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      PROP1 Gene Mutations and Pituitary Size: A Unique Case of Two Consecutive Cycles of Enlargement and Regression

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          Abstract

          Background: Pituitary enlargement, which can regress with time, has been described in a number of PROP1-deficient patients. We report a PROP1-deficient patient with a unique variation in pituitary size. Case Description: A 4-year-old boy was first examined in 1989 for short stature (–2.3 standard deviation score). Growth hormone (GH) insufficiency was confirmed, and human GH (hGH) therapy was initiated and administered up to the age of 18.2 years. Levothyroxine was added 6 months after hGH initiation. Pituitary magnetic resonance imaging (MRI) obtained when the patient was 5 years old showed an enlarged pituitary gland, which grew larger by the age of 8.5 years and then regressed to normal size by the time the patient was 9.8 years old. MRI when the patient was 19 years old disclosed pituitary reenlargement, and another 3 years later indicated regression. On DNA analysis, the patient was found to be homozygous for the mutation 301–302ΔGA of the PROP1 gene. When the patient was 18.8 years old and asymptomatic, an impaired cortisol response to glucagon was detected. Conclusions: Regression of the pituitary enlargement in PROP1-deficient patients does not seem to constitute an end stage with respect to pituitary pathology. Further changes in pituitary morphology and size can be expected; therefore, long-term follow-up with pituitary MRI is advised.

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          Most cited references 13

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          Pituitary lineage determination by the Prophet of Pit-1 homeodomain factor defective in Ames dwarfism.

          The gene apparently responsible for a heritable form of murine pituitary-dependent dwarfism (Ames dwarf, df) has been positionally cloned, identifying a novel, tissue-specific, paired-like homeodomain transcription factor, termed Prophet of Pit-1 (Prop-1). The df phenotype results from an apparent failure of initial determination of the Pit-1 lineage required for production of growth hormone, prolactin or thyroid-stimulating hormone, resulting in dysmorphogenesis and failure to activate Pit-1 gene expression. These results imply that a cascade of tissue-specific regulators is responsible for the determination and differentiation of specific cell lineages in pituitary organogenesis.
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            Mutations in PROP1 cause familial combined pituitary hormone deficiency.

            Combined pituitary hormone deficiency (CPHD) in man denotes impaired production of growth hormone (GH) and one or more of the other five anterior pituitary hormones. Mutations of the pituitary transcription factor gene POU1F1 (the human homologue of mouse Pit1) are responsible for deficiencies of GH, prolactin and thyroid stimulating hormone (TSH) in Snell and Jackson dwarf mice and in man, while the production of adrenocorticotrophic hormone (ACTH), luteinizing hormone (LH) and follicle stimulating hormone (FSH) is preserved. The Ames dwarf (df) mouse displays a similar phenotype, and appears to be epistatic to Snell and Jackson dwarfism. We have recently positionally cloned the putative Ames dwarf gene Prop1, which encodes a paired-like homeodomain protein that is expressed specifically in embryonic pituitary and is necessary for Pit1 expression. In this report, we have identified four CPHD families with homozygosity or compound heterozygosity for inactivating mutations of PROP1. These mutations in the human PROP1 gene result in a gene product with reduced DNA-binding and transcriptional activation ability in comparison to the product of the murine df mutation. In contrast to individuals with POU1F1 mutations, those with PROP1 mutations cannot produce LH and FSH at a sufficient level and do not enter puberty spontaneously. Our results identify a major cause of CPHD in humans and suggest a direct or indirect role for PROP1 in the ontogenesis of pituitary gonadotropes, as well as somatotropes, lactotropes and caudomedial thyrotropes.
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              Role of PROP1 in pituitary gland growth.

              Mutations in the PROP1 transcription factor gene lead to reduced production of thyrotropin, GH, prolactin, and gonadotropins as well as to pituitary hypoplasia in adult humans and mice. Some PROP1-deficient patients initially exhibit pituitary hyperplasia that resolves to hypoplasia. To understand this feature and to explore the mechanism whereby PROP1 regulates anterior pituitary gland growth, we carried out longitudinal studies in normal and Prop1-deficient dwarf mice from early embryogenesis through adulthood, examining the volume of Rathke's pouch and its derivatives, the position and number of dividing cells, the rate of apoptosis, and cell migration by pulse labeling. The results suggest that anterior pituitary progenitors normally leave the perilumenal region of Rathke's pouch and migrate to form the anterior lobe as they differentiate. Some of the cells that seed the anterior lobe during organogenesis have proliferative potential, supporting the expansion of the anterior lobe after birth. Prop1-deficient fetal pituitaries are dysmorphic because mutant cells are retained in the perilumenal area and fail to differentiate. After birth, mutant pituitaries exhibit enhanced apoptosis and reduced proliferation, apparently because the mutant anterior lobe is not seeded with progenitors. These studies suggest a mechanism for Prop1 action and an explanation for some of the clinical findings in human patients.
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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
                : 109-113
                Affiliations
                aEndocrine Unit, First Department of Pediatrics, Athens University School of Medicine, Athens, and bDepartment of Radiology, University of Ioannina School of Medicine, Ioannina, Greece
                Article
                97564 Horm Res 2007;67:109–113
                10.1159/000097564
                © 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: 5, References: 20, Pages: 5
                Categories
                Pediatric Clinical Case Sessions

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