Besides improving understanding of the COPD susceptibility locus on chromosome 15q25, we identified a potential novel COPD locus on chromosome 6. The SNP maps to gene PSORS1C1, but it is associated with expression levels of the neighboring gene PSORS1C3. Variants in PSORS1C3 have been reported to be associated with psoriasis [48], an immune-mediated skin disease. PSORS1C3 is located in the major histocompatability (MHC) region, and subsequent papers have found that the associations with psoriasis may be due to variants in HLA-C (MIM 142840) [49], [50]. Interestingly, one study has reported an epidemiologic association between psoriasis and COPD [51], and cigarette smoking is a risk factor for psoriasis as well [52]. Although there are no reports of HLA-C associations with COPD, alleles of other MHC class I genes, HLA-A and HLA-B, have been associated with COPD [53], [54]. The locus encompassing PSORS1C1/3 and HLA-C will require additional replication studies and functional validation to confirm its role in COPD susceptibility.
