This paper will review genetic variations in the structure of three importa
nt candidate genes with varying effects in atopy and asthma that may have s
ignificant overall susceptibility associations in relation to the developme
nt of atopy and asthma. The three cytokine genes involved are interleukin (
IL)-4, IL-9 and transforming growth factor beta 1, and the nature of the po
lymorphisms may be related to significantly higher outputs of these cytokin
es in atopy and asthma.