Coronary artery disease: anatomy and presentation in identical twins.

Editor,

A 47 year old man (twin 1) was admitted electively for coronary angiography following an acute myocardial infarction (MI) one month previously. His risk factor profile included smoking, a positive family history, hypertension and hypercholesterolaemia. On the day of admission, it was discovered that his identical twin brother (twin 2) was an elective inpatient for coronary angiography. His history included acute MI aged 42 years, with subsequent percutaneous coronary intervention to the circumflex. His risk factor profile included previous MI, a positive family history, hypertension and hypercholesterolaemia.

Coronary angiograms were performed on consecutive days. Coronary arterial anatomy was discordant between the twins. Angiographic images from twin 1 are shown in figure 1 (panels 1a-1c), beside matched images from twin 2 (panels 2a-2c). In twin 1 the left main stem bifurcates into left anterior descending (LAD) and circumflex (CX) branches (panel 1a), while in twin 2 it trifurcates into an LAD, CX and ramus intermedius branch (panel 2a). The first obtuse marginal branch (OM1) arises and bifurcates proximally in twin 1 (panels 1a and 1b) but arises and bifurcates more distally in twin 2 (panels 2a and 2b). The right coronary artery supplies a prominent sinus node branch in twin 1 (SA node, panel 1c) which is not apparent in twin 2 (panel 2c).

Fig 1

Coronary angiograms from twin I (left panel, 1a-c) and twin 2 (Right panel, 2a-c)

Coronary artery disease distribution was also discordant between the twins. Twin 1 was found to have a normal left main stem, with a long area of moderate to severe disease in the mid part of the LAD. A large diagonal branch had a 90% ostial lesion. There was a 50% lesion in the main CX and a 90% lesion in its first marginal branch. The right coronary artery was diffusely diseased. Twin 2 had a normal left main stem, with an angiographically near-normal LAD. The CX was diffusely diseased. The right coronary artery was diffusely diseased but with no significant stenosis.

Our observation of discordant coronary artery distribution and coronary atherosclerosis in identical twins supports the findings of previous observational studies1,2. Furthermore age at first cardiac event, type of cardiac event and risk factor profile show concordance in this pair of identical twins, also consistent with previous observations2.

We conclude that coronary anatomy is independent of the human genome. Disease lesion sites are at least partly independent of the human genome. In contrast, age at first cardiac event, type of cardiac event and risk factor profile appear to be more closely related to genetic profile. We suggest that when one twin presents with IHD, the second should be subject to increased medical surveillance