Studies of the presymptomatic diagnosis of Huntington's disease have f
ocused attention on the need to provide information and support to pat
ients before and throughout the testing process. Many patients decline
testing and many others test negative for the disease. An analysis of
several clinical cases suggests that far from being an instance of ir
rational or paradoxical behavior refusal to undergo testing may be due
to psychological identification with other family members and to the
fear that this identification might be imperilled by the results of te
sting. This form of identification, which is distinct from the rationa
l concept of lineage, involves a desire to represent the family, if ne
eded via the development of an illness. Although unusually conspicuous
in families affected with inherited diseases, this mechanism is proba
bly operative in every individual.