At least twelve genome-wide association studies (GWAS) of asthma have been conducted and have yielded numerous associations, with the most significant (and in most cases replicated) associations occurring in or near the following genes: ORMDL3[1,2], PDE4D[3], HLA-DRB1[2], HLA-DQ[2,4], RAD50-IL13[4], DENND1B[5], TLE4[6], SMAD3[2], IL1RL1[7], IL18R1[2], IL33[2], IL2RB[2], RORA[2], and SLC22A5[2]. The gene discussed is PDE4D; the disease is asthma.