Occurrence of acute lymphoblastic leukemia and juvenile myelomonocytic leukemia in a patient with Noonan syndrome carrying the germline PTPN11 mutation p.E139D

Noonan syndrome (NS) is a common autosomal dominant condition characterized by short stature, congenital heart defects, and dysmorphic facial features caused in approximately 50% of cases by missense mutations in the PTPN11 gene. NS patients are predisposed to malignancies including myeloproliferative disorders or leukemias. We report a female NS patient carrying a PTPN11 germline mutation c.417 G?>?C (p.E139D), who developed in her second year of life an acute lymphoblastic leukemia (ALL) and after remission, she developed at 4 years of age a juvenile myelomonocytic leukemia (JMML). Molecular genetic analysis of lymphoblastic blasts at the time of the ALL diagnosis revealed the germline mutation in a heterozygous state, while in the myelomonocytic blasts occurring with JMML diagnosis, the mutation p.E139D was found in a homozygous state due to a uniparental disomy (UPD). These findings lead to the suggestion that the pathogenesis of ALL and JMML in our patient is due to different mechanisms including somatically acquired secondary chromosomal abnormalities.     

Genotypic and phenotypic characterization of Noonan syndrome: new data and review of the literature

Noonan syndrome (NS) is an autosomal dominant disorder, characterized by short stature, minor facial anomalies, and congenital heart defects. In approximately 50% of cases the condition is caused by missense mutations in the PTPN11 gene on chromosome 12, resulting in a gain of function of the protein SHP-2. In this study, PTPN11 mutation analysis was performed in 170 NS patients. In 76 (45%) of them a mutation was identified. We report on the distribution of these mutations, as well as on genotype-phenotype relationships. The benefit of the NS scoring system developed by van der Burgt et al. [(1994); Am J Med Genet 53:187-191] is shown, among physicians who consequently based their diagnosis on the NS scoring system the percentage mutation positive subjects was 54%, whereas this percentage was only 39% among physicians who made less use of the scoring system. In two patients with some uncommon manifestations mutations were found in the C-SH2 domain, a region in which defects are not often identified in NS. A trend was observed in patients carrying the 922A --> G change (Asn308Asp) receiving normal education. In one patient with NS and mild juvenile myelomonocytic leukemia (JMML) the mutation 218C --> T (Thr73Ile) was found. This confirms previous findings indicating that individuals with NS with specific mutations in PTPN11 are at risk of developing JMML.     

Germline PTPN11 missense mutation in a case of Noonan syndrome associated with mediastinal and retroperitoneal neuroblastic tumors

Noonan syndrome (NS) is an autosomal dominant disorder characterized by short stature, typical craniofacial dysmorphism, skeletal anomalies, congenital heart defects, and predisposition to malignant tumors. In approximately 50% of cases, the disease is caused by missense mutations in the PTPN11 gene. To date, solid tumors, and particularly brain tumors and rhabdomyosarcomas, have been documented in patients with NS; however, few cases of neuroblastoma associated with NS have been reported. Here we report an unusual case of neuroblastoma with mediastinal, retroperitoneal, and medullar locations associated in a NS patient carrying a PTPN11 germline missense mutation (p.G60A). This missense mutation occurs within the N-SH2 domain of the PTPN11 gene and has been reported to be associated with acute leukemia in NS patients. The association of this p.G60A PTPN11 mutation with neuroblastoma provides new evidence that gain of function PTPN11 mutations may play an important role in the pathogenesis of solid tumors associated with Noonan syndrome.     

Noonan syndrome,the SOS1 gene and embryonal rhabdomyosarcoma

Noonan Syndrome (NS) is an autosomal dominant condition characterized by short stature, facial dysmorphisms, and congenital heart defects, and is caused by mutations in either PTPN11, KRAS, NRAS, SHOC2, RAF1, or SOS1. Furthermore, NS is known for its predisposition to develop cancer, particularly hematological malignancies and specific solid tumors, mainly neuroblastoma and embryonal rhabdomyosacroma (ERMS). Until recently, however, cancer predisposition in NS patients with SOS1 mutations was not reported. Here we present a NS patient with a de novo germline SOS1 mutation (p.Lys728Ile) and ERMS. This heterozygous germline mutation was homozygously present in the ERMS of this patient due to an acquired uniparental disomy (UPD) of chromosome 2. In addition, several other chromosomal aberrations were encountered, some of which are known to recurrently occur in ERMS. Sequence analysis of the SOS1 gene in 20 sporadic ERMS tumors failed to reveal any pathogenic mutations, implicating that SOS1 is not a major player in the development of this tumor outside the context of NS. © 2010 Wiley‐Liss, Inc.     

SOS1 mutations are rare in human malignancies: implications for Noonan Syndrome patients

Germ line gain-of-function mutations in several members of the RAS/ERK pathway, including PTPN11, KRAS, and RAF1, cause the autosomal dominant genetic disorder Noonan Syndrome (NS). NS patients are at increased risk of leukemia/myeloproliferative disease and possibly some solid tumors, such as neuroblastoma. Recently, SOS1 gain of function mutations have also been shown to cause NS. Somatic PTPN11, KRAS, and RAF1 mutations occur (although at different frequencies) in a variety of sporadic neoplasms, but whether SOS1 mutations are associated with human cancer has not been evaluated. We sequenced DNA from a total of 810 primary malignancies, including pancreatic, lung, breast, and colon carcinomas, and acute myelogenous leukemia, as well as several neuroblastoma cell lines. From this large, diverse series, missense SOS1 mutations were identified in a single pancreatic tumor, one lung adenocarcinoma, and a T-cell acute lymphoblastic leukemia cell line. Our findings suggest that SOS1 is not a significant human oncogene in most cancers. Furthermore, NS patients with SOS1 mutations may not be at increased risk of developing cancer.     

Functional analysis of PTPN11/SHP-2 mutants identified in Noonan syndrome and childhood leukemia

Noonan syndrome (NS) is characterized by short stature, characteristic facial features, and heart defects. Recently, missense mutations of PTPN11, the gene encoding protein tyrosine phosphatase (PTP) SHP-2, were identified in patients with NS. Further, somatic mutations in PTPN11 were detected in childhood leukemia. Recent studies showed that the phosphatase activities of five mutations identified in NS and juvenile myelomonocytic leukemia (JMML) were increased. However, the functional properties of the other mutations remain unidentified. In this study, in order to clarify the differences between the mutations identified in NS and leukemia, we examined the phosphatase activity of 14 mutants of SHP-2. We identified nine mutations, including a novel F71I mutation, in 16 of 41 NS patients and two mutations, including a novel G503V mutation, in three of 29 patients with leukemia. Immune complex phosphatase assays of individual mutants transfected in COS7 cells showed that ten mutants identified in NS and four mutants in leukemia showed 1.4-fold to 12.7-fold increased activation compared with wild-type SHP-2. These results suggest that the pathogenesis of NS and leukemia is associated with enhanced phosphatase activity of mutant SHP-2. A comparison of the phosphatase activity in each mutant and a review of previously reported cases showed that high phosphatase activity observed in mutations at codons 61, 71, 72, and 76 was significantly associated with leukemogenesis.     

Activating PTPN11 mutations play a minor role in pediatric and adult solid tumors

The PTPN11 gene encodes SHP-2, a widely expressed cytoplasmic protein tyrosine phosphatase functioning as a signaling transducer. Germ-line PTPN11 mutations cause Noonan syndrome (NS), a developmental disorder characterized by an increased risk of malignancies. Recently, a novel class of activating mutations in PTPN11 has been documented as a somatic event in a heterogeneous group of leukemias. Because of the relatively higher prevalence of certain solid tumors in children with NS and the positive modulatory function of SHP-2 in RAS signaling, a wider role for activating PTPN11 mutations in cancer has been hypothesized. Here, we screened a number of solid tumors, including those documented in NS or in which deregulated RAS signaling occurs at significant frequency, for PTPN11 mutations. No disease-associated mutation was identified in rhabdomyosarcoma (n = 13), neuroblastoma (n = 32), melanoma (n = 50), thyroid (n = 85), and colon (n = 48) tumors; a novel missense change, promoting an increased basal phosphatase activity of SHP-2, was observed in one glioma specimen. Our data document that deregulated SHP-2 function does not represent a major molecular event in pediatric and adult tumors, further supporting our previous evidence indicating that the oncogenic role of PTPN11 mutations is cell-context specific.     

Cancer risk in patients with Noonan syndrome carrying a PTPN11 mutation

Noonan syndrome (NS) is characterized by short stature, facial dysmorphisms and congenital heart defects. PTPN11 mutations are the most common cause of NS. Patients with NS have a predisposition for leukemia and certain solid tumors. Data on the incidence of malignancies in NS are lacking. Our objective was to estimate the cancer risk and spectrum in patients with NS carrying a PTPN11 mutation. In addition, we have investigated whether specific PTPN11 mutations result in an increased malignancy risk. We have performed a cohort study among 297 Dutch NS patients with a PTPN11 mutation (mean age 18 years). The cancer histories were collected from the referral forms for DNA diagnostics, and by consulting the Dutch national registry of pathology and the Netherlands Cancer Registry. The reported frequencies of cancer among NS patients were compared with the expected frequencies using population-based incidence rates. In total, 12 patients with NS developed a malignancy, providing a cumulative risk for developing cancer of 23% (95% confidence interval (CI), 8-38%) up to age 55 years, which represents a 3.5-fold (95% CI, 2.0-5.9) increased risk compared with that in the general population. Hematological malignancies occurred most frequently. Two malignancies, not previously observed in NS, were found: a malignant mastocytosis and malignant epithelioid angiosarcoma. No correlation was found between specific PTPN11 mutations and cancer occurrence. In conclusion, this study provides first evidence of an increased risk of cancer in patients with NS and a PTPN11 mutation, compared with that in the general population. Our data do not warrant specific cancer surveillance.     

RAS signaling dysregulation in human embryonal Rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is a common childhood solid tumor, resulting from dysregulation of the skeletal myogenesis program. Two major histological subtypes occur in childhood RMS, embryonal and alveolar. While chromosomal rearrangements account for the majority of alveolar tumors, the genetic defects underlying the pathogenesis of embryonal RMS remain largely undetermined. A few studies performed on small series of embryonal tumors suggest that dysregulation of RAS function may be relevant to disease pathogenesis. To explore further the biological and clinical relevance of mutations with perturbing consequences on RAS signaling in embryonal RMS, we investigated the prevalence of PTPN11, HRAS, KRAS, NRAS, BRAF, MEK1, and MEK2 mutations in a relatively large cohort of primary tumors. While HRAS and KRAS were found to be rarely mutated, we identified somatic NRAS lesions in 20% of cases. All mutations were missense and affected codon 61, with the introduction of a positive charged amino acid residue representing the most common event. PTPN11 was found mutated in one tumor specimen, confirming that somatic defects in this gene are relatively uncommon in RMS, while no mutation was observed in BRAF and MEK genes. Although no clear association of mutations with any clinical variable was observed, comparison of the outcome between mutation‐positive and mutation‐negative cases indicated a trend for a higher percentage of patients exhibiting a better outcome in the former. Our findings provide evidence that dysregulation of RAS signaling is a major event contributing to embryonal RMS pathogenesis. © 2009 Wiley‐Liss, Inc.     

Low frequency of NRAS and KRAS2 gene mutations in childhood myelodysplastic syndromes

In children, myelodysplastic syndromes (MDS) represent less then 10% of all hematological malignancies; consequently, molecular genetic studies dealing with this group of patients are scarce. We have analyzed 35 archival bone marrow samples of children with MDS for the presence of mutations in the first and second exons of the NRAS and KRAS2 genes. Mutations were detected with single-strand conformation polymorphism analysis in three patients. One patient harbored a mutation in the second exon of NRAS and two patients in the second exon of KRAS2. Sequencing was performed in two samples and novel mutations were found in both. One patient had a missense mutation in codon 45 of NRAS; the other had a silent mutation in codon 53 and a missense mutation in codon 55 of KRAS2.     

Mutations of FLT3, NRAS, KRAS, and PTPN11 are frequent and possibly mutually exclusive in high hyperdiploid childhood acute lymphoblastic leukemia

Although it has been suggested that mutations of the FLT3, NRAS, KRAS, and PTPN11 genes are particularly frequent in high hyperdiploid (>50 chromosomes) pediatric acute lymphoblastic leukemias (ALLs), this has as yet not been confirmed in a large patient cohort. Furthermore, it is unknown whether mutations of these genes coexist in hyperdiploid cases. We performed mutation analyses of FLT3, NRAS, KRAS, and PTPN11 in a consecutive series of 78 high hyperdiploid ALLs. Twenty-six (33%) of the cases harbored a mutation, comprising six activating point mutations and one internal tandem duplication of FLT3 (7/78 cases; 9.0%), eight codon 12, 13, or 61 NRAS mutations (8/78 cases; 10%), five codon 12 or 13 KRAS mutations (5/78 cases, 6.4%), and seven exon 3 or 13 PTPN11 mutations (7/78 cases; 9.0%). No association was seen between the presence of a mutation in FLT3, NRAS, KRAS, or PTPN11 and gender, age, white blood cell count, or relapse, suggesting that they do not confer a negative prognostic impact. Only one case harbored mutations in two different genes, suggesting that mutations of these four genes are generally mutually exclusive. In total, one third of the cases harbored a FLT3, NRAS, KRAS, or PTPN11 mutation, identifying the RTK-RAS signaling pathway as a potential target for novel therapies of high hyperdiploid pediatric ALLs.     

A novel PTPN11 gene mutation bridges Noonan syndrome, multiple lentigines/LEOPARD syndrome and Noonan-like/multiple giant cell lesion syndrome

Noonan (NS) and multiple lentigines/LEOPARD syndromes (LS) have proved to be associated with distinct PTPN11 mutations. Noonan-like/multiple giant cell lesion syndrome (NLS) is a rare disease, characterised by short stature, facial dysmorphisms, congenital heart defect (CHD) and central giant cell lesions. PTPN11 gene mutations have been reported in a single NLS family and two sporadic patients. Here we report a patient with a complex phenotype progressing throughout the years from NS at birth towards LS and NLS. PTPN11 gene analysis disclosed a novel missense mutation (Ala461Thr) in exon 12, affecting the consensus sequence of the SHP2-active site. This observation joins together NS and LS to NLS into a unique genetic defect, broadening the clinical and molecular spectrum of PTPN11-related disorders.     

Co-occurring SHOC2 and PTPN11 mutations in a patient with severe/complex Noonan syndrome-like phenotype

Noonan syndrome (NS) is a heterogeneous disorder caused by activating mutations in the RAS-MAPK signaling pathway. It is associated with variable clinical expression including short stature, congenital heart defect, unusual pectus deformity, and typical facial features and the inheritance is autosomal dominant. Here, we present a clinical and molecular characterization of a patient with Noonan-like syndrome with loose anagen hair phenotype and additional features including mild psychomotor developmental delay, osteoporosis, gingival hyperplasia, spinal neuroblastoma, intrathoracic extramedullary hematopoiesis, and liver hemangioma. Mutation analysis of PTPN11, SOS1, RAF1, KRAS, BRAF, MEK1, MEK2, NRAS, and SHOC2 was conducted, revealing a co-occurrence of two heterozygous previously identified mutations in the index patient. The mutation SHOC2 c.4A > G; p.Ser2Gly represents a de novo mutation, whereas, PTPN11 c.1226G > C; p.Gly409Ala was inherited from the mother and also identified in the brother. The mother and the brother present with some NS manifestations, such as short stature, delayed puberty, keratosis pilaris, café-au-lait spots, refraction error (mother), and undescended testis (brother), but no NS facial features, supporting the notion that the PTPN11 p.Gly409Ala mutation leads to a relatively mild phenotype. We propose that, the atypical phenotype of the young woman with NS reported here is an additive effect, where the PTPN11 mutation acts as a modifier. Interestingly, co-occurrence of RAS-MAPK mutations has been previously identified in a few patients with variable NS or neurofibromatosis-NS phenotypes. Taken together, the results suggest that co-occurrence of mutations or modifying loci in the RAS-MAPK pathway may contribute to the clinical variability observed among NS patients.     

PTPN11 mutation in a large family with Noonan syndrome and dizygous twinning

Noonan syndrome (NS, MIM 163950) is an autosomal dominant condition characterised by facial dysmorphy, congenital cardiac defects and short stature. Recently missense mutations in PTPN11, the gene encoding the nonreceptor protein tyrosine phosphatase SHP-2 on 12q24, were identified in 50% of analysed Noonan cases. A large four-generation Belgian family with NS and some features suggestive of cardio-facio-cutaneous syndrome (CFC) was previously used to fine map the Noonan syndrome candidate region to a 5 cM region in 12q24. We now report the identification of a mutation (Gln79Arg) in the PTPN11 gene in this large family. In D. melanogaster and C. elegans the PTPN11 gene has been implicated in oogenesis. In this family two affected females had dizygous twins. This suggests that PTPN11 might also be involved in oogenesis and twinning in humans.     

Tumor spectrum in children with Noonan syndrome and SOS1 or RAF1 mutations

Noonan syndrome (NS) is an autosomal dominant disorder caused by mutations in PTPN11, KRAS, SOS1, and RAF1. We performed SOS1, RAF1, BRAF, MEK1, and MEK2 mutation analysis in a cohort of 102 PTPN11‐ and KRAS‐negative NS patients and found pathogenic SOS1 mutations in 10, RAF1 mutations in 4, and BRAF mutations in 2 patients. Three novel SOS1 mutations were found. One was classified as a rare benign variant and the other remains unclassified. We confirm a high prevalence of pulmonic stenosis and ectodermal abnormalities in SOS1‐positive patients. Three patients with SOS1 mutations presented with tumors (embryonal rhabdomyosarcoma, Sertoli cell testis tumor, and granular cell tumors of the skin). One patient with a RAF1 mutation had a lesion suggestive for a giant cell tumor. This is the first report describing different tumor types in NS patients with germ line SOS1 mutations. © 2009 Wiley‐Liss, Inc.     

PTPN11 gene mutation associated with abnormal gonadal determination

Germline mutations in the PTPN11 gene have been associated with Noonan syndrome (NS) and LEOPARD syndrome. Both germline and somatic mutations in this gene have been reported in association with malignancies. However, the T507K mutation in the PTPN11 gene, has only been reported in malignancies and in a fetus with hydrops fetalis but not in a live patient with NS. We report the autopsy findings in a fetus with the T507K mutation who presented prenatally with hydrops fetalis, cystic hygroma and 46, XX karyotype. On autopsy, the patient was found to have testes, male external genitalia, but absent Wolffian ducts.     

PTPN11 analysis for the prenatal diagnosis of Noonan syndrome in fetuses with abnormal ultrasound findings

Noonan syndrome (NS) is an autosomal dominant disorder characterized by short stature, congenital heart defects and distinctive facies. The disorder is genetically heterogeneous with approximately 50% of patients having PTPN11 mutations. Prenatally, the diagnosis of NS has been suspected following certain ultrasound findings, such as cystic hygroma, increased nuchal translucency (NT) and hydrops fetalis. Studies of fetuses with cystic hygroma have suggested an NS prevalence of 1–3%. A retrospective review was performed to assess the utility of PTPN11 testing based on prenatal sonographic findings ( n = 134). The most commonly reported indications for testing were increased NT and cystic hygroma. Analysis showed heterozygous missense mutations in 12 fetuses, corresponding to a positive test rate of 9%. PTPN11 mutations were identified in 16% and 2% of fetuses with cystic hygroma and increased NT, respectively. Among fetuses with isolated cystic hygroma, PTPN11 mutation prevalence was 11%. The mutations observed in the three fetuses with hydrops fetalis had previously been reported as somatic cancer mutations. Prenatal PTPN11 testing has diagnostic and possible prognostic properties that can aid in risk assessment and genetic counseling. As NS is genetically heterogeneous, negative PTPN11 testing cannot exclude the diagnosis and further study is warranted regarding the other NS genes.     

PHOX2B analysis in non-syndromic neuroblastoma cases shows novel mutations and genotype-phenotype associations

Neuroblastoma (NB) is an embryonal tumor originating from neural crest cells and is one of the most common solid tumors of childhood. Recently, constitutional mutations in PHOX2B have been shown to confer an increased risk of NB. To date, mutations predisposing to neural crest tumors have been reported in 20 individuals from 16 families. These families included additional clinical features such as Hirschsprung (HSCR) disease or congenital central hypoventilation syndrome, either in the index case or relatives. The contribution of PHOX2B mutations to NB cases without additional features is unclear. To address this we sequenced PHOX2B in constitutional DNA from 86 individuals with non-syndromic NB (4 cases had a family history of NB). We identified two mutations, 600delC, a frameshift mutation in an individual with isolated, unifocal NB and G197D, a missense mutation that was present in a family with multiple individuals with NB but no evidence of autonomic dysfunction. These data demonstrate that PHOX2B mutations are a rare cause of non-syndromic NB. The mutations we identified are outside the domains typically mutated in PHOX2B syndromes. This provides further evidence that the underlying PHOX2B mutational mechanism influences tumor risk and suggests that the position of missense mutations may influence the resulting phenotype.