Gain-of-function RAF1 mutations cause Noonan and LEOPARD syndromes with hypertrophic cardiomyopathy.

Noonan and LEOPARD syndromes are developmental disorders with overlapping features, including cardiac abnormalities, short stature and facial dysmorphia. Increased RAS signaling owing to PTPN11, SOS1 and KRAS mutations causes approximately 60% of Noonan syndrome cases, and PTPN11 mutations cause 90% of LEOPARD syndrome cases. Here, we report that 18 of 231 individuals with Noonan syndrome without known mutations (corresponding to 3% of all affected individuals) and two of six individuals with LEOPARD syndrome without PTPN11 mutations have missense mutations in RAF1, which encodes a serine-threonine kinase that activates MEK1 and MEK2. Most mutations altered a motif flanking Ser259, a residue critical for autoinhibition of RAF1 through 14-3-3 binding. Of 19 subjects with a RAF1 mutation in two hotspots, 18 (or 95%) showed hypertrophic cardiomyopathy (HCM), compared with the 18% prevalence of HCM among individuals with Noonan syndrome in general. Ectopically expressed RAF1 mutants from the two HCM hotspots had increased kinase activity and enhanced ERK activation, whereas non-HCM-associated mutants were kinase impaired. Our findings further implicate increased RAS signaling in pathological cardiomyocyte hypertrophy.

Signalling to chromatin through post-translational modifications of HMGN.

The DNA of eukaryotic genomes is highly packaged by its organisation into chromatin, the fundamental repeating unit of which is the nucleosome core particle, consisting of 147 base pairs of DNA wrapped around an octamer of two copies each of the four core histone proteins H2A, H2B, H3 and H4 (K. Luger, A.W. Mader, R.K. Richmond, D.F. Sargent, T.J. Richmond, Crystal structure of the nucleosome core particle at 2.8 A resolution, Nature 389 (1997) 251-260 [1] and references therein). Accessibility of DNA within chromatin is a central factor that affects DNA-dependent nuclear function such as transcription, replication, recombination and repair. To integrate complex signalling networks associated with these events, many protein and multi-protein complexes associate transiently with nucleosomes. One class of such are the High-Mobility Group (HMG) proteins which are architectural DNA and nucleosome-binding proteins that may be subdivided into three families; HMGA (HMGI/Y/C), HMGB (HMG1/2) and HMGN (HMG14/17). The structure of chromatin and nucleosomes can be altered, both locally and globally, by interaction with such architectural proteins thereby influencing accessibility of DNA. This chapter deals with the HMGN protein family, specifically their post-translational modification as part of regulatory networks. We focus particularly on HMGN1, the most extensively studied family member to date, and to a lesser extent on HMGN2. We critically evaluate evidence for the role of post-translational modification of these proteins in response to different signals, exploring the sites and potential significance of such modification.

Characterization and treatment of immune thrombocytopenia in Europe: a qualitative observational study.

BACKGROUND: Immune thrombocytopenia (ITP) is a rare disease, characterized by increased platelet destruction/suboptimal platelet production, leading to thrombocytopenia and risk of severe bleeding events. METHODS: Interviews with 23 physicians and 12 payors, a survey with 113 physicians and validation using published data were used to define the current treatment paradigm and healthcare resource utilization and to determine the costs associated with managing acute bleeds in six European countries (Germany, Spain, France, Italy, Netherlands, UK). The study estimated a prevalence of 9 to 10 per 100,000 adults in 2020 across all six countries (disease severity split: 34% mild, 32% moderate, 33% severe (due to rounding up some values might not sum up to 100%). RESULTS: Physician feedback showed that most patients with ITP (60%) received first-line treatment or were monitored by their physician; ∼75% of patients relapsed within 3-4 months. Thrombopoietin-receptor agonists (TPO-RAs) and rituximab were used to achieve disease stabilization in patients who relapse; patients could switch to an alternative TPO-RA to control symptoms, manage side-effects or improve adherence. The costs of rescue therapies and hospital services (e.g. surgery and admissions) accounted for the majority of healthcare resources to manage bleeding events. CONCLUSION: Physicians would welcome earlier use of TPO-RAs to help maintain long-term control of ITP bleeds and potentially reduce both hospitalization and therapy costs.

Diversity, parental germline origin, and phenotypic spectrum of de novo HRAS missense changes in Costello syndrome.

Activating mutations in v-Ha-ras Harvey rat sarcoma viral oncogene homolog (HRAS) have recently been identified as the molecular cause underlying Costello syndrome (CS). To further investigate the phenotypic spectrum associated with germline HRAS mutations and characterize their molecular diversity, subjects with a diagnosis of CS (N = 9), Noonan syndrome (NS; N = 36), cardiofaciocutaneous syndrome (CFCS; N = 4), or with a phenotype suggestive of these conditions but without a definitive diagnosis (N = 12) were screened for the entire coding sequence of the gene. A de novo heterozygous HRAS change was detected in all the subjects diagnosed with CS, while no lesion was observed with any of the other phenotypes. While eight cases shared the recurrent c.34G>A change, a novel c.436G>A transition was observed in one individual. The latter affected residue, p.Ala146, which contributes to guanosine triphosphate (GTP)/guanosine diphosphate (GDP) binding, defining a novel class of activating HRAS lesions that perturb development. Clinical characterization indicated that p.Gly12Ser was associated with a homogeneous phenotype. By analyzing the genomic region flanking the HRAS mutations, we traced the parental origin of lesions in nine informative families and demonstrated that de novo mutations were inherited from the father in all cases. We noted an advanced age at conception in unaffected fathers transmitting the mutation.