A BREAKTHROUGH in the genetics of twinning has been made with the recent identification of genes that increase the prospect of dizygotic (DZ) twins, a discovery that has enabled greater insight into female fertility.
DZ twins are regarded as a commonplace occurrence; at least one case of twinning is recorded per 100 maternities, and roughly two-thirds of all twins are non-identical. Until recently, the precise nature of the maternal genes that cause spontaneous DZ twinning had not been identified. However, an international collaboration led by Dr Hamdi Mbarek, Postdoctoral Fellow, and Prof Dorret Boomsma, Professor of Biological Psychology, Vrije Universiteit Amsterdam, Amsterdam, Netherlands, has uncovered the ways in which these genes function. The study shed new light on the significance of maternal genetics in female fertility measures, particularly in significant life stages such as menstruation, menopause, pregnancy, and the development of fertility disorders such as polycystic ovary syndrome.
The team reported on two genetic variants involved in the process of multiple follicle growth, a key factor in the development of non-identical twins. The first variant is found near the gene coding for the secretion of follicle stimulation hormone by the pituitary gland, while the second is closely related to the SMAD3 gene. After inviting mothers of spontaneous DZ twins to participate in the study, a comparison was made between their genetic profiles and those of a large group of participants who had no familial relation to DZ twins. The likelihood of a mother having DZ twins was found to increase by 29% if she has one copy of the twinning gene at both contributing locations in the genome. Dr Mbarek remarked on the pivotal role of the findings in fertility research: “In the future, developing a simple genetic test based on the top hits could assist in the identification of women at risk of a high response to hormonal treatment and allow calibration in order to prevent the severe complication of ovarian hyperstimulation syndrome with IVF.”
There may be scope for further discoveries, but this study has taken the lead by revealing that the occurrence of DZ twins can be predicted by analysing the intricacies of maternal genetics. Above all, the findings demonstrate important progress in identifying the fundamental mechanisms controlling ovarian function, thus providing critical understanding of female fertility and infertility.
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