Genetic forms of neurohypophyseal diabetes insipidus

New developments and concepts in the diagnosis and management of diabetes insipidus (AVP-deficiency and resistance)

Diabetes insipidus (DI) is a disorder characterised by the excretion of large amounts of hypotonic urine, with a prevalence of 1 per 25,000 population. Central DI (CDI), better now referred to as arginine vasopressin (AVP)-deficiency, is the most common form of DI resulting from deficiency of the hormone AVP from the pituitary. The less common nephrogenic DI (NDI) or AVP-resistance develops secondary to AVP resistance in the kidneys. The majority of causes of DI are acquired, with CDI developing when more than 80% of AVP-secreting neurons are damaged. Inherited/familial CDI causes account for approximately 1% of cases. Although the pathogenesis of NDI is unclear, more than 280 disease-causing mutations affecting the AVP2 protein or AVP V2 receptor, as well as in aquaporin 2 (AQP2), have been described. Although the cAMP/protein kinase A pathway remains the major regulatory pathway of AVP/AQP2 action, in vitro data have also revealed additional cAMP independent pathways of NDI pathogenesis. Diagnosing partial forms of DI, and distinguishing them from primary polydipsia, can be challenging, previously necessitating the use of the water deprivation test. However, measurements of circulating copeptin levels, especially after stimulation, are increasingly replacing the classical tests in clinical practice because of their ease of use and high sensitivity and specificity. The treatment of CDI relies on desmopressin administration, whereas NDI requires the management of any underlying diseases, removal of offending drugs and, in some cases, administration of diuretics. A better understanding of the pathophysiology of DI has led to novel evolving therapeutic agents that are under clinical trial.

Evaluation of the etiological and clinical characteristics of pediatric central diabetes insipidus

OBJECTIVES

Central diabetes insipidus (CDI) is a rare but important disease of varying etiology that poses challenges in diagnosis and follow-up. Identifying diagnostic difficulties in patients with CDI will help ensure an optimal approach to their management and follow-up. This study aimed to characterize the clinical and etiological characteristics of CDI in pediatric patients.

METHODS

We analyzed the admission and follow-up data of CDI patients aged 0-18 years who were followed in our center between 2010 and 2019.

RESULTS

The study included 56 patients with a mean age at diagnosis of 7.92 ± 5.11 years and symptom duration of 8.65 ± 21.3 months. The patients were grouped by etiology into those with organic causes, such as structural anomalies, tumors, and trauma (group 1, n=41) and other causes (group 2, n=15). The prevalence of idiopathic CDI was 16%. At least one pituitary hormone deficiency was detected in 60.7%, the most common being thyroid stimulating hormone deficiency. Patients in group 1 had a higher mean age at diagnosis, shorter symptom duration, and higher frequency of other pituitary hormone deficiencies compared to group 2. Additionally, germinoma was detected 1 year subsequent to normal MRI findings at diagnosis and another patient was diagnosed with Langerhans cell histiocytosis (LCH) 5 years after diagnosis. All patients responded well to replacement therapies, but two patients with germinoma died during follow-up.

CONCLUSIONS

In the pediatric age group, intracranial organic pathologies are an important etiology of CDI, and despite a short symptomatic period, determining the cause may be challenging and prolonged. Patients presenting at a young age with a long history of symptoms and no other pituitary hormone deficiency are unlikely to have organic CDI. However, organic causes such as LCH should be evaluated at all ages. Patients with idiopathic disease are candidates for further etiological studies, and repeated cranial imaging is important during follow-up.

Fluid management in hospitalized pediatric patients

The proper use of intravenous fluids has likely been responsible for saving more lives than any other group of substances. Proper use includes prescribing an appropriate electrolyte and carbohydrate solution, at a calculated rate or volume, for the right child, at the right time. Forming intravenous fluid plans for hospitalized children requires an understanding of water and electrolyte physiology in healthy children and how different pathology deviates from the norm. This review highlights fluid management in several disease types, including liver disease, diabetic ketoacidosis, syndrome of inappropriate antidiuretic hormone, diabetes insipidus, kidney disease, and intestinal failure as well as in those with nonphysiologic fluid losses. For each disease, the review discusses specific considerations, evaluations, and management strategies to consider when customizing intravenous fluid plans. Ultimately, all hospitalized children should receive an individualized fluid plan with recurrent evaluations and fluid modifications to provide optimal care.

A Novel Form of Familial Vasopressin Deficient Diabetes Insipidus Transmitted in an X-linked Recessive Manner

CONTEXT

Familial pituitary diabetes insipidus has been described only in an autosomal dominant or recessive mode of inheritance.

OBJECTIVE

This work aims to determine the cause of a novel form of familial diabetes insipidus (DI) that is controlled by desmopressin therapy but segregates in an X-linked recessive manner.

METHODS

Thirteen members from 3 generations of the kindred with familial DI were studied. Water intake, urine volume, urine osmolality, plasma osmolality, and plasma vasopressin were measured under basal conditions, during fluid deprivation, 3% saline infusion, and water loading. Magnetic resonance images of the posterior pituitary also were obtained. In affected males, the effects of desmopressin therapy and linkage of the DI to markers for chromosome Xq28 were determined. In addition, the genes encoding vasopressin, aquaporin-2, the AVPR2 receptor, and its flanking regions were sequenced.

RESULTS

This study showed that 4 males from 3 generations of the kindred have DI that is due to a deficiency of vasopressin, is corrected by standard doses of desmopressin, and segregates with markers for the AVPR2 gene in Xq28. However, no mutations were found in AVPR2 or its highly conserved flanking regions. Exome sequencing confirmed these findings and also revealed no deleterious variants in the provasopressin and aquaporin-2 genes. The 4 obligate female carriers osmo-regulated vasopressin in the low normal range.

CONCLUSION

X-linked recessive transmission of DI can be due to a defect in either the secretion or the action of vasopressin. Other criteria are necessary to differentiate and manage the 2 disorders correctly.

A Novel Gene CDC27 Causes SLE and Is Associated With the Disease Activity

Background

As genetic genetic factors are important in SLE, so screening causative genes is of great significance for the prediction and early prevention in people who may develop SLE. At present, it is very difficult to screen causative genes through pedigrees. The analytical method described herein can be used to screen causative genes for SLE and other complex diseases through pedigrees.

Methods

For the first time, 24 lupus pedigrees were analyzed by combining whole exon sequencing and a variety of biological information tools including common-specific analysis, pVAAST (pedigree variant annotation, analysis and search tool), Exomiser (Combining phenotype and PPI associated analysis), and FARVAT (family based gene burden), and the causative genes of these families with lupus identified. Selected causative genes in peripheral-blood mononuclear cells (PBMCs) were evaluated by quantitative polymerase chain reaction (qPCR).

Results

Cell division cycle 27 (CDC27) was screened out by common-specific analysis and Exomiser causative gene screening. FARVAT analysis on these families detected only CDC27 at the extremely significant level (false discovery rate <0.05) by three family-based burden analyses (BURDEN, CALPHA, and SKATO). QPCR was performed to detect for CDC27 in the PBMCs of the SLE family patients, sporadic lupus patients, and healthy people. Compared with the healthy control group, CDC27 expression was low in lupus patients (familial and sporadic patients) (P<0.05) and correlated with lupus activity indicators: negatively with C-reactive protein (CRP) (P<0.05) and erythrocyte sedimentation rate (P<0.05) and positively with complement C3 and C4 (P<0.05). The CDC27 expression was upregulated in PBMCs from SLE patients with reduced lupus activity after immunotherapy (P<0.05). Based on Receiver operating characteristic (ROC) curve analysis, the sensitivity and specificity of CDC27 in diagnosing SLE were 82.30% and 94.40%.

Conclusion

The CDC27 gene, as found through WES combined with multiple analytical method may be a causative gene of lupus. CDC27 may serve as a marker for the diagnosis of SLE and is closely related to the lupus activity. We hope that the analytical method in this study will be used to screen causative genes for other diseases through small pedigrees, especially among non-close relatives.

Functional analyses of three different mutations in the AVP-NPII gene causing familial neurohypophyseal diabetes insipidus

PURPOSE

Familial neurohypophyseal diabetes insipidus (FNDI), a rare disorder, which is clinically characterized by polyuria and polydipsia, results from mutations in the arginine vasopressin-neurophysin II (AVP-NPII) gene. The aim of this study was to perform functional analyses of three different mutations (p.G45C, 207_209delGGC, and p.G88V) defined in the AVP-NPII gene of patients diagnosed with FNDI, which are not included in the literature.

METHODS

For functional analysis studies, the relevant mutations were created using PCR-based site-directed mutagenesis and restriction fragment replacement strategy and expressed in Neuro2A cells. AVP secretion into the cell culture medium was determined by radioimmunoassay (RIA) analysis. Fluorescence imaging studies were conducted to determine the differences in the intracellular trafficking of wild-type (WT) and mutant AVP-NPII precursors. Molecular dynamics (MD) simulations were performed to determine the changing of the conformational properties of domains for both WT and 207-209delGGC mutant structures and dynamics behavior of residues.

RESULTS

Reduced levels of AVP in the supernatant culture medium of p.G45C and p.G88V transfected cells compared to 207_209delGGC and WT cells were found. Fluorescence imaging studies showed that a substantial portion of the mutant p.G45C and p.G88V AVP-NPII precursors appeared to be located in the endoplasmic reticulum (ER), whereas 207_209delGGC and WT AVP-NPII precursors were distributed throughout the cytoplasm.

CONCLUSIONS

The mutations p.G45C and p.G88V cause a failure in the intracellular trafficking of mutant AVP-NPII precursors. However, 207_209delGGC mutation does not result in impaired cellular trafficking, probably due to not having any significant effect in processes such as the proper folding, gain of three-dimensional structure, or processing. These results will provide valuable information for understanding the influence of mutations on the function of the AVP precursor hormone and cellular trafficking. Therefore, this study will contribute to elucidate the mechanisms of the molecular pathology of AVP-NPII mutations.

Efficiency of cell-type specific and generic promoters in transducing oxytocin neurons and monitoring their neural activity during lactation

Hypothalamic oxytocin (OXT) and arginine-vasopressin (AVP) neurons have been at the center of several physiological and behavioral studies. Advances in viral vector biology and the development of transgenic rodent models have allowed for targeted gene expression to study the functions of specific cell populations and brain circuits. In this study, we compared the efficiency of various adeno-associated viral vectors in these cell populations and demonstrated that none of the widely used promoters were, on their own, effective at driving expression of a down-stream fluorescent protein in OXT or AVP neurons. As anticipated, the OXT promoter could efficiently drive gene expression in OXT neurons and this efficiency is solely attributed to the promoter and not the viral serotype. We also report that a dual virus approach using an OXT promoter driven Cre recombinase significantly improved the efficiency of viral transduction in OXT neurons. Finally, we demonstrate the utility of the OXT promoter for conducting functional studies on OXT neurons by using an OXT specific viral system to record neural activity of OXT neurons in lactating female rats across time. We conclude that extreme caution is needed when employing non-neuron-specific viral approaches/promoters to study neural populations within the paraventricular nucleus of the hypothalamus.

Urinary Tract Involvement in Wolfram Syndrome: A Narrative Review

Wolfram Syndrome (WS) is a rare neurodegenerative disease with autosomal recessive inheritance and characterized by juvenile onset, non-autoimmune diabetes mellitus and later followed by optic atrophy leading to blindness, diabetes insipidus, hearing loss, and other neurological and endocrine dysfunctions. A wide spectrum of neurodegenerative abnormalities affecting the central nervous system has been described. Among these complications, neurogenic bladder and urodynamic abnormalities also deserve attention. Urinary tract dysfunctions (UTD) up to end stage renal disease are a life-threatening complication of WS patients. Notably, end stage renal disease is reported as one of the most common causes of death among WS patients. UTD have been also reported in affected adolescents. Involvement of the urinary tract occurs in about 90% of affected patients, at a median age of 20 years and with peaks at 13, 21 and 33 years. The aim of our narrative review was to provide an overview of the most important papers regarding urological impairment in Wolfram Syndrome. A comprehensive search on PubMed including Wolfram Syndrome and one or more of the following terms: chronic renal failure, bladder dysfunction, urological aspects, and urinary tract dysfunction, was done. The exclusion criteria were studies not written in English and not including urinary tract dysfunction deep evaluation and description. Studies mentioning general urologic abnormalities without deep description and/or follow-up were not considered. Due to the rarity of the condition, we considered not only papers including pediatric patients, but also papers with pediatric and adult case reports

A Rare Case of Familial Neurogenic Diabetes Insipidus in a 22-Year-Old Man

Objective

Diabetes insipidus (DI) can be classified into 2 types: central/neurogenic DI and nephrogenic DI. Most cases of central DI occur after brain surgery, trauma, tumor, or infection. Here we report a rare case of familial central DI due to a heterozygous AVP gene mutation.

Methods

A case of familial neurogenic DI has been described with thorough clinical, laboratory, and genetic workup. PubMed and Google scholar databases were used for literature discussion.

Results

A 22-year-old man presented with polyuria and polydipsia. He drank about 4 gallons of water everyday and urinated large volumes very frequently. His physical examination was unremarkable. After 2 hours of water-deprivation, his serum sodium level was 147 mmol/L, serum osmolality was 302 mOsm/kg with concurrent urine osmolality of 78 mOsm/kg, vasopressin level was <0.8 pg/mL, and copeptin level was <2.8 pmol/L, suggesting neurogenic DI. His brain magnetic resonance imaging revealed the absence of the posterior pituitary bright spot but a normal anterior pituitary gland. Genetic analysis revealed a nonfunctional heterozygous mutation in the AVP gene. Further questioning revealed that his mother also had the disease and that he had been treated with desmopressin as a child; however, it was later self-stopped. The patient was reinitiated on desmopressin, which improved his symptoms.

Conclusion

Genetic mutations in the AVP gene represent a very rare etiology of DI, and patients with DI respond well to desmopressin treatment.

Vasopressin-Dependent Disorders: What Is New in Children?

Arginine vasopressin (AVP)-mediated osmoregulatory disorders, such as diabetes insipidus (DI) and syndrome of inappropriate secretion of antidiuretic hormone (SIADH) are common in the differential diagnosis for children with hypo- and hypernatremia and require timely recognition and treatment. DI is caused by a failure to concentrate urine secondary to impaired production of or response to AVP, resulting in hypernatremia. Newer methods of diagnosing DI include measuring copeptin levels; copeptin is AVP's chaperone protein and serves as a surrogate biomarker of AVP secretion. Intraoperative copeptin levels may also help predict the risk for developing DI after neurosurgical procedures. Copeptin levels hold diagnostic promise in other pediatric conditions, too. Recently, expanded genotype and phenotype correlations in inherited DI disorders have been described and may better predict the clinical course in affected children and infants. Similarly, newer formulations of synthetic AVP may improve pediatric DI treatment. In contrast to DI, SIADH, characterized by inappropriate AVP secretion, commonly leads to severe hyponatremia. Contemporary methods aid clinicians in distinguishing SIADH from other hyponatremic conditions, particularly cerebral salt wasting. Further research on the efficacy of therapies for pediatric SIADH is needed, although some adult treatments hold promise for pediatrics. Lastly, expansion of home point-of-care sodium testing may transform management of SIADH and DI in children. In this article, we review recent developments in the understanding of pathophysiology, diagnostic workup, and treatment of better outcomes and quality of life for children with these challenging disorders.

Differential diagnosis of familial diabetes insipidus

Diabetes insipidus (DI) is a syndrome characterized by the persistent excretion of abnormally large volumes of dilute urine. It can be caused by any of four fundamentally different abnormalities: deficient production of the antidiuretic hormone, arginine vasopressin (AVP) by magnocellular neurons that form the posterior pituitary (hypothalamic DI); impaired renal effects of AVP (nephrogenic DI); reduced AVP secretion due to excessive water intake (primary polydipsia); or degradation of AVP by placental vasopressinase (gestational DI). Each type of DI can be caused or potentiated by other disorders. Hypothalamic and nephrogenic DI can also be caused by mutation of the gene that encodes the AVP prohormone, the AVP-2 receptors in the kidney, or the aquaporin-2 water channels that mediate antidiuresis. Familial hypothalamic DI is usually transmitted in an autosomal dominant mode, but autosomal recessive or X-linked recessive forms also exist. Familial nephrogenic DI is usually transmitted in an X-linked recessive mode but can also be autosomal recessive or dominant. Hence the mode of inheritance does not always indicate the type of DI. Indirect methods of differential diagnosis are also unreliable and the pituitary MRI signal is diminished in both types of familial DI. Thus the determination of plasma AVP and/or the response to desmopressin therapy plus gene sequencing provides the best basis for effective management and family counseling.

Central Diabetes Insipidus Caused by Arginine Vasopressin Gene Mutation: Report of a Novel Mutation and Review of Literature

Familial neurohypophyseal diabetes insipidus (FNDI) is an autosomal dominant hereditary disorder characterized by severe polydipsia and polyuria that usually presents in early childhood. In this study, we describe a new arginine vasopressin (AVP) gene mutation in an ethnic German family with FNDI and provide an overview of disease-associated AVP-gene mutations that are already described in literature. Three members of a German family with neurohypophyseal diabetes insipidus were studied. Isolated DNA from peripheral blood samples was used for mutation analysis by sequencing the whole coding region of AVP-NPII gene. Furthermore, we searched the electronic databases MEDLINE (Pubmed) as well as HGMD, LOVD-ClinVar, db-SNP and genomAD in order to compare our cases to that of other patients with FNDI. Genetic analysis of the patients revealed a novel heterozygote missense mutation in exon 2 of the AVP gene (c.274T>G), which has not yet been described in literature. We identified reports of more than 90 disease-associated mutations in the AVP gene in literature. The novel mutation of the AVP gene seems to cause FNDI in the presented German family. Similar to our newly detected mutation, most mutations causing FNDI are found in exon 2 of the AVP gene coding for neurophysin II. Clinically, it is important to think of FNDI in young children presenting with polydipsia and polyuria.

Diagnosis and differential diagnosis of diabetes insipidus: Update

The two main differential diagnoses of central diabetes insipidus are nephrogenic diabetes insipidus and primary polydipsia. Reliable distinction between those entities is essential as treatment differs substantially with the wrong treatment potentially leading to serious complications. Past diagnostic measures using the indirect water deprivation test had several pitfalls, resulting in a low diagnostic accuracy. With the introduction of copeptin, a stable and reliable surrogate marker for arginine vasopressin, diagnosis of diabetes insipidus was new evaluated. While unstimulated basal copeptin measurement reliably diagnoses nephrogenic diabetes insipidus, a stimulation test is needed to differentiate patients with central diabetes insipidus from patients with primary polydipsia. Stimulation can either be achieved through hypertonic saline infusion or arginine infusion. While the former showed high diagnostic accuracy and superiority over the indirect water deprivation test in a recent validation study, the diagnostic accuracy for arginine-stimulated copeptin was slightly lower, but superior in test tolerance. In summary of the recent findings, a new copeptin based diagnostic algorithm is proposed for the reliable diagnosis of diabetes insipidus.

Role of protein aggregation and degradation in autosomal dominant neurohypophyseal diabetes insipidus

This review focuses on the cellular and molecular aspects underlying familial neurohypophyseal diabetes insipidus (DI), a rare disorder that is usually transmitted in an autosomal-dominant fashion. The disease, manifesting in infancy or early childhood and gradually progressing in severity, is caused by fully penetrant heterozygous mutations in the gene encoding prepro-vasopressin-neurophysin II, the precursor of the antidiuretic hormone arginine vasopressin (AVP). Post mortem studies in affected adults have shown cell degeneration in vasopressinergic hypothalamic nuclei. Studies in cells expressing pathogenic mutants and knock-in rodent models have shown that the mutant precursors are folding incompetent and fail to exit the endoplasmic reticulum (ER), as occurs normally with proteins that have entered the regulated secretory pathway. A portion of these mutants is eliminated via ER-associated degradation (ERAD) by proteasomes after retrotranslocation to the cytosol. Another portion forms large disulfide-linked fibrillar aggregates within the ER, in which wild-type precursor is trapped. Aggregation capacity is independently conferred by two domains of the prohormone, namely the AVP moiety and the C-terminal glycopeptide (copeptin). The same domains are also required for packaging into dense-core secretory granules and regulated secretion, suggesting a disturbed balance between the physiological self-aggregation at the trans-Golgi network and avoiding premature aggregate formation at the ER in the disease. The critical role of ERAD in maintaining physiological water balance has been underscored by experiments in mice expressing wild-type AVP but lacking critical components of the ERAD machinery. These animals also develop DI and show amyloid-like aggregates in the ER lumen. Thus, the capacity of the ERAD is exceeded in autosomal dominant DI, which can be viewed as a neurodegenerative disorder associated with the formation of amyloid ER aggregates. While DI symptoms develop prior to detectable cell death in transgenic DI mice, the eventual loss of vasopressinergic neurons is accompanied by autophagy, but the mechanism leading to cell degeneration in autosomal dominant neurohypophyseal DI still remains unknown.

Lessons from animal models of endocrine disorders caused by defects of protein folding in the secretory pathway

Most peptide hormones originate from secretory protein precursors synthesized within the endoplasmic reticulum (ER). In this specialized organelle, the newly-made prohormones must fold to their native state. Completion of prohormone folding usually occurs prior to migration through the secretory pathway, as unfolded/misfolded prohormones are retained by mechanisms collectively known as ER quality control. Not only do most monomeric prohormones need to fold properly, but many also dimerize or oligomerize within the ER. If oligomerization occurs before completion of monomer folding then when a poorly folded peptide prohormone is retained by quality control mechanisms, it may confer ER retention upon its oligomerization partners. Conversely, oligomerization between well-folded and improperly folded partners might help to override ER quality control, resulting in rescue of misfolded forms. Both scenarios appear to be possible in different animal models of endocrine disorders caused by genetic defects of protein folding in the secretory pathway. In this paper, we briefly review three such conditions, including familial neurohypophyseal diabetes insipidus, insulin-deficient diabetes mellitus, and hypothyroidism with defective thyroglobulin.

Polyuria-polydipsia syndrome: a diagnostic challenge

The main determinants for the maintenance of water homeostasis are the hormone arginine vasopressin (AVP) and thirst. Disturbances in these regulatory mechanisms can lead to polyuria-polydipsia syndrome, which comprises of three different conditions: central diabetes insipidus (DI) due to insufficient secretion of AVP, nephrogenic DI caused by renal insensitivity to AVP action and primary polydipsia due to excessive fluid intake and consequent physiological suppression of AVP. It is crucial to determine the exact diagnosis because treatment strategies vary substantially. To differentiate between the causes of the polyuria-polydipsia syndrome, a water deprivation test combined with desmopressin administration is the diagnostic 'gold standard'. Thereby, AVP activity is indirectly evaluated through the measurement of urine osmolality after prolonged dehydration. However, this test has several limitations and may fail to distinguish precisely between patients with primary polydipsia and mild forms of central and nephrogenic DI. The direct measurement of AVP during the water deprivation test, which was reported in the 1980s, has not been widely adopted due to availability, assay issues and diagnostic performance. Recently, copeptin, the c-terminal portion of the larger precursor peptide of AVP, has been evaluated in the setting of polyuria-polydipsia syndrome and appears to be a useful candidate biomarker for the differential diagnosis. A standardised method for the water deprivation test is presented as part of a joint initiative of the Endocrine Society of Australia, the Australasian Association of Clinical Biochemists and the Royal College of Pathologists of Australasia to harmonise dynamic endocrine tests across Australia.

Mice deficient for ERAD machinery component Sel1L develop central diabetes insipidus

Deficiency of the antidiuretic hormone arginine vasopressin (AVP) underlies diabetes insipidus, which is characterized by the excretion of abnormally large volumes of dilute urine and persistent thirst. In this issue of the JCI, Shi et al. report that Sel1L-Hrd1 ER-associated degradation (ERAD) is responsible for the clearance of misfolded pro-arginine vasopressin (proAVP) in the ER. Additionally, mice with Sel1L deficiency, either globally or specifically within AVP-expressing neurons, developed central diabetes insipidus. The results of this study demonstrate a role for ERAD in neuroendocrine cells and serve as a clinical example of the effect of misfolded ER proteins retrotranslocated through the membrane into the cytosol, where they are polyubiquitinated, extracted from the ER membrane, and degraded by the proteasome. Moreover, proAVP misfolding in hereditary central diabetes insipidus likely shares common physiopathological mechanisms with proinsulin misfolding in hereditary diabetes mellitus of youth.

Genetics of Diabetes Insipidus

Diabetes insipidus is a disease characterized by polyuria and polydipsia due to inadequate release of arginine vasopressin from the posterior pituitary gland (neurohypophyseal diabetes insipidus) or due to arginine vasopressin insensitivity by the renal distal tubule, leading to a deficiency in tubular water reabsorption (nephrogenic diabetes insipidus). This article reviews the genetics of diabetes insipidus in the context of its diagnosis, clinical presentation, and therapy.

Endocrine Glands and Hearing: Auditory Manifestations of Various Endocrine and Metabolic Conditions

The aetiology of hearing loss in humans is multifactorial. Besides genetic, environmental and infectious causes, several endocrine and metabolic abnormalities are associated with varying degrees of hearing impairment. The pattern of hearing loss may be conductive, sensori-neural or mixed. The neurophysiology of hearing as well as the anatomical structure of the auditory system may be influenced by changes in the hormonal and metabolic milieu. Optimal management of these conditions requires the integrated efforts of the otolaryngologist and the endocrinologist. The presence of hearing loss especially in the young age group should prompt the clinician to explore the possibility of an associated endocrine or metabolic disorder for timely referral and early initiation of treatment.