Abstract: This case report highlights the difficulties in diagnosing non-ketotic hyperglycinemia in a neonate with maternal substance abuse and neonatal abstinence syndrome. Despite initial treatment for neonatal abstinence syndrome, the neonate suffered sudden cardiopulmonary arrest and had elevated glycine levels in the serum, cerebrospinal fluid, and urine, suggestive of non-ketotic hyperglycinemia. However, immediate treatment failed to improve the newborn’s condition, and the infant died of ventilator-associated pneumonia. The report underscores the importance of considering other differential diagnoses in infants with neonatal abstinence syndrome and highlights the challenges of diagnosing and treating rare genetic disorders, such as non-ketotic hyperglycinemia, in the neonatal period.

Keywords: Drug misuse, hyperglycinemia, neonatal abstinence syndrome, nonketotic