Common acute lymphoblastic leukemia in a girl with genetically confirmed LEOPARD syndrome

Transient Myeloproliferative Disorder (TMD), Acute Lymphoblastic Leukemia (ALL), and Juvenile Myelomonocytic Leukemia (JMML) in a Child with Noonan Syndrome: Sequential Occurrence, Single Center Experience, and Review of the Literature

Noonan syndrome (NS) is an autosomal dominant disorder that varies in severity and can involve multiple organ systems. In approximately 50% of cases, it is caused by missense mutations in the PTPN11 gene (12q24.13). NS is associated with a higher risk of cancer occurrence, specifically hematological disorders. Here, we report a case of a child who was diagnosed at birth with a transient myeloproliferative disorder (TMD). After two years, the child developed hyperdiploid B-cell precursor acute lymphoblastic leukemia (BCP-ALL), receiving a two-year course of treatment. During her continuous complete remission (CCR), a heterozygous germline mutation in the PTPN11 gene [c.218 C>T (p.Thr73lle)] was identified. At the age of ten, the child presented with massive splenomegaly, hyperleukocytosis, and thrombocytopenia, resulting in the diagnosis of juvenile myelomonocytic leukemia (JMML). After an initial response to antimetabolite therapy (6-mercaptopurine), she underwent haploidentical hematopoietic stem cell transplantation (HSCT) and is currently in complete remission. The goal of this review is to gain insight into the various hematological diseases associated with NS, starting from our unique case.

SHP2 clinical phenotype, cancer, or RASopathies, can be predicted by mutant conformational propensities

SHP2 phosphatase promotes full activation of the RTK-dependent Ras/MAPK pathway. Its mutations can drive cancer and RASopathies, a group of neurodevelopmental disorders (NDDs). Here we ask how same residue mutations in SHP2 can lead to both cancer and NDD phenotypes, and whether we can predict what the outcome will be. We collected and analyzed mutation data from the literature and cancer databases and performed molecular dynamics simulations of SHP2 mutants. We show that both cancer and Noonan syndrome (NS, a RASopathy) mutations favor catalysis-prone conformations. As to cancer versus RASopathies, we demonstrate that cancer mutations are more likely to accelerate SHP2 activation than the NS mutations at the same genomic loci, in line with NMR data for K-Ras4B more aggressive mutations. The compiled experimental data and dynamic features of SHP2 mutants lead us to propose that different from strong oncogenic mutations, SHP2 activation by NS mutations is less likely to induce a transition of the ensemble from the SHP2 inactive state to the active state. Strong signaling promotes cell proliferation, a hallmark of cancer. Weak, or moderate signals are associated with differentiation. In embryonic neural cells, dysregulated differentiation is connected to NDDs. Our innovative work offers structural guidelines for identifying and correlating mutations with clinical outcomes, and an explanation for why bearers of RASopathy mutations may have a higher probability of cancer. Finally, we propose a drug strategy against SHP2 variants-promoting cancer and RASopathies.

Cancer incidence and surveillance strategies in individuals with RASopathies

RASopathies are a set of clinical syndromes that have molecular and clinical overlap. Genetically, these syndromes are defined by germline pathogenic variants in RAS/MAPK pathway genes resulting in activation of this pathway. Clinically, their common molecular signature leads to comparable phenotypes, including cardiac anomalies, neurologic disorders and notably, elevated cancer risk. Cancer risk in individuals with RASopathies has been estimated from retrospective reviews and cohort studies. For example, in Costello syndrome, cancer incidence is significantly elevated over the general population, largely due to solid tumors. In some forms of Noonan syndrome, cancer risk is also elevated over the general population and is enriched for hematologic malignancies. Thus, cancer surveillance guidelines have been developed to monitor for the occurrence of such cancers in individuals with some RASopathies. These include abdominal ultrasound and urinalyses for individuals with Costello syndrome, while complete blood counts and splenic examination are recommended in Noonan syndrome. Improved cancer risk estimates and refinement of surveillance recommendations will improve the care of individuals with RASopathies.

Recombinant human growth hormone in the treatment of C.836A/G-caused short stature in a girl: a case report and literature review

BACKGROUND

When we treated the C.836A/G-caused short stature girls with rhGH (recombinant growth hormone) for short stature, the effect of height improvement was good, but in the course of treatment, there was a side effect of leukopenia, which led to the interruption of treatment. We consult the literature, did not find such relevant reports, therefore, the objective of this study is to share the novel treatment method of C.836A/G-caused short stature and report the treatment response and adverse events of the child with C.836A/G-caused short stature.

CASE DESCRIPTION

The clinical data of 1 child with C.836A/G-caused short stature were collected, and the efficacy of rhGH in the treatment of this child was observed. The female child aged 5 years and 5 months old was treated at our hospital for growth retardation of >5 years. The child was a slightly picky eater, had good sleep quality (she often fell asleep after 21:00), and did not exercise much before the age of 3-4 years. Routine blood results and other relevant indicators were also monitored during the treatment. The growth rate of the child was followed up over a period of 16 months using needle withdrawal, and routine blood examinations were conducted regularly. With the application of rhGH, the child with C.836A/G-caused short stature gained 9.6 cm in height at 11 months, and had a height of standard deviation score of -1.01. Throughout the treatment, the blood hemoglobin and platelets of the child were normal, but the content of the granulocytes was lower than the normal value. Some 16 months after the discontinuation of the rhGH therapy, the granulocytes gradually returned to the normal range, but the growth rate of the child declined obviously.

CONCLUSIONS

Recombinant growth hormone treatment of this case of C.836A/G-caused short stature is effective, but in the course of treatment, we need to pay attention to the side effects of the hematological system. Due to our limited clinical experience with these cases, please correct us for any inaccuracies.

Phase Separation of Disease-Associated SHP2 Mutants Underlies MAPK Hyperactivation

The non-receptor protein tyrosine phosphatase (PTP) SHP2, encoded by PTPN11, plays an essential role in RAS-mitogen-activated protein kinase (MAPK) signaling during normal development. It has been perplexing as to why both enzymatically activating and inactivating mutations in PTPN11 result in human developmental disorders with overlapping clinical manifestations. Here, we uncover a common liquid-liquid phase separation (LLPS) behavior shared by these disease-associated SHP2 mutants. SHP2 LLPS is mediated by the conserved well-folded PTP domain through multivalent electrostatic interactions and regulated by an intrinsic autoinhibitory mechanism through conformational changes. SHP2 allosteric inhibitors can attenuate LLPS of SHP2 mutants, which boosts SHP2 PTP activity. Moreover, disease-associated SHP2 mutants can recruit and activate wild-type (WT) SHP2 in LLPS to promote MAPK activation. These results not only suggest that LLPS serves as a gain-of-function mechanism involved in the pathogenesis of SHP2-associated human diseases but also provide evidence that PTP may be regulated by LLPS that can be therapeutically targeted.

Predisposing germline mutations in high hyperdiploid acute lymphoblastic leukemia in children

High hyperdiploidy (HD) is the most common cytogenetic subtype of childhood acute lymphoblastic leukemia (ALL), and a higher incidence of HD has been reported in ALL patients with congenital cancer syndromes. We assessed the frequency of predisposing germline mutations in 57 HD-ALL patients from the California Childhood Leukemia Study via targeted sequencing of cancer-relevant genes. Three out of 57 patients (5.3%) harbored confirmed germline mutations that were likely causal, in NBN, ETV6, and FLT3, with an additional six patients (10.5%) harboring putative predisposing mutations that were rare in unselected individuals (<0.01% allele frequency in the Exome Aggregation Consortium, ExAC) and predicted functional (scaled CADD score ≥ 20) in known or potential ALL predisposition genes (SH2B3, CREBBP, PMS2, MLL, ABL1, and MYH9). Three additional patients carried rare and predicted damaging germline mutations in GAB2, a known activator of the ERK/MAPK and PI3K/AKT pathways and binding partner of PTPN11-encoded SHP2. The frequency of rare and predicted functional germline GAB2 mutations was significantly higher in our patients (2.6%) than in ExAC (0.28%, P = 4.4 × 10^-3 ), an observation that was replicated in ALL patients from the TARGET project (P = .034). We cloned patient GAB2 mutations and expressed mutant proteins in HEK293 cells and found that frameshift mutation P621fs led to reduced SHP2 binding and ERK1/2 phosphorylation but significantly increased AKT phosphorylation, suggesting possible RAS-independent leukemogenic effects. Our results support a significant contribution of rare, high penetrance germline mutations to HD-ALL etiology, and pinpoint GAB2 as a putative novel ALL predisposition gene.

Acute lymphoblastic leukemia in the context of RASopathies

Noonan syndrome is associated with a range of malignancies including acute lymphoblastic leukemia (ALL). However, little information is available regarding the frequency, natural history, characteristics and prognosis of ALL in Noonan syndrome or RASopathies in general. Cross-referencing data from a large prospective cohort of 1176 patients having a molecularly confirmed RASopathy with data from the French childhood cancer registry allowed us to identify ALL in 6 (0.5%) patients including 4/778 (0.5%) with a germline PTPN11 mutation and 2/94 (2.1%) with a germline SOS1 mutation. None of the patients of our series with CFC syndrome (with germline BRAF or MAP2K1/MAP2K2 mutation - n = 121) or Costello syndrome (with HRAS mutation - n = 35) had an ALL. A total of 19 Noonan-ALL were gathered by adding our patients to those of the International Berlin-Munster-Frankfurt (I-BFM) study group and previously reported patients. Strikingly, all Noonan-associated ALL were B-cell precursor ALL, and high hyperdiploidy with more than 50 chromosomes was found in the leukemia cells of 13/17 (76%) patients with available genetics data. Our data suggest that children with Noonan syndrome are at higher risk to develop ALL. Like what is observed for somatic PTPN11 mutations, NS is preferentially associated with the development of hyperdiploid ALL that will usually respond well to chemotherapy. However, Noonan syndrome patients seem to have a propensity to develop post therapy myelodysplasia that can eventually be fatal. Hence, one should be particularly cautious when treating these patients.

SHP2 sails from physiology to pathology

Over the two past decades, mutations of the PTPN11 gene, encoding the ubiquitous protein tyrosine phosphatase SHP2 (SH2 domain-containing tyrosine phosphatase 2), have been identified as the causal factor of several developmental diseases (Noonan syndrome (NS), Noonan syndrome with multiple lentigines (NS-ML), and metachondromatosis), and malignancies (juvenile myelomonocytic leukemia). SHP2 plays essential physiological functions in organism development and homeostasis maintenance by regulating fundamental intracellular signaling pathways in response to a wide range of growth factors and hormones, notably the pleiotropic Ras/Mitogen-Activated Protein Kinase (MAPK) and the Phosphoinositide-3 Kinase (PI3K)/AKT cascades. Analysis of the biochemical impacts of PTPN11 mutations first identified both loss-of-function and gain-of-function mutations, as well as more subtle defects, highlighting the major pathophysiological consequences of SHP2 dysregulation. Then, functional genetic studies provided insights into the molecular dysregulations that link SHP2 mutants to the development of specific traits of the diseases, paving the way for the design of specific therapies for affected patients. In this review, we first provide an overview of SHP2's structure and regulation, then describe its molecular roles, notably its functions in modulating the Ras/MAPK and PI3K/AKT signaling pathways, and its physiological roles in organism development and homeostasis. In the second part, we describe the different PTPN11 mutation-associated pathologies and their clinical manifestations, with particular focus on the biochemical and signaling outcomes of NS and NS-ML-associated mutations, and on the recent advances regarding the pathophysiology of these diseases.

Cancer spectrum and frequency among children with Noonan, Costello, and cardio-facio-cutaneous syndromes

Background:

Somatic mutations affecting components of the Ras-MAPK pathway are a common feature of cancer, whereas germline Ras pathway mutations cause developmental disorders including Noonan, Costello, and cardio-facio-cutaneous syndromes. These ‘RASopathies' also represent cancer-prone syndromes, but the quantitative cancer risks remain unknown.

Methods:

We investigated the occurrence of childhood cancer including benign and malignant tumours of the central nervous system in a group of 735 individuals with germline mutations in Ras signalling pathway genes by matching their information with the German Childhood Cancer Registry.

Results:

We observed 12 cases of cancer in the entire RASopathy cohort vs 1.12 expected (based on German population-based incidence rates). This corresponds to a 10.5-fold increased risk of all childhood cancers combined (standardised incidence ratio (SIR)=10.5, 95% confidence interval=5.4–18.3). The specific cancers included juvenile myelomonocytic leukaemia=4; brain tumour=3; acute lymphoblastic leukaemia=2; rhabdomyosarcoma=2; and neuroblastoma=1. The childhood cancer SIR in Noonan syndrome patients was 8.1, whereas that for Costello syndrome patients was 42.4.

Conclusions:

These data comprise the first quantitative evidence documenting that the germline mutations in Ras signalling pathway genes are associated with increased risks of both childhood leukaemia and solid tumours.

LEOPARD Syndrome: Clinical Features and Gene Mutations

The RAS/MAPK pathway proteins with germline mutations in their respective genes are associated with some disorders such as Noonan, LEOPARD (LS), neurofibromatosis type 1, Costello and cardio-facio-cutaneous syndromes. LEOPARD is an acronym, mnemonic for the major manifestations of this disorder, characterized by multiple lentigines, electrocardiographic abnormalities, ocular hypertelorism, pulmonic stenosis, abnormal genitalia, retardation of growth, and sensorineural deafness. Though it is not included in the acronym, hypertrophic cardiomyopathy is the most frequent cardiac anomaly observed, representing a potentially life-threatening problem in these patients. PTPN11, RAF1 and BRAF are the genes known to be associated with LS, identifying molecular genetic testing of the 3 gene mutations in about 95% of affected individuals. PTPN11 mutations are the most frequently found. Eleven different missense PTPN11 mutations (Tyr279Cys/Ser, Ala461Thr, Gly464Ala, Thr468Met/Pro, Arg498Trp/Leu, Gln506Pro, and Gln510Glu/Pro) have been reported so far in LS, 2 of which (Tyr279Cys and Thr468Met) occur in about 65% of the cases. Here, we provide an overview of clinical aspects of this disorder, the molecular mechanisms underlying pathogenesis and major genotype-phenotype correlations.

LEOPARD Syndrome with PTPN11 Gene Mutation Showing Six Cardinal Symptoms of LEOPARD

LEOPARD multiple congenital anomaly syndrome inherited in an autosomal dominant manner. LEOPARD is an acronym for Lentigines, Eletrocardiographic conduction defects, Ocular hypertelorism, Pulmonary valve stenosis, Abnormalities of the genitalia, Retardation of growth, and Deafness. Clinical diagnosis is primarily based on multiple lentigines, typical facial features, and the presence of hypertrophic cardiomyopathy and/or café-au-lait macules. We report a typical case of LEOPARD syndrome with PTPN11 gene mutation associated with lentigines, electrocardiograph abnormality, ocular hypertelorism, pulmonary valve stenosis, growth retardation, and sensorineural hearing loss.

Raf family kinases: old dogs have learned new tricks

First identified in the early 1980s as retroviral oncogenes, the Raf proteins have been the objects of intense research. The discoveries 10 years later that the Raf family members (Raf-1, B-Raf, and A-Raf) are bona fide Ras effectors and upstream activators of the ubiquitous ERK pathway increased the interest in these proteins primarily because of the central role that this cascade plays in cancer development. The important role of Raf in cancer was corroborated in 2002 with the discovery of B-Raf genetic mutations in a large number of tumors. This led to intensified drug development efforts to target Raf signaling in cancer. This work yielded not only recent clinical successes but also surprising insights into the regulation of Raf proteins by homodimerization and heterodimerization. Surprising insights also came from the hunt for new Raf targets. Although MEK remains the only widely accepted Raf substrate, new kinase-independent roles for Raf proteins have emerged. These include the regulation of apoptosis by suppressing the activity of the proapoptotic kinases, ASK1 and MST2, and the regulation of cell motility and differentiation by controlling the activity of Rok-α. In this review, we discuss the regulation of Raf proteins and their role in cancer, with special focus on the interacting proteins that modulate Raf signaling. We also describe the new pathways controlled by Raf proteins and summarize the successes and failures in the development of efficient anticancer therapies targeting Raf. Finally, we also argue for the necessity of more systemic approaches to obtain a better understanding of how the Ras-Raf signaling network generates biological specificity.

Patient-specific induced pluripotent stem-cell-derived models of LEOPARD syndrome

Generation of reprogrammed induced pluripotent stem cells (iPSC) from patients with defined genetic disorders promises important avenues to understand the etiologies of complex diseases, and the development of novel therapeutic interventions. We have generated iPSC from patients with LEOPARD syndrome (LS; acronym of its main features: Lentigines, Electrocardiographic abnormalities, Ocular hypertelorism, Pulmonary valve stenosis, Abnormal genitalia, Retardation of growth and Deafness), an autosomal dominant developmental disorder belonging to a relatively prevalent class of inherited RAS-MAPK signaling diseases, which also includes Noonan syndrome (NS), with pleiomorphic effects on several tissues and organ systems1,2. The patient-derived cells have a mutation in the PTPN11 gene, which encodes the SHP2 phosphatase. The iPSC have been extensively characterized and produce multiple differentiated cell lineages. A major disease phenotype in patients with LEOPARD syndrome is hypertrophic cardiomyopathy. We show that in vitro-derived cardiomyocytes from LS-iPSC are larger, have a higher degree of sarcomeric organization and preferential localization of NFATc4 in the nucleus when compared to cardiomyocytes derived from human embryonic stem cells (HESC) or wild type (wt) iPSC derived from a healthy brother of one of the LS patients. These features correlate with a potential hypertrophic state. We also provide molecular insights into signaling pathways that may promote the disease phenotype.