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Genetic susceptibility to adverse drug effects - Epidemiology ...

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Chapter 4.2<br />

Introduction<br />

Digoxin (digitalis) has been used in the treatment of heart disease for over 200 years. More<br />

recently, digoxin was demonstrated <strong>to</strong> reduce the number of admissions for heart failure and<br />

<strong>to</strong> worsen heart failure on its withdrawal, without clear mortality advantage. 1-3 Digoxin is now<br />

widely used for treatment of atrial fibrillation and heart failure. Digoxin exerts its action, in part,<br />

by increasing intracellular Ca ++ concentration ([Ca ++ ] i<br />

), leading <strong>to</strong> higher contractile force and<br />

QT-shortening. 4 Digoxin has a narrow therapeutic window, and ever since its introduction, it<br />

has been associated with <strong>to</strong>xicity and, in the past, high risk of life-threatening arrhythmias and<br />

mortality.<br />

Common variants of the nitric oxide synthase 1 adap<strong>to</strong>r protein (NOS1AP) gene were recently<br />

discovered <strong>to</strong> be associated with QT-interval prolongation in a genome wide association<br />

study. 5 We replicated this finding in the Rotterdam Study, a large population based cohort<br />

of persons 55 years and older. 6 NOS1AP was not previously known <strong>to</strong> play a role in cardiac<br />

repolarization. So far, not much is known about the mechanism by which NOS1AP influences<br />

QT duration. NOS1AP activates neuronal nitric oxide synthase (NOS1). NOS1 deficiency increases<br />

[Ca ++ ] i<br />

and causes QT prolongation. 7-10<br />

We hypothesized that subjects carrying the minor variants of two NOS1AP SNPs known <strong>to</strong><br />

prolong the QT interval might be less sensitive <strong>to</strong> the QT shortening <strong>effects</strong> of digoxin. If so,<br />

they might also be less sensitive <strong>to</strong> its pro-arrhythmogenic <strong>effects</strong>. 11-13 In the present study,<br />

we tested for interaction of NOS1AP variants with digoxin use on QTc interval duration in a<br />

population based cohort study comprising both digoxin users and non-users. In addition, we<br />

studied whether these NOS1AP variants were associated with a reduced risk of sudden cardiac<br />

death (SCD) in digoxin users.<br />

Methods<br />

Study population. The Rotterdam Study is a prospective population-based cohort study of<br />

chronic diseases in the elderly. Starting from March 1990, 7983 inhabitants of Ommoord, a<br />

Rotterdam suburb, aged 55 years and older <strong>to</strong>ok part in the baseline examination. In 2000,<br />

a second cohort of 3011 inhabitants of Ommoord, aged 55 years and older at that time,<br />

was added. Follow-up examinations <strong>to</strong>ok place at 4 year intervals (Figure 1). Objectives and<br />

methods of the Rotterdam Study have been described in detail. 14, 15 ECGs are taken at every<br />

follow-up round. Clinical characteristics including smoking, body mass index (BMI), hypertension,<br />

diabetes mellitus, heart failure and myocardial infarction were ascertained as previously<br />

described. 16-21 Active surveillance for incident diabetes mellitus, heart failure and myocardial<br />

infarction is conducted continuously between follow-up examinations. In addition, exposure of<br />

study participants <strong>to</strong> medications has been gathered on a continuous basis since January 1 st ,<br />

1991 through computerized pharmacy records from the study area covering >99% of prescriptions<br />

<strong>to</strong> the study population.<br />

90

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