HTR4 and chronic obstructive pulmonary disease: GWAS of forced expiratory volume in one second (FEV1) and FEV1-to-forced vital capacity (FVC) ratio have found that SNPs in genes modifying lung function in healthy adults overlap with some of those that confer COPD risk, including FAM13A, HHIP, and HTR4, suggesting that these genes modulate COPD risk via changes in lung function [48].