Advances in genomics have allowed unbiased genetic studies of human disease with unexpected insights into the molecular mechanisms of cellular immunity and autoimmunity1. We performed whole exome sequencing (WES) and targeted sequencing in patients with an apparent Mendelian syndrome of autoimmune disease characterized by high-titer autoantibodies, inflammatory arthritis and interstitial lung disease (ILD). In five families, we identified four unique deleterious variants in the Coatomer subunit alpha (COPA) gene all located within the same functional domain. We hypothesized that mutant COPA leads to a defect in intracellular transport mediated by coat protein complex I (COPI)2–4. We show that COPA variants impair binding of proteins targeted for retrograde Golgi to ER transport and demonstrate that expression of mutant COPA leads to ER stress and the upregulation of Th17 priming cytokines. Consistent with this pattern of cytokine expression, patients demonstrated a significant skewing of CD4+ T cells toward a T helper 17 (Th17) phenotype, an effector T cell population implicated in autoimmunity5,6. Our findings uncover an unexpected molecular link between a vesicular transport protein and a syndrome of autoimmunity manifested by lung and joint disease. These findings provide a unique opportunity to understand how alterations in cellular homeostasis caused by a defect in the intracellular trafficking pathway leads to the generation of human autoimmune disease.

A predisposition for thoracic aortic aneurysms leading to acute aortic dissections can be inherited in families in an autosomal dominant manner. Genome-wide linkage analysis of two large unrelated families with thoracic aortic disease, followed by whole exome sequencing of affected relatives, identified causative mutations in TGFB2. These mutations, a frameshift mutation in exon 6 and a nonsense mutation in exon 4, segregated with disease with a combined LOD score of 7.7. Sanger sequencing of 276 probands from families with inherited thoracic aortic disease identified two additional TGFB2 mutations. TGFB2 encodes the transforming growth factor beta-2 (TGF-β2) and the mutations are predicted to cause haploinsufficiency for TGFB2, but aortic tissue from cases paradoxically shows increased TGF-β2 expression and immunostaining. Thus, haploinsufficiency of TGFB2 predisposes to thoracic aortic disease, suggesting the initial pathway driving disease is decreased cellular TGF-β2 levels leading to a secondary increase in TGF-β2 production in the diseased aorta.

Rationale Thoracic aortic aneurysms leading to acute aortic dissections (TAAD) can be inherited in families in an autosomal dominant manner. As part of the spectrum of clinical heterogeneity of familial TAAD, we recently described families with multiple members that had TAAD and intracranial aneurysms or TAAD and intracranial and abdominal aortic aneurysms inherited in an autosomal dominant manner. Objective To identify the causative mutation in a large family with autosomal dominant inheritance of TAAD with intracranial and abdominal aortic aneurysms by performing exome sequencing of two distantly related individuals with TAAD and identifying shared rare variants. Methods and Results A novel frame shift mutation, p. N218fs (c.652delA), was identified in the SMAD3 gene and segregated with the vascular diseases in this family with a LOD score of 2.52. Sequencing of 181 probands with familial TAAD identified three additional SMAD3 mutations in 4 families, p.R279K (c.836G>A), p.E239K (c.715G>A), and p.A112V (c.235C>T) resulting in a combined LOD score of 5.21. These four mutations were notably absent in 2300 control exomes. SMAD3 mutations were recently described in patients with Aneurysms Osteoarthritis Syndrome and some of the features of this syndrome were identified in individuals in our cohort, but these features were notably absent in many SMAD3 mutation carriers. Conclusions SMAD3 mutations are responsible for 2% of familial TAAD. Mutations are found in families with TAAD alone, along with families with TAAD, intracranial aneurysms, aortic and bilateral iliac aneurysms segregating in an autosomal dominant manner.

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.