A 1-week-old newborn has had poor feeding, vomiting, and progressive lethargy over the past 4 days. She was born at term; pregnancy, labor, and delivery were uncomplicated, and she had no congenital anomalies. She is being breast-fed. She has a healthy 2-year-old brother; a sister died at 10 days of age after a full-term birth. Examination shows decreased muscle tone and poor responsiveness; reflexes are normal. Serum bicarbonate level is 8 mEq/L, pH is 7.15, and plasma ammonia level is 10 times the upper limit of normal. Which of the following is the most likely cause?
- A) Mitochondrial disorder
- B) Mucopolysaccharidoses disorder
- C) Organic acid metabolism disorder
- D) Renal tubular acidosis
- E) X-linked leukodystrophy