Acta Genet Med Gemellol 41: 113-121 (1992) ©1992 by The Mendel Institute, Rome Seventh International Congress on Twin Studies A Twin Study of Odor Identification and Olfactory Sensitivity N.L. Segal, K.W. Brown, T.D. Topolski Department of Psychology and Twin Studies Center, California State University, Fullerton, California, USA Abstract. Interindividual variation in odor identification and olfactory sensitivity has been explained primarily with reference to age, sex and/or experiential factors. A twin study of olfaction can, therefore, substantially contribute to current research in this area. Thirty-nine monozygotic and twenty dizygotic twin pairs have completed the University of Pennsylvania Smell Identification Test (UPSIT), an olfactory preference questionnaire, and two odor detection threshold tests (phenyl ethyl alcohol and butanol). A genetic influence on odor identification, as assessed by the UPSIT, has been demonstrated. Future plans and directions for this research program are discussed. Key words: Olfactory sensitivity, Odor detection threshold test INTRODUCTION Individual differences in odor identification and olfactory sensitivity have been of research interest for some time. Attention has primarily focused on age, sex and various experiential factors as possible contributors to individual variation in olfactory function [7, 9,15, 17, 25, 32]. An association between nostril asymmetry and handedness has also been reported [18]. In contrast, relatively few analyses concerned with genetic influences on olfaction are available [40]. Sensitivity thresholds for acetic acid, isobutyric acid and 2-sec-butyl-cyclohexanone were compared between 51 monozygotic (MZ) male twin pairs and 46 dizygotic (DZ) male twin pairs [21,22]. Genetic effects on odor sensitivity were not detected for these substances, nor was evidence of twin concordance for specific anosmias provided. Rela- tively reduced sensitivity to isobutyric acid and to 2-sec-butyl-cyclohexanone was shown by twins who smoked, or who were light in weight. Reduced sensitivity to isobutyric acid was also associated with infrequent consumption of alcoholic beverages. These measures were, however, able to account for only a small portion of the variance. Sensitivity to https://doi.org/10.1017/S0001566000002312 Published online by Cambridge University Press