This study uses two sequential approaches to identify genetic determinants of COPD in the absence of α₁-antitrypsin deficiency. Firstly, using subjects from the Boston Early-Onset COPD Study (FEV₁ ⩽40% predicted, age <53 years, not α₁-antitrypsin deficient), linkage analysis was performed between short tandem repeat markers on chromosome 19 (this chromosome having previously been identified as linked to COPD) and physiologically based COPD phenotypes. There was significant evidence of linkage in smokers between chromosome 19q and the pre-bronchodilator FEV₁ (LOD = 3.30). This linkage peak was located near the TGFB1 gene.

Following on from this, five single nucleotide polymorphisms (SNPs) in or near the TGFB1 gene were used to look for associations between variants of TGFB1 and COPD phenotypes in two independent populations. There was a significant association between three of the SNPs and physiological COPD phenotypes in the Boston study (n = 585, p<0.05). There was also a significant association with COPD (p⩽0.02) between three of the SNPs in subjects from the National Emphysema Treatment Trial (n = 304, all ex or current smokers, FEV₁ <45% predicted) compared with normal ex or current smoking controls from the Normative Aging Study (n = 441).

Chromosome 19q probably contains a gene that controls susceptibility to smoking induced COPD, and TGFB1 is a potential candidate for this role.