A 3-day-old male infant presents with seizures and tetany. Serum calcium is 6.2 mg/dL (normal 8.5–10.5). On examination, he has a small mouth, malar flattening, and hooded eyelids. Cardiac auscultation reveals a single S2 with a systolic murmur. The structure marked **C** in the diagram (22q11.2 deletion) is suspected. Which of the following best explains the neonatal hypocalcemia in this condition?