Investigating the suitability of mortuary samples to assess survival bias in myocardial infarction

Abstract

Cardiovascular disease (CVD), including myocardial infarction (MI), is the commonest cause of death worldwide (Doost et al., 2016). Although the various traditional risk factors of MI are quite well-recognised, the genetic factors influencing it are still unclear with large amounts of conflicting evidence, possibly due to most studies being conducted on survivors of MI, which could lead to survival bias. In this study, DNA was extracted from formalin-fixed paraffin-embedded (FFPE) tissues from post-mortem samples of people who died of coronary artery disease (CAD) to try to identify survival bias. Polymerase chain reaction (PCR) followed by restriction enzyme digestion was used to assess the samples’ genotypes. However, FFPE tissue from mortuary samples gave DNA that was degraded with variability in DNA quantity and fragment size. Samples from liver gave better results than samples from heart. PCR amplification was not always reliable despite several attempts at optimisation. This was not due to PCR inhibitors. PCR on PCR was also unsuccessful. PCR products obtained were to0 faint to allow restriction enzyme digestion, or they developed contamination—probably since the number of cycles was very high (40 cycles). Hence, changes in allele and genotype frequencies of cases and controls with age were analysed using results from the Maltese Acute Myocardial Infarction (MAMI) Study. None of the differences in frequency reached statistical significance and therefore there was no conclusive identification of survival bias.