Siblings with profound connective tissue disease: First report of biallelic TGFBR1-related Loeys-Dietz syndrome.

Heterozygous missense variants in TGFBR1, encoding one subunit of the transforming growth factor-beta receptor, are a well-established cause of Loeys-Dietz syndrome (LDS)-an autosomal dominant disorder with variable phenotypic expression. Patients with LDS have compromised connective tissues that can result in life-threatening arterial aneurysms, craniosynostosis, characteristic craniofacial and skeletal anomalies, skin translucency, and abnormal wound healing. We report a full sibship with a biallelic type of TGFBR1-related disease. Each born at 38 weeks had aortic root dilation, congenital diaphragmatic hernia (CDH), skin translucency, and profound joint laxity at birth. Both had progressive dilation of the aorta and recurrence of a diaphragmatic defect after plication early in infancy. Patient 1 died at 66 days of age and Patient 2 is alive at 4 years and 4 months of age with multiple morbidities including cystic lung disease complicated by recurrent pneumothoraces and ventilator dependence, craniosynostosis, cervical spine instability, progressive dilation of the aorta, worsening pectus excavatum, large lateral abdominal wall hernia, and diffuse aortic ectasia. Fibroblasts cultured from Patient 2 showed decreased TGF-ß responsiveness when compared to control fibroblasts, consistent with previous observations in cells from individuals with autosomal dominant LDS. Whole genome copy number evaluation and sequencing for both patients including their parents as reference revealed compound heterozygous variants of uncertain clinical significance in exon 2 of TGFBR1 (c.239G>A; p.Arg80Gln paternal and c.313C>G; p.His105Asp maternal) in both siblings in trans. Each parent with their respective variant has no apparent medical issues and specifically no LDS characteristics. Neither of these variants have been previously reported. Thousands of patients have been diagnosed with LDS-an established autosomal dominant disease. These siblings represent the first reports of biallelic TGFBR1-related LDS and expand the differential diagnosis of CDH.

Extracellular Tuning of Mitochondrial Respiration Leads to Aortic Aneurysm.

BACKGROUND: Marfan syndrome (MFS) is an autosomal dominant disorder of the connective tissue caused by mutations in the FBN1 (fibrillin-1) gene encoding a large glycoprotein in the extracellular matrix called fibrillin-1. The major complication of this connective disorder is the risk to develop thoracic aortic aneurysm. To date, no effective pharmacologic therapies have been identified for the management of thoracic aortic disease and the only options capable of preventing aneurysm rupture are endovascular repair or open surgery. Here, we have studied the role of mitochondrial dysfunction in the progression of thoracic aortic aneurysm and mitochondrial boosting strategies as a potential treatment to managing aortic aneurysms. METHODS: Combining transcriptomics and metabolic analysis of aortas from an MFS mouse model (Fbn1c1039g/+) and MFS patients, we have identified mitochondrial dysfunction alongside with mtDNA depletion as a new hallmark of aortic aneurysm disease in MFS. To demonstrate the importance of mitochondrial decline in the development of aneurysms, we generated a conditional mouse model with mitochondrial dysfunction specifically in vascular smooth muscle cells (VSMC) by conditional depleting Tfam (mitochondrial transcription factor A; Myh11-CreERT2Tfamflox/flox mice). We used a mouse model of MFS to test for drugs that can revert aortic disease by enhancing Tfam levels and mitochondrial respiration. RESULTS: The main canonical pathways highlighted in the transcriptomic analysis in aortas from Fbn1c1039g/+ mice were those related to metabolic function, such as mitochondrial dysfunction. Mitochondrial complexes, whose transcription depends on Tfam and mitochondrial DNA content, were reduced in aortas from young Fbn1c1039g/+ mice. In vitro experiments in Fbn1-silenced VSMCs presented increased lactate production and decreased oxygen consumption. Similar results were found in MFS patients. VSMCs seeded in matrices produced by Fbn1-deficient VSMCs undergo mitochondrial dysfunction. Conditional Tfam-deficient VSMC mice lose their contractile capacity, showed aortic aneurysms, and died prematurely. Restoring mitochondrial metabolism with the NAD precursor nicotinamide riboside rapidly reverses aortic aneurysm in Fbn1c1039g/+ mice. CONCLUSIONS: Mitochondrial function of VSMCs is controlled by the extracellular matrix and drives the development of aortic aneurysm in Marfan syndrome. Targeting vascular metabolism is a new available therapeutic strategy for managing aortic aneurysms associated with genetic disorders.