Unravelling the familial tendency to aneurysmal disease: popliteal aneurysm, hypertension and fibrillin genotype

Comparison of Genes Associated with Thoracic and Abdominal Aortic Aneurysms

Aneurysms impacting the ascending thoracic aorta and the abdominal aorta affect patient populations with distinct clinical characteristics. Through a literature review, this paper compares the genetic associations of ascending thoracic aortic aneurysm (ATAA) with abdominal aortic aneurysms (AAA). Genes related to atherosclerosis, lipid metabolism, and tumor development are associated specifically with sporadic AAA, while genes controlling extracellular matrix (ECM) structure, ECM remodeling, and tumor growth factor β function are associated with both AAA and ATAA. Contractile element genes uniquely predispose to ATAA. Aside from known syndromic connective tissue disease and poly-aneurysmal syndromes (Marfan disease, Loeys-Dietz syndrome, and Ehlers-Danlos syndrome), there is only limited genetic overlap between AAA and ATAA. The rapid advances in genotyping and bioinformatics will elucidate further the various pathways associated with the development of aneurysms affecting various parts of the aorta.

Higher blood pressure in elderly hypertensive females, with increased arterial stiffness and blood pressure in females with the Fibrillin-1 2/3 genotype

BACKGROUND

Elderly patients have a relatively high cardiovascular risk due to increased arterial stiffness, elevated blood pressure and decreased amounts of elastin in the arteries. The composition of the media layer in the arterial wall, comprising elastin, collagen, smooth muscle cells, proteoglycans, fibronectin and fibrillin-1, influences its mechanical properties. Mutations in the fibrillin-1 gene leads to increased aortic stiffness, elevated pulse pressure and aortic root dilatation. This study investigates whether there is a sex difference among hypertensive elderly patients regarding blood pressure, arterial stiffness and fibrillin-1 genotypes.

METHODS

A total of 315 hypertensive subjects (systolic blood pressure > 140 mmHg) were included in this study (155 men and 160 women aged 71-88 years). Aortic pulse wave velocity and augmentation index were determined using SphygmoCor, and brachial blood pressure was measured using an oscillometric technique. Fibrillin-1 was genotyped by polymerase chain reaction and with a capillary electrophoresis system.

RESULTS

Females showed a significantly higher peripheral mean arterial pressure (females; 107.20 mmHg, males 101.6 mmHg, p = 0.008), central mean arterial pressure (females; 107.2 mmHg, males 101.6 mmHg p = 0.008), central systolic blood pressure (females; 148.1 mmHg, males 139.2 mmHg, p <  0.001) and central pulse pressure (females; 68.9 mmHg, males 61.6 mmHg, p = 0.035) than males. Females with the Fibrillin-1 2/3 genotype showed a significantly higher augmentation index (FBN1 2/3; 39.9%, FBN1 2/2 35.0%, FBN1 2/4 35.8, p = 0.029) and systolic blood pressure (FBN1 2/3; 174.6 mmHg, FBN1 2/2168.9 mmHg, FBN1 2/4169.9 mmHg, p = 0.025) than females with the 2/2 and 2/4 genotypes.

CONCLUSION

The findings of this study may indicate that hypertensive elderly females, especially elderly females with Fibrillin-1 2/3, have increased systolic blood pressure and arterial stiffness.

Novel genetic variation in exon 28 of FBN1 gene is associated with essential hypertension

BACKGROUND

Recently, fibrillin-1 (FBN1) was reported to play an important role in maintaining the physiological arterial stiffness of essential hypertension (EH). Here, we designed a two-stage case-control study to investigate whether the FBN1 gene harbored any genetic variations associated with EH.

METHODS

In stage 1, six candidate single-nucleotide polymorphisms (SNPs) of the FBN1 gene were genotyped and tested in 503 cases and 490 controls. SNPs associated with EH (P < 0.05) in stage 1 would be genotyped in stage 2 (814 cases and 779 controls), and analyzed in all the individuals by allele, genotype, haplotype, and diplotype. A meta-analysis was performed and inverse-variance method with random effect model was employed to estimate combined odds ratio (OR) and its 95% confidence interval (CI) for the identified SNPs.

RESULTS

In stage 1, rs140598 and rs6493333 had statistical association with EH (P < 0.05) and enter stage 2. Multiple logistic regression analysis confirmed that rs140598 but not rs6493333 significantly associated with EH in stage 2 sample. Meta-analysis showed that there was nearly no heterogeneity (I(2) = 0) of genetic variance of rs140598 in the two stages, and the associations of rs140598 in all three genetic models presented statistical significance. Further haplotype analyses showed that the Hap2 (G-C) might decreased the risk of EH when compared with reference haplotype Hap1 (C-C), adjusted OR (95%CI) was 0.823 (0.715-0.948), P = 0.006.

CONCLUSION

Our finding suggested there is a significant association of rs140598 of FBN1 gene with EH and further replication in other population for association study or prospective study should be warranted.

Genes and abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is a multifactorial disease with a strong genetic component. Since the first candidate gene studies were published 20 years ago, approximately 100 genetic association studies using single nucleotide polymorphisms (SNPs) in biologically relevant genes have been reported on AAA. These studies investigated SNPs in genes of the extracellular matrix, the cardiovascular system, the immune system, and signaling pathways. Very few studies were large enough to draw firm conclusions and very few results could be replicated in another sample set. The more recent unbiased approaches are family-based DNA linkage studies and genome-wide genetic association studies, which have the potential of identifying the genetic basis for AAA, only when appropriately powered and well-characterized large AAA cohorts are used. SNPs associated with AAA have already been identified in these large multicenter studies. One significant association was of a variant in a gene called contactin-3, which is located on chromosome 3p12.3. However, two follow-up studies could not replicate this association. Two other SNPs, which are located on chromosome 9p21 and 9q33, were replicated in other samples. The two genes with the strongest supporting evidence of contribution to the genetic risk for AAA are the CDKN2BAS gene, also known as ANRIL, which encodes an antisense ribonucleic acid that regulates expression of the cyclin-dependent kinase inhibitors CDKN2A and CDKN2B, and DAB2IP, which encodes an inhibitor of cell growth and survival. Functional studies are now needed to establish the mechanisms by which these genes contribute toward AAA pathogenesis.

Pattern of femoro-popliteal aneurysms in an African population

Objective: To describe the pattern of femoro-popliteal aneurysms in an African Kenyan population. Patients and methods: Records of African in-patients with diagnosis of femoral or popliteal aneurysms admitted at the Kenyatta National Hospital, Nairobi, Kenya, from January 1998 to December 2007 were examined for presentation, diagnosis, risk/comorbid factors, site, age, and gender distribution. Data were analyzed using SPSS 13.0 and presented using tables. Results: Femoro-popliteal aneurysms constitute 33 out of 96 of peripheral cases (34.4%). The most common presentations were pulsatile mass (48.5%) and pain and swelling (33.3%). Pain alone and bleeding occurred in 9.1% each. Diagnosis was performed through Doppler ultrasound (45.5%), angiography (30.3%) and ultrasonography (24.3%). Aneurysms were associated with trauma (51.5%), atherosclerosis (21.2%), smoking (9.1%) and hypertension (6.1%). Site distribution was common femoral (33.3%), superficial femoral (36.4%) and popliteal (30.3%). Mean age was 46 years (range 13-79 years); with 20 (60.6%) of them occurring in individuals aged 50 years and younger. Male:female ratio was 15:1. Conclusion: In the present study, femoro-popliteal aneurysms constituted less than 40% of peripheral aneurysms, and superficial femoral artery was the most common site. They occurred predominantly in males aged 50 years and younger and were associated mainly with trauma and atherosclerosis. Prevalence, site and age distribution of these aneurysms in the Kenyan population differs from that described in studies of Caucasian populations.

Influence of fibrillin-1 genotype on aortic stiffness in men: a note of caution

Aortic stiffness is a predictor of cardiovascular mortality. The mechanical properties of the arterial wall depend on the connective tissue framework, with variation in fibrillin-1 and collagen I genes being associated with aortic stiffness and/or pulse pressure elevation. The aim of this study was to investigate whether variation in fibrillin-1 genotype was associated with aortic stiffness in men. The mechanical properties of the abdominal aorta of 79 healthy men (range 28–81 yr) were investigated by ultrasonographic phase-locked echo tracking. Fibrillin-1 genotype, characterized by the variable tandem repeat in intron 28, and collagen type I alpha 1 genotype characterized by the 2,064 G\?\T polymorphism, were determined by using DNA from peripheral blood cells. Three common fibrillin-1 genotypes, 2-2, 2-3, and 2-4, were observed in 50 (64%), 10 (13%), and 11 (14%) of the men, respectively. Those of 2-3 genotype had higher pressure strain elastic modulus and aortic stiffness compared with men of 2-2 or 2-4 genotype ( P = 0.005). Pulse pressure also was increased in the 2-3 genotype ( P = 0.04). There was no significant association between type 1 collagen genotype and aortic stiffness in this cohort. In conclusion, the fibrillin-1 2-3 genotype in men was associated with increased aortic stiffness and pulse pressure, indicative of an increased risk for cardiovascular disease.

Elastic fibres and vascular structure in hypertension

Blood vessels are dynamic structures composed of cells and extracellular matrix (ECM), which are in continuous cross-talk with each other. Thus, cellular changes in phenotype or in proliferation/death rate affect ECM synthesis. In turn, ECM elements not only provide the structural framework for vascular cells, but they also modulate cellular function through specific receptors. These ECM-cell interactions, together with neurotransmitters, hormones and the mechanical forces imposed by the heart, modulate the structural organization of the vascular wall. It is not surprising that pathological states related to alterations in the nervous, humoral or haemodynamic environment-such as hypertension-are associated with vascular wall remodeling, which, in the end, is deleterious for cardiovascular function. However, the question remains whether these structural alterations are simply a consequence of the disease or if there are early cellular or ECM alterations-determined either genetically or by environmental factors-that can predispose to vascular remodeling independent of hypertension. Elastic fibres might be key elements in the pathophysiology of hypertensive vascular remodeling. In addition to the well known effects of hypertension on elastic fibre fatigue and accelerated degradation, leading to loss of arterial wall resilience, recent investigations have highlighted new roles for individual components of elastic fibres and their degradation products. These elements can act as signal transducers and regulate cellular proliferation, migration, phenotype, and ECM degradation. In this paper, we review current knowledge regarding components of elastic fibres and discuss their possible pathomechanistic associations with vascular structural abnormalities and with hypertension development or progression.

Influence of fibrillin-1 genotype on the aortic stiffness in men

Aortic stiffness is a predictor of cardiovascular mortality. The mechanical properties of the arterial wall depend on the connective tissue framework, with variation in fibrillin-1 and collagen I genes being associated with aortic stiffness and/or pulse pressure elevation. The aim of this study was to investigate whether variation in fibrillin-1 genotype was associated with aortic stiffness in men. The mechanical properties of the abdominal aorta of 79 healthy men (range 28–81 yr) were investigated by ultrasonographic phase-locked echo tracking. Fibrillin-1 genotype, characterized by the variable tandem repeat in intron 28, and collagen type I alpha 1 genotype characterized by the 2,064 G>T polymorphism, were determined by using DNA from peripheral blood cells. Three common fibrillin-1 genotypes, 2-2, 2-3, and 2-4, were observed in 50 (64%), 10 (13%), and 11 (14%) of the men, respectively. Those of 2-3 genotype had higher pressure strain elastic modulus and aortic stiffness compared with men of 2-2 or 2-4 genotype ( P = 0.005). Pulse pressure also was increased in the 2-3 genotype ( P = 0.04). There was no significant association between type 1 collagen genotype and aortic stiffness in this cohort. In conclusion, the fibrillin-1 2-3 genotype in men was associated with increased aortic stiffness and pulse pressure, indicative of an increased risk for cardiovascular disease.

Familial abdominal aortic aneurysm: a systematic review of a genetic background

BACKGROUND

Familial clustering of the abdominal aortic aneurysm (AAA) is clear, 12-19% of AAA patients have one or more first-degree relatives with an aneurysm and 4-19% is detected with ultrasound screening.

OBJECTIVES

To review the genetic background of AAA. DESIGN, METHODS AND MATERIALS: Computer searches of the MEDLINE, EMBASE, SUMsearch database and the Cochrane Library and searched reference lists of English language articles concerning the genetics of AAA, candidate gene approach and linkage analysis.

RESULTS

Brothers of AAA patients are at high risk to develop an AAA. The candidate gene approach was performed to detect defects in one of the components of the connective tissue, i.e. type I and III collagen, elastin and fibrillin, the inflammatory cell-derived matrix metalloproteinase, there inhibitors, auto-immune components and components related to atherosclerosis.

CONCLUSION

These studies give us insight in the pathology but do not lead to the specific genetic factor(s) responsible for (familial) AAA. Considering the supposed autosomal dominant inheritance, a gene mutation in one of the structural proteins of the connective tissue is expected. In the future, linkage analysis may resolve the genetic background of AAA.

Arterial dimensions in the lower extremities of patients with abdominal aortic aneurysms--no indications of a generalized dilating diathesis

PURPOSE

This study assessed whether there is a dilating diathesis in peripheral arteries of patients with abdominal aortic aneurysms (AAAs).

METHODS

The anteroposterior diameters of the common femoral artery (CFA) and popliteal artery (PA) were measured in 183 consecutive patients with an AAA (158 men, 25 women; age range, 57-78 years) before elective surgery on the AAA and compared with that of healthy age-matched control subjects. The diameter registrations were performed on the right leg by using a noninvasive echo-tracking ultrasound scanning technique.

RESULTS

Eight CFA aneurysms and four PA aneurysms were found in the male patients with AAAs. Of the patients with AAAs in the CFA and in the PA who were investigated, 46% and 49%, respectively, were affected by peripheral vascular occlusive disease (PVOD). The CFA diameters in the patients with AAAs were 97.8% of those in healthy control subjects (P = not significant [NS]). After exclusion of the CFA aneurysms, the diameters were 92.7% of those in healthy control subjects (P = .0003). If patients with PVOD were also excluded, the CFA diameters were 95.2% of those in healthy control subjects (P = .022). The PA diameters in the patients with AAAs were 97.8% of those in healthy control subjects (P = NS). If PA aneurysms were excluded, the diameters were 94.4% of those in healthy control subjects (P = .0003). If patients with PVOD were also excluded, the PA diameters were 96.1% of those in healthy control subjects (P = NS).

CONCLUSION

After excluding the few patients with AAAs who had peripheral aneurysmal disease and the patients with PVOD, no dilating diathesis in CFAs and PAs was found. This supports the hypothesis that specific genetic, or other factors, not present in most AAAs are responsible for the occurrence of concomitant peripheral aneurysms. Furthermore, the generalized vascular dilating diathesis seen in some patients seems to be a specific entity that was not necessarily affiliated with AAA disease.

An association between arterial pulse pressure and variation in the fibrillin-1 gene

OBJECTIVE

To investigate whether variation in the fibrillin-1 gene was associated with blood pressure in healthy middle aged men, as had been observed in patients with abdominal aortic aneurysm.

DESIGN, SETTING, AND PATIENTS

Middle aged men (n = 245), aged 50 to 61 years, were recruited from one of the nine general practices participating in the second Northwick Park heart study. Blood samples were obtained for the preparation of genomic DNA and analysis of plasma variables.

MAIN OUTCOME MEASURES

Systolic, diastolic, and pulse pressures; fibrillin-1 genotype characterised with a four allele variable tandem nucleotide repeat polymorphism in intron 28.

RESULTS

In healthy middle aged men only three common genotypes were observed: 2-2 (frequency 54.1%), 2-3 (16%) and 2-4 (15%). The mean arterial systolic (and pulse) pressure varied according to fibrillin-1 genotype: 2-4 genotype, 126-3 (47.6) mm Hg; 2-2 genotype, 131.0 (51.3) mm Hg; and 2-3 genotype, 135.5 (54.2) mm Hg. The median pulse pressure was 50 mm Hg. Distribution of men around the median pulse pressure, according to genotype, showed a significant trend for patients of 2-4 genotype to have the lowest pulse pressures, those of 2-2 genotype to have intermediate pressures, and those of 2-3 genotype to have the highest pulse pressures (p = 0.003 for healthy men).

CONCLUSIONS

There appears to be a significant association between fibrillin-1 genotype and arterial pulse pressure in men aged 50 to 61 years.

Interaction between fibrillin genotype and blood pressure and the development of aneurysmal disease

Debate as to whether abdominal aortic aneurysms (AAA) are caused by atherosclerosis or whether they have a strong genetic etiology continues. We have investigated the hypothesis that risk factors are likely to be strongest in patients with generalized aneurysmal disease. We screened 232 consecutive AAA patients for popliteal aneurysm and investigated cardiovascular and genetic risk factors in these patients. Ultrasonography demonstrated the presence of a popliteal aneurysm in 24 of 232 (10%) patients. Multivariate analysis identified four independent factors associated with popliteal aneurysm: age (p = 0.013), height (p = 0.017), triglyceride concentration (p = 0.009), and systolic blood pressure (p = 0.037). In the AAA patients a significant association of fibrillin-1 genotype was present, determined by a tandem repeat polymorphism, with both systolic and pulse pressure. The genotypes associated with the highest pressures were significantly more common among the patients with popliteal aneurysm, p = 0.03. Following these findings we investigated whether there was an association between fibrillin-1 genotype and blood pressure in a healthy population, 245 men aged 50-61 years. Again we found a significant association between fibrillin genotype and pulse pressure, p = 0.003. We suggest that a strong interaction occurs between fibrillin genotype and blood pressure which contributes to the development of aneurysmal disease.