HLA-G and asthma: Finally, specific polymorphic variants of several genes including a disintegrin and metalloproteinase (ADAM) 33 (Holgate et al., 2007), G protein–coupled receptor for asthma susceptibility (GPRA; Laitinen et al., 2004), and human leukocyte antigen (HLA)-G (Nicolae et al., 2005) have been shown to be associated with asthma susceptibility.