SDK1 and Hypertension: The LMM GWAS for HCM reached suggestive significance (P = 2.76 × 10−7) with a marker on chromosome E3, located within the gene SDK1 (sidekick cell adhesion molecule 1) (Figure 4A), which is expressed especially in the kidney and retina (28, 29) but has also been associated with hypertension (30).