• Exome sequencing from extreme responders to aspirin identifies a novel variant associated with platelet aggregation

      Backman, Joshua David; Ning, B.; Lou, W.; Perry, James; Shi, L.; Lewis, J.; Shuldiner, Alan R.; Yerges-Armstrong, Laura M. (2015-03-09)
      Objective: To identify novel variants that may significantly impact platelet response to aspirin and DAPT (Dual Anti-Platelet Therapy).
    • Genetic and Environmental Determinants of Quantitative Platelet Markers in the Pharmacogenomics of Antiplatelet Intervention (PAPI) Study

      Bozzi, Laura; Yerges-Armstrong, Laura M. (2014)
      Platelet size and count are associated with cardiac ischemia and ischemic stroke, two of the most common forms of acute cardiovascular disease. While platelet count (PC) is a common clinical measure, assessment of platelet size using mean platelet volume (MPV), the average size of platelets in a blood sample, and platelet distribution width (PDW), the variance of the platelet volume curve, are less frequently used. The overall objective of my research is to characterize these three quantitative platelet measures in a population of healthy individuals and evaluate the genetic and environmental determinants of these traits. While, MPV and PDW are not correlated (ρ<sub>p</sub>=0.07), PC is inversely correlated with both MPV (ρ<sub>p</sub>=-0.37) and PDW (ρ<sub>p</sub>=-0.27). Clinical and anthropometric predictors explain little of the variation in these three traits, however, all three are heritable, in particular MPV (h<super>2</super>: 0.83) and PC (h<super>2</super>: 0.67). A genome-wide association study (GWAS) was conducted for each of these three quantitative platelet traits. While no single nucleotide polymorphism (SNP) reached genome-wide significance (p<5x10-8) for any of the traits, 23 SNPs were associated at a suggestive level of significance (p<1x10-5) and some associated loci were near plausible candidate genes. We also queried well-established ischemic stroke and MI-associated SNPs for association with these platelet traits. We observed an MI-associated SNP near ANKSIA to be nominally associated with both MPV and PC (p=0.00795 and 0.00139, respectively). MPV, PC, and PDW are heritable traits and improved understanding of their genetic and environmental underpinnings could provide novel insight into platelet biology.
    • A Macro View of a Micronutrient: Revealing the Genetics and Elucidating the Impact of Serum Sulfate on Human Health in the Old Order Amish

      Perry, Christina Gayle; Shuldiner, Alan R.; Yerges-Armstrong, Laura M. (2016)
      Sulfate (SO42-) is integral in the biotransformation of multiple compounds through sulfotransferase-mediated sulfate conjugation (sulfation). These compounds include xenobiotics, hormones, glycosaminoglycans, and neurotransmitters. Two non-linked, nonsense variants (R12X and W48X) in SLC13A1, which encodes the sodium-sulfate cotransporter, NaS1, responsible for sulfate (re)absorption in the intestines and kidneys, were found to be enriched in an Old Order Amish (Amish) cohort compared to outbred populations. Serum sulfate was measured in 977 Amish subjects and established to be heritable (h2=0.40). Both SLC13A1 R12X and W48X were independently associated with a 27.6% (P=2.7x10-8) and 27.3% (P=6.9x10-14) decrease in serum sulfate, respectively (P=8.8x10-20 for carriers of either SLC13A1 nonsense variant). We further performed the first exome- and genome-wide association study (ExWAS/GWAS) of serum sulfate and identified a missense variant (L348P) in SLC26A1, also associated with decreased serum sulfate (P=4.4x10-12) and enriched in this Amish cohort. SLC26A1 encodes the basolateral sulfate-anion transporter (Sat1), indicative of this locus as a true determinant of serum sulfate. Consistent with sulfate's role in xenobiotic detoxification and protection against acetaminophen-induced hepatotoxicity, SLC13A1 nonsense variant carriers had higher aminotransferase levels. Contrary to our hypothesis that sulfate-lowering variants would be associated with decreased DHEA-S and DHEA-S/DHEA ratio, we instead observed a 16% decrease in DHEA amongst SLC13A1 nonsense variant carriers, compared to non-carriers (P=0.01). SLC26A1 L348P was associated with lower whole-body bone mineral density and higher serum calcium, consistent with the osteochondrodysplasia exhibited by dogs and sheep with naturally-occurring, homozygous, loss-of-function mutations in Slc13a1, and the nephrocalcinosis and increased calcium oxalate kidney stone formation in Slc26a1-knockout mice. However, serum sulfate was not associated directly with any of these clinical phenotypes. In addition, we created and validated a novel slc13a1-knockdown zebrafish model, resulting in slc13a1 morphants that appear phenotypically analogous to the phenotypes observed in Slc13a1/NaS1-null mammals, particularly in regard to their gross, tail, and gastrointestinal abnormalities and decreased body length. These findings provide important and novel insights into the genetic regulation of serum sulfate and its biological and clinical implications in humans while simultaneously demonstrating the power and translational potential of systematic identification and characterization of rare nonsense variants in founder populations.