Kullo, Iftikhar J.

Background— Coronary artery calcification (CAC), a marker of coronary artery atherosclerosis, can be measured accurately and noninvasively with the use of electron beam computed tomography. Serial measures of CAC quantify progression of calcified coronary artery plaque. Little is known about the role of genetic factors in progression of CAC quantity. Methods and Results— We quantified the relative contributions of measured risk factors and unmeasured genes to CAC progression measured by 2 electron beam computed tomography examinations an average of 7.3 years apart in 877 asymptomatic white adults (46% men) from 625 families in a community-based sample. After adjustment for baseline risk factors and CAC quantity, the estimated heritability of CAC progression was 0.40 ( P <0.001). Baseline risk factors and CAC quantity explained 64% of the variation in CAC progression. Thus, genetic factors explained 14% of the variation [(100−64)×(0.40)] in CAC progression. After adjustment for risk factors, the estimated genetic correlation (pleiotropy) between baseline CAC quantity and CAC progression was 0.80 and was significantly different than 0 ( P <0.001) and 1 ( P =0.037). The environmental correlation between baseline CAC quantity and CAC progression was 0.42 and was significantly different than 0 ( P =0.006). Conclusions— Evidence was found that many but not all genetic factors influencing baseline CAC quantity also influence CAC progression. The identification of common and unique genetic influences on these traits will provide important insights into the genetic architecture of coronary artery atherosclerosis.

In the present study, we investigated whether measures of brachial artery reactivity were associated with the presence and extent of subclinical coronary atherosclerosis in asymptomatic adults. Electron beam computed tomography was employed to assess the presence and quantity of CAC (coronary artery calcium) in 441 participants (mean age, 61 years; 49% men) without prior history of CHD (coronary heart disease) or stroke, and CAC score was calculated using the method described by Agatston and co-workers [(1990) J. Am. Coll. Cardiol. 15, 827–832] High-resolution ultrasound was employed to measure BAD (brachial artery diameter), FMD (flow-mediated dilatation) and NMD (nitroglycerine-mediated dilatation). CAC score and FMD were log-transformed after adding 1 to reduce skewness. Multivariable logistic and linear regression models based on generalized estimating equations were used to assess whether BAD, FMD and NMD were each independently associated with the presence and quantity of CAC after adjustment for CHD risk factors and use of statin and hypertension medication. CAC was detectable in 64% of participants. After adjustment for age and sex, FMD was not correlated (r=−0.06; P=0.27), BAD was positively correlated (r=0.16; P=0.004) and NMD was inversely correlated in a borderline significant manner (r=−0.10; P=0.084) with log(CAC+1). In multivariable logistic regression analyses, FMD was not associated, whereas higher BAD (P=0.021) and lower NMD (P=0.030) were independently associated with the presence of CAC. In multivariable linear regression analyses, higher BAD (P=0.004) and lower NMD (P=0.016), but not FMD, were independently associated with log(CAC+1). We conclude that greater diameter of the brachial artery and lower vasodilator response to nitroglycerine, but not FMD, are associated with subclinical coronary atherosclerosis.

Background and Purpose— Genetic factors that influence interindividual variation in levels of plasma homocysteine, a risk factor for vascular disease, are not fully understood. We performed linkage analyses to identify genomic regions that influence homocysteine levels in blacks and non-Hispanic whites. Methods— Subjects (n=2283) belonged to hypertensive sibships and included 1319 blacks (63±10 years, 70% women) and 964 non-Hispanic whites (61±7 years, 57% women). Fasting plasma homocysteine was measured by high-pressure liquid chromatography. Genotypes were measured at 366 microsatellite marker loci distributed across the 22 autosomes. Plasma homocysteine adjusted for age, sex, body mass index, serum creatinine, and estrogen use (in women) was used in the genetic analyses. Heritability and linkage analyses were performed using a variance components approach. Results— Mean (±SD) homocysteine levels were 10.4±5.27 μmol/L in blacks and 10.0±2.84 μmol/L in non-Hispanic whites ( P =0.58 for difference). Homocysteine levels were significantly ( P <0.0001) heritable in blacks ( h 2 =0.70) and in non-Hispanic whites ( h 2 =0.49). Linkage analyses demonstrated significant evidence of linkage (multipoint logarithm of odds≥3.0) for homocysteine on chromosomes 1q42, 14q32, and 19p13 in blacks and on chromosomes 9q34 and 12q24 in non-Hispanic whites. Tentative evidence of linkage (logarithm of odds 1.3 to 2.0) was present on chromosomes 2q32, 7p15, 8q24, 18q21, and 20p12 in blacks and chromosomes 6q26 and 18q21 in non-Hispanic whites. Four genes in the homocysteine metabolism pathway ( MTR , DNMT1 , GAMT , and CARM1 ) were present under 2 of the significant linkage signals in blacks (chromosomes 1q42 and 19p13). Conclusions— Plasma homocysteine is a significantly heritable trait. Linkage analyses reveal several unique genomic loci that may influence circulating levels of homocysteine and therefore susceptibility to vascular diseases including stroke.

We investigated the relationship of aortic pulse wave velocity (aPWV), a measure of central arterial stiffness, with the presence and quantity of coronary artery calcium (CAC) in a community-based sample of adults without prior history of heart attack or stroke (n=401, mean age 59.8 years, 53% men). ECG-gated waveforms of the right carotid and right femoral artery were obtained by applanation tonometry, and aPWV was calculated using established methods. CAC was measured noninvasively by electron beam computed tomography, and CAC score was calculated. aPWV was significantly correlated with log(CAC +1; r =0.41; P <0.0001) and pulse pressure ( r =0.47; P <0.0001). Multivariable logistic and linear regression models were used to identify independent predictors of the presence and quantity of CAC, respectively. In multivariable logistic regression analyses, aPWV was associated with the presence of CAC ( P =0.011) after adjustment for age, male sex, total cholesterol, high-density lipoprotein cholesterol, diabetes, history of smoking, systolic blood pressure, body mass index, and use of hypertension and statin medications. In multivariable linear regression analyses, aPWV was significantly associated with log(CAC +1) after adjustment for the covariates enumerated above ( P <0.0001). aPWV remained significantly associated with both the presence and quantity of CAC even after the additional adjustment for diastolic blood pressure. We conclude that aPWV is related to subclinical coronary atherosclerosis independent of conventional risk factors (including indices of blood pressure) and may be a biomarker of cardiovascular risk in asymptomatic individuals.

Background— Obesity is associated with coronary artery calcification (CAC), a marker of the presence and extent of subclinical coronary atherosclerosis. Obesity adds incremental information in identifying those at higher risk of coronary heart disease to traditional risk factor assessment. The present study examined associations between obesity measures and progression of CAC in those at higher (≥10%) and lower (<10%) 10-year coronary heart disease risk according to the Framingham risk equation. Methods and Results— In this study, 443 asymptomatic white individuals >30 years of age (243 men) had baseline and follow-up CAC measurements an average of 8.9 years apart. Multivariable linear regression models were fit to determine associations of obesity measures at baseline with progression of CAC defined as log e of the difference between follow-up and baseline CAC area plus 1 divided by time (in years) between examinations, adjusting for baseline CAC quantity, age, sex, baseline hypertension status, and baseline cholesterol level. Among 329 participants (74.3%) in the lower-risk group, waist circumference ( P =0.024), waist-to-hip ratio ( P <0.001), body mass index ( P =0.036), and being overweight compared with being underweight or of normal weight ( P =0.008) were each significantly positively associated with progression of CAC. Among those at higher coronary heart disease risk, no baseline obesity measures were associated with CAC progression. Conclusions— Various measures of obesity were associated with increased progression of CAC in those at lower risk of coronary heart disease. Future studies examining the effectiveness of weight reduction strategies in reducing CAC progression among those with an otherwise favorable risk factor profile may be warranted.

Markers of inflammation are predictive of cardiovascular events but their association with atherosclerotic burden remains poorly defined. We hypothesized that markers of inflammation, including C-reactive protein (CRP), white blood cell (WBC) count, and lipoprotein-associated phospholipase A2 (Lp-PLA2), would be associated with the ankle-brachial index (ABI), a marker of atherosclerotic burden. Subjects were 247 patients referred for lower extremity arterial evaluation to the non-invasive vascular laboratory excluding those with active infection or lower extremity revascularization within the previous year. ABI was measured at two sites in both legs and the lowest of four measurements was used in the analyses. CRP was measured by a high-sensitivity immunoturbidimetric assay and Lp-PLA2 was measured by ELISA. The mean patient age was 68±11 years, and 54% were men. Mean ABI was 0.84-0.31 and 49% had an ABI < 0.9. Age, hypertension, fasting plasma glucose, and ‘ever’ smoking were independently associated with the ABI. Spearman correlation coefficients of inflammatory markers with the ABI were: CRP (r 1/4-0.15, p 1/4-0.02), WBC count (r 1/4-0.27, p 1/4-0.001), and Lp-PLA2 (r 1/4-0.09, p 1/4-0.21). In a multiple regression model that included conventional risk factors and statin use, CRP and WBC count were no longer significantly associated with ABI, whereas Lp-PLA2 was a borderline-significant predictor of lower ABI (p 1/4-0.05). These data indicate that CRP and WBC count are not independently associated with ABI, a marker of atherosclerotic burden in subjects referred for non-invasive lower extremity arterial evaluation. The association of Lp-PLA2 with ABI merits further study.

Few studies have investigated whether ethnic groups differ in the prevalence of peripheral arterial disease (PAD). We compared the distribution of the ankle-brachial index (ABI), a measure of PAD, between African Americans and non-Hispanic white individuals. Subjects (n = 931) belonged to the Genetic Epidemiology Network of Arteriopathy (GENOA) study, a community-based study of hypertensive sibships, and included 453 African Americans from Jackson, Mississipi (mean age 72 6 years, 69% women) and 478 non-Hispanic white individuals from Rochester, Minnesota (mean age 58 7 years, 64% women). ABI was determined at two sites in each lower extremity and the lowest of four indices was used in the analyses. PAD was defined as an ABI of 0.95. Information about conventional risk factors was derived from interviews and from blood samples drawn at the study visit. The prevalence of diabetes and hypertension was significantly higher in African Americans than in non-Hispanic white individuals. After adjusting for age, African American subjects had a lower mean ABI (women 0.97 vs 1.04, p < 0.001; men 0.96 vs 1.12, p < 0.001) and a greater prevalence of PAD (women 34% vs 22%, p = 0.010; men 33% vs 11%, p < 0.001) than their non-Hispanic white counterparts. In multiple regression analyses, African American ethnicity was a predictor of a lower ABI and the presence of PAD in each sex after adjusting for age and other conventional risk factors. In conclusion, the lower ABI and greater prevalence of PAD in African Americans than in non-Hispanic white individuals is not explained by differences in conventional risk factors. Identifying additional ‘novel’ risk factors that account for the ethnic differences in PAD is an important next step towards understanding why such differences exist and developing more effective strategies to reduce the burden of PAD.

Early-onset peripheral lower extremity arterial occlusive disease (PAD) is an uncommon, poorly characterized manifestation of atherosclerotic vascular disease. We studied the clinical presentation and correlates of disease severity and location in patients with early-onset PAD identifi ed at non-invasive arterial evaluation. We identifi ed a series of 159 patients who were younger than 50 years and had an abnormal resting or postexercise ankle brachial index (ABI) (<0.9) or, if arteries were noncompressible, monophasic arterial Doppler signals. Disease severity and location were determined based on results of noninvasive vascular laboratory testing. Presence of coexisting atherosclerosis in other arterial beds was ascertained by review of patient records. Multivariable logistic regression analyses were used to identify risk factors associated with disease severity and location. Mean age of the patients was 42.7 6 4.2 years and 55% were women. Prevalence of risk factors was 76% for current or past smoking; 71%, dyslipidemia; 53%, hypertension; 35%, diabetes; and 53%, family history. Claudication was present in 50%, rest pain in 3%, ulceration in 31% and the remaining 16% did not have symptoms from PAD. Low high-density lipoprotein (HDL)-cholesterol and female sex were associated with severity. Of 102 patients in whom disease location could be determined noninvasively, 65% had aortoiliac disease. Female sex, low HDL-cholesterol, and absence of diabetes were associated with aortoiliac disease. Atherosclerosis in other arterial beds was identifi ed in 53% of the patients. Conclusion: In this study population of early-onset atherosclerotic PAD, men and women were equally represented. The disease involved predominantly the aortoiliac location. Low HDL-cholesterol and female sex were associated with disease severity. An aggressive approach to diagnosis and treatment may be warranted as atherosclerosis in other arterial beds was prevalent in half of the patients.