Abstract 19944: A PDE5A Gene Mutation Affecting Risk of Myocardial Infarction

INTRODUCTION: Multiple frequent genetic variants were shown to affect myocardial infarction (MI) risk. Genetic causes for familial clustering of MI are less clear. We aimed to identify and characterize the molecular underpinnings of premature MI in a family with 9 affected individuals. METHODS AND RESULTS: Employing cosegregation analysis and exome sequencing we identified a mutation in the phosphodiesterase 5A ( PDE5A ) gene in all affected individuals (LOD score 3.16). It is located in an alternative promoter site of PDE5A and leads to a premature stop codon in one of the PDE5A isoforms (p.Lys7Ter). PDE5A encodes for three isoforms catalyzing cGMP, a second messenger mediating vasodilation and platelet passivation. Effects of the stop codon were investigated by western blot analysis after in vitro mutagenesis. Overexpression in HEK cells did not reveal a loss of transcript but the expression of a N-terminally truncated protein. Deeper analyses of translation initiation by deletion of possible transcription starts via in vitro mutagenesis uncovered a protein lacking 91 amino acids compared to the full-length isoform. Activity of the truncated PDE5A was measured using PDEGlo (Promega). Moreover, the effect of the variant on the alternative promoter site was analyzed by luciferase assays. Therefore, a 600 bp fragment containing either the mutated or WT allele was cloned into a pGL4.10 vector (Promega). Overexpression in HEK cells showed 40% increase of promoter activity with the mutated allele (p<0.05). Similar results could be shown in other cell lines. CONCLUSION: We identified a mutation in the PDE5A gene associated with premature MI. While a gain of function of PDE5A makes sense from a pathophysiological stance, the particular variant seemed to result in a premature stop codon. However, we could demonstrate that the variant might lead to increased promoter activity and that the presumable stop codon does not result into a loss of transcript but rather a truncated, potentially more active PDE5A isoform. Along with our homology modeling results and x-ray crystallographic and biochemical studies of Wang et al. (2010), these data support the idea of overexpression of a truncated though functional PDE5A in mutation carriers, possibly resulting in a gain function.