Genetic heterogeneity in LEOPARD syndrome: two families with no mutations in PTPN11

LEOPARD syndrome (lentigines, electrocardiographic conduction abnormalities, ocular hypertelorism, pulmonary stenosis, abnormal genitalia, retardation of growth, and sensorineural deafness) is an autosomal dominant condition. The main clinical features include multiple lentigines, cardiovascular defects, and facial anomalies, some of which are shared with Noonan syndrome (NS). Recent reports have shown that LEOPARD syndrome can be caused by mutations in PTPN11, the gene in which mutations can produce NS. Here we report the findings of mutation screening and linkage analysis of PTPN11 in three families with LEOPARD syndrome. We identified a novel mutation in one family. The mutation (1529A>C) substitutes proline for glutamine at amino acid 510 (Gln510Pro). No variations in sequence were observed in the other two families, and negative LOD scores excluded linkage to the PTPN11 locus, showing that LEOPARD syndrome is genetically heterogeneous.     

Mild variable Noonan syndrome in a family with a novel PTPN11 mutation

Noonan syndrome (OMIM 163950) is a common genetic condition with variable clinical expression and genetic heterogeneity. About half of the cases can be accounted to activating mutations in the PTPN11 gene encoding SHP-2. We report on a family with mild, variable expression of Noonan syndrome in five individuals. Clinical manifestations included short stature, craniofacial anomalies and thorax deformity, but none of the affected family members had a heart defect. Sequencing of the entire coding region of PTPN11 revealed a novel mutation c.1226G-->C in exon 11 predicting the amino acid exchange G409A. This mutation is not located in the previously known mutation clusters. Our observation and the recent report of a mutation affecting a neighbouring residue (T411M) in a family with a variable phenotype suggest that mutations in this particular region of SHP-2 may have effects on the protein that differ from those of the classical mutations.     

Novel BRAF mutation in a patient with LEOPARD syndrome and normal intelligence

Noonan syndrome (NS) and related disorders are caused by mutations in various genes encoding molecules involved in the RAS–MAPK signalling cascade. There are strong genotype–phenotype correlations. BRAF is the major gene for cardio-facio-cutaneous syndrome (CFCS), and usually patients with a BRAF mutation have significant cognitive impairment. We report on a patient with LEOPARD syndrome and normal intelligence who was found to carry a novel sequence change in BRAF. The mutation p.L245F was demonstrated to be de novo with no evidence of somatic mosaicism. This observation illustrates that the phenotypic spectrum caused by BRAF mutations is broader than previously assumed and that mental retardation is not necessarily associated. We speculate that the impact of p.L245F on BRAF protein function differs either qualitatively or quantitatively from those mutations associated with CFCS.     

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.     

Neurofibromatosis type I gene mutation in a patient with features of LEOPARD syndrome

Multiple lentigines (LEOPARD) syndrome has been delineated as an autosomal dominant disorder with lentigines, cardiac abnormalities, variable mental retardation, and typical craniofacial features as the most characteristic findings. LEOPARD syndrome shows a great clinical overlap with neurofibromatosis type 1 (NF1). In this report we describe a de novo missense mutation (M 1035R) in exon 18 of the NF1 gene in a young woman with a prior diagnosis of LEOPARD syndrome. We hypothesize that some patients now diagnosed with LEOPARD syndrome have in fact a mutation in the NF1 gene, whereas in other patients with LEOPARD syndrome, a different gene might be involved. © 1996 Wiley-Liss, Inc.     

Mid-septal hypertrophy and apical ballooning; potential mechanism of ventricular tachycardia storm in patients with hypertrophic cardiomyopathy

Medically refractory ventricular tachycardia (VT) storm can be controlled with radiofrequency catheter ablation (RFCA), however, it may be difficult to control in some patients with hemodynamic overload. We experienced a patient with intractable VT storm controlled by hemodynamic unloading. The patient had mid-septal hypertrophic cardiomyopathy with an implantable cardioverter defibrillator (ICD) back-up. Because of the severe mid-septal hypertrophy, his left ventricle (LV) had an hourglass-like morphology and showed apical ballooning; the focus of VT was at the border of apical ballooning. Although we performed VT ablation because of electrical storm with multiple ICD shocks, VT recurred 1 hour after procedure. As the post-RFCA monomorphic VT was refractory to anti-tachycardia pacing or ICD shock, we reduced the hemodynamic overload of LV with β-blockade, hydration, and sedation. VT spontaneously stopped 1.5 hours later and the patient has remained free of VT for 24 months with β-blockade alone. In patients with VT storm refractory to antiarrhythmic drugs or RFCA, the mechanism of mechano-electrical feedback should be considered and hemodynamic unloading may be an essential component of treatment.     

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.     

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.     

Exclusion of PTPN11 mutations in Costello syndrome: further evidence for distinct genetic etiologies for Noonan,cardio-facio-cutaneous and Costello syndromes

Costello syndrome (CS) is a rare, multiple congenital anomaly syndrome with characteristic dysmorphic features, cardiac anomalies and a tendency to develop certain cancers. Phenotypically there is some overlap with other genetic disorders, notably cardio-facio-cutaneous (CFC) syndrome and Noonan syndrome (NS), suggesting that these syndromes may be allelic. We recently identified PTPN11, which encodes the non-receptor protein tyrosine phosphatase, SHP-2, as a major NS disease gene. In this report, we screened a cohort of 27 patients, with the clinical diagnosis of CS, for PTPN11 mutations using denaturing high performance liquid chromatography analysis. No mutations of the PTPN11 gene were found in the CS patients. Common polymorphisms in introns 6 and 7 and exon 8 were identified in four individuals. With our previous exclusion of PTPN11 mutations in CFC syndrome, these data suggest distinct genetic etiologies for Noonan, CFC and Costello syndromes.     

Molecular and clinical analysis of RAF1 in Noonan syndrome and related disorders: dephosphorylation of serine 259 as the essential mechanism for mutant activation

Noonan syndrome (NS) and related disorders are autosomal dominant disorders characterized by heart defects, facial dysmorphism, ectodermal abnormalities, and mental retardation. The dysregulation of the RAS/MAPK pathway appears to be a common molecular pathogenesis of these disorders: mutations in PTPN11, KRAS, and SOS1 have been identified in patients with NS, those in KRAS, BRAF, MAP2K1, and MAP2K2 in patients with CFC syndrome, and those in HRAS mutations in Costello syndrome patients. Recently, mutations in RAF1 have been also identified in patients with NS and two patients with LEOPARD (multiple lentigines, electrocardiographic conduction abnormalities, ocular hypertelorism, pulmonary stenosis, abnormal genitalia, retardation of growth, and sensorineural deafness) syndrome. In the current study, we identified eight RAF1 mutations in 18 of 119 patients with NS and related conditions without mutations in known genes. We summarized clinical manifestations in patients with RAF1 mutations as well as those in NS patients withPTPN11, SOS1, or KRAS mutations previously reported. Hypertrophic cardiomyopathy and short stature were found to be more frequently observed in patients with RAF1 mutations. Mutations in RAF1 were clustered in the conserved region 2 (CR2) domain, which carries an inhibitory phosphorylation site (serine at position 259; S259). Functional studies revealed that the RAF1 mutants located in the CR2 domain resulted in the decreased phosphorylation of S259, and that mutant RAF1 then dissociated from 14‐3‐3, leading to a partial ERK activation. Our results suggest that the dephosphorylation of S259 is the primary pathogenic mechanism in the activation of RAF1 mutants located in the CR2 domain as well as of downstream ERK. Hum Mutat 30:1–11, 2010. © 2010 Wiley‐Liss, Inc.     

Clinical and functional characterization of a novel RASopathy‐causing SHOC2 mutation associated with prenatal‐onset hypertrophic cardiomyopathy

SHOC2 is a scaffold protein mediating RAS‐promoted activation of mitogen‐activated protein kinase (MAPK) signaling in response to extracellular stimuli. A recurrent activating mutation in SHOC2 (p.Ser2Gly) causes Mazzanti syndrome, a RASopathy characterized by features resembling Noonan syndrome and distinctive ectodermal abnormalities. A second mutation (p.Met173Ile) supposed to cause loss‐of‐function was more recently identified in two individuals with milder phenotypes. Here, we report on the third RASopathy‐causing SHOC2 mutation (c.807_808delinsTT, p.Gln269_His270delinsHisTyr), which was found associated with prenatal‐onset hypertrophic cardiomyopathy. Structural analyses indicated a possible impact of the mutation on the relative orientation of the two SHOC2's leucine‐rich repeat domains. Functional studies provided evidence of its activating role, revealing enhanced binding of the mutant protein to MRAS and PPP1CB, and increased signaling through the MAPK cascade. Differing from SHOC2 ^S2G, SHOC2 ^{Q269_H270delinsHY} is not constitutively targeted to the plasma membrane. These data document that diverse mechanisms in SHOC2 functional dysregulation converge toward MAPK signaling upregulation.     

Leigh syndrome and hypertrophic cardiomyopathy in an infant with a mitochondrial DNA point mutation (T8993G)

Mutation of mitochondria) (mt) DNA at nucleotide (nt) 8993 has been reported to cause neurogenic weakness, ataxia, retinitis pigmentosa (NARP), or Leigh syndrome (LS). We report a family in whom the mutation was expressed clinically as LS and hypertrophic cardiomyopathy (CMP) in a boy who presented with a history of developmental delay and hypotonia, and who had recurrent lactic acidosis. The mother's first pregnancy resulted in the birth of a stillborn female; an apparently healthy older brother had died suddenly (SIDS) at age 2 months. MtDNA analysis identified the presence of the T8993G point mutation, which was found to be heteroplasmic in the patient's skeletal muscle (90%) and fibroblasts (90%). The identical mutation was present in leukocytes (38%) isolated from the mother, but not from the father or maternal grandmother. Our findings expand the clinical phenotype of the nt 8993 mtDNA mutation to include hypertrophic cardiomyopathy and confirm its cause of LS. © 1994 Wiley-Liss, Inc.     

SOS1 and PTPN11 mutations in five cases of Noonan syndrome with multiple giant cell lesions

We report five cases of multiple giant cell lesions in patients with typical Noonan syndrome. Such association has frequently been referred to as Noonan-like/multiple giant cell (NL/MGCL) syndrome before the molecular definition of Noonan syndrome. Two patients show mutations in PTPN11 (p.Tyr62Asp and p.Asn308Asp) and three in SOS1 (p.Arg552Ser and p.Arg552Thr). The latter are the first SOS1 mutations reported outside PTPN11 in NL/MGCL syndrome. MGCL lesions were observed in jaws (‘cherubism'') and joints (‘pigmented villonodular synovitis''). We show through those patients that both types of MGCL are not PTPN11-specific, but rather represent a low penetrant (or perhaps overlooked) complication of the dysregulated RAS/MAPK signaling pathway. We recommend discarding NL/MGCL syndrome from the nosology, as this presentation is neither gene-nor allele-specific of Noonan syndrome; these patients should be described as Noonan syndrome with MGCL (of the mandible, the long bone…). The term cherubism should be used only when multiple giant cell lesions occur without any other clinical and molecular evidence of Noonan syndrome, with or without mutations of the SH3BP2 gene.     

A rasopathy phenotype with severe congenital hypertrophic obstructive cardiomyopathy associated with a PTPN11 mutation and a novel variant in SOS1

The RAS-MAPK pathway is critical for human growth and development. Abnormalities at different steps of this signaling cascade result in neuro-cardio-facial-cutaneous syndromes, or the RASopathies, a group of disorders with overlapping yet distinct phenotypes. RASopathy patients have variable degrees of intellectual disability, poor growth, relative macrocephaly, ectodermal abnormalities, dysmorphic features, and increased risk for certain malignancies. Congenital heart disease, particularly hypertrophic cardiomyopathy (HCM) and pulmonic stenosis, are prominent features in these disorders. Significant locus heterogeneity exists for many of the RASopathies. Traditionally, these diseases were thought to be inherited in an autosomal dominant manner. However, recently patients with defects in two components of this pathway and overlapping features of various forms of Noonan syndrome and neurofibromatosis 1 and have been reported. Here we present a patient with severe, progressive neonatal HCM, elevated urinary catecholamine metabolites, and dysmorphic features in whom we identified a known LEOPARD syndrome-associated PTPN11 mutation (c.1403 C > T; p.T468M) and a novel, potentially pathogenic missense SOS1 variant (c.1018 C > T; p.P340S) replacing a rigid nonpolar imino acid with a polar amino acid at a highly conserved position. We describe detailed clinical manifestations, cardiac histopathology, and the molecular genetic findings. Oligogenic models of inheritance with potential synergistic effects should be considered in the RASopathies.     

Proximal trisomy of 1q mosaicism in a girl with hypertrophic cardiomyopathy associated with Wolff‐Parkinson‐White syndrome and multiple congenital anomalies

We report an African American female who is mosaic for partial trisomy of 1q due to a direct duplication of 1q12 to 1q25. The child has hypertrophic cardiomyopathy with Wolff‐Parkinson‐White syndrome. The physical features include micrognathia, cleft palate, low set ears, posteriorly placed thumbs, and syndactyly of the second and third toes of both feet. Other abnormalities include intestinal malrotation, scoliosis, mental retardation, cerebral palsy, and hydrocephalus. There was also a selective deficiency of antibody responses to polysaccharide antigens. Proximal duplication of chromosome 1q is rare and has not been previously associated with hypertrophic cardiomyopathy. Most known gene disorders related to hypertrophic cardiomyopathy are autosomal dominant missense mutations in sarcomeric protein genes; however, none of the sarcomeric genes previously linked to hypertrophic cardiomyopathy are in this region. This finding thus highlights the possibility of additional genetic mechanisms for hypertrophic cardiomyopathy. © 2001 Wiley‐Liss, Inc.