Pituitary-ovarian function in mothers who have had two sets of dizygotic twins

Increased Levels and Pulsatility of Follicle-Stimulating Hormone in Mothers of Hereditary Dizygotic Twins

“…In line with Milham's (9) hypothesis and in agreement with earlier findings by Martin et al (10,11) we observed elevated follicular phase levels of FSH in mothers with a hereditary history of dizygotic twins. We found that this is associated with a rise in the FSH pulse frequency without any changes in other characteristics of pulsatile FSH.…”

A Deletion Mutation in GDF9 in Sisters with Spontaneous DZ Twins

“…The concentrations of follicle-stimulating hormone (FSH) above some threshold at the critical phase of the menstrual cycle contribute to selection of the dominant follicle (Baird, 1983;Macklon & Fauser, 2000) and paracrine signaling within the ovary influences FSH action in the follicle to regulate granulosa cell differentiation, follicle development and twinning rate (Erickson & Shimasaki, 2001;Matzuk et al, 2002). Concentrations of FSH are higher in mothers of DZ twins (MODZT) in some (Lambalk et al, 1998;Martin et al, 1984), but not all (Gilfillan et al, 1996) studies. No obvious differences were seen in concentrations of inhibin A or B in MODZT with or without double ovulations (Gilfillan et al, 2003), suggesting changes in endocrine signaling to the ovary may not be the primary mechanism responsible for DZ twinning.…”

Heritability of Testis Size

“…These observations lead to the hypothesis that there may be genetic factors responsible for both DZ twinning and larger testis size. The folliclestimulating hormone (FSH) may play a role in the association: mothers of DZ twins have shown increased FSH concentrations (Lambalk et al, 1998;Martin et al, 1984;Nylander, 1974), and smaller testes have been observed in men who lack a functional FSH receptor (Tapanainen et al, 1997). However, results from a study using a mouse model for the Fragile X syndrome (Slegtenhorst-Eegdeman et al, 1998), showed that macro-orchidism is caused by an increased rate of Sertoli cell proliferation in the Note: -2LL = -2 log likelihood, df = degrees of freedom, χ 2 = chi-square statistic, Δdf = difference in degrees of freedom, c.t.m.…”