Germline mutation of CBL is associated with moyamoya disease in a child with juvenile myelomonocytic leukemia and Noonan syndrome-like disorder

Long-term remission of infantile Takayasu arteritis associated with germline CBL syndrome after allogeneic hematopoietic stem cell transplantation: A case report and literature review

Takayasu arteritis (TA) is a large-vessel vasculitis that rarely presents in infancy. Casitas B-lineage lymphoma (CBL) syndrome is a rare genetic disorder due to heterozygous CBL gene germline pathogenic variants that is characterized by a predisposition to develop juvenile myelomonocytic leukemia (JMML). Vasculitis, including TA, has been reported in several patients. Herein, we describe a patient with CBL syndrome, JMML, and TA, developing long-term remission of this vasculitis after allogeneic hematopoietic stem cell transplant (HSCT), and perform a literature review of CBL syndrome with vasculitis or vasculopathy. We report a female patient with growth delay, developmental issues, and congenital heart disease who was admitted at 14 months of age with massive splenomegaly, lymphadenopathy, fever, and hypertension. Body imaging studies revealed arterial stenosis and wall inflammation of the aorta and multiple thoracic and abdominal branches. Whole exome sequencing revealed a pathogenic variant in CBL with loss of heterozygosity in blood cells, diagnosing CBL syndrome, complicated by JMML and TA. Allogeneic HSCT induced remission of JMML and TA, permitting discontinuation of immunosuppression after 12 months. Six years later, her TA is in complete remission off therapy. A literature review identified 18 additional cases of CBL syndrome with vasculitis or vasculopathy. The pathogenesis of vasculitis in CBL syndrome appears to involve dysregulated T cell function and possibly increased angiogenesis. This case advances the understanding of vascular involvement in CBL syndrome and of the genetic, immune, and vascular interplay in TA, offering insights for treating CBL syndrome and broader TA.

A Noonan-like pediatric patient with a de novo CBL pathogenic variant and an RNF213 polymorphism p.R4810K presenting with cardiopulmonary arrest due to left main coronary artery ostial atresia

Left main coronary artery ostial atresia (LMCAOA) is an extremely rare condition. Here, we report the case of a 14-year-old boy with Noonan syndrome-like disorder in whom LMCAOA was detected following cardiopulmonary arrest. The patient had been diagnosed with Noonan syndrome-like disorder with a pathogenic splice site variant of CBL c.1228-2 A > G. He suddenly collapsed when he was running. After administering two electric shocks using an automated external defibrillator, the patient's heartbeat resumed. Cardiac catheterization confirmed the diagnosis of LMCAOA. Left main coronary artery angioplasty was performed. The patient was discharged without neurological sequelae. Brain magnetic resonance imaging revealed asymptomatic Moyamoya disease. In addition, RNF213 c.14429 G > A p.R4810K was identified. There are no reports on congenital coronary malformations of compound variations of RNF213 and CBL. In contrast, the RNF213 p.R4810K polymorphism has been established as a risk factor for angina pectoris and myocardial infarction in adults, and several congenital coronary malformations due to genetic abnormalities within the RAS/MAPK signaling pathway have been reported. This report aims to highlight the risk of sudden death in patients with RASopathy and RNF213 p.R4810K polymorphism and emphasize the significance of actively searching for coronary artery morphological abnormalities in these patients.

Physiological and pathophysiological mechanisms of the molecular and cellular biology of angiogenesis and inflammation in moyamoya angiopathy and related vascular diseases

Rationale

The etiology and pathophysiological mechanisms of moyamoya angiopathy (MMA) remain largely unknown. MMA is a progressive, occlusive cerebrovascular disorder characterized by recurrent ischemic and hemorrhagic strokes; with compensatory formation of an abnormal network of perforating blood vessels that creates a collateral circulation; and by aberrant angiogenesis at the base of the brain. Imbalance of angiogenic and vasculogenic mechanisms has been proposed as a potential cause of MMA. Moyamoya vessels suggest that aberrant angiogenic, arteriogenic, and vasculogenic processes may be involved in the pathophysiology of MMA. Circulating endothelial progenitor cells have been hypothesized to contribute to vascular remodeling in MMA. MMA is associated with increased expression of angiogenic factors and proinflammatory molecules. Systemic inflammation may be related to MMA pathogenesis.

Objective

This literature review describes the molecular mechanisms associated with cerebrovascular dysfunction, aberrant angiogenesis, and inflammation in MMA and related cerebrovascular diseases along with treatment strategies and future research perspectives.

Methods and results

References were identified through a systematic computerized search of the medical literature from January 1, 1983, through July 29, 2022, using the PubMed, EMBASE, BIOSIS Previews, CNKI, ISI web of science, and Medline databases and various combinations of the keywords "moyamoya," "angiogenesis," "anastomotic network," "molecular mechanism," "physiology," "pathophysiology," "pathogenesis," "biomarker," "genetics," "signaling pathway," "blood-brain barrier," "endothelial progenitor cells," "endothelial function," "inflammation," "intracranial hemorrhage," and "stroke." Relevant articles and supplemental basic science articles almost exclusively published in English were included. Review of the reference lists of relevant publications for additional sources resulted in 350 publications which met the study inclusion criteria. Detection of growth factors, chemokines, and cytokines in MMA patients suggests the hypothesis of aberrant angiogenesis being involved in MMA pathogenesis. It remains to be ascertained whether these findings are consequences of MMA or are etiological factors of MMA.

Conclusions

MMA is a heterogeneous disorder, comprising various genotypes and phenotypes, with a complex pathophysiology. Additional research may advance our understanding of the pathophysiology involved in aberrant angiogenesis, arterial stenosis, and the formation of moyamoya collaterals and anastomotic networks. Future research will benefit from researching molecular pathophysiologic mechanisms and the correlation of clinical and basic research results.

Updated Stroke Gene Panels: Rapid evolution of knowledge on monogenic causes of stroke

This article updates our previous Stroke Gene Panels (SGP) from 2017. Online Mendelian Inheritance in Man and PubMed were searched. We divided detected genes into two SGP groups, SGP1: genes reported in at least one person with stroke and associated with one or more clinical subgroups: large artery atherosclerotic, large artery non-atherosclerotic (tortuosity, dolichoectasia, aneurysm, non-atherosclerotic dissection or occlusion), cerebral small vessel diseases, cardio-embolic (arrhythmia, heart defect, cardiomyopathy), coagulation dysfunctions (venous thrombosis, arterial thrombosis, bleeding tendency), intracerebral hemorrhage, vascular malformations (cavernoma, arteriovenous malformations) and metabolism disorders; and SGP2: genes related to diseases that may predispose to stroke. We identified 168 SGP1 genes, 70 of these were validated for clinical practice. We also detected 72 SGP2 genes. Nine genes were removed because of conflicting evidence. The number of genes increased from 168 to 240 during 4.5-years, reflecting a dynamic evolution and the need for regular updates for research and clinical use.

Central nervous system involvement in individuals with RASopathies

Central nervous system (CNS) anomalies are common in individuals with RASopathies. While certain findings, including relative or absolute macrocephaly, are typical for most RASopathies, other findings are more common in certain conditions, with rare low-grade gliomas in Noonan syndrome (NS); Chiari 1 malformation and tethered cord in Costello syndrome (CS); and variable structural anomalies including heterotopia and hydrocephalus in cardio-facio-cutaneous syndrome (CFC). We performed a literature review and present aggregate data on the common and uncommon CNS manifestations in individuals with RASopathies. A gene-based approach to defining risk for specific abnormalities may be considered. However, limited information on the CNS findings of rare RASopathies, such as autosomal recessive LZTR1-related NS or PPP1CB-related NS with loose anagen hair (NSLH), is currently available. Thus, consideration of the RASopathies as a group of distinct syndromic conditions with shared underlying causes and overlapping clinical presentations remains relevant, and individuals with a RASopathy are at risk for many findings seen in these conditions.

Immune dysregulation associated with co-occurring germline CBL and SH2B3 variants

Background

CBL syndrome is a RASopathy caused by heterozygous germline mutations of the Casitas B-lineage lymphoma (CBL) gene. It is characterized by heterogeneous clinical phenotype, including developmental delay, facial dysmorphisms, cardiovascular malformations and an increased risk of cancer development, particularly juvenile myelomonocytic leukemia (JMML). Although the clinical phenotype has been progressively defined in recent years, immunological manifestations have not been well elucidated to date.

Methods

We studied the genetic, immunological, coagulative, and clinical profile of a family with CBL syndrome that came to our observation after the diagnosis of JMML, with homozygous CBL mutation, in one of the members.

Results

Variant analysis revealed the co-occurrence of CBL heterozygous mutation (c.1141 T > C) and SH2B3 mutation (c.1697G > A) in two other members. Patients carrying both mutations showed an ALPS-like phenotype characterized by lymphoproliferation, cytopenia, increased double-negative T-cells, impaired Fas-mediated lymphocyte apoptosis, altered cell death in PBMC and low TRECs expression. A coagulative work-up was also performed and showed the presence of subclinical coagulative alterations in patients carrying both mutations.

Conclusion

In the reported family, we described immune dysregulation, as part of the clinical spectrum of CBL mutation with the co-occurrence of SH2B3.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40246-022-00414-y.

Casitas B-lineage lymphoma Gene Mutation Ocular Phenotype

This article describes the ocular phenotype associated with the identified Casitas B-lineage lymphoma (CBL) gene mutation and reviews the current literature. This work also includes the longitudinal follow-up of five unrelated cases of unexplained fundus lesions with visual loss associated with a history of hepatosplenomegaly. Wide repeated workup was made to rule out infections, inflammatory diseases, and lysosomal diseases. No variants in genes associated with retinitis pigmentosa, cone–rod dystrophy, and inherited optic neuropathy were found. Molecular analysis was made using next-generation sequencing (NGS) and whole-exome sequencing (WES). The results included two cases sharing ophthalmological signs including chronic macular edema, vascular leakage, visual field narrowing, and electroretinography alteration. Two other cases showed damage to the optic nerve head and a fifth young patient exhibited bilateral complicated vitreoretinal traction and carried a heterozygous mutation in the CBL gene associated with a mutation in the IKAROS gene. Ruxolitinib as a treatment for RASopathy did not improve eye conditions, whereas systemic lesions were resolved in one patient. Mutations in the CBL gene were found in all five cases. In conclusion, a detailed description may pave the way for the CBL mutation ocular phenotype. Genetic analysis using whole-exome sequencing could be useful in the diagnosis of unusual clinical features.

Cytokine profile and brain biopsy in a case of childhood-onset central nervous system vasculitis in Noonan syndrome-like disorder due to a novel CBL variant

The authors describe a 5-year-old girl who developed a Noonan syndrome-like disorder as a result of the CBL c.1194C>G/p.His398Gln variant, including headache, papilledema, intracranial hypertension, hyperproteinorrhachia, leucorrhachia, and brain inflammation and vasculitis with CD3 positive lymphocyte infiltration. The patient responded partially to corticosteroids, acetazolamide, and ventriculoperitoneal valve placement. The serum cytokine profile revealed persistently elevated levels of IL-1 RA, IL-2R alpha, IL-6, IL-18, MCP-1, and MCP-3. Cyclophosphamide was used as a bridge to allogeneic hematopoietic stem cell transplantation in this case.

Role of CBL Mutations in Cancer and Non-Malignant Phenotype

Simple Summary

CBL mutations are progressively being described as involved in different clinical manifestations. Somatic CBL mutations can be found in different type of cancer. The clinical spectrum of germline mutations configures the so-called CBL syndrome, a cancer-predisposing condition that includes multisystemic involvement characterized by variable phenotypic expression and expressivity. In this review we provide an up-to-date review of the clinical manifestation of CBL mutations and of the molecular mechanisms in which CBL exerts its pathogenic role.

Abstract

CBL plays a key role in different cell pathways, mainly related to cancer onset and progression, hematopoietic development and T cell receptor regulation. Somatic CBL mutations have been reported in a variety of malignancies, ranging from acute myeloid leukemia to lung cancer. Growing evidence have defined the clinical spectrum of germline CBL mutations configuring the so-called CBL syndrome; a cancer-predisposing condition that also includes multisystemic involvement characterized by variable phenotypic expression and expressivity. This review provides a comprehensive overview of the molecular mechanisms in which CBL exerts its function and describes the clinical manifestation of CBL mutations in humans.

Juvenile myelomonocytic leukemia in CBL syndrome associated with germline splice-site mutations: Two case reports and a literature review

The clinical and laboratory criteria for hemophagocytic lymphohistiocytosis should be taken into account during the juvenile myelomonocytic leukemia diagnosis, specifically in CBL syndrome, to reveal the presence of primary rather than secondary associated hemophagocytosis.

Pediatric Neoplasms Presenting with Monocytosis

PURPOSE OF REVIEW

Juvenile myelomonocytic leukemia (JMML) is a rare but severe pediatric neoplasm with hematopoietic stem cell transplant as its only established curative option. The development of targeted therapeutics for JMML is being guided by an understanding of the pathobiology of this condition. Here, we review JMML with an emphasis on genetics in order to (i) demonstrate the relationship between JMML genotype and clinical phenotype and (ii) explore potential genetic targets of novel JMML therapies.

RECENT FINDINGS

DNA hypermethylation studies have demonstrated consistently that methylation is related to disease severity. Increasing understanding of methylation in JMML may open the door to novel therapies, such as DNA methyltransferase inhibitors. The PI3K/AKT/MTOR, JAK/STAT, and RAF/MEK/ERK pathways are being investigated as therapeutic targets for JMML. Future therapy for JMML will be driven by an increased understanding of pathobiology. Targeted therapeutic approaches hold potential for improving outcomes in patients with JMML.

Cerebral arteriopathy associated with heterozygous variants in the casitas B-lineage lymphoma gene

Objective

To report a series of patients with cerebral arteriopathy associated with heterozygous variants in the casitas B-lineage lymphoma (CBL) gene and examine the functional role of the identified mutant Cbl protein. We hypothesized that mutated Cbl fails to act as a negative regulator of the RAS-mitogen-activated protein kinases (MAPK) signaling pathway, resulting in enhanced vascular fibroblast proliferation and migration and enhanced angiogenesis and collateral vessel formation.

Methods

We performed whole-exome sequencing in 11 separate families referred to Great Ormond Street Hospital, London, with suspected genetic cause for clinical presentation with severe progressive cerebral arteriopathy.

Results

We identified heterozygous variants in the CBL gene in 5 affected cases from 3 families. We show that impaired CBL-mediated degradation of cell surface tyrosine kinase receptors and dysregulated intracellular signaling through the RAS-MAPK pathway contribute to the pathogenesis of the observed arteriopathy. Mutated CBL failed to control the angiogenic signal relay of vascular endothelial growth factor receptor 2, leading to prolonged tyrosine kinase signaling, thus driving angiogenesis and collateral vessel formation. Mutant Cbl promoted myofibroblast migration and proliferation contributing to vascular occlusive disease; these effects were abrogated following treatment with a RAF-RAS-MAPK pathway inhibitor.

Conclusions

We provide a possible mechanism for the arteriopathy associated with heterozygous CBL variants. Identification of the key role for the RAS-MAPK pathway in CBL-mediated cerebral arteriopathy could facilitate identification of novel or repurposed druggable targets for treating these patients and may also provide therapeutic clues for other cerebral arteriopathies.

A Case of Uveitis in a Patient With Juvenile Myelomonocytic Leukemia Successfully Treated With Adalimumab

Patients with juvenile myelomonocytic leukemia due to germline CBL mutation (10% to 15%) may have a subacute course occasionally associated with autoimmune disorders, which may resemble RAS-associated autoimmune lymphoproliferative disorder. In both conditions, prognosis and standard treatment for autoimmune phenomena remain poorly understood. We report the case of a 7-year-old boy with juvenile myelomonocytic leukemia with severe steroid-dependent uveitis, who did not respond to several therapeutic attempts with immunosuppressant agents, including sirolimus, and was finally successfully treated with adalimumab. This case offers further insight into the management of autoimmune disorders in the context of predisposing genetic conditions.

Congenital heart defects in Noonan syndrome: Diagnosis, management, and treatment

Noonan syndrome is a pleomorphic genetic disorder, in which a high percentage of affected individuals have cardiovascular involvement, most prevalently various forms of congenital heart disease (i.e., pulmonary valve stenosis, septal defects, left-sided lesions, and complex forms with multiple anomalies). Care includes attentiveness to several comorbidities, some directly impacting cardiac management (bleeding diatheses and lymphatic anomalies). More than 50% of patients with Noonan syndrome harbor PTPN11 pathogenic variation, which results in hyperactivation of RAS/mitogen-activated protein kinase signaling. Several other disease genes with similar biological effects have been uncovered for NS and phenotypically related disorders, collectively called the RASopathies. Molecular diagnosis with gene resequencing panels is now widely available, but phenotype variability and in some cases, subtlety, continues to make identification of Noonan syndrome difficult. Until genetic testing becomes universal for patients with congenital heart disease, alertness to Noonan syndrome's broad clinical presentations remains crucial. Genotype-phenotype associations for Noonan syndrome enable better prognostication for affected patients when a molecular diagnosis is established. We still lack Noonan syndrome-specific treatment; however, newly developed anticancer RAS pathway inhibitors could fill that gap if safety and efficacy can be established for indications such as pulmonary valve stenosis.

After 95 years, it's time to eRASe JMML

Juvenile myelomonocytic leukaemia (JMML) is a rare clonal disorder of early childhood. Constitutive activation of the RAS pathway is the initial event in JMML. Around 90% of patients diagnosed with JMML carry a mutation in the PTPN11, NRAS, KRAS, NF1 or CBL genes. It has been demonstrated that after this first genetic event, an additional somatic mutation or epigenetic modification is involved in disease progression. The available genetic and clinical data have enabled researchers to establish relationships between JMML and several clinical conditions, including Noonan syndrome, Ras-associated lymphoproliferative disease, and Moyamoya disease. Despite scientific progress and the development of more effective treatments, JMML is still a deadly disease: the 5-year survival rate is ~50%. Here, we report on recent research having led to a better understanding of the genetic and molecular mechanisms involved in JMML.

Therapeutic effect of autologous bone marrow stem cell mobilization combined with anti-infective therapy on moyamoya disease

Objective

The purpose of this study is to explore the therapeutic effect of autologous bone marrow stem cell (ABMSC) mobilization combined anti-infection therapy on patients with moyamoya disease (MMD), and to provide reference for the clinical treatment of MMD and cerebrovascular disease.

Methods

54 adult patients with MMD diagnosed in Henan Provincial People's Hospital from March 2017 to March 2019 were chosen as research objects. All patients were randomly divided into study group (SG) and control group (CG), with 27 patients in each group. Patients in both groups received conventional drug treatment after diagnosis of MMD, and received dura turnover of brain - temporal muscle - superficial temporal artery application surgery during indirect vascular reconstruction. On the basis of surgical treatment, patients in the SG were given ABMSC mobilization combined with low-dose dexamethasone for anti-inflammatory and anti-infection treatment. ABMSCs were mobilized by recombinant human granulocyte colony stimulating factor (rhG-csF) and recombinant human granulocyte - macrophage colony stimulating factor (rhoM-esF). The therapeutic effects of the patients were evaluated BF, one month after treatment (AF), three months AF, and six months AF. The number of hematopoietic stem cells (HpCs) and inflammatory indicators were compared between the two groups before and 4 weeks AF.

Results

Firstly, the Barthcl index of patients in the two groups showed a gradual increase trend at the 3rd and 6th months AF, and the ascensional range in the research group was higher than that in the CG (P < 0.05). Secondly, at the 3rd and 6th month AF, national institute of heath stroke scale (NIHSS) scores of patients in the CG were lower than those before treatment (BF), and there was an important change in NIHSS scores between the two groups at the same period (P < 0.05). Thirdly, after 1 month of treatment and 3 months of treatment, Chinese stroke scale (CSS) scores of patients in both groups decreased obviously compared with those BF, and the SG was lower than the CG, with statistical changes (P < 0.05). Fourthly, after 4 weeks of treatment, the hematopoietic stem cell counts in both groups were higher than those BF, and the hematopoietic stem cell counts in the SG were obviously higher than those in the CG (P < 0.05). All three inflammatory indicators were improved compared with those BF, and the SG was better than the CG (P < 0.05).

Conclusion

Autogenous bone marrow stem cell mobilization combined with dexamethasone anti-inflammation and anti-infection treatment after revascularization in patients with MMD can accelerate the recovery of nerve function and promote the formation of new blood vessels. At the same time, it can reduce inflammation and improve patients' quality of life, which is worthy of clinical reference.

Juvenile myelomonocytic leukemia: who's the driver at the wheel?

Juvenile myelomonocytic leukemia (JMML) is a unique clonal hematopoietic disorder of early childhood. It is classified as an overlap myeloproliferative/myelodysplastic neoplasm by the World Health Organization and shares some features with chronic myelomonocytic leukemia in adults. JMML pathobiology is characterized by constitutive activation of the Ras signal transduction pathway. About 90% of patients harbor molecular alterations in 1 of 5 genes (PTPN11, NRAS, KRAS, NF1, or CBL), which define genetically and clinically distinct subtypes. Three of these subtypes, PTPN11-, NRAS-, and KRAS-mutated JMML, are characterized by heterozygous somatic gain-of-function mutations in nonsyndromic children, whereas 2 subtypes, JMML in neurofibromatosis type 1 and JMML in children with CBL syndrome, are defined by germline Ras disease and acquired biallelic inactivation of the respective genes in hematopoietic cells. The clinical course of the disease varies widely and can in part be predicted by age, level of hemoglobin F, and platelet count. The majority of children require allogeneic hematopoietic stem cell transplantation for long-term leukemia-free survival, but the disease will eventually resolve spontaneously in ∼15% of patients, rendering the prospective identification of these cases a clinical necessity. Most recently, genome-wide DNA methylation profiles identified distinct methylation signatures correlating with clinical and genetic features and highly predictive for outcome. Understanding the genomic and epigenomic basis of JMML will not only greatly improve precise decision making but also be fundamental for drug development and future collaborative trials.

When and why is surgical revascularization indicated for the treatment of moyamoya syndrome in patients with RASopathies? A systematic review of the literature and a single institute experience

BACKGROUND

Moyamoya disease (MMD) is a cerebrovascular disorder characterized by the progressive occlusion of the supraclinoid internal carotid artery (ICA), resulting in the formation of an abnormal cerebral vascular network. When MMD occurs in association with an underlying medical condition, including some distinctive genetic disorders, it is named moyamoya syndrome (MMS). The discrimination between MMD and MMS has been validated by recent genetic researches and international reviews. Similarly to patients suffering from MMD, patients with MMS generally become symptomatic because of ischemic complications, which lead to hemiparesis, transient ischemic events, seizures, and sensory symptoms. RASopathies are a group of neurodevelopmental disorders that can be associated with MMS.

RESULTS

We retrospectively reviewed 18 RASopathy patients with MMS treated at our institution from 2000 to 2015 (16 neurofibromatosis type 1, 1 Costello syndrome, and 1 Schimmelpenning syndrome). Here, we report clinical data, performed surgical procedures, and clinic-radiological outcome of these patients. Most of them received both indirect revascularization and medical therapy.

CONCLUSIONS

At the moment, there are no univocal recommendations on which of these two treatment strategies is the treatment of choice in patients with RASopathies and MMS. We suggest that patients with a good overall prognosis (primarily depending on the distinctive underlying genetic disorder) and initial cerebrovascular disease could benefit from a prophylactic surgical revascularization, in order to prevent the cognitive impairment due to the progression of the vasculopathy.

Mutation-specific signaling profiles and kinase inhibitor sensitivities of juvenile myelomonocytic leukemia revealed by induced pluripotent stem cells

Juvenile myelomonocytic leukemia (JMML) is an uncommon myeloproliferative neoplasm driven by Ras pathway mutations and hyperactive Ras/MAPK signaling. Outcomes for many children with JMML remain dismal with current standard-of-care cytoreductive chemotherapy and hematopoietic stem cell transplantation. We used patient-derived induced pluripotent stem cells (iPSCs) to characterize the signaling profiles and potential therapeutic vulnerabilities of PTPN11-mutant and CBL-mutant JMML. We assessed whether MEK, JAK, and PI3K/mTOR kinase inhibitors (i) could inhibit myeloproliferation and aberrant signaling in iPSC-derived hematopoietic progenitors with PTPN11 E76K or CBL Y371H mutations. We detected constitutive Ras/MAPK and PI3K/mTOR signaling in PTPN11 and CBL iPSC-derived myeloid cells. Activated signaling and growth of PTPN11 iPSCs were preferentially inhibited in vitro by the MEKi PD0325901 and trametinib. Conversely, JAK/STAT signaling was selectively activated in CBL iPSCs and abrogated by the JAKi momelotinib and ruxolitinib. The PI3Kδi idelalisib and mTORi rapamycin inhibited signaling and myeloproliferation in both PTPN11 and CBL iPSCs. These findings demonstrate differential sensitivity of PTPN11 iPSCs to MEKi and of CBL iPSCs to JAKi, but similar sensitivity to PI3Ki and mTORi. Clinical investigation of mutation-specific kinase inhibitor therapies in children with JMML may be warranted.

Down syndrome, RASopathies, and other rare syndromes

In this article we discuss the occurrence of myeloid neoplasms in patients with a range of syndromes that are due to germline defects of the RAS signaling pathway and in patients with trisomy 21. Both RAS mutations and trisomy 21 are common somatic events contributing to leukemogenis. Thus, the increased leukemia risk observed in children affected by these conditions is biologically highly plausible. Children with myeloid neoplasms in the context of these syndromes require different treatments than children with sporadic myeloid neoplasms and provide an opportunity to study the role of trisomy 21 and RAS signaling during leukemogenesis and development.

A case of splenomegaly in CBL syndrome

INTRODUCTION

We present a child with unexplained splenomegaly to highlight this feature as a presenting sign of the RASopathy CBL syndrome and to draw attention to the power and utility of next generation genomic sequencing for providing rapid diagnosis and critical information to guide care in the pediatric clinical setting.

CLINICAL REPORT

A 7-year-old boy presented with unexplained splenomegaly, attention deficit hyperactivity disorder, mild learning difficulties, easy bruising, mild thrombocytopenia, and subtle dysmorphic features. Extensive haematological testing including a bone marrow biopsy showed mild megaloblastoid erythropoiesis and borderline fibrosis. There were no haematological cytogenetic anomalies or other haematological pathology to explain the splenomegaly. Metabolic testing and chromosomal microarray were unremarkable. Trio whole-exome sequencing (WES) identified a pathogenic de novo heterozygous germline CBL variant (c.1111T > C, p.Y371H), previously reported to cause CBL syndrome and implicated in development of juvenile myelomonocytic leukemia (JMML).

DISCUSSION

CBL syndrome (more formally known as "Noonan-syndrome-like disorder with or without juvenile myelomonocytic leukemia") has overlapping features to Noonan syndrome with significant variability. CBL syndrome and other RASopathy disorders-including Noonan syndrome, neurofibromatosis 1, and Costello syndrome-are important to recognize as these are associated with a cancer-predisposition. CBL syndrome carries a very high risk for JMML, thus accurate diagnosis is of utmost importance. The diagnosis of CBL syndrome in this patient would not have been possible based on clinical features alone. Through WES, a specific genetic diagnosis was made, allowing for an optimized management and surveillance plan, illustrating the power of genomics in clinical practice.

De novo mutations in CBL causing early-onset paediatric moyamoya angiopathy

BACKGROUND

Moyamoya angiopathy (MMA) is characterised by a progressive stenosis of the terminal part of the internal carotid arteries and the development of abnormal collateral deep vessels. Its pathophysiology is unknown. MMA can be the sole manifestation of the disease (moyamoya disease) or be associated with various conditions (moyamoya syndrome) including some Mendelian diseases. We aimed to investigate the genetic basis of moyamoya using a whole exome sequencing (WES) approach conducted in sporadic cases without any overt symptom suggestive of a known Mendelian moyamoya syndrome.

METHODS

A WES was performed in four unrelated early-onset moyamoya sporadic cases and their parents (trios). Exome data were analysed under dominant de novo, autosomal recessive and X-linked hypotheses. A panel of 17 additional sporadic cases with early-onset moyamoya was available for mutation recurrence analysis.

RESULTS

We identified two germline de novo mutations in CBL in two out of the four trio probands, two girls presenting with an infancy-onset severe MMA. Both mutations were predicted to alter the ubiquitin ligase activity of the CBL protein that acts as a negative regulator of the RAS pathway. These two germline CBL mutations have previously been described in association with a developmental Noonan-like syndrome and susceptibility to juvenile myelomonocytic leukaemia (JMML). Notably, the two mutated girls never developed JMML and presented only subtle signs of RASopathy that did not lead to evoke this diagnosis during follow-up.

CONCLUSIONS

These data suggest that CBL gene screening should be considered in early-onset moyamoya, even in the absence of obvious signs of RASopathy.

Unexpected Findings in a Child with Atypical Hemolytic Uremic Syndrome: An Example of How Genomics Is Changing the Clinical Diagnostic Paradigm

CBL is a tumor suppressor gene on chromosome 11 encoding a multivalent adaptor protein with E3 ubiquitin ligase activity. Germline CBL mutations are dominant. Pathogenic de novo mutations result in a phenotype that overlaps Noonan syndrome (1). Some patients with CBL mutations go on to develop juvenile myelomonocytic leukemia (JMML), an aggressive malignancy that usually necessitates bone marrow transplantation. Using whole exome sequencing methods, we identified a known mutation in CBL in a 4-year-old Caucasian boy with atypical hemolytic uremic syndrome, moyamoya phenomenon, and dysmorphology consistent with a mild Noonan-like phenotype. Exome data revealed loss of heterozygosity across chromosome 11q consistent with JMML but in the absence of clinical leukemia. Our finding challenges conventional clinical diagnostics since we have identified a pathogenic variant in the CBL gene previously only ascertained in children presenting with leukemia. The increasing affordability of expansive sequencing is likely to increase the scope of clinical profiles observed for previously identified pathogenic variants and calls into question the interpretability and indications for clinical management.

Neovascular glaucoma: a review

Neovascular glaucoma (NVG) is a secondary glaucoma generally associated with poor visual prognosis. The development of new vessels over the iris and the iridocorneal angle can obstruct aqueous humor outflow and lead to increased intraocular pressure. The underlying pathogenesis in most cases is posterior segment ischemia, which is most commonly secondary to proliferative diabetic retinopathy or central vein retinal occlusion. The neovascularization process in the eye is driven by the events that alter the homeostatic balance between pro-angiogenic factors, such as the vascular endothelial growth factor and anti-angiogenic factors, such as the pigment-epithelium-derived factor. Early diagnosis of this condition through slit lamp examination of the iris, iridocorneal angle and retina can help to avoid the development of goniosynechia and obstruction of aqueous humor outflow, with consequent intraocular pressure elevation. Historically, NVG treatment was focused on reducing the posterior segment ischemic process that caused the formation of new vessels, through panretinal photocoagulation. Recently, several studies have investigated the application of intravitreal anti-VEGF therapies in NVG. If clinical treatment with the use of hypotensive topical drops is not sufficient, laser and/or surgical procedures are required for intraocular pressure control.

Research Progress of Moyamoya Disease in Children

During the onset of Moyamoya disease (MMD), progressive occlusion occurs at the end of the intracranial internal carotid artery, and compensatory net-like abnormal vessels develop in the skull base, generating the corresponding clinical symptoms. MMD can affect both children and adults, but MMD in pediatric patients exhibits distinct clinical features, and the treatment prognoses are different from adult patients. Children are the group at highest risk for MMD. In children, the disease mainly manifests as ischemia, while bleeding is the primary symptom in adults. The pathogenesis of MMD in children is still unknown, and some factors are distinct from those in adults. MMD in children could result in progressive, irreversible nerve functional impairment, and an earlier the onset corresponds to a worse prognosis. Therefore, active treatment at an early stage is highly recommended. The treatment methods for MMD in children mainly include indirect and direct surgeries. Indirect surgeries mainly include multiple burr-hole surgery (MBHS), encephalomyosynangiosis (EMS), and encephaloduroarteriosynangiosis (EDAS); direct surgeries mainly include intra- and extracranial vascular reconstructions that primarily consist of superficial temporal artery-middle cerebral artery (STA-MCA) anastomosis. Indirect surgery, as a treatment for MMD in children, has shown a certain level of efficacy. However, a standard treatment approach should combine both indirect and direct procedures. Compared to MMD in adults, the treatment and prognosis of MMD in children has higher clinical significance. If the treatment is adequate, a satisfactory outcome is often achieved.

A point mutation of zebrafish c-cbl gene in the ring finger domain produces a phenotype mimicking human myeloproliferative disease

Controlled self-renewal and differentiation of hematopoietic stem/progenitor cells (HSPCs) are critical for vertebrate development and survival. These processes are tightly regulated by the transcription factors, signaling molecules and epigenetic factors. Impaired regulations of their function could result in hematological malignancies. Using a large-scale zebrafish N-ethyl-N-nitrosourea mutagenesis screening, we identified a line named LDD731, which presented significantly increased HSPCs in hematopoietic organs. Further analysis revealed that the cells of erythroid/myeloid lineages in definitive hematopoiesis were increased while the primitive hematopoiesis was not affected. The homozygous mutation was lethal with a median survival time around 14-15 days post fertilization. The causal mutation was located by positional cloning in the c-cbl gene, the human ortholog of which, c-CBL, is found frequently mutated in myeloproliferative neoplasms (MPN) or acute leukemia. Sequence analysis showed the mutation in LDD731 caused a histidine-to-tyrosine substitution of the amino acid codon 382 within the RING finger domain of c-Cbl. Moreover, the myeloproliferative phenotype in zebrafish seemed dependent on the Flt3 (fms-like tyrosine kinase 3) signaling, consistent with that observed in both mice and humans. Our study may shed new light on the pathogenesis of MPN and provide a useful in vivo vertebrate model of this syndrome for screening drugs.

Molecular Diversity and Associated Phenotypic Spectrum of Germline CBL Mutations

Noonan syndrome (NS) is a relatively common developmental disorder with a pleomorphic phenotype. Mutations causing NS alter genes encoding proteins involved in the RAS-MAPK pathway. We and others identified Casitas B-lineage lymphoma proto-oncogene (CBL), which encodes an E3-ubiquitin ligase acting as a tumor suppressor in myeloid malignancies, as a disease gene underlying a condition clinically related to NS. Here, we further explored the spectrum of germline CBL mutations and their associated phenotype. CBL mutation scanning performed on 349 affected subjects with features overlapping NS and no mutation in NS genes allowed the identification of five different variants with pathological significance. Among them, two splice-site changes, one in-frame deletion, and one missense mutation affected the RING domain and/or the adjacent linker region, overlapping cancer-associated defects. A novel nonsense mutation generating a v-Cbl-like protein able to enhance signal flow through RAS was also identified. Genotype-phenotype correlation analysis performed on available records indicated that germline CBL mutations cause a variable phenotype characterized by a relatively high frequency of neurological features, predisposition to juvenile myelomonocytic leukemia, and low prevalence of cardiac defects, reduced growth, and cryptorchidism. Finally, we excluded a major contribution of two additional members of the CBL family, CBLB and CBLC, to NS and related disorders.