mTOR-Activating Mutations in RRAGD Are Causative for Kidney Tubulopathy and Cardiomyopathy.

BACKGROUND: Over the last decade, advances in genetic techniques have resulted in the identification of rare hereditary disorders of renal magnesium and salt handling. Nevertheless, approximately 20% of all patients with tubulopathy lack a genetic diagnosis. METHODS: We performed whole-exome and -genome sequencing of a patient cohort with a novel, inherited, salt-losing tubulopathy; hypomagnesemia; and dilated cardiomyopathy. We also conducted subsequent in vitro functional analyses of identified variants of RRAGD, a gene that encodes a small Rag guanosine triphosphatase (GTPase). RESULTS: In eight children from unrelated families with a tubulopathy characterized by hypomagnesemia, hypokalemia, salt wasting, and nephrocalcinosis, we identified heterozygous missense variants in RRAGD that mostly occurred de novo. Six of these patients also had dilated cardiomyopathy and three underwent heart transplantation. We identified a heterozygous variant in RRAGD that segregated with the phenotype in eight members of a large family with similar kidney manifestations. The GTPase RagD, encoded by RRAGD, plays a role in mediating amino acid signaling to the mechanistic target of rapamycin complex 1 (mTORC1). RagD expression along the mammalian nephron included the thick ascending limb and the distal convoluted tubule. The identified RRAGD variants were shown to induce a constitutive activation of mTOR signaling in vitro. CONCLUSIONS: Our findings establish a novel disease, which we call autosomal dominant kidney hypomagnesemia (ADKH-RRAGD), that combines an electrolyte-losing tubulopathy and dilated cardiomyopathy. The condition is caused by variants in the RRAGD gene, which encodes Rag GTPase D; these variants lead to an activation of mTOR signaling, suggesting a critical role of Rag GTPase D for renal electrolyte handling and cardiac function.

Extubation in the Operating Room After Fontan Procedure: Does It Make a Difference?

Early extubation appears to have beneficial effects on the Fontan circulation. The goal of this study was to assess the impact of extubation on the operating table in comparison with extubation during the first hours after Fontan operation (FO) on the early postoperative course. Between 2013 and 2016, 114 children with a single ventricle heart malformations (mean age, 3.8 ± 2.3 years) underwent FO: 60 patients were extubated in the operating room (ORE) and 54 in the intensive care unit (ICUE) in the median time of 195 min (range 30-515 min) after procedure. Pre-, peri-, and postoperative records were retrospectively analyzed. The hospital survival rate was 100%. One patient from the ORE group needed an immediate reintubation because of laryngospasm. The ORE group showed lower heart rate (106.5 vs. 120.3 bpm; p < 0.001) and lower central venous pressure (10.4 vs. 11.4 mmHg; p = 0.001) than patients in the ICUE group within the first 24 h after FO, as well as higher systolic blood pressure within 7 h after operation (88.6 ± 2.5 vs. 85.6 ± 2.6 mmHg; p = 0.036). The ORE children manifested significantly less pleural effusions during 48 h after FO (38.0 vs. 49.5 ml/kg; p = 0.004), received less intravenous fluid administration within 24 h after FO (54.1 vs. 73.8 ml/kg; p = 0.019), less inotropic support (9.8 vs. 12.8 h of dopamine; p = 0.033), and less antibiotics (4.7 vs. 5.8 days; p = 0.037). ICUE children manifested metabolic acidosis more frequently than the ORE group 3-4 h after FO (p < 0.05). Immediate extubation after FO in comparison with extubation in the ICU appears to be associated with improved hemodynamics and reduced application of therapeutic interventions in the postoperative course.

Microfluidic reveals generation of platelet-strings on tumor-activated endothelium.

Neoplastic diseases are often associated with thromboembolic events, however the precise mechanism underlying this observation is a matter of ongoing investigation. It is known that matrixmetalloproteinase-1 (MMP-1) canonically activates the thrombin receptor (PAR-1) and we recently reported that highly metastatic tumor cells of melanoma and colon cancer are secreting matrixmetalloproteinase-1. This tumor-derived MMP1 was shown to be a major activator of endothelial PAR-1, thus leading to endothelial cell activation. As tumor-induced thrombosis is a characteristic of metastazing tumors, we investigated whether tumor-derived supernatant (TUSN) from melanoma and colon cancer may induce adhesion of circulating platelets, an initial step in thrombus formation. A time-course study revealed that TU-SN induces a rapid secretion of von Willebrand factor (VWF) within minutes. Using a novel microfluidic device we analyzed platelet-endothelial interactions in a closed circuit. Immunofluorescence imaging showed that TU-SN rapidly induces platelet-string formation via secreted VWF. We demonstrated that tumor-derived supernatant is a potent agonist inducing platelet adhesion under flow conditions.