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      Genetics of Hypogonadotropic Hypogonadism

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          Abstract

          Background: Idiopathic hypogonadotropic hypogonadism (HH) results from a defect in the normal pulsatile secretion pattern of gonadotropin-releasing hormone (GnRH) from the hypothalamus. Clinically it can be categorized as one of two types: HH associated with anosmia, known as Kallmann syndrome, and isolated HH. The anatomical explanation for Kallmann syndrome stems from incomplete or total failure of GnRH-secreting neurons to migrate from the olfactory epithelium to their final destination in the mediobasal hypothalamus. Several genes are involved in the migration of the GnRH neurons. Conclusions: Mutations of the KAL1 gene, encoding for anosmin 1, and of the FGFR1 (or KAL2) gene, encoding for fibroblast growth factor receptor 1, can be found in familial cases of Kallmann syndrome. KAL1 mutations are responsible for X-linked recessive inheritance, and FGFR1 mutations are the autosomal dominant form. Moreover, mutations of the gonadotropin-releasing hormone receptor gene and G-protein-coupled receptor 54 gene are found in over 50% of familial cases of isolated HH with autosomal recessive inheritance.

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          Most cited references 17

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          Kisspeptin Activation of Gonadotropin Releasing Hormone Neurons and Regulation of KiSS-1 mRNA in the Male Rat

          The KiSS-1 gene codes for a family of neuropeptides called kisspeptins which bind to the G-protein-coupled receptor GPR54. To assess the possible effects of kisspeptins on gonadotropin secretion, we injected kisspeptin-52 into the lateral cerebral ventricles of adult male rats and found that kisspeptin-52 increased the serum levels of luteinizing hormone (p < 0.05). To determine whether the kisspeptin-52-induced stimulation of luteinizing hormone secretion was mediated by gonadotropin-releasing hormone (GnRH), we pretreated adult male rats with a GnRH antagonist (acyline), then challenged the animals with intracerebroventricularly administered kisspeptin-52. The GnRH antagonist blocked the kisspeptin-52-induced increase in luteinizing hormone. To examine whether kisspeptins stimulate transcriptional activity in GnRH neurons, we administered kisspeptin-52 intracerebroventricularly and found by immunocytochemistry that 86% of the GnRH neurons coexpressed Fos 2 h after the kisspeptin-52 challenge, whereas fewer than 1% of the GnRH neurons expressed Fos following injection of the vehicle alone (p < 0.001). To assess whether kisspeptins can directly act on GnRH neurons, we used double-label in situ hybridization and found that 77% of the GnRH neurons coexpress GPR54 mRNA. Finally, to determine whether KiSS-1 gene expression is regulated by gonadal hormones, we measured KiSS-1 mRNA levels by single-label in situ hybridization in intact and castrated males and found significantly higher levels in the arcuate nucleus of castrates. These results demonstrate that GnRH neurons are direct targets for regulation by kisspeptins and that KiSS-1 mRNA is regulated by gonadal hormones, suggesting that KiSS-1 neurons play an important role in the feedback regulation of gonadotropin secretion.
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            Loss-of-function mutations in FGFR1 cause autosomal dominant Kallmann syndrome.

            We took advantage of overlapping interstitial deletions at chromosome 8p11-p12 in two individuals with contiguous gene syndromes and defined an interval of roughly 540 kb associated with a dominant form of Kallmann syndrome, KAL2. We establish here that loss-of-function mutations in FGFR1 underlie KAL2 whereas a gain-of-function mutation in FGFR1 has been shown to cause a form of craniosynostosis. Moreover, we suggest that the KAL1 gene product, the extracellular matrix protein anosmin-1, is involved in FGF signaling and propose that the gender difference in anosmin-1 dosage (because KAL1 partially escapes X inactivation) explains the higher prevalence of the disease in males.
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              A gene deleted in Kallmann's syndrome shares homology with neural cell adhesion and axonal path-finding molecules.

              Kallmann's syndrome (clinically characterized by hypogonadotropic hypogonadism and inability to smell) is caused by a defect in the migration of olfactory neurons, and neurons producing hypothalamic gonadotropin-releasing hormone. A gene has now been isolated from the critical region on Xp22.3 to which the syndrome locus has been assigned: this gene escapes X inactivation, has a homologue on the Y chromosome, and shows an unusual pattern of conservation across species. The predicted protein has significant similarities with proteins involved in neural cell adhesion and axonal pathfinding, as well as with protein kinases and phosphatases, which suggests that this gene could have a specific role in neuronal migration.
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                Author and article information

                Journal
                HRE
                Horm Res Paediatr
                10.1159/issn.1663-2818
                Hormone Research in Paediatrics
                S. Karger AG
                978-3-8055-8255-1
                978-3-318-01446-4
                1663-2818
                1663-2826
                2007
                February 2007
                15 February 2007
                : 67
                : Suppl 1
                : 149-154
                Affiliations
                Institute of Reproductive Medicine, University Hospital, Münster, Germany
                Article
                97572 Horm Res 2007;67:149–154
                10.1159/000097572
                © 2007 S. Karger AG, Basel

                Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher. Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug. Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.

                Page count
                Figures: 3, Tables: 2, References: 24, Pages: 6
                Categories
                Adult Workshop 3

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