Q. A 4-day-old male infant is brought to the pediatric emergency department by his parents due to poor feeding and increased irritability. His mother reports that the baby was feeding well initially, but for the past 24 hours, he has been refusing feeds and seems unusually lethargic. On examination, the infant has an altered level of consciousness, and blood tests reveal hyperammonemia, increased orotic acid in urine and blood, decreased BUN and citrulline levels, and elevated carbamoyl phosphate. Based on the history, examination and laboratory findings, which of the following is the most likely diagnosis in this infant?