The TNF [GenBank accession no. X02910 (http://www.ncbi.nlm.nih.gov/entrez/viewer.fcgi?val=X02910)] and LTA [GenBank accession no. X01393 (http://www.ncbi.nlm.nih.gov/entrez/viewer.fcgi?val=X01393)] genes are located consecutively in the class III region of the human major histocompatibility complex (MHC) on chromosome 6p21, which has shown evidence of linkage to asthma, atopy, and related phenotypes in multiple genome-wide studies (Collaborative Study on the Genetics of Asthma 1997; Daniels et al. 1996). This evidence concerns the gene TNF and asthma.