is a rare genetic disorder, first described by Costello in 1971, caused by mutations in the HRAS proto-oncogene. Clinical findings include facial dysmorphism, skin disorders, cognitive impairment, cardiac and musculoskeletal defects. There is an increased risk of malignancies in these patients, due to the proto-oncogene mutation, and also sudden death secondary to heart disease. We report a case with characteristic phenotype, highlighting the peculiar skin changes.

BRAF gene: From human cancers to developmental syndromes

The BRAF gene encodes for a serine/threonine protein kinase that participates in the MAPK/ERK signalling pathway and plays a vital role in cancers and developmental syndromes (RASopathies). The current review discusses the clinical significance of the BRAF gene and other members of RAS/RAF cascade in human cancers and RAS/MAPK syndromes, and focuses the molecular basis and clinical genetics of BRAF to better understand its parallel involvement in both tumourigenesis and RAS/MAPK syndromes—Noonan syndrome, cardio-facio-cutaneous syndrome and LEOPARD syndrome.

Diagnostically relevant facial gestalt information from ordinary photos

Craniofacial characteristics are highly informative for clinical geneticists when diagnosing genetic diseases. As a first step towards the high-throughput diagnosis of ultra-rare developmental diseases we introduce an automatic approach that implements recent developments in computer vision. This algorithm extracts phenotypic information from ordinary non-clinical photographs and, using machine learning, models human facial dysmorphisms in a multidimensional 'Clinical Face Phenotype Space'. The space locates patients in the context of known syndromes and thereby facilitates the generation of diagnostic hypotheses. Consequently, the approach will aid clinicians by greatly narrowing (by 27.6-fold) the search space of potential diagnoses for patients with suspected developmental disorders. Furthermore, this Clinical Face Phenotype Space allows the clustering of patients by phenotype even when no known syndrome diagnosis exists, thereby aiding disease identification. We demonstrate that this approach provides a novel method for inferring causative genetic variants from clinical sequencing data through functional genetic pathway comparisons.DOI: http://dx.doi.org/10.7554/eLife.02020.001.

Diagnostically relevant facial gestalt information from ordinary photos

Craniofacial characteristics are highly informative for clinical geneticists when diagnosing genetic diseases. As a first step towards the high-throughput diagnosis of ultra-rare developmental diseases we introduce an automatic approach that implements recent developments in computer vision. This algorithm extracts phenotypic information from ordinary non-clinical photographs and, using machine learning, models human facial dysmorphisms in a multidimensional 'Clinical Face Phenotype Space'. The space locates patients in the context of known syndromes and thereby facilitates the generation of diagnostic hypotheses. Consequently, the approach will aid clinicians by greatly narrowing (by 27.6-fold) the search space of potential diagnoses for patients with suspected developmental disorders. Furthermore, this Clinical Face Phenotype Space allows the clustering of patients by phenotype even when no known syndrome diagnosis exists, thereby aiding disease identification. We demonstrate that this approach provides a novel method for inferring causative genetic variants from clinical sequencing data through functional genetic pathway comparisons.DOI: http://dx.doi.org/10.7554/eLife.02020.001.

Putative role of HIF transcriptional activity in melanocytes and melanoma biology

Hypoxia-inducible factor-1α (HIF-1α) is a highly oxygen sensitive bHLH protein that is part of the heterodimeric HIF-1 transcription factor. Under hypoxic stress, HIF-1 activity is induced to control expression of multiple downstream target genes, including vascular endothelial growth factor (VEGF). The normal epidermis exists in a constant mild hypoxic microenvironment and constitutively expresses HIF-1α and HIF-2α. Expression of HIF-1α and/or HIF-2α has been suggested to correlate with the increased malignant potential of melanocytes, therefore, failures of melanoma therapies may be partially linked to high HIF activity. Notably, melanomas that have the V600E BRAF mutation exhibit increased HIF-1α expression. We have utilized a bioinformatics approach to identify putative hypoxia response elements (HREs) in a set of genes known to participate in the process of melanogenesis (includingTRPM1, SLC45A2, HRAS, C-KIT, PMEL and CRH). While some of the mechanistic links between these genes and the HIF pathway have been previously explored, others await further investigation. Although agents targeting HIF activity have been proposed as novel treatment modalities for melanoma, there are currently no clinical trials in progress to test their efficacy in melanoma.

Comprehensive massive parallel DNA sequencing strategy for the genetic diagnosis of the neuro-cardio-facio-cutaneous syndromes

Variants in 11 genes of the RAS/MAPK signaling pathway have been causally linked to the neuro-cardio-facio-cutaneous syndromes group (NCFCS). Recently, A2ML1 and RIT1 were also associated with these syndromes. Because of the genetic and clinical heterogeneity of NCFCS, it is challenging to define strategies for their molecular diagnosis. The aim of this study was to develop and validate a massive parallel sequencing (MPS)-based strategy for the molecular diagnosis of NCFCS. A multiplex PCR-based strategy for the enrichment of the 13 genes and a variant prioritization pipeline was established. Two sets of genomic DNA samples were studied using the Ion PGM System: (1) training set (n =15) to optimize the strategy and (2) validation set (n = 20) to validate and evaluate the power of the new methodology. Sanger sequencing was performed to confirm all variants and low covered regions. All variants identified by Sanger sequencing were detected with our MPS approach. The methodology resulted in an experimental approach with a specificity of 99.0% and a maximum analytical sensitivity of ≥ 98.2% with a confidence of 99%. Importantly, two patients (out of 20) harbored described disease-causing variants in genes that are not routinely tested (RIT1 and SHOC2). The addition of less frequently altered genes increased in ≈ 10% the diagnostic yield of the strategy currently used. The presented workflow provides a comprehensive genetic screening strategy for patients with NCFCS in a fast and cost-efficient manner. This approach demonstrates the potential of a combined MPS-Sanger sequencing-based strategy as an effective diagnostic tool for heterogeneous diseases.

PZR coordinates Shp2 Noonan and LEOPARD syndrome signaling in zebrafish and mice

Noonan syndrome (NS) is an autosomal dominant disorder caused by activating mutations in the PTPN11 gene encoding Shp2, which manifests in congenital heart disease, short stature, and facial dysmorphia. The complexity of Shp2 signaling is exemplified by the observation that LEOPARD syndrome (LS) patients possess inactivating PTPN11 mutations yet exhibit similar symptoms to NS. Here, we identify "protein zero-related" (PZR), a transmembrane glycoprotein that interfaces with the extracellular matrix to promote cell migration, as a major hyper-tyrosyl-phosphorylated protein in mouse and zebrafish models of NS and LS. PZR hyper-tyrosyl phosphorylation is facilitated in a phosphatase-independent manner by enhanced Src recruitment to NS and LS Shp2. In zebrafish, PZR overexpression recapitulated NS and LS phenotypes. PZR was required for zebrafish gastrulation in a manner dependent upon PZR tyrosyl phosphorylation. Hence, we identify PZR as an NS and LS target. Enhanced PZR-mediated membrane recruitment of Shp2 serves as a common mechanism to direct overlapping pathophysiological characteristics of these PTPN11 mutations.

Cardio-facio-cutaneous syndrome with precocious puberty, growth hormone deficiency and hyperprolactinemia

Cardio-facio-cutaneous (CFC) syndrome is a rare disorder characterized by craniofacial dysmorphia, ectodermal abnormalities, cardiac malformations, as well as growth and developmental delay. Although some endocrine abnormalities have been reported in this syndrome, very little is known about CFC syndrome-related endocrine disorders. A 7.5-year-old boy was admitted to our endocrinology clinic with the complaint of short stature. He had a height of 103 cm [-4 standard deviation (SD)], a weight of 16 kg (<3(th) percentile, -1.7 SD), a facial appearance typical for the CFC syndrome, optic nerve hypoplasia and pulmonary stenosis. Genetic investigation revealed a heterozygous mutation in exon 3 of the MEK1 gene, c.389A>G (p. Y130C). During his long-term follow-up, the patient developed a variety of endocrine disorders including precocious puberty, growth hormone deficiency and hyperprolactinemia.

Fetal autopsy findings of cardiofaciocutaneous syndrome with a unique BRAF mutation

Cardiofaciocutaneous (CFC) syndrome is a RASopathy phenotypically characterized by facial, cardiac, and ectodermal abnormalities. The extent to which this phenotype is expressed in the affected fetus is unclear, and a better understanding of the fetal autopsy findings in CFC syndrome could facilitate diagnosis and understanding of the developmental effects of dysregulated BRAF activity. Here we describe the fetal autopsy findings in a case of CFC syndrome in a 17-week fetus with a novel BRAF mutation that demonstrates potential similarities and differences with the postnatal presentation of CFC syndrome.

Autism traits in the RASopathies

BACKGROUND

Mutations in Ras/mitogen-activated protein kinase (Ras/MAPK) pathway genes lead to a class of disorders known as RASopathies, including neurofibromatosis type 1 (NF1), Noonan syndrome (NS), Costello syndrome (CS), and cardio-facio-cutaneous syndrome (CFC). Previous work has suggested potential genetic and phenotypic overlap between dysregulation of Ras/MAPK signalling and autism spectrum disorders (ASD). Although the literature offers conflicting evidence for association of NF1 and autism, there has been no systematic evaluation of autism traits in the RASopathies as a class to support a role for germline Ras/MAPK activation in ASDs.

METHODS

We examined the association of autism traits with NF1, NS, CS and CFC, comparing affected probands with unaffected sibling controls and subjects with idiopathic ASDs using the qualitative Social Communication Questionnaire (SCQ) and the quantitative Social Responsiveness Scale (SRS).

RESULTS

Each of the four major RASopathies showed evidence for increased qualitative and quantitative autism traits compared with sibling controls. Further, each RASopathy exhibited a distinct distribution of quantitative social impairment. Levels of social responsiveness show some evidence of correlation between sibling pairs, and autism-like impairment showed a male bias similar to idiopathic ASDs.

CONCLUSIONS

Higher prevalence and severity of autism traits in RASopathies compared to unaffected siblings suggests that dysregulation of Ras/MAPK signalling during development may be implicated in ASD risk. Evidence for sex bias and potential sibling correlation suggests that autism traits in the RASopathies share characteristics with autism traits in the general population and clinical ASD population and can shed light on idiopathic ASDs.

Fibroblast growth factor receptor 1 signaling in adult cardiomyocytes increases contractility and results in a hypertrophic cardiomyopathy

Fibroblast growth factors (FGFs) and their receptors are highly conserved signaling molecules that have been implicated in postnatal cardiac remodeling. However, it is not known whether cardiomyocyte-expressed FGF receptors are necessary or sufficient for ventricular remodeling in the adult heart. To determine whether cardiomyocytes were competent to respond to an activated FGF receptor, and to determine if this signal would result in the development of hypertrophy, we engineered a doxycycline (DOX)-inducible, cardiomyocyte-specific, constitutively active FGF receptor mouse model (αMHC-rtTA, TRE-caFgfr1-myc). Echocardiographic and hemodynamic analysis indicated that acute expression of caFGFR1 rapidly and directly increased cardiac contractility, while chronic expression resulted in significant hypertrophy with preservation of systolic function. Subsequent histologic analysis showed increased cardiomyocyte cross-sectional area and regions of myocyte disarray and fibrosis, classic features of hypertrophic cardiomyopathy (HCM). Analysis of downstream pathways revealed a lack of clear activation of classical FGF-mediated signaling pathways, but did demonstrate a reduction in Serca2 expression and troponin I phosphorylation. Isolated ventricular myocytes showed enhanced contractility and reduced relaxation, an effect that was partially reversed by inhibition of actin-myosin interactions. We conclude that adult cardiomyocytes are competent to transduce FGF signaling and that FGF signaling is sufficient to promote increased cardiomyocyte contractility in vitro and in vivo through enhanced intrinsic actin-myosin interactions. Long-term, FGFR overexpression results in HCM with a dynamic outflow tract obstruction, and may serve as a unique model of HCM.

Nf1 loss and Ras hyperactivation in oligodendrocytes induce NOS-driven defects in myelin and vasculature

Patients with neurofibromatosis type 1 (NF1) and Costello syndrome Rasopathy have behavioral deficits. In NF1 patients, these may correlate with white matter enlargement and aberrant myelin. To model these features, we induced Nf1 loss or HRas hyperactivation in mouse oligodendrocytes. Enlarged brain white matter tracts correlated with myelin decompaction, downregulation of claudin-11, and mislocalization of connexin-32. Surprisingly, non-cell-autonomous defects in perivascular astrocytes and the blood-brain barrier (BBB) developed, implicating a soluble mediator. Nitric oxide (NO) can disrupt tight junctions and gap junctions, and NO and NO synthases (NOS1–NOS3) were upregulated in mutant white matter. Treating mice with the NOS inhibitor NG-nitro-L-arginine methyl ester or the antioxidant N-acetyl cysteine corrected cellular phenotypes. CNP-HRasG12V mice also displayed locomotor hyperactivity, which could be rescued by antioxidant treatment. We conclude that Nf1/Ras regulates oligodendrocyte NOS and that dysregulated NO signaling in oligodendrocytes can alter the surrounding vasculature. The data suggest that anti-oxidants may improve some behavioral deficits in Rasopathy patients.

The moyamoya disease susceptibility variant RNF213 R4810K (rs112735431) induces genomic instability by mitotic abnormality

Moyamoya disease (MMD) is a cerebrovascular disease characterized by occlusive lesions in the Circle of Willis. The RNF213 R4810K polymorphism increases susceptibility to MMD. In the present study, we characterized phenotypes caused by overexpression of RNF213 wild type and R4810K variant in the cell cycle to investigate the mechanism of proliferation inhibition. Overexpression of RNF213 R4810K in HeLa cells inhibited cell proliferation and extended the time of mitosis 4-fold. Ablation of spindle checkpoint by depletion of mitotic arrest deficiency 2 (MAD2) did not shorten the time of mitosis. Mitotic morphology in HeLa cells revealed that MAD2 colocalized with RNF213 R4810K. Immunoprecipitation revealed an RNF213/MAD2 complex: R4810K formed a complex with MAD2 more readily than RNF213 wild-type. Desynchronized localization of MAD2 was observed more frequently during mitosis in fibroblasts from patients (n=3, 61.0 ± 8.2%) compared with wild-type subjects (n=6, 13.1 ± 7.7%; p<0.01). Aneuploidy was observed more frequently in fibroblasts (p<0.01) and induced pluripotent stem cells (iPSCs) (p<0.03) from patients than from wild-type subjects. Vascular endothelial cells differentiated from iPSCs (iPSECs) of patients and an unaffected carrier had a longer time from prometaphase to metaphase than those from controls (p<0.05). iPSECs from the patients and unaffected carrier had significantly increased mitotic failure rates compared with controls (p<0.05). Thus, RNF213 R4810K induced mitotic abnormalities and increased risk of genomic instability.

The RASopathies

The RASopathies are a clinically defined group of medical genetic syndromes caused by germline mutations in genes that encode components or regulators of the Ras/mitogen-activated protein kinase (MAPK) pathway. These disorders include neurofibromatosis type 1, Noonan syndrome, Noonan syndrome with multiple lentigines, capillary malformation-arteriovenous malformation syndrome, Costello syndrome, cardio-facio-cutaneous syndrome, and Legius syndrome. Because of the common underlying Ras/MAPK pathway dysregulation, the RASopathies exhibit numerous overlapping phenotypic features. The Ras/MAPK pathway plays an essential role in regulating the cell cycle and cellular growth, differentiation, and senescence, all of which are critical to normal development. Therefore, it is not surprising that Ras/MAPK pathway dysregulation has profound deleterious effects on both embryonic and later stages of development. The Ras/MAPK pathway has been well studied in cancer and is an attractive target for small-molecule inhibition to treat various malignancies. The use of these molecules to ameliorate developmental defects in the RASopathies is under consideration.

Protein tyrosine phosphatase variants in human hereditary disorders and disease susceptibilities

Reversible tyrosine phosphorylation of proteins is a key regulatory mechanism to steer normal development and physiological functioning of multicellular organisms. Phosphotyrosine dephosphorylation is exerted by members of the super-family of protein tyrosine phosphatase (PTP) enzymes and many play such essential roles that a wide variety of hereditary disorders and disease susceptibilities in man are caused by PTP alleles. More than two decades of PTP research has resulted in a collection of PTP genetic variants with corresponding consequences at the molecular, cellular and physiological level. Here we present a comprehensive overview of these PTP gene variants that have been linked to disease states in man. Although the findings have direct bearing for disease diagnostics and for research on disease etiology, more work is necessary to translate this into therapies that alleviate the burden of these hereditary disorders and disease susceptibilities in man.

Desmoglein-1/Erbin interaction suppresses ERK activation to support epidermal differentiation

Genetic disorders of the Ras/MAPK pathway, termed RASopathies, produce numerous abnormalities, including cutaneous keratodermas. The desmosomal cadherin, desmoglein-1 (DSG1), promotes keratinocyte differentiation by attenuating MAPK/ERK signaling and is linked to striate palmoplantar keratoderma (SPPK). This raises the possibility that cutaneous defects associated with SPPK and RASopathies share certain molecular faults. To identify intermediates responsible for executing the inhibition of ERK by DSG1, we conducted a yeast 2-hybrid screen. The screen revealed that Erbin (also known as ERBB2IP), a known ERK regulator, binds DSG1. Erbin silencing disrupted keratinocyte differentiation in culture, mimicking aspects of DSG1 deficiency. Furthermore, ERK inhibition and the induction of differentiation markers by DSG1 required both Erbin and DSG1 domains that participate in binding Erbin. Erbin blocks ERK signaling by interacting with and disrupting Ras-Raf scaffolds mediated by SHOC2, a protein genetically linked to the RASopathy, Noonan-like syndrome with loose anagen hair (NS/LAH). DSG1 overexpression enhanced this inhibitory function, increasing Erbin-SHOC2 interactions and decreasing Ras-SHOC2 interactions. Conversely, analysis of epidermis from DSG1-deficient patients with SPPK demonstrated increased Ras-SHOC2 colocalization and decreased Erbin-SHOC2 colocalization, offering a possible explanation for the observed epidermal defects. These findings suggest a mechanism by which DSG1 and Erbin cooperate to repress MAPK signaling and promote keratinocyte differentiation.