Regulatory variants in TCF7L2 are associated with thoracic aortic aneurysm.

Thoracic aortic aneurysm (TAA) is characterized by dilation of the aortic root or ascending/descending aorta. TAA is a heritable disease that can be potentially life threatening. While 10%-20% of TAA cases are caused by rare, pathogenic variants in single genes, the origin of the majority of TAA cases remains unknown. A previous study implicated common variants in FBN1 with TAA disease risk. Here, we report a genome-wide scan of 1,351 TAA-affected individuals and 18,295 control individuals from the Cardiovascular Health Improvement Project and Michigan Genomics Initiative at the University of Michigan. We identified a genome-wide significant association with TAA for variants within the third intron of TCF7L2 following replication with meta-analysis of four additional independent cohorts. Common variants in this locus are the strongest known genetic risk factor for type 2 diabetes. Although evidence indicates the presence of different causal variants for TAA and type 2 diabetes at this locus, we observed an opposite direction of effect. The genetic association for TAA colocalizes with an aortic eQTL of TCF7L2, suggesting a functional relationship. These analyses predict an association of higher expression of TCF7L2 with TAA disease risk. In vitro, we show that upregulation of TCF7L2 is associated with BCL2 repression promoting vascular smooth muscle cell apoptosis, a key driver of TAA disease.

An FBN1 deep intronic variant is associated with pseudoexon formation and a variable Marfan phenotype in a five generation family.

Exome sequencing of genes associated with heritable thoracic aortic disease (HTAD) failed to identify a pathogenic variant in a large family with Marfan syndrome (MFS). A genome-wide linkage analysis for thoracic aortic disease identified a peak at 15q21.1, and genome sequencing identified a novel deep intronic FBN1 variant that segregated with thoracic aortic disease in the family (LOD score 2.7) and was predicted to alter splicing. RT-PCR and bulk RNA sequencing of RNA harvested from fibroblasts explanted from the affected proband revealed an insertion of a pseudoexon between exons 13 and 14 of the FBN1 transcript, predicted to lead to nonsense mediated decay (NMD). Treating the fibroblasts with an NMD inhibitor, cycloheximide, greatly improved the detection of the pseudoexon-containing transcript. Family members with the FBN1 variant had later onset aortic events and fewer MFS systemic features than typical for individuals with haploinsufficiency of FBN1. Variable penetrance of the phenotype and negative genetic testing in MFS families should raise the possibility of deep intronic FBN1 variants and the need for additional molecular studies.

LTBP3 Pathogenic Variants Predispose Individuals to Thoracic Aortic Aneurysms and Dissections.

The major diseases affecting the thoracic aorta are aneurysms and acute dissections, and pathogenic variants in 11 genes are confirmed to lead to heritable thoracic aortic disease. However, many families in which multiple members have thoracic aortic disease do not have alterations in the known aortopathy genes. Genes highly expressed in the aorta were assessed for rare variants in exome sequencing data from such families, and compound rare heterozygous variants (p.Pro45Argfs∗25 and p.Glu750∗) in LTBP3 were identified in affected members of one family. A homozygous variant (p.Asn678_Gly681delinsThrCys) that introduces an additional cysteine into an epidermal growth factor (EGF)-like domain in the corresponding protein, latent TGF-ß binding protein (LTBP-3), was identified in a second family. Individuals with compound heterozygous or homozygous variants in these families have aneurysms and dissections of the thoracic aorta, as well as aneurysms of the abdominal aorta and other arteries, along with dental abnormalities and short stature. Heterozygous carriers of the p.Asn678_Gly681delinsThrCys variant have later onset of thoracic aortic disease, as well as dental abnormalities. In these families, LTBP3 variants segregated with thoracic aortic disease with a combined LOD score of 3.9. Additionally, heterozygous rare LTBP3 variants were found in individuals with early onset of acute aortic dissections, and some of these variants disrupted LTBP-3 levels or EGF-like domains. When compared to wild-type mice, Ltbp3-/- mice have enlarged aortic roots and ascending aortas. In summary, homozygous LTBP3 pathogenic variants predispose individuals to thoracic aortic aneurysms and dissections, along with the previously described skeletal and dental abnormalities.

Pathogenic variants in THSD4, encoding the ADAMTS-like 6 protein, predispose to inherited thoracic aortic aneurysm.

PURPOSE: Thoracic aortic aneurysm and dissection (TAAD) is a life-threatening disease with often unrecognized inherited forms. We sought to identify novel pathogenic variants associated with autosomal dominant inheritance of TAAD. METHODS: We analyzed exome sequencing data from 35 French TAAD families and performed next-generation sequencing capture panel of genes in 1114 unrelated TAAD patients. Functional effects of pathogenic variants identified were validated in cell, tissue, and mouse models. RESULTS: We identified five functional variants in THSD4 of which two heterozygous variants lead to a premature termination codon. THSD4 encodes ADAMTSL6 (member of the ADAMTS/L superfamily), a microfibril-associated protein that promotes fibrillin-1 matrix assembly. The THSD4 variants studied lead to haploinsufficiency or impaired assembly of fibrillin-1 microfibrils. Thsd4+/- mice showed progressive dilation of the thoracic aorta. Histologic examination of aortic samples from a patient carrying a THSD4 variant and from Thsd4+/- mice, revealed typical medial degeneration and diffuse disruption of extracellular matrix. CONCLUSION: These findings highlight the role of ADAMTSL6 in aortic physiology and TAAD pathogenesis. They will improve TAAD management and help develop new targeted therapies.

Loss-of-Function Mutations in YY1AP1 Lead to Grange Syndrome and a Fibromuscular Dysplasia-Like Vascular Disease.

Fibromuscular dysplasia (FMD) is a heterogeneous group of non-atherosclerotic and non-inflammatory arterial diseases that primarily involves the renal and cerebrovascular arteries. Grange syndrome is an autosomal-recessive condition characterized by severe and early-onset vascular disease similar to FMD and variable penetrance of brachydactyly, syndactyly, bone fragility, and learning disabilities. Exome-sequencing analysis of DNA from three affected siblings with Grange syndrome identified compound heterozygous nonsense variants in YY1AP1, and homozygous nonsense or frameshift YY1AP1 variants were subsequently identified in additional unrelated probands with Grange syndrome. YY1AP1 encodes yin yang 1 (YY1)-associated protein 1 and is an activator of the YY1 transcription factor. We determined that YY1AP1 localizes to the nucleus and is a component of the INO80 chromatin remodeling complex, which is responsible for transcriptional regulation, DNA repair, and replication. Molecular studies revealed that loss of YY1AP1 in vascular smooth muscle cells leads to cell cycle arrest with decreased proliferation and increased levels of the cell cycle regulator p21/WAF/CDKN1A and disrupts TGF-ß-driven differentiation of smooth muscle cells. Identification of YY1AP1 mutations as a cause of FMD indicates that this condition can result from underlying genetic variants that significantly alter the phenotype of vascular smooth muscle cells.

SMAD3 pathogenic variants: risk for thoracic aortic disease and associated complications from the Montalcino Aortic Consortium.

BACKGROUND: Pathogenic variants in SMAD3 cause thoracic aortic aneurysms and dissections, along with aneurysms and rupture of other arteries. Here, we examined differences in clinical presentation of aortic events (dissection or surgical repair of an aneurysm) with respect to age and variant type in an international cohort of individuals with SMAD3 variants. METHODS: Aortic status and events, vital status and clinical features were abstracted through retrospective review of medical records of 212 individuals with 51 unique SMAD3 variants, including haploinsufficiency (HI) and missense substitutions in the MH2 domain, as well as novel in-frame deletions and missense variants in the MH1 domain. RESULTS: Aortic events were documented in 37% of cases, with dissections accounting for 70% of events. The median age at first aortic event was significantly lower in individuals with SMAD3 MH2 missense variants than those with HI variants (42years vs 49 years; p=0.003), but there was no difference in frequency of aortic events by variant type. The cumulative risk of an aortic event was 50% at 54 years of age. No aortic events in childhood were observed. CONCLUSIONS: SMAD3 pathogenic variants cause thoracic aortic aneurysms and dissections in the majority of individuals with variable age of onset and reduced penetrance. Of the covariates examined, the type of underlying SMAD3 variant was responsible for some of this variation. Later onset of aortic events and the absence of aortic events in children associated with SMAD3 variants support gene-specific management of this disorder.

Genetic Variants in LRP1 and ULK4 Are Associated with Acute Aortic Dissections.

Acute aortic dissections are a preventable cause of sudden death if individuals at risk are identified and surgically repaired in a non-emergency setting. Although mutations in single genes can be used to identify at-risk individuals, the majority of dissection case subjects do not have evidence of a single gene disorder, but rather have the other major risk factor for dissections, hypertension. Initial genome-wide association studies (GWASs) identified SNPs at the FBN1 locus associated with both thoracic aortic aneurysms and dissections. Here, we used the Illumina HumanExome array to genotype 753 individuals of European descent presenting specifically with non-familial, sporadic thoracic aortic dissection (STAD) and compared them to the genotypes of 2,259 control subjects from the Atherosclerosis Risk in Communities (ARIC) study matched for age, gender, and, for the majority of cases, hypertension. SNPs in FBN1, LRP1, and ULK4 were identified to be significantly associated with STAD, and these results were replicated in two independent cohorts. Combining the data from all cohorts confirmed an inverse association between LRP1 rs11172113 and STAD (p = 2.74 × 10(-8); OR = 0.82, 95% CI = 0.76-0.89) and a direct association between ULK4 rs2272007 and STAD (p = 1.15 × 10(-9); OR = 1.35, 95% CI = 1.23-1.49). Genomic copy-number variation analysis independently confirmed that ULK4 deletions were significantly associated with development of thoracic aortic disease. These results indicate that genetic variations in LRP1 and ULK4 contribute to risk for presenting with an acute aortic dissection.

MYLK pathogenic variants aortic disease presentation, pregnancy risk, and characterization of pathogenic missense variants.

PURPOSE: Heritable thoracic aortic disease can result from null variants in MYLK, which encodes myosin light-chain kinase (MLCK). Data on which MYLK missense variants are pathogenic and information to guide aortic disease management are limited. METHODS: Clinical data from 60 cases with MYLK pathogenic variants were analyzed (five null and two missense variants), and the effect of missense variants on kinase activity was assessed. RESULTS: Twenty-three individuals (39%) experienced an aortic event (defined as aneurysm repair or dissection); the majority of these events (87%) were aortic dissections. Aortic diameters were minimally enlarged at the time of dissection in many cases. Time-to-aortic-event curves showed that missense pathogenic variant (PV) carriers have earlier-onset aortic events than null PV carriers. An MYLK missense variant segregated with aortic disease over five generations but decreases MYLK kinase acitivity marginally. Functional Assays fail to identify all pathogenic variants in MYLK. CONCLUSION: These data further define the aortic phenotype associated with MYLK pathogenic variants. Given minimal aortic enlargement before dissection, an alternative approach to guide the timing of aortic repair is proposed based on the probability of a dissection at a given age.

The natural history of type B aortic dissection in patients with PRKG1 mutation c.530G>A (p.Arg177Gln).

OBJECTIVE: The c.530G>A (p.Arg177Gln) mutation in PRKG1 has been shown to be associated with thoracic aortic aneurysms and dissections. This rare mutation accounts for an estimated 1% of nonsyndromic heritable thoracic aortic disease. We sought to describe the clinical presentation of type B aortic dissection (TBAD), management, and outcomes in patients with this mutation. METHODS: This is a descriptive multi-institutional retrospective study of patients from six families with the PRKG1 mutation. Patients with TBAD were selected for analysis. Demographics, family histories, TBAD management, and outcomes were reviewed. RESULTS: Of the 29 individuals diagnosed with the PRKG1 mutation, 12 (41.3%) had TBAD (50% male, TBAD median age: 31 years [range, 16-58 years], median follow-up: 6 years [range, 3-15 years] after TBAD). All had a family history of aortic dissections and none had features of Marfan syndrome. The median size of the descending thoracic aorta (DTA) at TBAD was 4.1 cm (range, 3.8-5 cm). Most cases (9 acute TBAD, 1 incidental TBAD diagnosis during screening) were managed medically. One case had open DTA repair the acute phase. Repair for dissection-related aneurysmal degeneration was performed in seven cases (58.3%) in the chronic phase at a median of 2 years (range, 1-8 years) after TBAD. In four cases (33.3%), the DTA remained stable in size over a range of 1 to 7 years after TBAD. Type A aortic dissection subsequent to TBAD occurred in three cases (25%). There were four (33.3%) deaths in the series, all aortic related at a median age of 24 years (range, 19-43 years). CONCLUSIONS: The PRKG1 (p.Arg177Gln) mutation although rare is associated with nonsyndromic TBAD in young and middle-aged patients. Workup for this gene mutation should be included as part of the workup for TBAD etiology in relatively young patients and those with familial history of aortic dissections. Once diagnosed, testing of first-degree family members is warranted. In all individuals with a PRKG1 mutation, close follow-up for aortic root dilatation and hypertension control is essential to reduce the risk of type A or type B aortic dissection, and in cases of TBAD, to decrease the risk of dissection-related aneurysmal degeneration.

Grange syndrome due to homozygous YY1AP1 missense rare variants.

Grange syndrome (OMIM 602531) is an autosomal recessive condition characterized by severe early onset vascular occlusive disease and variable penetrance of brachydactyly, syndactyly, bone fragility, and learning disabilities. Grange syndrome is caused by homozygous or compound heterozygous loss-of-function variants in the YYA1P1 gene. We report on the case of a 53-year old female with novel homozygous missense variants in YYA1P1 (c.1079C>T, p.Pro360Leu), presenting with a history of brachysyndactyly, hypertension, and ischemic stroke. Imaging studies revealed stenosis of the bilateral internal carotid with extensive collateralization of cerebral vessels in a moyamoya-like pattern, along with stenosis in the splenic, common hepatic, celiac, left renal, and superior mesenteric arteries. Functional studies conducted with the patient's dermal fibroblasts suggest that the p.Pro360Leu variant decreases the stability of the YY1AP1 protein. This is the first report of a missense variant associated with Grange syndrome characterized by later onset of vascular disease and a lack of developmental delay and bone fragility.

MAT2A mutations predispose individuals to thoracic aortic aneurysms.

Up to 20% of individuals who have thoracic aortic aneurysms or acute aortic dissections but who do not have syndromic features have a family history of thoracic aortic disease. Significant genetic heterogeneity is established for this familial condition. Whole-genome linkage analysis and exome sequencing of distant relatives from a large family with autosomal-dominant inheritance of thoracic aortic aneurysms variably associated with the bicuspid aortic valve was used for identification of additional genes predisposing individuals to this condition. A rare variant, c.1031A>C (p.Glu344Ala), was identified in MAT2A, which encodes methionine adenosyltransferase II alpha (MAT IIα). This variant segregated with disease in the family, and Sanger sequencing of DNA from affected probands from unrelated families with thoracic aortic disease identified another MAT2A rare variant, c.1067G>A (p.Arg356His). Evidence that these variants predispose individuals to thoracic aortic aneurysms and dissections includes the following: there is a paucity of rare variants in MAT2A in the population; amino acids Glu344 and Arg356 are conserved from humans to zebrafish; and substitutions of these amino acids in MAT Iα are found in individuals with hypermethioninemia. Structural analysis suggested that p.Glu344Ala and p.Arg356His disrupt MAT IIα enzyme function. Knockdown of mat2aa in zebrafish via morpholino oligomers disrupted cardiovascular development. Co-transfected wild-type human MAT2A mRNA rescued defects of zebrafish cardiovascular development at significantly higher levels than mRNA edited to express either the Glu344 or Arg356 mutants, providing further evidence that the p.Glu344Ala and p.Arg356His substitutions impair MAT IIα function. The data presented here support the conclusion that rare genetic variants in MAT2A predispose individuals to thoracic aortic disease.

LOX Mutations Predispose to Thoracic Aortic Aneurysms and Dissections.

RATIONALE: Mutations in several genes have been identified that are responsible for 25% of families with familial thoracic aortic aneurysms and dissections. However, the causative gene remains unknown in 75% of families. OBJECTIVES: To identify the causative mutation in families with autosomal dominant inheritance of thoracic aortic aneurysms and dissections. METHODS AND RESULTS: Exome sequencing was used to identify the mutation responsible for a large family with thoracic aortic aneurysms and dissections. A heterozygous rare variant, c.839G>T (p.Ser280Arg), was identified in LOX, encoding a lysyl oxidase, that segregated with disease in the family. Sanger and exome sequencing was used to investigate mutations in LOX in an additional 410 probands from unrelated families. Additional LOX rare variants that segregated with disease in families were identified, including c.125G>A (p.Trp42*), c.604G>T (p.Gly202*), c.743C>T (p.Thr248Ile), c.800A>C (p.Gln267Pro), and c.1044T>A (p.Ser348Arg). The altered amino acids cause haploinsufficiency for LOX or are located at a highly conserved LOX catalytic domain, which is relatively invariant in the population. Expression of the LOX variants p.Ser280Arg and p.Ser348Arg resulted in significantly lower lysyl oxidase activity when compared with the wild-type protein. Individuals with LOX variants had fusiform enlargement of the root and ascending thoracic aorta, leading to ascending aortic dissections. CONCLUSIONS: These data, along with previous studies showing that the deficiency of LOX in mice or inhibition of lysyl oxidases in turkeys and rats causes aortic dissections, support the conclusion that rare genetic variants in LOX predispose to thoracic aortic disease.

Altered Smooth Muscle Cell Force Generation as a Driver of Thoracic Aortic Aneurysms and Dissections.

The importance of maintaining contractile function in aortic smooth muscle cells (SMCs) is evident by the fact that heterozygous mutations in the major structural proteins or kinases controlling contraction lead to the formation of aneurysms of the ascending thoracic aorta that predispose to life-threatening aortic dissections. Force generation by SMC requires ATP-dependent cyclic interactions between filaments composed of SMC-specific isoforms of α-actin (encoded by ACTA2) and myosin heavy chain (MYH11). ACTA2 and MYH11 mutations are predicted or have been shown to disrupt this cyclic interaction predispose to thoracic aortic disease. Movement of the myosin motor domain is controlled by phosphorylation of the regulatory light chain on the myosin filament, and loss-of-function mutations in the dedicated kinase for this phosphorylation, myosin light chain kinase (MYLK) also predispose to thoracic aortic disease. Finally, a mutation in the cGMP-activated protein kinase (PRKG1) results in constitutive activation of the kinase in the absence of cGMP, thus driving SMC relaxation in part through increased dephosphorylation of the regulatory light chain and predisposes to thoracic aortic disease. Furthermore, SMCs cannot generate force without connections to the extracellular matrix through focal adhesions, and mutations in the major protein in the extracellular matrix, fibrillin-1, linking SMCs to the matrix also cause thoracic aortic disease in individuals with Marfan syndrome. Thus, disruption of the ability of the aortic SMC to generate force through the elastin-contractile units in response to pulsatile blood flow may be a primary driver for thoracic aortic aneurysms and dissections.

MFAP5 loss-of-function mutations underscore the involvement of matrix alteration in the pathogenesis of familial thoracic aortic aneurysms and dissections.

Thoracic aortic aneurysm and dissection (TAAD) is an autosomal-dominant disorder with major life-threatening complications. The disease displays great genetic heterogeneity with some forms allelic to Marfan and Loeys-Dietz syndrome, and an important number of cases still remain unexplained at the molecular level. Through whole-exome sequencing of affected members in a large TAAD-affected family, we identified the c.472C>T (p.Arg158(∗)) nonsense mutation in MFAP5 encoding the extracellular matrix component MAGP-2. This protein interacts with elastin fibers and the microfibrillar network. Mutation screening of 403 additional probands identified an additional missense mutation of MFAP5 (c.62G>T [p.Trp21Leu]) segregating with the disease in a second family. Functional analyses performed on both affected individual's cells and in vitro models showed that these two mutations caused pure or partial haploinsufficiency. Thus, alteration of MAGP-2, a component of microfibrils and elastic fibers, appears as an initiating mechanism of inherited TAAD.

Recurrent gain-of-function mutation in PRKG1 causes thoracic aortic aneurysms and acute aortic dissections.

Gene mutations that lead to decreased contraction of vascular smooth-muscle cells (SMCs) can cause inherited thoracic aortic aneurysms and dissections. Exome sequencing of distant relatives affected by thoracic aortic disease and subsequent Sanger sequencing of additional probands with familial thoracic aortic disease identified the same rare variant, PRKG1 c.530G>A (p.Arg177Gln), in four families. This mutation segregated with aortic disease in these families with a combined two-point LOD score of 7.88. The majority of affected individuals presented with acute aortic dissections (63%) at relatively young ages (mean 31 years, range 17-51 years). PRKG1 encodes type I cGMP-dependent protein kinase (PKG-1), which is activated upon binding of cGMP and controls SMC relaxation. Although the p.Arg177Gln alteration disrupts binding to the high-affinity cGMP binding site within the regulatory domain, the altered PKG-1 is constitutively active even in the absence of cGMP. The increased PKG-1 activity leads to decreased phosphorylation of the myosin regulatory light chain in fibroblasts and is predicted to cause decreased contraction of vascular SMCs. Thus, identification of a gain-of-function mutation in PRKG1 as a cause of thoracic aortic disease provides further evidence that proper SMC contractile function is critical for maintaining the integrity of the thoracic aorta throughout a lifetime.

SMAD2 Mutations Are Associated with Arterial Aneurysms and Dissections.

We report three families with arterial aneurysms and dissections in which variants predicted to be pathogenic were identified in SMAD2. Moreover, one variant occurred de novo in a proband with unaffected parents. SMAD2 is a strong candidate gene for arterial aneurysms and dissections given its role in the TGF-ß signaling pathway. Furthermore, although SMAD2 and SMAD3 probably have functionally distinct roles in cell signaling, they are structurally very similar. Our findings indicate that SMAD2 mutations are associated with arterial aneurysms and dissections and are in accordance with the observation that patients with pathogenic variants in genes encoding proteins involved in the TGF-ß signaling pathway exhibit arterial aneurysms and dissections as key features.

Acute aortic dissections with pregnancy in women with ACTA2 mutations.

Mutations in ACTA2 predispose to thoracic aortic aneurysms and dissection as well as coronary artery and cerebrovascular disease. Here we examined the risk of aortic dissections, stroke and myocardial infarct with pregnancy in women with ACTA2 mutations. Of the 53 women who had a total of 137 pregnancies, eight had aortic dissections in the third trimester or the postpartum period (6% of pregnancies). One woman also had a myocardial infarct that occurred during pregnancy that was independent of her aortic dissection. Compared to the population-based frequency of peripartum aortic dissections of 0.6%, the rate of peripartum aortic dissections in women with ACTA2 mutations is much higher (8 out of 39; 20%). Six of these dissections initiated in the ascending aorta (Stanford type A), three were fatal. Three women had ascending aortic dissections at diameters less that 5.0 cm (range 3.8-4.7 cm). Aortic pathology showed mild to moderate medial degeneration of the aorta in three women. Of note, five of the women had hypertension either during or before the pregnancy. In summary, the majority of women with ACTA2 mutations did not have aortic or other vascular complications with pregnancy. However, these findings show that pregnancy is associated with significant risk for aortic dissection in women with ACTA2 mutations. Women with ACTA2 mutations who are planning to get pregnant should be counseled about this risk of aortic dissection, and proper clinical management should be initiated to reduce this risk.

Interleukin-6-signal transducer and activator of transcription-3 signaling mediates aortic dissections induced by angiotensin II via the T-helper lymphocyte 17-interleukin 17 axis in C57BL/6 mice.

OBJECTIVE: Dysregulated angiotensin II (Ang II) signaling induces local vascular interleukin-6 (IL-6) secretion, producing leukocyte infiltration and life-threatening aortic dissections. Precise mechanisms by which IL-6 signaling induces leukocyte recruitment remain unknown. T-helper 17 lymphocytes (Th17) have been implicated in vascular pathology, but their role in the development of aortic dissections is poorly understood. Here, we tested the relationship of IL-6-signal transducer and activator of transcription-3 signaling with Th17-induced inflammation in the formation of Ang II-induced dissections in C57BL/6 mice. APPROACH AND RESULTS: Ang II infusion induced aortic dissections and CD4(+)-interleukin 17A (IL-17A)-expressing Th17 cell accumulation in C57BL/6 mice. A blunted local Th17 activation, macrophage recruitment, and reduced incidence of aortic dissections were seen in IL-6(-/-) mice. To determine the pathological roles of Th17 lymphocytes, we treated Ang II-infused mice with IL-17A-neutralizing antibody or infused Ang II in genetically deficient IL-17A mice and found decreased aortic chemokine monocytic chemotactic protein-1 production and macrophage recruitment, leading to a reduction in aortic dissections. This effect was independent of blood pressure in IL-17A-neutralizing antibody experiment. Application of a cell-permeable signal transducer and activator of transcription-3 inhibitor to downregulate the IL-6 pathway decreased aortic dilation and Th17 cell recruitment. We also observed increased aortic Th17 infiltration and IL-17 mRNA expression in patients with thoracic aortic dissections. Finally, we found that Ang II-mediated aortic dissections occurred independent of blood pressure changes. CONCLUSIONS: Our results indicate that the IL-6-signal transducer and activator of transcription-3 signaling pathway converges on Th17 recruitment and IL-17A signaling upstream of macrophage recruitment, mediating aortic dissections.

Recurrent chromosome 16p13.1 duplications are a risk factor for aortic dissections.

Chromosomal deletions or reciprocal duplications of the 16p13.1 region have been implicated in a variety of neuropsychiatric disorders such as autism, schizophrenia, epilepsies, and attention-deficit hyperactivity disorder (ADHD). In this study, we investigated the association of recurrent genomic copy number variants (CNVs) with thoracic aortic aneurysms and dissections (TAAD). By using SNP arrays to screen and comparative genomic hybridization microarrays to validate, we identified 16p13.1 duplications in 8 out of 765 patients of European descent with adult-onset TAAD compared with 4 of 4,569 controls matched for ethnicity (P = 5.0 × 10⁻5, OR = 12.2). The findings were replicated in an independent cohort of 467 patients of European descent with TAAD (P = 0.005, OR = 14.7). Patients with 16p13.1 duplications were more likely to harbor a second rare CNV (P = 0.012) and to present with aortic dissections (P = 0.010) than patients without duplications. Duplications of 16p13.1 were identified in 2 of 130 patients with familial TAAD, but the duplications did not segregate with TAAD in the families. MYH11, a gene known to predispose to TAAD, lies in the duplicated region of 16p13.1, and increased MYH11 expression was found in aortic tissues from TAAD patients with 16p13.1 duplications compared with control aortas. These data suggest chromosome 16p13.1 duplications confer a risk for TAAD in addition to the established risk for neuropsychiatric disorders. It also indicates that recurrent CNVs may predispose to disorders involving more than one organ system, an observation critical to the understanding of the role of recurrent CNVs in human disease and a finding that may be common to other recurrent CNVs involving multiple genes.

Mutations in myosin light chain kinase cause familial aortic dissections.

Mutations in smooth muscle cell (SMC)-specific isoforms of α-actin and ß-myosin heavy chain, two major components of the SMC contractile unit, cause familial thoracic aortic aneurysms leading to acute aortic dissections (FTAAD). To investigate whether mutations in the kinase that controls SMC contractile function (myosin light chain kinase [MYLK]) cause FTAAD, we sequenced MYLK by using DNA from 193 affected probands from unrelated FTAAD families. One nonsense and four missense variants were identified in MYLK and were not present in matched controls. Two variants, p.R1480X (c.4438C>T) and p.S1759P (c.5275T>C), segregated with aortic dissections in two families with a maximum LOD score of 2.1, providing evidence of linkage of these rare variants to the disease (p = 0.0009). Both families demonstrated a similar phenotype characterized by presentation with an acute aortic dissection with little to no enlargement of the aorta. The p.R1480X mutation leads to a truncated protein lacking the kinase and calmodulin binding domains, and p.S1759P alters amino acids in the α-helix of the calmodulin binding sequence, which disrupts kinase binding to calmodulin and reduces kinase activity in vitro. Furthermore, mice with SMC-specific knockdown of Mylk demonstrate altered gene expression and pathology consistent with medial degeneration of the aorta. Thus, genetic and functional studies support the conclusion that heterozygous loss-of-function mutations in MYLK are associated with aortic dissections.