Disorder in the Serotonergic System due to Tryptophan Hydroxylation Impairment: A Cause of Hypothalamic Syndrome?

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Abstract

Background: The hypothalamus regulates basic homeostasis such as appetite, circadian rhythm, autonomic and pituitary functions. Dysregulation in these functions results in the hypothalamic syndrome, a rare disorder of various origins. Since serotonin (5-HT) modulates most of the above-mentioned homeostasis, a defect in the serotonergic system can possibly participate in this syndrome. Methods: We describe a girl suffering from hypothalamic syndrome with a decreased concentration of 5-hydroxytryptophan (5-HTP) and a normal level of tryptophan in the cerebrospinal fluid (CSF) suggesting a functional defect in tryptophan hydroxylase (TPH). TPH is a rate-limiting enzyme in the synthesis of the neurotransmitter 5-HT. Results: Therapeutic intervention with 5-HTP, carbidopa and a specific serotonin reuptake inhibitor significantly improved her clinical symptoms and caused biochemical normalisation of neurotransmitters. Conclusion: The girl described had the typical symptoms of a hypothalamic disorder and a defective serotonergic metabolism, a relationship which has not been reported before. Therapeutic interventions to restore 5-HT metabolism resulted in clinical improvement. We suggest that investigation of 5-HT metabolism in CSF of patients with this rare disorder is included in the aetiological work-up.

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Most cited references 25

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A unique central tryptophan hydroxylase isoform

Diego J Walther, Michael Bader (2003)

Biochemical Pharmacology, 66(9), 1673-1680

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Robust and tissue-specific expression of TPH2 versus TPH1 in rat raphe and pineal gland.

Paresh D. Patel, Crystal G Pontrello, Sharon Burke (2004)

Regulation of raphe serotonergic cells is fundamental to the prevailing hypothesis of major depression pathophysiology. Tryptophan hydroxylase (TPH) is the rate-limiting enzyme in serotonin biosynthesis, but brainstem TPH mRNA expression has been difficult to measure and study. Recently, a novel paralog of TPH, TPH2 (or neuronal TPH), was described, but its anatomic expression is unknown. In situ hybridization histochemical survey was conducted across Sprague-Dawley rat brain for TPH1 and TPH2 mRNA. Semiquantitative techniques were used to estimate relative mRNA levels in individual cells. Almost exclusively, TPH2 mRNA is expressed in raphe, in a pattern overlapping the histologically defined raphe nuclei. In sharp contrast, TPH1 (the previously known TPH) is expressed predominantly in pineal gland. There is no appreciable overlap in the expression of these paralogs. The level of TPH2 mRNA expression in individual raphe cells is approximately 2.5-fold greater than the level of TPH1 expression in pinealocytes. TPH2 mRNA has an anatomic expression pattern consistent with brainstem raphe nuclei and is likely to be the gene giving rise to the majority of TPH activity in these cells. The robust expression of TPH2 in brainstem should facilitate studies on the transcriptional regulation of raphe serotonin biosynthesis.

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Pharmacogenetics and the serotonin system: initial studies and future directions.

Tyler J. VanderWeele, David Anderson, Charles Cook (2000)

Serotonin (5-hydroxytryptamine, 5-HT) appears to play a role in the pathophysiology of a range of neuropsychiatric disorders, and serotonergic agents are of central importance in neuropharmacology. Genes encoding various components of the 5-HT system are being studied as risk factors in depression, schizophrenia, obsessive-compulsive disorder, aggression, alcoholism, and autism. Recently, pharmacogenetic research has begun to examine possible genetic influences on therapeutic response to drugs affecting the serotonin system. Genes regulating the synthesis (TPH), storage (VMAT2), membrane uptake (HTT), and metabolism (MAOA) of 5-HT, as well as a number of 5-HT receptors (HTR1A, HTR1B, HTR2A, HTR2C, and HTR5A), have been studied and this initial research is reviewed here. After a brief introduction to serotonin neurobiology and a general discussion of appropriate genetic methodology, each of the major 5-HT-related genes and their encoded proteins are reviewed in turn. For each gene, relevant polymorphisms and research on functional variants are discussed; following brief reviews of the disorder or trait association and linkage studies, pharmacogenetic studies performed to date are covered. The critical and manifold roles of the serotonin system, the great abundance of targets within the system, the wide range of serotonergic agents-available and in development-and the promising preliminary results suggest that the serotonin system offers a particularly rich area for pharmacogenetic research.

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Author and article information

Journal

Journal ID (publisher-id): HRP

Journal ID (nlm-ta): Horm Res Paediatr

Journal ID (doi): 10.1159/issn.1663-2818

Title: Hormone Research in Paediatrics

Publisher: S. Karger AG

ISSN (Print): 1663-2818

ISSN (Electronic): 1663-2826

Publication date Subscription-year: 2010

Publication date (Print): January 2010

Publication date (Electronic): 15 January 2010

Volume: 73

Issue: 1

Pages: 68-73

Affiliations

Departments of ^aPaediatrics, ^bNeurology and ^cBiochemical Genetics, Maastricht University Medical Centre, Maastricht, The Netherlands

Article

Publisher ID: 271918 Other ID: Horm Res Paediatr 2010;73:68–73

DOI: 10.1159/000271918

PubMed ID: 20190542

SO-VID: ba7a133c-261c-4d54-9893-4c72fdeb7526

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