GENETIC ANTICIPATION AND IMPRINTING IN BIPOLAR-I ILLNESS

Background The study focused on: (1) the existence of genetic anticipa tion in a randomly selected samp le of bi polar I patients using broad and narrow definitions of the affection status in the parental genera tion; (2) the relationship between anticipation and the age at investi gation in probands and in their relatives; and (3) the relationship be tween anticipation and imprinting. Method One hundred and fifteen bipo lar 1 patients and their first- to third degree relatives were diagnos ed according to DSM-III-R criteria using the Diagnostic Interview for Genetic Studies and the Family Interview for Genetic Studies. Results Age at onset was found to be 6-10 years younger in probands with affec ted parents or uncles/aunts. Two thirds of these families showed posit ive anticipation under both the broad and the narrow definitions of af fection status in the parents' generation. The age at investigation wa s younger in probands showing positive anticipation. Anticipation was found only in probands inheriting the disorder from the paternal side. Conclusions In spite of the inevitable association between young curr ent age and young age at onset, which could result in spurious anticip ation effects, our findings suggest that this phenomenon is not the so le cause of observed anticipation.