Clinical manifestations of mutations in RAS and related intracellular signal transduction factors.
ABSTRACT Recent advances in molecular genetic research have led to the definition of the new group of genetic syndromes, the RAS-mitogen-activated protein kinase (MAPK) pathway disorders or 'RASopathies'. They comprise Noonan syndrome and related disorders (cardio-facio-cutaneous and Costello syndromes), as well as neurofibromatosis type 1. This review summarizes the recent literature with a special focus on genotype-phenotype correlations.
Although the picture is still incomplete, and additional genes are likely to exist, the underlying genetic alteration can now be found in a large majority of patients with a RASopathy phenotype. The most recently discovered novel genes for Noonan syndrome or Noonan syndrome-like disorders, NRAS, SHOC2, and CBL, account for small fractions of the patient population. The increasing knowledge about the spectrum of gene mutations and associated clinical manifestations has led to a refinement of genotype-phenotype correlations. Recent studies have added new insights into tumor predisposition and prenatal manifestations. Model systems are being developed to investigate innovative treatment approaches.
Constitutional overactivation at various levels of the RAS-MAPK pathway causes overlapping syndromes, comprising characteristic facial features, cardiac defects, cutaneous abnormalities, growth deficit, neurocognitive delay, and predisposition to malignancies. Each syndrome also exhibits unique features that probably reflect genotype-related specific biological effects.
- SourceAvailable from: Brandon S. Sheffield[Show abstract] [Hide abstract]
ABSTRACT: Costello syndrome is characterized by constitutional mutations in the proto-oncogene HRAS, causing dysmorphic features, multiple cardiac problems, intellectual disability and an increased risk of neoplasia. We report a male infant with dysmorphic features, born prematurely at 32 weeks, who, during his 3-month lifespan, had an unusually severe and ultimately fatal manifestation of hypertrophic cardiomyopathy, and hyperinsulinemic hypoglycemia. Molecular studies in this patient demonstrated the uncommon Q22K mutation in the HRAS gene, diagnostic of Costello syndrome. The major autopsy findings revealed hypertrophic cardiomyopathy, congenital myopathy, and a 1.4 cm pancreatic nodule, positive for insulin expression, morphologically identical to a focal lesion of congenital hyperinsulinism. Sequencing of KCNJ11 and ABCC8, the two most commonly mutated genes in focal lesion of congenital hyperinsulinism, revealed no mutations. While hyperinsulinism is a recognized feature of RASopathies, a focal proliferation of endocrine cells similar to a focal lesion of hyperinsulinism is a novel pathologic finding in Costello syndrome.Pediatric and Developmental Pathology 02/2015; 18(3). DOI:10.2350/14-07-1525-CR.1 · 0.86 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: -Adams-Oliver syndrome (AOS) is a rare disorder characterized by congenital limb defects and scalp cutis aplasia. In a proportion of cases, notable cardiac involvement is also apparent. Despite recent advances in the understanding of the genetic basis of AOS, for the majority of affected subjects the underlying molecular defect remains unresolved. This study aimed to identify novel genetic determinants of AOS. -Whole-exome sequencing was performed for 12 probands, each with a clinical diagnosis of AOS. Analyses led to the identification of novel heterozygous truncating NOTCH1 mutations (c.1649dupA and c.6049_6050delTC) in two kindreds in which AOS was segregating as an autosomal dominant trait. Screening a cohort of 52 unrelated AOS subjects, we detected 8 additional unique NOTCH1 mutations, including three de novo amino-acid substitutions, all within the ligand-binding domain. Congenital heart anomalies were noted in 47% (8/17) of NOTCH1-positive probands and affected family members. In leucocyte-derived RNA from subjects harboring NOTCH1 extracellular domain mutations, we observed significant reduction of NOTCH1 expression, suggesting instability and degradation of mutant mRNA transcripts by the cellular machinery. Transient transfection of mutagenized NOTCH1 missense constructs also revealed significant reduction in gene expression. Mutant NOTCH1 expression was associated with down-regulation of the Notch target genes HEY1 and HES1, indicating that NOTCH1-related AOS arises through dysregulation of the Notch signaling pathway. -These findings highlight a key role for NOTCH1 across a range of developmental anomalies that include cardiac defects, and implicate NOTCH1 haploinsufficiency as a likely molecular mechanism for this group of disorders.Circulation Cardiovascular Genetics 05/2015; DOI:10.1161/CIRCGENETICS.115.001086 · 5.34 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: Astrocytes produce an assortment of signals that promote neuronal maturation according to a precise developmental timeline. Is this orchestrated timing and signaling altered in human neurodevelopmental disorders? To address this question, the astroglial lineage was investigated in two model systems of a developmental disorder with intellectual disability caused by mutant Harvey rat sarcoma viral oncogene homolog (HRAS) termed Costello syndrome: mutant HRAS human induced pluripotent stem cells (iPSCs) and transgenic mice. Human iPSCs derived from patients with Costello syndrome differentiated to astroglia more rapidly in vitro than those derived from wild-type cell lines with normal HRAS, exhibited hyperplasia, and also generated an abundance of extracellular matrix remodeling factors and proteoglycans. Acute treatment with a farnesyl transferase inhibitor and knockdown of the transcription factor SNAI2 reduced expression of several proteoglycans in Costello syndrome iPSC-derived astrocytes. Similarly, mice in which mutant HRAS was expressed selectively in astrocytes exhibited experience-independent increased accumulation of perineuronal net proteoglycans in cortex, as well as increased parvalbumin expression in interneurons, when compared to wild-type mice. Our data indicate that astrocytes expressing mutant HRAS dysregulate cortical maturation during development as shown by abnormal extracellular matrix remodeling and implicate excessive astrocyte-to-neuron signaling as a possible drug target for treating mental impairment and enhancing neuroplasticity. Copyright © 2015, American Association for the Advancement of Science.Science translational medicine 05/2015; 7(286):286ra66. DOI:10.1126/scitranslmed.aaa5645 · 14.41 Impact Factor