On the cover: Distributions of serum potassium levels by pR642G SLC12A3 genotype. Heterozygous carriers (CG) are displayed in green and noncarriers (CC) are displayed in blue. Serum potassium levels are lower in heterozygous carriers than non-carriers. Figure provided by Mao Fu, Program in Personalized and Genomic Medicine, and Division of Endocrinology, Diabetes & Nutrition, Department of Medicine, University of Maryland School of Medicine, Baltimore, MD.