Differenzialdiagnose des Polyhydramnions beim Hyperprostaglandin-E-Syndrom: Case-Report

Nephrogenic diabetes insipidus

PURPOSE OF REVIEW

In nephrogenic diabetes insipidus (NDI), the kidney is unable to concentrate urine despite elevated concentrations of the antidiuretic hormone arginine-vasopressin. In congenital NDI, polyuria and polydipsia are present from birth and should be immediately recognized to avoid severe episodes of dehydration. Unfortunately, NDI is still often recognized late after a 'diagnostic odyssey' involving false leads and dangerous treatments.Once diagnosed, appropriate treatment can be started. Moreover, laboratory studies have identified promising new compounds, which may help achieve urinary concentration independent of vasopressin.

RECENT FINDINGS

MAGED2 mutations caused X-linked polyhydramnios with prematurity and a severe but transient form of antenatal Bartter's syndrome.We distinguish two types of hereditary NDI: a 'pure' type with loss of water only and a complex type with loss of water and ions. Mutations in the AVPR2 or AQP2 genes, encoding the vasopressin V2 receptor and the water channel Aquaporin2, respectively, lead to a 'pure' NDI with loss of water but normal conservation of ions. Mutations in genes that encode membrane proteins involved in sodium chloride reabsorption in the thick ascending limb of Henle's loop lead to Bartter syndrome, a complex polyuric-polydipsic disorder often presenting with polyhydramnios. A new variant of this was recently identified: seven families were described with transient antenatal Bartter's syndrome, polyhydramnios and MAGED2 mutations.Multiple compounds have been identified experimentally that may stimulate urinary concentration independently of the vasopressin V2 receptor. These compounds may provide new treatments for patients with X-linked NDI.

SUMMARY

A plea for early consideration of the diagnosis of NDI, confirmation by phenotypic and/or genetic testing and appropriate adjustment of treatment in affected patients.

Electrolyte disorders

Electrolyte disorders can result in life-threatening complications. The kidneys are tasked with maintaining electrolyte homoeostasis, yet the low glomerular filtration rate of neonatal kidneys, tubular immaturity, and high extrarenal fluid losses contribute to increased occurrence of electrolyte disorders in neonates. Understanding the physiologic basis of renal electrolyte handling is crucial in identifying underlying causes and initiation of proper treatment. This article reviews key aspects of renal physiology, the diagnostic workup of disorders of plasma sodium and potassium, and the appropriate treatment, in addition to inherited disorders associated with neonatal electrolyte disturbances that illuminate the physiology of renal electrolyte handling.

GABA(A) receptors in normal development and seizures: friends or foes?

GABA(A) receptors have an age-adapted function in the brain. During early development, they mediate excitatory effects resulting in activation of calcium sensitive signaling processes that are important for the differentiation of the brain. In more mature stages of development and in adults, GABA(A) receptors transmit inhibitory signals. The maturation of GABA(A) signaling follows sex-specific patterns, which appear to also be important for the sexual differentiation of the brain. The inhibitory effects of GABA(A) receptor activation have been widely exploited in the treatment of conditions where neuronal silencing is necessary. For instance, drugs that target GABA(A) receptors are the mainstay of treatment of seizures. Recent evidence suggests however that the physiology and function of GABA(A) receptors changes in the brain of a subject that has epilepsy or status epilepticus.This review will summarize the physiology of and the developmental factors regulating the signaling and function of GABA(A) receptors; how these may change in the brain that has experienced prior seizures; what are the implications for the age and sex specific treatment of seizures and status epilepticus. Finally, the implications of these changes for the treatment of certain forms of medically refractory epilepsies and status epilepticus will be discussed.

Hereditary polyuric disorders: new concepts and differential diagnosis

The identification, characterization, and mutational analysis of genes coding for key proteins to the mechanisms of urine concentration provide the basis for understanding the 2 types of hereditary nephrogenic diabetes insipidus (NDI): a pure type characterized by loss of water only, and a complex type characterized by loss of water and ions. Patients with hereditary NDI bearing mutations in AVPR2, the gene coding for the arginine vasopressin 2 receptor, or in AQP2, the gene coding for the vasopressin-sensitive water channel, have a pure NDI phenotype with loss of water, but normal conservation of sodium, potassium, chloride, and calcium. Patients bearing inactivating mutations in 1 of the 5 genes (SLC12A1, KCNJ1, CLCNKB, CLCNKA, and CLCNKB in combination, or BSND) that encode the membrane proteins of the thick ascending limb of the loop of Henle have a complex polyuro-polydipsic syndrome with loss of water, sodium, chloride, calcium, magnesium, and potassium. The purpose of this article is to increase the general awareness of these congenital NDI patients to prevent severe episodes of dehydration and provide precise molecular diagnosis and treatment.

Molecular biology of hereditary diabetes insipidus

The identification, characterization, and mutational analysis of three different genes-the arginine vasopressin gene (AVP), the arginine vasopressin receptor 2 gene (AVPR2), and the vasopressin-sensitive water channel gene (aquaporin 2 [AQP2])-provide the basis for understanding of three different hereditary forms of "pure" diabetes insipidus: Neurohypophyseal diabetes insipidus, X-linked nephrogenic diabetes insipidus (NDI), and non-X-linked NDI, respectively. It is clinically useful to distinguish two types of hereditary NDI: A "pure" type characterized by loss of water only and a complex type characterized by loss of water and ions. Patients who have congenital NDI and bear mutations in the AVPR2 or AQP2 genes have a "pure" NDI phenotype with loss of water but normal conservation of sodium, potassium, chloride, and calcium. Patients who bear inactivating mutations in genes (SLC12A1, KCNJ1, CLCNKB, CLCNKA and CLCNKB in combination, or BSND) that encode the membrane proteins of the thick ascending limb of the loop of Henle have a complex polyuro-polydipsic syndrome with loss of water, sodium, chloride, calcium, magnesium, and potassium. These advances provide diagnostic and clinical tools for physicians who care for these patients.