(Grant Montgomery, Zhen Zhen Zhao)
Why do twins run in some families? The tendency to conceive spontaneous dizygotic twins is a complex trait influenced by genetic and environmental factors with contributions from family history and maternal age. Finding the gene(s) responsible for twinning is likely to provide fundamental insights into mechanisms of female fertility and may have practical implications for controlling fertility and infertility. We expanded our study to recruit one 900 pairs of sisters from Australia and the Netherlands to complete a genome scan and subsequent fine mapping of candidate regions in these families.
A novel finding from our work was the discovery of a loss of function mutation in the oocyte specific growth factor (GDF9) in two sisters with twins. We showed that several rare genetic variants in GDF9 contribute to increased twinning in a small number of families. We recently reported results of a study including over 500 of our families that revealed several chromosomal locations that may contain more genes for twinning. It is now clear that many genes are likely to be responsible for increased non-identical twinning and the search for their identity continues.