Digenic inheritance of myocardial infarction risk implicates dysfunctional nitric oxide signaling.

The systematic identification of rare variants and novel pathways associated with myocardial infarction (MI) has introduced next-generation sequencing technology to large clinical cohorts. 1 Although this population-wide approach to uncover the full spectrum of rare variation is promising, it has not replaced the smaller scale sequencing of well-phenotyped families with Mendelian disorders. Erdmann and colleagues 2 recently presented a thorough evaluation of one such family in which they identified mutations in 2 functionally related genes that seem linked to disease. With careful genetic analysis, resequencing in independent cohorts, and functional validation experiments, they tested the hypothesis that 2 nitric oxide pathway-modifying genes can contribute to the pathogenesis of MI. Erdmann and colleagues 2 began with the identification of a large family of 32 members with coronary artery disease, 22 of whom had an MI before the age of 60 years. After mic-rosatellite-based linkage analysis failed to identify a causal locus, they sequenced 3 family members with early onset MI. Initially, 4 functional variants segregated with disease; however , only 2 gene mutations withstood testing with 2-locus linkage analysis. The nonsynonymous p.Leu163Phefs*24 and p.Ser525Leu mutations, in GUCY1A3 and CCT7, respectively, demonstrated insignificant logarithm of odds scores independently but with 2-locus linkage analysis had a maximum logarithm of odds score of 5.68. All 7 carriers of both mutations had early coronary artery disease. Because evidence beyond sequencing in this single family is required to claim causality, 3 the authors extensively validated their initial observation with gene resequencing in large numbers of control patients and other familial cohorts of early MI. Functional experiments in HEK 293 cells and in patient-derived platelets sought to validate a role for both genes in the soluble guanylyl cyclase (sGC) pathway. Finally, an in vivo murine model of thrombus formation provided the last link from genotype to phenotype for these potential disease-causing genes. To assess the linkage between GUCY1A3/CCT7 and MI beyond the index family, the authors first confirmed that both mutations were absent in large cohorts of control patients. However, their efforts to identify GUCY1A3 and CCT7 mutations in families other than the index family did not significantly strengthen the case for causality. A distinct GUCY1A3 mutation (p.Gly537Arg) was present in one of the 22 families , but no families had a digenic pattern of mutations in both genes. Whole-exome sequencing studies of many individuals with and without early MI found a statistically significant enrichment of missense …