Review Question - QID 214255

A 5-year-old boy presents to his primary care doctor for weakness and fatigue. He recently immigrated to the US after he was adopted by a local family. The child is smaller than his peers and has struggled to gain weight. He also has had several episodes of seizures of unknown etiology. His past medical history is unknown, and he is not currently taking any medications. His temperature is 97.5°F (36.4°C), blood pressure is 86/54 mmHg, pulse is 100/min, respirations are 19/min, and oxygen saturation is 98% on room air. Physical exam is notable for a small child. Abdominal exam reveals an enlarged, nontender liver. Laboratory studies are ordered as seen below.

Hemoglobin: 12 g/dL
Hematocrit: 36%
Leukocyte count: 6,500/mm^3 with normal differential
Platelet count: 188,000/mm^3

Serum:
Na+: 139 mEq/L
Cl-: 100 mEq/L
K+: 4.3 mEq/L
HCO3-: 25 mEq/L
BUN: 14 mg/dL
Glucose: 49 mg/dL
Creatinine: 0.7 mg/dL
Ca2+: 10.2 mg/dL
AST: 12 U/L
ALT: 10 U/L
Uric acid: 15.0 mg/dL

Which of the following is the most likely diagnosis?