Transmission of the rare HRAS mutation (c. 173C > T; p.T58I) further illustrates its attenuated phenotype
Division of Medical Genetics, A I duPont Hospital for Children, Wilmington, Delaware 19803, USA.American Journal of Medical Genetics Part A (Impact Factor: 2.16). 05/2012; 158A(5):1095-101. DOI: 10.1002/ajmg.a.35294
Costello syndrome was delineated based on its distinctive phenotype including severe failure-to-thrive with macrocephaly, characteristic facial features, hypertrophic cardiomyopathy, papillomata, malignant tumors, and cognitive impairment. Heterozygous germline mutations in the proto-oncogene HRAS cause Costello syndrome, and its inheritance pattern would thus be autosomal dominant. With exception of two instances of parental mosaicism, one presumed gonadal and the other proven somatic mosaicism for the p.G12S change, all published cases resulted from de novo mutations, typically arising in the paternal germline. More than 90% of these mutations affect the glycine residues in position 12 or 13, and result in a gain-of-function of the altered protein. A rare heterozygous HRAS alteration (c.173C > T; p.T58I) associated with an attenuated phenotype was previously reported in one patient. We identified two additional individuals with this mutation, father and son. Further studies supported origin of the alteration in the grand-paternal germline. Transmission of the mutation underscores its attenuated phenotype compatible with reproduction. We reviewed the phenotype in the newly identified individuals (Patient 1, 2) and include updated information on the first previously reported individual with HRAS p.T58I (Patient 3). Macrocephaly was present in all three. Cardiac findings included hypertrophic cardiomyopathy with double-chambered right ventricle; or mitral valve prolapse in one patient each. While subtle neurologic abnormalities or developmental delay were present in all, only one showed significant cognitive and functional impairment. None developed papillomata or a malignant tumor. Genetic counseling for Costello syndrome needs to take into consideration the particular HRAS mutation.
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ABSTRACT: Costello syndrome (CS) is a rare congenital disorder characterized by severe failure to thrive, coarse facial appearance, cardiac and skin abnormalities, developmental delay, intellectual disability, and predisposition to malignancies. Heterozygous de novo germline mutations in the proto-oncogene HRAS cause CS. About 80% of patients share the same mutation resulting in the amino acid change p.G12S and present a relatively homogeneous phenotype. Other less common lesions in HRAS can induce a milder phenotype on the one hand and a more severe phenotype on the other broadening the spectrum of clinical manifestations in CS-affected individuals. We report two new patients with the HRAS p.G12C and p.G12D substitutions and a severe neonatal manifestation causing death at the age of three months and 13 days, respectively. Both patients had particularly severe heart involvement with hypertrophic cardiomyopathy and tachyarrhythmia, generalized edema, and respiratory distress. In one case, hypertrophic cardiomyopathy was already noted prenatally. These cases together with other individuals harboring the rare HRAS mutations p.G12C, p.G12V, p.G12D, and p.G12E provide further evidence for a genotype-phenotype correlation that could be of importance for counseling and medical management.
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ABSTRACT: Costello syndrome is caused by HRAS germline mutations affecting Gly(12) or Gly(13) in >90% of cases and these are associated with a relatively homogeneous phenotype. Rarer mutations in other HRAS codons were reported in patients with an attenuated or mild phenotype. Disease-associated HRAS missense mutations result in constitutive HRAS activation and increased RAF-MEK-ERK and PI3K-AKT signal flow. Here we report on a novel heterozygous HRAS germline alteration, c.266C>G (p.S89C), in a girl presenting with severe fetal hydrops and pleural effusion, followed by a more benign postnatal course. A sibling with the same mutation and fetal polyhydramnios showed a Dandy-Walker malformation; his postnatal course was complicated by severe feeding difficulties. Their apparently asymptomatic father is heterozygous for the c.266C>G change. By functional analyses we identified reduced levels of active HRAS(S89C) and diminished MEK, ERK and AKT phosphorylation in cells overexpressing HRAS(S89C) , which represent novel consequences of disease-associated HRAS mutations. Given our patients' difficult neonatal course and presence of this change in their asymptomatic father, we hypothesize that its harmful consequences may be time limited, with the late fetal stage being most sensitive. Alternatively, the phenotype may develop only in the presence of an additional as-yet-unknown genetic modifier. While the pathogenicity of the HRAS c.266C>G change remains unproven, our data may illustrate wide functional and phenotypic variability of germline HRAS mutations.
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ABSTRACT: Noonan syndrome is a heterogenous rasopathy typically presenting with short stature, characteristic facial features, cardiac abnormalities including pulmonic valve stenosis, ASD and hypertrophic cardiomyopathy (HCM), cryptorchidism, ectodermal abnormalities, and learning differences. The phenotype is variable, and limited genotype phenotype correlation exists with SOS1 mutations often associated with normal cognition and stature, RAF1 mutations entailing a high HCM risk, and certain PTPN11 mutations predisposing to juvenile myelomonocytic leukemia. The recently identified SHOC2 mutation (p.Ser2Gly) causes Noonan syndrome with loose anagen hair. We report five patients with this mutation. All had skin hyperpigmentation, sparse light colored hair, increased fine wrinkles, ligamentous laxity, developmental delay, and 4/4 had a structural cardiac anomaly. Hypotonia and macrocephaly occurred in 4/5 (80%); 3/5 (60%) had polyhydramnios, increased birth weight or required use of a feeding tube. Distinctive brain abnormalities included relative megalencephaly and enlarged subarachnoid spaces suggestive of benign external hydrocephalus, and a relatively small posterior fossa as indicated by a vertical tentorium. The combination of a large brain with a small posterior fossa likely resulted in the high rate of cerebellar tonsillar ectopia (3/4; 75%). Periventricular nodular heterotopia was seen in one patient with a thick and dysplastic corpus callosum. We report on the first hematologic neoplasm, myelofibrosis, in a 2-year-old patient with SHOC2 mutation. Myelofibrosis is exceedingly rare in children and young adults. The absence of a somatic JAK2 mutation, seen in the majority of patients with myelofibrosis, is noteworthy as it suggests that germline or somatic SHOC2 mutations are causally involved in myelofibrosis. © 2013 Wiley Periodicals, Inc.
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