Demographic and olfactory data are presented in . There were no differences in mean age among the three groups. The difference among groups in the percentage of smokers was significant and was accounted for by the low number of smokers in the healthy volunteer group. Among family members who were smokers, there were no differences between the psychotic group and the nonpsychotic group in the amount smoked, as measured in pack-years (average number of packs smoked per day times the number of years of smoking) (t=0.76, df=22, n.s.). Olfactory detection (acuity) threshold scores, a measure of peripheral sensing ability, were not significantly different among the three groups.
The first analysis sought to examine the effect of family membership on olfactory performance. The ANCOVA performed on University of Pennsylvania Smell Identification Test scores showed that the effect of diagnosis (psychotic versus nonpsychotic) was significant (χ2=4.8, df=1, p<0.03) but the effect of family membership and the interaction of family membership and diagnosis were not (χ2= 0.002, df=1, n.s.; and χ2<0.01, df=1, n.s., respectively). The effect of age was also significant (beta=−0.12, p<0.04), while the effect of sex was not (beta=2.01, n.s.).
As the effect of family membership was nonsignificant, we performed a second analysis using data from all subjects to test for differences in smell identification test scores between groups (psychotic and nonpsychotic family members and healthy volunteers). There was an overall significant difference (), with pairwise differences between the psychotic patients and their nonpsychotic relatives (t=2.5, df=44, p<0.02) and between the nonpsychotic relatives and the healthy volunteers (t=2.5, df=68, p<0.02).
Because there were so few smokers in the healthy volunteer group, we examined the effects of smoking status on olfactory performance within each of the two family groups. A two-way ANOVA was performed on the smell identification test scores, with smoking status (current smoker versus nonsmoker) and diagnosis (psychotic versus nonpsychotic) as between-group factors. The main effect for diagnosis was significant (F=4.8, df=1, 45, p<0.05). Neither the main effect of smoking status nor the interaction of smoking status and diagnosis was significant (F= 0.04, df=1, 45, n.s.; and F=0.08, df=1, 34, n.s., respectively).
Another analysis was completed to determine if olfactory identification ability differed between relatives with or without a prior diagnosis of mental disorder. No difference was observed (mean score=35.4, SD=2.8, for relatives with a diagnosis versus mean=35.1, SD=3.3, for relatives without a diagnosis; t=0.21, df=25, n.s.)
We used the standardization data for the University of Pennsylvania Smell Identification Test derived by Doty et al. (8
) to classify subjects by whether they had an olfactory deficit (were microsmic), represented by a score of less than 34 of 40 for men and less than 35 of 40 for women. A high percentage of family members were microsmic, compared with comparison subjects ().
Percentage of Microsmic Subjects Among Psychotic and Nonpsychotic Members of Multigenerational Families With Familial Schizophrenia and Among Healthy Volunteersa