Neonatal Vitamin B12 Deficiency Secondary to Maternal Subclinical Pernicious Anemia: Identification by Expanded Newborn Screening

A neonate with elevated propionylcarnitine on the newborn screen was found to have methylmalonic acidemia due to vitamin B 12 deficiency. The mother was also vitamin B 12 -deficient. This case illustrates the utility of expanded newborn screening for detection of vitamin B 12 deficiency, allowing prompt treatment and prevention of potential sequelae.