Zygosity Diagnosis of Twins by Questionnaire for Twins’ Mothers

Abstract

Subjects were 74 twin pairs, 61 MZs and 13 same-sexed DZs who entered the High School affiliated with Tokyo University, Japan. Their mothers also participated. The twins’ zygosity was previously identified by many genetic markers. This study aimed at clarifying the effectiveness of zygosity diagnosis by questionnaires distributed to twins’ mothers. The questionnaire consisted of three questions concerning the degree of similarity of twins at one year of age; whether they were confused, and if so, by whom. It was slightly modified from that reported earlier by Ooki et al [11] for twins themselves. According to the degree of similarity of the twins, points were allotted thus: from 1 to 3 points for answers to questions (1) and (2) and from 1 to 4 points for answers to questions (3). The sum of the points was calculated, then ranged from 3 to 10. Zygosity was determined by the sum of these points. If the sum was 3-6, the twin pairs were considered MZ and if the sum was 7-10 DZ. It was revealed that more than 90% of twins were identified correctly as MZ or DZ by applying this cutting point and this result was in accordance with that obtained by use of discriminant function analysis. Moreover, the accuracy of the mothers’ responses was nearly the same as that obtained by the questionnaire for twins themselves. It was concluded, therefore, that the information from twins’ mothers is as correct as that from twins themselves. This questionnaire is simple, practical and especially useful when twins are still too young to participate personally.

Dimensions of temperament as vulnerability factors in depression

“…The final sample size was 201 pairs: 89 female and 32 male MZ pairs (MZf and MZm), 36 female DZ and 19 male DZ pairs (DZf and DZm), and 25 opposite sex pairs (DZo). Zygosity was determined from the questionnaires based upon the twins' physical resemblance 25 and the results of the polymorphism of the D4 dopamine receptor and serotonin transporter genes. The average ages were 20.7 (Ϯ3.3) for women and 19.5 (Ϯ3.0) for men.…”

Increasing Phenotypic and Genetic variations in Hyperactivity/Inattention Problems from Age 3 to 13 Years: A Cross-Sectional Twin Study

“…Twins' zygosity was determined from mothers' responses to a zygosity questionnaire that includes questions regarding physical similarities and frequency of confusion of the twins by family members and others (Ooki et al, 1993). To minimize misclassification of zygosity, we excluded twins whose zygosity was ambiguous.…”

The South Korean Twin Registry

“…When compared to serological tests, the questionnaire method in determining zygosity has yielded over 90% accuracy in Asian twin samples (Ooki et al, 1993).…”