STUDIES ON SIMILARITY DIAGNOSIS IN TWINS WITH THE AID OF MAILED QUESTIONNAIRES

Abstract

Questionnaires with questions regarding the similarity and confusion of twins were sent to 200 pairs of twins of the same sex between 35 and 75 years of age, resident within a limited area of south-west Sweden. Replies were received from 91% of the twins, equalling 86% of the pairs. Blood group determinations were made according to grouping systems A1A2BO, MN, Kh, haptoglobin and Gm. The mean probability of monozygosity in concordant pairs was 0.96. Based on the answers to one of the questions only ("When growing up, were you and your twin "as like as two peas" or of ordinary family likeness only?") the diagnosis of monozygosity was correct in 71 cases out of 72. In this way 81% of the total number of twin pairs serologically concordant were diagnosed as monozygotic. When elaborating also the answers to a second question ("Were you and your twin mixed up as children by parents, brothers and sisters or teachers?") the obtained result was a correct diagnosis of monozygosity in 72 cases out of 73. On the basis of the above-mentioned questions the diagnosis of dizygosity was correct in 99 cases out of 108. In this way 88% of the total number of serologically discordant twin pairs were diagnosed as dizygotic. A group of 19 pairs was obtained in which no diagnosis could be made by means of the questionnaire.