Four of these genes were located in the linked region for asthma on chromosome 5q: interleukin (IL) 4 (IL4), IL13, CD14 and the β2-adrenergic receptor (ADRB2); one gene was located in the linked region 6p21: the tumor necrosis factor (TNF); one was the first positionally cloned asthma gene, ADAM metallopeptidase domain 33 (ADAM33); another was the gene encoding the α chain of the IL-4 and IL-13 receptors (IL4R); and finally, the gene encoding the IgE Fc receptor beta-subunit (MS4A2, alias FCER1B). Here, IL13 is linked to asthma.