2. A 6-month-old infant brought to ED by his parents with feeding difficulties. Following a relatively normal early developmental period, a boy becomes pale and lethargic and begins to
Sow signs of developmental delay. Ine inrant nas megaloblastic anemia. In order to identify
the cause of anemia vou order to measure the levels of orotic acid and homocysteine.
Laboratory evaluation reveals normal orotate levels and high plasma homocysteine levels.
Based on laboratory results, it is suggested that the patient nas inherited detect in the
methylcobalamin synthesis. Which of the following reactions is most likely affected in this
patient?