Q. A 7-year-old boy was referred to a tertiary pediatric center due to a progressive history of proximal muscle weakness. Over the past year, he exhibited difficulty in climbing stairs and frequent falls. During a routine examination, an unusually enlarged tongue (macroglossia) was noted. Additionally, the parents reported that he had experienced episodes of nocturnal dyspnea. Despite aggressive management and close monitoring, the child died. An autopsy revealed hypertrophic cardiomyopathy and significant glycogen accumulation within cardiac and skeletal muscle cells. Given the patient's clinical presentation and autopsy findings, which enzyme is most likely deficient in this patient?