Shared genetic architecture of hernias: A genome-wide association study with multivariable meta-analysis of multiple hernia phenotypes.

Abdominal hernias are common and characterised by the abnormal protrusion of a viscus through the wall of the abdominal cavity. The global incidence is 18.5 million annually and there are limited non-surgical treatments. To improve understanding of common hernia aetiopathology, we performed a six-stage genome-wide association study (GWAS) of 62,637 UK Biobank participants with either single or multiple hernia phenotypes including inguinal, femoral, umbilical and hiatus hernia. Additionally, we performed multivariable meta-analysis with metaUSAT, to allow integration of summary data across traits to generate combined effect estimates. On individual hernia analysis, we identified 3404 variants across 38 genome-wide significant (p < 5×10-8) loci of which 11 are previously unreported. Robust evidence for five shared susceptibility loci was discovered: ZC3H11B, EFEMP1, MHC region, WT1 and CALD1. Combined hernia phenotype analyses with additional multivariable meta-analysis of summary statistics in metaUSAT revealed 28 independent (seven previously unreported) shared susceptibility loci. These clustered in functional categories related to connective tissue and elastic fibre homeostasis. Weighted genetic risk scores also correlated with disease severity suggesting a phenotypic-genotypic severity correlation, an important finding to inform future personalised therapeutic approaches to hernia.

Biological findings from the PheWAS catalog: focus on connective tissue-related disorders (pelvic floor dysfunction, abdominal hernia, varicose veins and hemorrhoids).

Pelvic floor dysfunction, specifically genital prolapse (GP) and stress urinary inconsistency (SUI) presumably co-occur with other connective tissue disorders such as hernia, hemorrhoids, and varicose veins. Observations on non-random coexistence of these disorders have never been summarized in a meta-analysis. The performed meta-analysis demonstrated that varicose veins and hernia are associated with GP. Disease connections on the molecular level may be partially based on shared genetic susceptibility. A unique opportunity to estimate shared genetic susceptibility to disorders is provided by a PheWAS (phenome-wide association study) designed to utilize GWAS data concurrently to many phenotypes. We searched the PheWAS Catalog, which includes the results of the PheWAS study with P value < 0.05, for genes associated with GP, SUI, abdominal hernia, varicose veins and hemorrhoids. We found pronounced signals for the associations of the SLC2A9 gene with SUI (P = 6.0e-05) and the MYH9 gene with varicose veins of lower extremity (P = 0.0001) and hemorrhoids (P = 0.0007). The comparison of the PheWAS Catalog and the NHGRI Catalog data revealed enrichment of genes associated with bone mineral density in GP and with activated partial thromboplastin time in varicose veins of lower extremity. In cross-phenotype associations, genes responsible for peripheral nerve functions seem to predominate. This study not only established novel biologically plausible associations that may warrant further studies but also exemplified an effective use of the PheWAS Catalog data.

Dermatan sulfate epimerase 1 deficient mice as a model for human abdominal wall defects.

BACKGROUND: Dermatan sulfate (DS) is a highly sulfated polysaccharide with a variety of biological functions in extracellular matrix organization and processes such as tumorigenesis and wound healing. A distinct feature of DS is the presence of iduronic acid, produced by the two enzymes, DS-epimerase 1 and 2, which are encoded by Dse and Dsel, respectively. METHODS: We have previously shown that Dse knockout (KO) mice in a mixed C57BL/6-129/SvJ background have an altered collagen matrix structure in skin. In the current work we studied Dse KO mice in a pure NFR genetic background. RESULTS: Dse KO embryos and newborns had kinked tails and histological staining revealed significantly thicker epidermal layers in Dse KO mice when compared with heterozygote (Het) or wild-type (WT) littermates. Immunochemical analysis of the epidermal layers in newborn pups showed increased expression of keratin 5 in the basal layer and keratin 1 in the spinous layer. In addition, we observed an abdominal wall defect with herniated intestines in 16% of the Dse KO embryos. Other, less frequent, developmental defects were exencephaly and spina bifida. CONCLUSION: We conclude that the combination of defective collagen structure in the dermis and imbalanced keratinocyte maturation could be responsible for the observed developmental defects in Dse KO mice. In addition, we propose that Dse KO mice could be used as a model in pathogenetic studies of human fetal abdominal wall defects.

Shared and nonshared familial susceptibility to surgically treated inguinal hernia, femoral hernia, incisional hernia, epigastric hernia, and umbilical hernia.

BACKGROUND: The familial risk of abdominal wall hernia (AWH) is largely unknown. In addition, it is unknown whether inguinal hernia (IH), femoral hernia (FH), incisional hernia (INH), epigastric hernia (EH), and umbilical hernia (UH) share familial susceptibility. The aim of this nationwide study was to determine the familial risks of concordant AWH (same disease in proband and exposed relative) and discordant AWH (different disease in proband and exposed relative). STUDY DESIGN: Data from the Swedish Multigeneration Register on individuals aged 0 to 78 years were linked to the Swedish hospital discharge register and the Swedish outpatient register for the period from 1964 to 2010. Standardized incidence ratios (SIRs) and 95% CIs for surgically treated IH (n = 209,814 cases), FH (n = 4,576), INH (n = 19,494), EH (n = 8,257), and UH (n = 22,761) were calculated for siblings of individuals with hernia compared with the siblings of unaffected individuals. The procedure was repeated for spouses. RESULTS: All concordant and most discordant familial sibling risks were increased. Familial concordant SIRs for siblings were IH = 1.97 (95% CI, 1.94-1.99), FH = 3.40 (95% CI, 2.44-4.62), INH = 2.24 (95% CI, 2.04-2.46), EH = 5.57 (95% CI, 4.64-6.64), and UH = 3.61 (95% CI, 3.33-3.91). Concordant familial risks were higher than discordant risks. For example, when the proband sibling had IH, the discordant SIRs were FH = 1.74 (95% CI, 1.61-1.88), INH = 1.22 (95% CI, 1.16-1.28), EH = 1.30 (95% CI, 1.20-1.40), and UH = 1.35 (95% CI, 1.29-1.41). Concordant SIRs for spouses were lower: IH = 1.23 (95% CI, 1.20-1.26), FH = 0.97 (95% CI, 0.64-1.36), INH = 1.56 (95% CI, 1.41-1.71), EH = 1.70 (95% CI, 1.09-2.45), and UH = 1.31 (95% CI, 1.09-1.56). CONCLUSIONS: Family history of surgically treated AWH is an important risk factor for surgical treatment of AWH. The 5 forms of AWH studied share familial susceptibility, but site-specific familial factors might exist. Several spouse risks were increased, suggesting the possibility of a nongenetic contribution to familial risks.

Abdominal aortic aneurysm and abdominal wall hernia as manifestations of a connective tissue disorder.

BACKGROUND: Abdominal aortic aneurysms (AAAs) and abdominal wall hernias represent chronic degenerative conditions. Both aortic aneurysms and inguinal hernias share common epidemiologic features, and several investigators have found an increased propensity for hernia development in patients treated for aortic aneurysms. Chronic inflammation and dysregulation in connective tissue metabolism constitute underlying biological processes, whereas genetic influences appear to be independently associated with both disease states. A literature review was conducted to identify all published evidence correlating aneurysms and hernias to a common pathology. METHODS: PubMed/Medline was searched for studies investigating the clinical, biochemical, and genetic associations of AAAs and abdominal wall hernias. The literature was searched using the MeSH terms "aortic aneurysm, abdominal," "hernia, inguinal," "hernia, ventral," "collagen," "connective tissue," "matrix metalloproteinases," and "genetics" in all possible combinations. An evaluation, analysis, and critical overview of current clinical data and pathogenic mechanisms suggesting an association between aneurysms and hernias were undertaken. RESULTS: Ample evidence lending support to the clinical correlation between AAAs and abdominal wall hernias exists. Pooled analysis demonstrated that patients undergoing aortic aneurysm repair through a midline abdominal incision have a 2.9-fold increased risk of developing a postoperative incisional hernia compared with patients treated for aortoiliac occlusive disease (odds ratio, 2.86; 95% confidence interval, 1.97-4.16; P < .00001), whereas the risk of inguinal hernia was 2.3 (odds ratio, 2.30; 95% confidence interval, 1.52-3.48; P < .0001). Emerging evidence has identified inguinal hernia as an independent risk factor for aneurysm development. Although mechanisms of extracellular matrix remodeling and the imbalance between connective tissue degrading enzymes and their inhibitors instigating inflammatory responses have separately been described for both disease states, comparative studies investigating these biological processes in aneurysm and hernia populations are scarce. A genetic predisposition has been documented in familial and observational segregation studies; however, the pertinent literature lacks sufficient supporting evidence for a common genetic basis for aneurysm and hernia. CONCLUSIONS: Insufficient data are currently available to support a systemic connective tissue defect affecting the structural integrity of the aortic and abdominal wall. Future investigations may elucidate obscure aspects of aneurysm and hernia pathophysiology and create novel targets for pharmaceutical and gene strategies for disease prevention and treatment.

Epigenetic effect of cadmium on global de novo DNA hypomethylation in the cadmium-induced ventral body wall defect (VBWD) in the chick model.

Administration of the heavy metal cadmium (Cd) induces ventral body wall defects (VBWD) in the chick embryo. In this model, the expression of most genes involved in body wall formation is altered 4h-posttreatment. However, the mechanism by which Cd results in the initiation of altered gene expression remains unclear. Epigenetic mechanisms can change genome function under exogenous influences. Moreover, Cd is one of the environmental factors that can affect epigenomic programming. De novo DNA methylation is essential for normal embryogenesis and is regulated by the DNA methyltransferases (DNMT)3A and DNMT3B. The objective of this study was to investigate the hypothesis that gene expression levels of DNMT3A/3B were altered, resulting in global DNA methylation changes during the critical period of embryogenesis in the Cd chick model. After 60-h incubation, chick embryos (n = 48) were harvested at 1, 4, and 8 h after treatment with saline or Cd, and divided into controls and Cd groups. Quantitative reverse transcription PCR was performed to evaluate the gene expression levels of DNMT3A/3B in the chick embryos and was statistically analyzed using Student's t-test. Immunohistochemistry was performed using a monoclonal antibody against 5-methylcytidine (5'MeC), which labels methyl-rich regions within the nucleus. DNMT3A/3B gene expression levels at 4 h were significantly downregulated in the Cd group compared with controls (p < 0.005/p < 0.00001, respectively). Immunoreactivity of 5'MeC was markedly diminished in the Cd group at 4 h. Our findings demonstrates for the first time that Cd impacts on the expression levels of DNMT3A/3B, which may underlie the pathogenesis of VBWD in the Cd chick model.

Expression in SPARC-null mice of collagen type I lacking the globular domain of the α1(I) N-propeptide results in abdominal hernias and loss of dermal collagen.

The sequence encoding the N-propeptide of collagen I is characterized by significant conservation of amino acids across species; however, the function of the N-propeptide remains poorly defined. Studies in vitro have suggested that one activity of this propeptide might be to act as a feedback inhibitor of collagen I synthesis. To determine whether the N-propeptide contributed to decreased collagen content in SPARC-null mice, mice carrying a deletion of exon 2, which encodes the globular domain of the N-propeptide of collagen I, were crossed to SPARC-null animals. Mice lacking SPARC and expressing collagen I without the globular domain of the N-propeptide were viable and fertile. However, a significant number of animals developed abdominal hernias within the first 2 months of life with an approximate 20% penetrance (~35% of males). The dermis of SPARC-null/exon 2-deleted mice was thinner and contained fewer large collagen fibers in comparison with wild-type or in either single transgenic animal. The average collagen fibril diameter of exon 2-deleted mice did not significantly differ from wild-type mice (WT: 87.9 nm versus exon 2-deleted: 88.2 nm), whereas SPARC-null/exon 2-deleted fibrils were smaller than that of SPARC-null dermis (SPARC-null: 60.2 nm, SPARC-null/exon 2-deleted: 40.8 nm). As measured by hydroxyproline analysis, double transgenic skin biopsies contained significantly less collagen than those of wild-type, those of exon 2-deleted, and those of SPARC-null biopsies. Acetic acid extraction of collagen from skin biopsies revealed an increase in the proportion of soluble collagen in the SPARC-null/exon 2-deleted mice. These results support a function of the N-propeptide of collagen I in facilitating incorporation and stabilization of collagen I into the insoluble ECM and argue against a primary function of the N-propeptide as a negative regulator of collagen synthesis.

Total RNA-isolation of abdominal hernia of rats for quantitative real-time reverse transcription (RT) PCR assays.

Increasing complications in incisional hernia surgery call for novel treatments. A gene expression analysis of injured tissues displays important parameters for tissue regeneration. Until today, no reliable method has been described for a quantitative gene expression analysis of hernia tissues. In this work, a protocol is described for the isolation of DNA-free total RNA of incisional hernias for the first time. Moreover, real-time RT PCR assays for collagen type I and III and TGF-beta1 are demonstrated for relative gene expression analyses. Both methods enable relative gene expression analyses of hernia tissues for the first time.

Posterior polymorphous corneal dystrophy is associated with TCF8 gene mutations and abdominal hernia.

Mutations in the two-handed zinc-finger homeodomain transcription factor gene (TCF8) have been associated with posterior polymorphous corneal dystrophy (PPCD) and extraocular developmental abnormalities. We performed screening of TCF8 in 32 affected, unrelated probands, affected and unaffected family members of probands identified with a TCF8 mutation, and in 100 control individuals. Eight different pathogenic mutations were identified in eight probands: four frameshift (c.953_954insA, c.1506dupA, c.1592delA, and c.3012_3013delAG); three nonsense (Gln12X, Gln214X, Arg325X); and one missense (Met1Arg). Screening of TCF8 in affected and unaffected family members in six families demonstrated that each identified mutation segregated with the disease phenotype in each family; two probands did not have additional family members available for analysis. None of the eight TCF8 mutations was identified in 200 control chromosomes. The prevalence of hernias of the abdominal region in affected individuals with PPCD associated with TCF8 mutations was significantly higher than the prevalence in both individuals with PPCD not associated with a TCF8 mutation and in unaffected individuals. Therefore, PPCD is associated with TCF8 mutations in one quarter of affected families in this study, or about one third of all PPCD families that have been screened thus far. In these families, the presence of apparently causative TCF8 mutations is associated with abdominal and inguinal hernias.

Ventral abdominal wall dysmorphogenesis of Msx1/Msx2 double-mutant mice.

Msx1 and Msx2 genes encode the homeodomain transcription factors. Several gene knockout mice and expression studies suggest that they possess functionally redundant roles in embryogenesis. In this study, we revealed that Msx1 and Msx2 were expressed during ventral body wall formation in an overlapping manner. Msx1/Msx2 double-mutant mice displayed embryonic abdominal wall defects with disorganized muscle layers and connective tissues. These findings indicate that Msx1 and Msx2 play roles in concert during embryonic ventral abdominal wall formation.