CLINICAL HISTORY AND BACKGROUND A 22-month-old boy with no medical history, born from consanguineous parents, was referred to the pediatric emergency department for respiratory distress, recurrent vomiting, hepatomegaly, and asthenia in the context of acute otitis media. First-line blood analyses showed acidosis (pH 7.00; reference, 7.37-7.43), normal lactate (1.8 mmol/L; reference, 0.5-2.2 mmol/L), decreased bicarbonate (3.1 mmol/L; reference, 22-26 mmol/L), abnormal base excess (-26 mmol/L; reference, -2 to +2 mmol/L), hyperketonemia (Abbott Diabetes Care Freestyle Optium Neo, 4.6 mmol/L; threshold, 0.06 mmol/ L), hyperammonemia (99 ^mol/L; reference, 15-55 ^mol/L), and blood glucose of 2.3 mmol/L (reference, 1.65-5.50 mmol/L). ...an amino acid profile will reveal an important increase of alloisoleucine, pointing to an isoleucine catabolism disorder because alloisoleucine is alternatively built up when isoleucine accumulates.