Q. A 62-year-old man presents to your primary care clinic with complaints of persistent fatigue, tingling and numbness in the feet, and difficulty with balance for over a year. He is a known diabetic and hypertensive on regular treatment. His temperature is 98.6°F (37°C), pulse is 86 beats per minute, blood pressure is 130/70 mmHg and respiratory rate is 14 per minute. Physical examination shows pallor and glossitis. Neurological examination shows symmetric impaired position and vibration sensation in the toes. Deep tendon reflexes are reduced in the achilles and normal at the patellae. Initial lab investigations are shown below. The peripheral blood smear shows RBC macrocytosis and hypersegmented neutrophils. What is the most probable pathogenic mechanism that can explain the neurologic complications experienced by this patient?