Adapted from Theorell C, Degenhardt M: Assessment and management of metabolic dysfunction. In: Kenner C et al, editors: Comprehensive neonatal nursing: a physiologic perspective, ed 2, Philadelphia, 1998, WB Saunders.

Metabolic disorders in the newborn are not necessarily identified in the hospital, because the clinical manifestations may not become evident until weeks or even months later. Clinical manifestations can be specific or general, depending on the disorder. Metabolic disorders have been categorized into three types: (1) those that are “silent” or slowly manifest symptoms, such as phenylketonuria (PKU), and that if not treated early can result in mental retardation; (2) those such as urea cycle disorders or organic acidemias that manifest as an acute metabolic crisis shortly after birth (a few days), in which the infant demonstrates symptoms of respiratory distress, vomiting, and lethargy leading to coma, and which can be life threatening if not identified and treated; and (3) those that cause progressive neurologic disorders, such as Tay-Sachs disease. It is important that these disorders be detected and treated as soon as possible to prevent or minimize serious outcomes of developmental delays, learning disabilities, attention-deficit/hyperactivity disorder, or mental retardation. Widespread screening exists for the following inborn errors of metabolism: (1) PKU, (2) congenital hypothyroidism, (3) galactosemia, (4) maple syrup urine disease, and (5) congenital adrenal hyperplasia. Note that PKU, congenital hypothyroidism, and galactosemia are the only three newborn screening tests required by all states (Box 55-2).

Box 55-2 Newborn Screening Programs

Newborn screening is a general term for a nationwide program, governed by individual states, that uses a simple blood test called tandem mass spectrometry to screen for three categories of disorders: inborn errors of metabolism (e.g., PKU; galactosemia; maple syrup urine disease [MSUD]); hemoglobinopathies (e.g., sickle cell disease [see Chapter 71]; and hemophilia [see Chapter 32]); and endocrinopathies (e.g., congenital hypothyroidism; congenital adrenal hyperplasia; and cystic fibrosis (see Chapter 17). There are over 100 different tests that newborns could be screened with. A complete listing of the tests that are required by each state can be found at www.genes-r-us.uthscsa.edu/nbsdisorders.pdf. A list of resources is included at the end of this chapter for families who may wish to have optional testing done. This chapter focuses primarily on inborn errors of metabolism since sickle cell disease, hemophilia, and cystic fibrosis are covered elsewhere in this book. Newborn screening guidelines are available from the Health Resources and Services Administration of the U.S. Department of Health and Human Services, under the title “U.S. Newborn Screening System Guidelines II: Follow-Up of Children, Diagnosis, Management, and Evaluation: Statement of the Council of Regional Networks for Genetic Services (CORN)” (available from www.ask.hrsa.gov/detail.cfm?id=MCHN011).

In the future, gene-based therapy may offer promising options to correct the deficiency of the enzyme or substrate. Risk factors associated with inborn errors of metabolism include past family history of unexplained neonatal and/or sibling deaths, consanguinity, multiple spontaneous abortions, psychomotor difficulties in family members, and symptoms in previous children associated with metabolic diseases, such as metabolic acidosis, ataxia, and hypoglycemia.