 This region contains a cytokine gene cluster which includes three genes whose protein products function in regulating the development and proliferation of eosinophils viz., interleukin 3, interleukin 5, and colony stimulating factor 2.However, no functional sequence genetic polylmophisms are found within the promoter, exons, or introns, of these genes or within the common gene enhancer for interleukin 3 or colony stimulating factor 2.This suggests that the primary defect in familial eosinophilia is not a mutation in one of these genes but rather in another gene within this chromosome area.