E-Mail karger@karger.com Mini Review Horm Res Paediatr 2016;86:143–153 DOI: 10.1159/000449057 Water Balance and ‘Salt Wasting’ in the First Year of Life: The Role of Aldosterone-Signaling Defects Carla Bizzarri   a Stefania Pedicelli   a Marco Cappa   a Stefano Cianfarani   b, c a  Unit of Endocrinology and Diabetes, ‘Bambino Gesù’ Children’s Hospital, and b  Molecular Endocrinology Unit, ‘Bambino Gesù’ Children’s Hospital-Tor Vergata University, Rome, Italy; c  Department of Women’s and Children’s Health, Karolinska Institutet, Stockholm, Sweden Introduction Water and electrolyte requirements are very high in early postnatal life and decrease with age until adult- hood. Studies on water and electrolyte metabolism in newborns and infants are limited. During the first months of life, kidneys show tubular immaturity leading to impaired sodium and water reabsorption. This may predispose to failure to thrive and dehydration under pathological circumstances [1]. The alteration of sodi- um reabsorption during the perinatal period has been related to a partial and transient renal resistance to aldo- sterone [1]. The initial paragraphs of this review analyze peculiar characteristics of water and electrolyte homeostasis and functional aspects of the renin-angiotensin-aldosterone system in the first year of life. The following paragraphs focus on the clinical presentation of salt wasting and the different forms of aldosterone resistance in infants. Fi- nally, the key points of emergency management and long-term follow-up of infants affected by these defects are discussed. Key Words Newborn and infant · Salt wasting · Sodium disturbances · Aldosterone · Pseudohypoaldosteronism Abstract In newborns and infants, dehydration and salt wasting rep- resent a relatively common cause of admission to hospital and may result in life-threatening complications. Kidneys are responsible for electrolyte homoeostasis, but neonatal kid- neys show low glomerular filtration rate and immaturity of the distal nephron, leading to reduced ability to concentrate urine. High extrarenal fluid losses often contribute to the in- creased occurrence of electrolyte disorders. Aldosterone is essential for sodium retention in the kidney, salivary glands, sweat glands and colon. A partial and transient aldosterone resistance is present in newborns and infants, thus reducing the capability of maintaining sodium balance in specific pathological conditions. The present review examines the mechanisms making infants more susceptible to salt wast- ing. Peculiar aspects of renal physiology in the first year of life and management of electrolyte disorders (i.e. sodium and potassium) are considered. Finally, inherited disorders associated with neonatal salt wasting are examined in detail. © 2016 S. Karger AG, Basel Received: April 19, 2016 Accepted: August 10, 2016 Published online: September 7, 2016 HORMONE RESEARCH IN PÆDIATRICS Carla Bizzarri, MD ‘Bambino Gesù’ Children’s Hospital Piazza S. Onofrio 4 IT–00165 Rome (Italy) E-Mail carla.bizzarri  @  opbg.net © 2016 S. Karger AG, Basel www.karger.com/hrp