As with COPD, promising candidate genes such as CHRNA3 and CHRNA5 have been discovered in association with lung cancer [40], and as discussed in the section on COPD, these genes are in strong linkage disequilibrium with IREB2. As well as being identified in relation to lung cancer, these genes are also relevant to nicotine addiction [41–43]. Here, CHRNA5 is linked to chronic obstructive pulmonary disease.