Inborn Errors of Metabolism: From Preconception to Adulthood.

Inborn errors of metabolism (IEM), although individually rare, occur in 1 out of every 1,500 births. The first opportunity to detect IEM occurs during preconception counseling, when pregnant women and couples considering future pregnancies can undergo carrier screening. For individuals of all ethnic backgrounds, the screening includes testing for a variety of IEM and non-IEM. For individuals of Ashkenazi Jewish descent, carrier screening, per the American College of Medical Genetics and Genomics, also includes testing for Tay-Sachs disease and four other IEM. Inborn errors of metabolism can present in utero; in newborns; or in children, adolescents, and adults. Some IEM can be detected in utero with the use of ultrasonography. Most commonly, IEM are detected at newborn screening. Expanded newborn screening, which now includes 34 core conditions, allows for diagnosis in the newborn period and provides the opportunity for early institution of available treatments. However, some newborns present with symptoms consistent with an IEM before the availability of pending newborn screening results or present with symptoms attributable to an IEM not detectable with screening. Such situations are medical emergencies requiring immediate consultation with a metabolic specialist. If a delay occurs in obtaining consultation, initial treatment involves discontinuing feeding and providing high-rate glucose infusions. Some IEM present later in life. Children may develop and present with dysmorphic facial features. In some cases, symptoms may not appear until adolescence or adulthood when patients have residual enzyme activity that allows for slow accumulation of toxic molecules over time. Long-term treatments are effective for some IEM. Treatments include dietary restrictions and enzyme-replacement therapies.