B genetic and environmental factors are involved in the development of coronary artery disease (CAD). The degree of contribution of each individual risk factor on CAD is unknown. The influence of genetics in the development of CAD could be clarified by investigation of twins. A large cohort of twins with CAD had a significantly higher concordance of coronary heart death in monozygotic twins than dizygotic twins. This effect declined with age. These observations underscore the genetic influence in the development of CAD. Little is known about the angiographic expression of CAD in twins. To address this issue, we report findings of 2 monozygotic twin pairs with CAD and a systematic review of previous publications on this topic. • • • A search of systematic literature in the electronic database “Medline” via “Pubmed” was performed. With the search string “coronary disease” [MESH] and twin, 191 publications were retrieved. Further selections were made by applying the inclusion criteria: monozygotic twins with CAD, performance of coronary angiography, and case reports. The exclusion criterion was concomitant major congenital heart disease. By reading abstracts 20 publications were selected. Nine of these 20 publications were excluded by reading entire papers, because of (1) no performance of angiography, (2) no inclusion of monozygotic twins; and (3) concomitant major congenital heart disease. One additional publication was found by cross-reference search. Finally, 12 publications were suitable for the present review. A 1-page standard form was developed to process the selected publications systematically. This form was the basis for Table 1. Demographic, clinical, and angiographic characteristics of the retrieved case reports, together with the present twin pairs, were analyzed according to the following definitions: concordant coronary anatomy was defined as similar dominance or balance of the coronary system (according to Baim and Grossmann) between respective members of twin pairs. The extent of CAD was defined as (1) 1-, 2-, or 3-vessel disease according to significant lesions in 1 to 3 major epicardial coronary arteries; (2) diameter stenosis of the coronary artery 50%; (3) significant stenosis of the left main coronary artery reported separately as left main disease; (4) concordant coronary lesion defined as location of a coronary lesion in the same segment (American College of Cardiology/American Heart Association classification) in respective members of twin pairs; (5) 1 lesion in the same coronary segment, considered as 1 lesion; and (6) main lesion of major coronary arteries also including the origin of side branches, considered as 1 stenosis of only the major artery. A Pearson correlation coefficient was applied to correlate continuous data among twin members, and a chi-square test was performed for dichotomous data. Twin 1.1: A 58-year-old women with Canadian Cardiovascular Society classification 3 angina was referred to our hospital for coronary angioplasty. Ischemia was documented during the exercise test. Angioplasty of a type B2 lesion in segment 2 (American College of Cardiology/American Heart Association classification) of the right coronary artery was performed with implantation of a 3.0 20 mm stent (Figure 1). Twin 1.2: Six months later the monozygotic twin sister of twin 1.1 also underwent coronary angioplasty because of class 3 angina and ischemia on exercise testing. Angioplasty of a type B1 lesion of segment 2 of the right coronary artery was performed with implantation of a 3.5 13 mm stent. The left coronary arteries of both twins were normal (Figure 2). Twin 2.1: A 39-year-old patient was admitted to our hospital with class 4 angina. He had 3-vessel disease on the coronary angiogram (type B1 lesion in segment 2, type A lesion in segment 7, type B2 lesion in segment 11, and type B1 lesion in segment 12). Coronary artery bypass surgery was performed (Figure 3). Twin 2.2: A 34-year-old male patient, monozygotic twin brother of twin 2.1, was admitted to our hospital because of an acute inferior wall myocardial infarction and was treated with fibrinolysis. Because of postinfarction angina pectoris, coronary angiography was performed and 2-vessel coronary disease was found (type B1 lesion in segment 2 and type B2 lesion in segment 8, Figure 4). He also underwent a coronary artery bypass surgery. Twelve publications composed of 16 monozygotic twin pairs with angiographic assessment of CAD were found. Together with the 2 twin pairs of the present study, data of 18 twin pairs with documented CAD are listed in Table 1. Most patients were men (13 of 18). The age at which twins experienced their first coronary event was 42 12 years (mean SD), with From the Heart Lung Center Utrecht, Department of Cardiology, University Medical Center Utrecht, Utrecht, The Netherlands. Dr. Stella’s address is: Department of Cardiology, University Medical Center Utrecht, Room E01-207, PO Box 85500, 508 GA Utrecht, The Netherlands. E-mail: pstella@hli.azu.nl. Manuscript received September 25, 2001; revised manuscript received and accepted January 4, 2002.