TGFßRIIb mutations trigger aortic aneurysm pathogenesis by altering transforming growth factor ß2 signal transduction

Background-Thoracic aortic aneurysm (TAA) is a common progressive disorder involving gradual dilation of the ascending and/or descending thoracic aorta that eventually leads to dissection or rupture. Nonsydromic TAA can occur as a genetically triggered, familial disorder that is usually transmitted in a monogenic autosomal dominant fashion and is known as familial TAA. Genetic analyses of families affected with TAA have identified several chromosomal loci, and further mapping of familial TAA genes has highlighted disease-causing mutations in at least 4 genes: myosin heavy chain 11 (MYH11), a-smooth muscle actin (ACTA2), and transforming growth factor ß receptors I and II (TGFßRI and TGFßRII). Methods and Results-We evaluated 100 probands to determine the mutation frequency in MYH11, ACTA2, TGFßRI, and TGFßRII in an unbiased population of individuals with genetically mediated TAA. In this study, 9% of patients had a mutation in one of the genes analyzed, 3% of patients had mutations in ACTA2, 3% in MYH11, 1% in TGFßRII, and no mutations were found in TGFßRI. Additionally, we identified mutations in a 75 base pair alternatively spliced TGFßRII exon, exon 1a that produces the TGFßRIIb isoform and accounted for 2% of patients with mutations. Our in vitro analyses indicate that the TGFßRIIb activating mutations alter receptor function on TGFß2 signaling. Conclusions-We propose that TGFßRIIb expression is a regulatory mechanism for TGFß2 signal transduction. Dysregulation of the TGFß2 signaling pathway, as a consequence of TGFßRIIb mutations, results in aortic aneurysm pathogenesis.