association

association 1 In the study of birth defects (dysmorphology), the nonrandom occurrence in two or more individuals of a pattern of multiple anomalies not known to be a malformation syndrome (such as Down syndrome), a malformation sequence of events, or a field defect, in which all the defects are concentrated in one particular area of the body. An example of an association in dysmorphology is the VATER association. 2 In genetics, the occurrence together of two or more characteristics more often than would be expected by chance alone. Association is to be distinguished from linkage. An example of association involves a feature on the surface of white blood cells, the human leukocyte antigen (HLA) type. HLA type B-27 is associated with an increased risk for a number of diseases, including ankylosing spondylitis.