Metabolic Disorders Associated With Neonatal Hypoglycemia

Abstract

After completing this article, readers should be able to: 1. Describe four sources of glucose available to the neonate in the first 24 postnatal hours. 2. Select the best routine diagnostic test to recognize fatty acid oxidation defects. 3. List three or more metabolic disorders that can be identified by newborn screening performed using tandem mass spectrometry. Hypoglycemia is a common problem in neonates that has many causes. This review focuses on metabolic disorders that may be associated with hypoglycemia in the neonatal period. During intrauterine life, the fetus derives fuel, as glucose, from the mother via the placenta. After birth, the energy demands on the former fetus increase dramatically. The baby now must maintain its own body temperature and must undertake the work of breathing and other activities. Further, the maintenance of blood glucose levels requires glycogenolysis and gluconeogenesis. Postnatally, there are four sources of glucose: dietary glucose; glucose derived from the cleavage of more complex sugars in the gut (eg, lactose to glucose and galactose); glucose released from glycogen stores (primarily in the liver); and gluconeogenesis, in which glucose is synthesized from carbon skeletons derived from certain amino acids using energy derived from catabolism of fatty acids. Most term infants have sufficient glycogen stores to maintain blood glucose levels for several hours before gluconeogenesis is required. Infants who are breastfed in the United States typically are offered only water as a supplement to human milk during the first few postnatal days, a period when the mother’s milk supply is not yet established. In contrast, formula-fed babies receive calories by mouth by the end of the first postnatal day. Consequently, the metabolic stress of prolonged fasting occurs more frequently in breastfed than in formula-fed babies. Although breastfed babies have higher levels of ketone bodies that appear to provide adequate energy during this …