The 89th Annual Meeting of the American Association of Physical Anthropologists (2020)

Confirming an old-husband's tale: The frequency of same-sex twinning increases across the generations, following a Fragile X-syndrome-like pattern


1Anthropology, University of South Florida, 2Department of Anthropology, Purdue University, 3College of Communication, University of South Florida, 4College of Medicine, University of South Florida

April 18, 2020 2:45PM, Platinum Ballroom Add to calendar

Work on the inheritance of twinning has focused on dizygotic (DZ) twinning because most researchers assume that monozygotic (MZ) is a teratogenic event whose frequency is equal across all populations. Early work has argued that fragile-X-syndrome-carrier [Frag(X)] families tend to have higher frequencies of twins1-7 As Sherman3 said in 2000: “To date, data supporting increased twinning rates (among the carriers of the fragile X premutation) are conflicting and need to be resolved” (emphasis added). Using GWAS methods, we8 detected that MZ twins have a significantly different frequency of a SNP found in Xq27.2 from DZ twins. For this presentation we focus on families with a preponderance of same sex twinning (SST) who have a form of inheritance which mirrors that of the Frag(X). We propose that Frag(X), located at Xq27.3 may be linked to the MZ SNP, located at Xq27.2, in some families. We have assembled pedigrees with 5-10 generations with SST that follow our proposed pattern of inheritance. We tested for presence of an increase in the frequency of SST twinning by generation by using the Cochran-Armitage test for presence of a trend. Our results were significant (X2 = 239, df= 200, p= 0.02), supporting the assertion that SST increases through the generations in these families, following a Frag(X) pattern. Our results raise issues about the life history of these families, who may increase their fertility via twinning, at the risk of reducing it via their higher propensity to Fragile-X-syndrome.

Funded by an EAGER NSF award.