Genetic anomalies in women with POI are more frequent than previously believed. Digenic findings in several cases suggest that POI is not a purely monogenic disorder and points to a role of digenicity. The genotype-phenotype correlations in some kindreds suggest that a synergistic effect of several mutations may underlie the POI phenotype.

Hyperprolactinemia is the most common cause of hypogonadotropic anovulation and is one of the leading causes of infertility in women aged 25-34. Hyperprolactinemia has been proposed to block ovulation through inhibition of GnRH release. Kisspeptin neurons, which express prolactin receptors, were recently identified as major regulators of GnRH neurons. To mimic the human pathology of anovulation, we continuously infused female mice with prolactin. Our studies demonstrated that hyperprolactinemia in mice induced anovulation, reduced GnRH and gonadotropin secretion, and diminished kisspeptin expression. Kisspeptin administration restored gonadotropin secretion and ovarian cyclicity, suggesting that kisspeptin neurons play a major role in hyperprolactinemic anovulation. Our studies indicate that administration of kisspeptin may serve as an alternative therapeutic approach to restore the fertility of hyperprolactinemic women who are resistant or intolerant to dopamine agonists. IntroductionHyperprolactinemia is the most common cause of hypogonadotropic anovulation (WHO Group I) and represents a major etiology of infertility, with highest incidence in women aged 25-34 years (1). In men, hyperprolactinemia is also frequently associated with hypogonadotropic hypogonadism. This gonadotropic deficiency has been proposed to result from direct suppression of prolactin (PRL) on gonadotrophin-releasing hormone (GnRH) release, but evidence supporting this mechanism has never been provided. PRL is synthesized and secreted by the lactotrope cells of the pituitary, and high levels of circulating PRL are mainly caused by lactotroph adenomas, which account for approximately 40% of all pituitary tumors. Pulsatile GnRH replacement can reverse hypogonadotropic hypogonadism and infertility induced by hyperprolactinemia in women as well as men (2, 3), suggesting that PRL excess in humans affects hypothalamic release of GnRH rather than directly affecting pituitary or gonad function. However, very few GnRH neurons in mice express PRL receptors (PRLRs) (4), suggesting that PRL exerts its actions on upstream neurons regulating the GnRH neuron. Because GnRH neurons are stimulated by kisspeptin (Kp) neurons (5, 6), which unequivocally express PRLR (7), we hypothesized that GnRH deficiency resulting from hyperprolactinemia is caused by reduced Kp input, which is now considered to be a primary gatekeeper governing reproduction (8,9). Here, we show that hyperprolactinemia in mice induces hypogonadotropic anovulation and diminished Kp expression and that peripheral Kp administration restores GnRH and gonadotropin secretion and ovarian cyclicity. Therefore, we suggest that hyperprolactinemic women resistant or intolerant to dopamine agonists could take advantage of this therapeutic approach as a treatment for their infertility.

Primary ovarian insufficiency (POI) is a disorder associated with female infertility, which affects approximately 1% of women under 40 years of age. A genetic component has been suggested as one possible cause of the majority of cases of nonsyndromic forms. Newborn Ovary Homeobox (NOBOX) is an ovary-specific gene, playing a critical role in ovary in mice, as its absence leads to sterility mimicking a POI. In this study, we sequenced NOBOX in a cohort of 178 women with idiopathic POI. Among 19 identified variations, we described one nonsense (c.907C>T/p.R303X) and four missense (c.271G>T/p.G91W, c.349C>T/p.R117W, c.1025G>C/p.S342T, and c.1048G>T/p.V350L) NOBOX heterozygous mutations in 12 patients. We reproduced each of the five mutations and tested their effects on the signaling activity in transfected cells. We demonstrated that these mutations compromised the ability of the proteins to bind to and transactivate the well-known growth differentiation factor 9 (GDF9) promoter. The pattern of our findings suggests that the genetic mechanism in humans responsible for POI in women involves haploinsufficiency rather than dominant negative gene action. The identification, characterization, and the very high 6.2% prevalence of these new mutations in POI patients suggest considering NOBOX as the first autosomal candidate gene involved in this syndrome.

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Congenital hypogonadotropic hypogonadism (CHH) is a rare genetic form of isolated gonadotropin‐releasing hormone (GnRH) deficiency caused by mutations in > 30 genes. Fibroblast growth factor receptor 1 (FGFR1) is the most frequently mutated gene in CHH and is implicated in GnRH neuron development and maintenance. We note that a CHH FGFR1 mutation (p.L342S) decreases signaling of the metabolic regulator FGF21 by impairing the association of FGFR1 with β‐Klotho (KLB), the obligate co‐receptor for FGF21. We thus hypothesized that the metabolic FGF21/KLB/FGFR1 pathway is involved in CHH. Genetic screening of 334 CHH patients identified seven heterozygous loss‐of‐function KLB mutations in 13 patients (4%). Most patients with KLB mutations (9/13) exhibited metabolic defects. In mice, lack of Klb led to delayed puberty, altered estrous cyclicity, and subfertility due to a hypothalamic defect associated with inability of GnRH neurons to release GnRH in response to FGF21. Peripheral FGF21 administration could indeed reach GnRH neurons through circumventricular organs in the hypothalamus. We conclude that FGF21/KLB/FGFR1 signaling plays an essential role in GnRH biology, potentially linking metabolism with reproduction.

In our series, 5.6% of the patients with POI displayed heterozygous NOBOX mutations. We demonstrate that KIT-L could be now a direct NOBOX target. These findings replicate the high prevalence of the association between the NOBOX rare variants and POI.

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