Review Question - QID 214336

A 5-year-old boy presents to his primary care doctor for fatigue and weakness. The child is homeschooled, and his parents recently signed him up for basketball. They noticed that he is not as athletic as the other children. He tires easily and has little interest in playing. Their child has always been less athletically inclined and has preferred the classroom instead. His temperature is 98.1°F (36.7°C), blood pressure is 92/53 mmHg, pulse is 83/min, respirations are 13/min, and oxygen saturation is 98% on room air. Physical exam is notable for a young boy with decreased muscle tone and hepatomegaly. He has 3/5 muscle strength in all muscle groups. Laboratory values are ordered as seen below.

Serum:
Na+: 139 mEq/L
Cl-: 101 mEq/L
K+: 4.2 mEq/L
HCO3-: 24 mEq/L
BUN: 20 mg/dL
Glucose: 59 mg/dL
Creatinine: 1.0 mg/dL
Ca2+: 10.2 mg/dL

A biopsy is performed of the liver demonstrating glycogen chains with small branches. Which of the following is the most likely etiology of this patient's symptoms?