Unequivocal Determination of Zygosity of Same-Sex Twins by Molecular Genetic Analysis

摘要

Objective: In Germany, the zygosity of same-sex twins is only determined indirectly during or after delivery by chorionicity analysis. In mixed-sex twins, dizygosity is obvious while monocho-rionicity of same-sex twins clearly indicates monozygosity. If twins are same-sex and dicho-rial, zygosity can not be identified by chorionicity analysis. Aim of this study was the unequivocal determination of zygosity of same-sex twins by molecular genetic analysis. Material and Methods: We conducted a prospective study to determine the zygosity of 41 same-sex twins peripartally when there was no unequivocal sonographic information on zygosity in the maternity log. We extracted DNA from umbilical cord blood and performed multiplex PCR analysis of 11 different microsatellite markers followed by fragment size determination using capillary gel electrophoresis. In addition, we postpar-tally established the chorionicity of the analyzed twin pairs by macroscopic analysis of the amnion and placenta histology. Results: Using conventional methods, i.e. prepar-tal sonography and postpartal amnion analysis, or placental histology, 33 same-sex twin pairs were classified as dichorial/diamniotic and 8 as mono-chorial/monoamniotic. Molecular genetic analysis detected dizygosity in 24 twin pairs and monozygosity in 17 twin pairs. All 8 twin pairs determined as monochorial by both conventional methods were found to be monozygous using microsatellite PCR. PCR analysis of the 33 twin pairs classified as dichorial by both conventional methods demonstrated dizygosity for 24 twin pairs and monozygosity for 9 twin pairs. Conclusions: Multiplex microsatellite PCR represents a simple, fast, cost-effective and reliable method for zygosity analysis of same-sex twins.