Review Question - QID 109632

A 2-day-old male infant is seen in the newborn nursery for repeated emesis and lethargy. He was born at 39 weeks to a 24-year-old mother following an uncomplicated pregnancy and birth. The mother is of Mediterranean descent. The infant has been breastfeeding every 2 hours and has 10 wet diapers per day. The father is not involved in the mother or the infant's life, and his past medical history is unknown. Laboratory results are as follows:

Hemoglobin: 12 g/dL
Platelet count: 200,000/mm^3
Mean corpuscular volume: 95 µm^3
Reticulocyte count: 0.5%
Leukocyte count: 5,000/mm^3 with normal differential

Serum:
Na+: 134 mEq/L
Cl-: 100 mEq/L
K+: 3.3 mEq/L
HCO3-: 24 mEq/L
Urea nitrogen: 1 mg/dL
Creatinine: 0.6 mg/dL
Ammonnia: 150 µmol/L (normal: 11 to 32 µmol/L)

Which of the following is the most likely diagnosis?