The Role of Gonadotropin Pulsations in the Regulation of Puberty and Fertility At one extreme of pubertal development, isolated deficiency of GnRH results in the rare clinical syndrome of isolated GnRH deficiency (IGD), also known as idiopathic hypogonadotropic hypogonadism (IHH), which presents with delayed, incomplete, or absent sexual maturation. Non-reproductive phenotypic features of this spectrum have been identified in some individuals, including anosmia, auditory defects, and skeletal, neurological and renal anomalies. Defining the physiology of GnRH secretion is critical to understanding the clinical heterogeneity of IGD, particularly in light of emerging gene discoveries that aim to elucidate genotype-phenotype correlations. Our clinical protocol, which is a multicenter study in collaboration with the REU at MGH has identified a broad range of LH pulsatility patterns and other features that are being investigated in the context of genetic variants, where identified, in order to increase our understanding of the ontogeny of these disorders. Our phenotyping efforts have identified that uterine anomalies may represent a novel non-reproductive feature of IGD, which is now being investigated in our genetic study (below) to determine whether there is a common molecular cause for these phenotypes. In addition, reversal of IGD occurs in approximately 20% of cases, and no reliable predictive factors have yet been identified. The physical hallmark of reversal of IGD in male subjects is testicular enlargement in the absence of treatment with gonadotropins or pulsatile GnRH, but there is no such physical sign of reversal in female subjects. As a result, the frequency of reversal in female subjects is largely unknown, with only several cases described, which were identified retrospectively (J Clin Endocrinol Metab, 2014 Mar;99(3):861-70). We are now longitudinally monitoring our female subjects at approximately two year intervals after their initial visit for a prospective evaluation in order to determine the frequency of reversal in female patients. The findings of this study will have important clinical implications for female patients with IGD. Neurocognitive Effects of Sex Hormone Deficiency at or Before Puberty There is little existing evidence for the neurocognitive effects of delayed puberty. We have performed neurocognitive testing and structural and functional MRI on subjects with IGD, compared with healthy controls matched for age, sex, and race. Accounting for gender, our preliminary analysis found that cortical surface area was negatively correlated with age in the IHH group and positively or uncorrelated with age in controls in several brain regions. fMRI results showed that the magnitude and extent of blood oxygenation level dependent (BOLD) activation during a face recognition task was reduced bilaterally in occipital regions in the IHH subjects, compared with controls. Neurocognitive testing showed preserved verbal and overall IQ, but significant deficits in several neurocognitive domains in IHH patients, including performance IQ, verbal memory and fluency, and processing speed. Our findings suggest that in both sexes, pubertal sex steroid deficiency contributes to persistent structural and functional brain differences as well as to neurocognitive deficits primarily involving spatial ability and recognition memory, providing further direct evidence in humans about the critical spatiotemporal role played by appropriately timed pubertal sex steroids during normal brain development. The Molecular Basis of Inherited Reproductive Disorders Human and animal models have identified a number of genes responsible for IGD, but more than half of patients with clinical evidence of the disorder do not have a detectable mutation. In addition, there is significant clinical heterogeneity among affected individuals, including members of the same family harboring the same mutations, which is often explained by oligo-digenic inheritance patterns. Whole exome sequencing (WES) has been performed in the Molecular Genomics Lab (NICHD) on 25 probands, and some family members to identify novel genes responsible for IGD. Data analysis is underway, and our findings are likely to yield important insights into additional pathways involved in the regulation of GnRH secretion. In addition, we are recruiting additional families with IGD and known uterine anomalies, based on our discovery of several patients with this phenotypic combination. WES analysis in these families has the potential to identify a new non-reproductive feature of IGD, as well as a novel molecular pathway involved in the regulation of GnRH secretion and uterine development. At the other extreme of pubertal development are patients with premature reactivation of hypothalamic GnRH secretion, resulting in idiopathic central precocious puberty (CPP). There is evidence that familial cases account for anywhere from 20-45% of CPP, with most studies describing autosomal dominant inheritance patterns. Far less is known about the molecular basis of CPP, and it was only within the past year that convincing evidence for a causative mutation was identified, using WES, in MKRN3 (NEJM, 2013 Jun 27;368(26):2467-75). Candidate gene approaches have not been successful in identifying the molecular basis of this disorder, and an unbiased approach to gene discovery seems more likely to achieve the goal of identifying novel candidate genes responsible for premature GnRH secretion in CPP. We are now actively recruiting familial cases of idiopathic CPP to undergo WES analysis. We have established collaborations with Veronica Mericq, MD and Paulina Merino, MD at the University of Chile, Santiago, Chile, as well as the Division of Pediatric Endocrinology at Childrens National Medical Center, Washington, DC to increase enrollment, and we anticipate performing WES analysis on this cohort in the coming year. Examining the genetic characteristics of subjects with pubertal disorders will reveal insights into the mechanisms underlying the reawakening of the hypothalamic-pituitary-gonadal axis at puberty. This will provide opportunities for new diagnostic capabilities and therapeutic interventions for disorders of puberty and reproduction. Blockade of Kisspeptin Signaling in Women The neuropeptide hormone kisspeptin potently stimulates secretion of GnRH. While single doses of kisspeptin stimulate the reproductive endocrine axis, animal models suggest that continuous administration of kisspeptin paradoxically suppresses the reproductive endocrine axis temporarily through desensitization of the kisspeptin receptor. By administering 24-hour infusions of kisspeptin to healthy women and to patients with reproductive disorders, we hope to learn more about the role of kisspeptin both in normal physiology and in pathological conditions, such as polycystic ovary syndrome (PCOS), a common condition characterized by ovulatory dysfunction and hyperandrogenism. Among other disturbances of hormonal regulation, patients with PCOS have high amplitude, high frequency LH pulses which may contribute to the oligo-anovulation characteristic of this disorder. In collaboration with Stephanie Seminara, and funded through an NIH Bedside-to-Bench Award, we are currently enrolling healthy postmenopausal women to determine the safety of continuous kisspeptin administration in women and the proper dose and conditions required to achieve desensitization of the kisspeptin receptor. Subsequently, the peptide will be given to women with PCOS to determine if abnormal kisspeptin signaling is involved in these disturbed endocrine dynamics, as greater understanding of how kisspeptin modulates GnRH secretion in this condition could lead to novel therapeutic interventions for this patient population.
| Lippincott, Margaret F; Chan, Yee-Ming; Delaney, Angela et al. (2016) Kisspeptin Responsiveness Signals Emergence of Reproductive Endocrine Activity: Implications for Human Puberty. J Clin Endocrinol Metab 101:3061-9 |
