Evidence for association between the HLA-DQA locus and abdominal aortic aneurysms in the Belgian population: a case control study

BACKGROUND

Chronic inflammation and autoimmunity likely contribute to the pathogenesis of abdominal aortic aneurysms (AAAs). The aim of this study was to investigate the role of autoimmunity in the etiology of AAAs using a genetic association study approach with HLA polymorphisms.

METHODS

HLA-DQA1, -DQB1, -DRB1 and -DRB3-5 alleles were determined in 387 AAA cases (180 Belgian and 207 Canadian) and 426 controls (269 Belgian and 157 Canadian) by a PCR and single-strand oligonucleotide probe hybridization assay.

RESULTS

We observed a potential association with the HLA-DQA1 locus among Belgian males (empirical p = 0.027, asymptotic p = 0.071). Specifically, there was a significant difference in the HLA-DQA1*0102 allele frequencies between AAA cases (67/322 alleles, 20.8%) and controls (44/356 alleles, 12.4%) in Belgian males (empirical p = 0.019, asymptotic p = 0.003). In haplotype analyses, marginally significant association was found between AAA and haplotype HLA-DQA1-DRB1 (p = 0.049 with global score statistics and p = 0.002 with haplotype-specific score statistics).

CONCLUSION

This study showed potential evidence that the HLA-DQA1 locus harbors a genetic risk factor for AAAs suggesting that autoimmunity plays a role in the pathogenesis of AAAs.

The lifetime prevalence of abdominal aortic aneurysms among siblings of aneurysm patients is eightfold higher than among siblings of spouses: an analysis of 187 aneurysm families in Nova Scotia, Canada

BACKGROUND

Abdominal aortic aneurysms (AAAs) are frequently familial. The aim of this study was to compare the prevalence of AAA among the siblings of AAA patients with that in the spouses' siblings.

METHODS

The siblings of 375 AAA patients and the siblings of the spouses of the AAA patients were included in this study and offered ultrasonography screening for AAA. Participants were asked to complete a questionnaire to collect demographic and general health information. Statistical analysis was done with Fisher's exact test. Odds ratios and 95% confidence intervals were also calculated.

RESULTS

Abdominal ultrasonography examinations were done for 309 individuals. The results indicated that 11 (11.2%) of 98 brothers of AAA patients, 4 (2.7%) of 147 sisters, and none of the 64 siblings of the spouses of the AAA patients were found to have an AAA. Combining the information from the ultrasonography screening and medical records on already known cases of AAA in these families, altogether 29.0% (44/152) of the brothers of AAA patients, 11.1% (20/181) of the sisters of AAA patients, and 2.3% (2/88) of the siblings of the spouses had an AAA.

CONCLUSION

There was a significant difference between the siblings of the AAA patients and those of the spouses both in the frequency of AAA detected by ultrasonography screening and in the overall prevalence of AAA. The overall prevalence of AAA in the siblings of AAA patients was about eight times that observed among the siblings of their spouses (19.2% vs 2.3%). These findings confirmed previous reports on high prevalence of AAA among siblings of AAA patients and emphasized the importance of an ultrasonography screening program for siblings of AAA patients.

Genetic analysis of polymorphisms in biologically relevant candidate genes in patients with abdominal aortic aneurysms

BACKGROUND

Abdominal aortic aneurysms (AAAs) are characterized by histologic signs of chronic inflammation, destructive remodeling of extracellular matrix, and depletion of vascular smooth muscle cells. We investigated the process of extracellular matrix remodeling by performing a genetic association study with polymorphisms in the genes for matrix metalloproteinases (MMPs), tissue inhibitors of metalloproteinases (TIMPs), and structural extracellular matrix molecules in AAA. Our hypothesis was that genetic variations in one or more of these genes contribute to greater or lesser activity of these gene products, and thereby contribute to susceptibility for developing AAAs.

METHODS

DNA samples from 812 unrelated white subject (AAA, n = 387; controls, n = 425) were genotyped for 14 polymorphisms in 13 different candidate genes: MMP1(nt-1607), MMP2(nt-955), MMP3(nt-1612), MMP9(nt-1562), MMP10(nt+180), MMP12(nt-82), MMP13(nt-77), TIMP1(nt+434), TIMP1(rs2070584), TIMP2(rs2009196), TIMP3(nt-1296), TGFB1(nt-509), ELN(nt+422), and COL3A1(nt+581). Odds ratios and P values adjusted for gender and country of origin using logistic regression and stratified by family history of AAA were calculated to test for association between genotype and disease status. Haplotype analysis was carried out for the two TIMP1 polymorphisms in male subjects.

RESULTS

Analyses with one polymorphism per test without interactions showed an association with the two TIMP1 gene polymorphisms (nt+434, P = .0047; rs2070584, P = .015) in male subjects without a family history of AAA. The association remained significant when analyzing TIMP1 haplotypes (chi 2 P = .014 and empirical P = .009). In addition, we found a significant interaction between the polymorphism and gender for MMP10 ( P = .037) in cases without a family history of AAA, as well as between the polymorphism and country of origin for ELN ( P = .0169) and TIMP3 ( P = .0023) in cases with a family history of AAA.

CONCLUSIONS

These findings suggest that genetic variations in TIMP1, TIMP3, MMP10, and ELN genes may contribute to the pathogenesis of AAAs. Further work is needed to confirm the findings in an independent set of samples and to study the functional role of these variants in AAA. It is noteworthy that contrary to a previous study, we did not find an association between the MMP9 (nt-1562) polymorphism and AAA, suggesting genetic heterogeneity of the disease.

CLINICAL RELEVANCE

Abdominal aortic aneurysms (AAAs) are an important cardiovascular disease, but the genetic and environmental risk factors, which contribute to individual's risk to develop an aneurysm, are poorly understood. Histologically, AAAs are characterized by signs of chronic inflammation, destructive remodeling of the extracellular matrix, and depletion of vascular smooth muscle cells. We hypothesized that genes involved in these events could harbor changes that make individuals more susceptible to developing aneurysms. This study identified significant genetic associations between DNA sequence changes in tissue inhibitor of metalloproteinase 1 (TIMP1), TIMP3, matrix metalloproteinase 10 (MMP10) and elastin (ELN) genes, and AAA. The results will require confirmation using an independent set of samples. After replication it is possible that these sequence changes in combination with other risk factors could be used in the future to identify individuals who are at increased risk for developing an AAA.

Genome scan for familial abdominal aortic aneurysm using sex and family history as covariates suggests genetic heterogeneity and identifies linkage to chromosome 19q13

BACKGROUND

Abdominal aortic aneurysm (AAA) is a relatively common disease, with 1% to 2% of the population harboring aneurysms. Genetic risk factors are likely to contribute to the development of AAAs, although no such risk factors have been identified.

METHODS AND RESULTS

We performed a whole-genome scan of AAA using affected-relative-pair (ARP) linkage analysis that includes covariates to allow for genetic heterogeneity. We found strong evidence of linkage (logarithm of odds [LOD] score=4.64) to a region near marker D19S433 at 51.88 centimorgans (cM) on chromosome 19 with 36 families (75 ARPs) when including sex and the number of affected first-degree relatives of the proband (N(aff)) as covariates. We then genotyped 83 additional families for the same markers and typed additional markers for all families and obtained a LOD score of 4.75 (P=0.00014) with sex, N(aff), and their interaction as covariates near marker D19S416 (58.69 cM). We also identified a region on chromosome 4 with a LOD score of 3.73 (P=0.0012) near marker D4S1644 using the same covariate model as for chromosome 19.

CONCLUSIONS

Our results provide evidence for genetic heterogeneity and the presence of susceptibility loci for AAA on chromosomes 19q13 and 4q31.

Heparin-induced thrombosis treated with ancrod

Heparin used in the treatment of thromboembolic disease may produce an immune response in the patient, leading to thrombocytopenia and even thrombosis. These complications may arise at any time after the institution of heparin therapy. The authors report a case of heparin-induced thrombocytopenia with thrombosis in a 70-year-old woman. The complication was treated successfully with thrombectomy and the administration of warfarin and ancrod, which is a natural fibrinolytic agent. The nature of heparin-induced thrombosis and the mechanism of action of ancrod are discussed. The authors emphasize that all patients receiving heparin therapy should be closely monitored to detect hematologic disorders and to prevent their sequelae. Ancrod provides a reasonable therapeutic option if thrombosis does occur.