Abstract
Noonan syndrome (NS), the most common RASopathy, is caused by mutations affecting signaling through RAS and the MAPK cascade. Recently, genome scanning has discovered novel genes implicated ...in NS, whose function in RAS-MAPK signaling remains obscure, suggesting the existence of unrecognized circuits contributing to signal modulation in this pathway. Among these genes, leucine zipper-like transcriptional regulator 1 (LZTR1) encodes a functionally poorly characterized member of the BTB/POZ protein superfamily. Two classes of germline LZTR1 mutations underlie dominant and recessive forms of NS, while constitutional monoallelic, mostly inactivating, mutations in the same gene cause schwannomatosis, a cancer-prone disorder clinically distinct from NS. Here we show that dominant NS-causing LZTR1 mutations do not affect significantly protein stability and subcellular localization. We provide the first evidence that these mutations, but not the missense changes occurring as biallelic mutations in recessive NS, enhance stimulus-dependent RAS-MAPK signaling, which is triggered, at least in part, by an increased RAS protein pool. Moreover, we document that dominant NS-causing mutations do not perturb binding of LZTR1 to CUL3, a scaffold coordinating the assembly of a multimeric complex catalyzing protein ubiquitination but are predicted to affect the surface of the Kelch domain mediating substrate binding to the complex. Collectively, our data suggest a model in which LZTR1 contributes to the ubiquitinationof protein(s) functioning as positive modulator(s) of the RAS-MAPK signaling pathway. In this model, LZTR1 mutations are predicted to variably impair binding of these substrates to the multi-component ligase complex and their efficient ubiquitination and degradation, resulting in MAPK signaling upregulation.
RASopathies are caused by variants in genes encoding components or modulators of the RAS/MAPK signaling pathway. Noonan syndrome is the most common entity among this group of disorders and is ...characterized by heart defects, short stature, variable developmental delay, and typical facial features. Heterozygous variants in SOS2, encoding a guanine nucleotide exchange factor for RAS, have recently been identified in patients with Noonan syndrome. The number of published cases with SOS2-related Noonan syndrome is still limited and little is known about genotype-phenotype correlations. We collected previously unpublished clinical and genotype data from 17 individuals carrying a disease-causing SOS2 variant. Most individuals had one of the previously reported dominant pathogenic variants; only four had novel changes at the established hotspots for variants that affect protein function. The overall phenotype of the 17 patients fits well into the spectrum of Noonan syndrome and is most similar to the phenotype observed in patients with SOS1-related Noonan syndrome, with ectodermal anomalies as common features and short stature and learning disabilities as relatively infrequent findings compared to the average Noonan syndrome phenotype. The spectrum of heart defects in SOS2-related Noonan syndrome was consistent with the known spectrum of cardiac anomalies in RASopathies, but no specific heart defect was particularly predominating. Notably, lymphatic anomalies were extraordinarily frequent, affecting more than half of the patients. We therefore conclude that SOS2-related Noonan syndrome is associated with a particularly high risk of lymphatic complications that may have a significant impact on morbidity and quality of life.
Recent studies have identified suggestive prenatal features of RASopathies (e.g., increased nuchal translucency NT, cystic hygroma CH, hydrops, effusions, congenital heart diseases CHD, ...polyhydramnios, renal anomalies). Our objective is to clarify indications for RASopathy prenatal testing. We compare genotype distributions between pre- and postnatal populations and propose genotype–phenotype correlations.
Three hundred fifty-two chromosomal microarray–negative cases sent for prenatal RASopathy testing between 2012 and 2019 were collected. For most, 11 RASopathy genes were tested. Postnatal cohorts (25 patients with available prenatal information and 108 institutional database genotypes) and the NSeuroNet database were used for genotypic comparisons.
The overall diagnostic yield was 14% (50/352), with rates >20% for effusions, hydrops, and CHD. Diagnostic yield was significantly improved in presence of hypertrophic cardiomyopathy (HCM), persistent or associated CH, any suggestive finding combined with renal anomaly or polyhydramnios, or ≥2 ultrasound findings. Largest prenatal contributors of pathogenic variants were PTPN11 (30%), RIT1 (16%), RAF1 (14%), and HRAS (12%), which considerably differ from their prevalence in postnatal populations. HRAS, LZTR1, and RAF1 variants correlated with hydrops/effusions, and RIT1 with prenatal onset HCM.
After normal chromosomal microarray, RASopathies should be considered when any ultrasound finding of lymphatic dysplasia or suggestive CHD is found alone or in association.
Kabuki syndrome is a genetically heterogeneous disorder characterized by postnatal growth retardation, skeletal abnormalities, intellectual disability, facial dysmorphisms and a variable range of ...organ malformations. In ~30% of affected individuals, the underlying genetic defect remains unknown. A small number of inactivating heterozygous HNRNPK mutations has recently been reported to be associated with a condition partially overlapping or suggestive of Kabuki syndrome. Here, we report on an 11‐year‐old girl with a complex phenotype in whom the diagnosis of KS was suggested but molecular testing for the known causative disease genes was negative. Whole‐exome sequencing identified a previously undescribed de novo truncating mutation in HNRNPK as the molecular defect underlying the trait. Analysis of available records of patients with HNRNPK haploinsufficiency was performed to delineate the associated clinical phenotype and outline their distinguishing features in comparison with the KS clinical spectrum. The clinical profile associated with inactivating HNRNPK mutations supports the idea that the associated disorder should be considered as a distinct nosologic entity clinically related to KS, and that the condition should be considered in differential diagnosis with KS, in particular in subjects exhibiting brain malformation (nodular heterotopia), craniosynostosis, and polydactyly.
, the application of genomic sequencing in clinical practice has allowed us to appreciate the contribution of co-occurring pathogenic variants to complex and unclassified clinical phenotypes. Besides ...the clinical relevance, these findings have provided evidence of previously unrecognized functional links between genes in the context of developmental processes and physiology.
, a 5-year-old patient showing an unclassified phenotype characterized by developmental delay, speech delay, peculiar behavioral features, facial dysmorphism and severe cardiopathy was analyzed by trio-based whole exome sequencing (WES) analysis to identify the genomic events underlying the condition.
, two co-occurring heterozygous truncating variants in
and
were identified. Heterozygous loss-of-function variants in
, encoding a subunit of the CCR4-NOT protein complex, have recently been reported to cause a syndromic condition known as intellectual developmental disorder with speech delay, autism and dysmorphic facies (IDDSADF). Enrichment of rare/private variants in the
gene, encoding a protein negatively controlling transforming growth factor β/bone morphogenetic protein (TGFB/BMP) signaling, has been described in association with a wide spectrum of congenital heart defects. We dissected the contribution of individual variants to the complex clinical manifestations and profiled a previously unappreciated set of facial features and signs characterizing IDDSADF.
, two concomitant truncating variants in
and
are the cause of the combination of features documented in the patient resulting in the unique multisystem neurodevelopmental condition. These findings provide evidence for a functional link between the CCR4-NOT complex and TGFB/BMP signaling in processes controlling cardiac development. Finally, the present revision provides evidence that IDDSADF is characterized by a distinctive facial gestalt.
TARP syndrome (TARPS) is an X-linked syndromic condition including Robin sequence, congenital heart defects, developmental delay, feeding difficulties and talipes equinovarus, as major features. The ...disease is caused by inactivating mutations in RBM10 which encodes for a RNA binding motif protein involved in transcript processing. We herein report a male born from healthy and non-consanguineous parents, presenting prenatal record of intrauterine fetal growth retardation, and postnatal features including growth and developmental delays, CNS abnormalities, facial dysmorphisms, bilateral syndactyly at the hands, talipes equinovarus and congenital heart defects. By using trio-based Whole Exome Sequencing approach, a maternally inherited RBM10 frameshift variant causing decay of the RBM10 transcript was identified. Despite the syndrome is considered lethal in affected males, our subject with molecularly confirmed TARPS is still alive at 11 years of age supporting the chance of surviving. Long-term surviving in TARPS is extremely rare and should be considered in genetic counselling and clinical follow up of the syndrome. We provide the natural history of the syndrome, reviewing the major clinical characteristics. Congenital heart defects are confirmed as specific diagnostic markers for the syndrome. In addition, cardiac anatomical details are defining a possible clinical overlap with syndromic conditions related to the hedgehog pathway and/or primary cilium anomalies as Oral-Facial-Digital or Smith-Lemli-Opitz syndromes.
Cardio-facio-cutaneous syndrome (CFCS) is a rare disease characterized by mental retardation, facial dysmorphisms, ectodermal abnormalities, heart defects and developmental delay. CFCS is genetically ...heterogeneous and mutations in the KRAS, BRAF, MAP2K1 (MEK1) and MAP2K2 (MEK2) genes, encoding for components of the RAS-mitogen activated protein kinase (MAPK) signaling pathway, have been identified in up to 90% of cases. Here we screened a cohort of 33 individuals with CFCS for MEK1 and MEK2 gene mutations to further explore their molecular spectrum in this disorder, and to analyze genotype-phenotype correlations. Three MEK1 and two MEK2 mutations were detected in six patients. Two missense MEK1 (L42F and Y130H) changes and one in-frame MEK2 (K63_E66del) deletion had not been reported earlier. All mutations were localized within exon 2 or 3. Together with the available records, the present data document that MEK1 mutations are relatively more frequent than those in MEK2, with exons 2 and 3 being mutational hot spots in both genes. Mutational analysis of the affected MEK1 and MEK2 exons did not reveal occurrence of mutations among 75 patients with Noonan syndrome, confirming the low prevalence of MEK gene defects in this disorder. Clinical review of known individuals with MEK1/MEK2 mutations suggests that these patients show dysmorphic features, ectodermal abnormalities and cognitive deficit similar to what was observed in BRAF-mutated patients and in the general CFCS population. Conversely, congenital heart defects, particularly mitral valve and septal defects, and ocular anomalies seem to be less frequent among MEK1/MEK2 mutation-positive patients.
Hemophagocytic lymphohistiocytosis (HLH) is characterized by immune dysregulation due to inadequate restraint of overactivated immune cells and is associated with a variable clinical spectrum having ...overlap with more common pathophysiologies. HLH is difficult to diagnose and can be part of inflammatory syndromes. Here, we identify a novel hematological/autoinflammatory condition (NOCARH syndrome) in four unrelated patients with superimposable features, including neonatal-onset cytopenia with dyshematopoiesis, autoinflammation, rash, and HLH. Patients shared the same de novo
mutation (Chr1:22417990C>T, p.R186C) and altered hematopoietic compartment, immune dysregulation, and inflammation.
mutations had been associated with syndromic neurodevelopmental disorders. In vitro and in vivo assays documented unique effects of p.R186C on CDC42 localization and function, correlating with the distinctiveness of the trait. Emapalumab was critical to the survival of one patient, who underwent successful bone marrow transplantation. Early recognition of the disorder and establishment of treatment followed by bone marrow transplant are important to survival.
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