Previous studies revealed that rat oocytes carry only 40% MPF kinase activity of that in mouse oocytes (Ito et al., 2005), which could explain the susceptibility of rat oocytes to OSA, although variation in MPF activity has been detected among different rat strains (Hirabayashi et al., 2003; Ross et al., 2006; Sterthaus et al., 2009). The gene discussed is MSLN; the disease is obstructive sleep apnea syndrome.