Question 248

Question:

A 3-month-old female infant from South America is adopted. She has been exclusively breast-fed. The only known medical history is treatment with an antibiotic for a gastrointestinal infection prior to arrival in the USA; the specific antibiotic is not known. Three days after receiving the infant, the adoptive parents note that she no longer moves her left upper and lower extremities. Radiologic examination shows an intracranial hemorrhage without signs of head trauma. Laboratory studies show anemia and prolonged partial thromboplastin and prothrombin times. Her condition is most likely associated with a deficiency in which of the following?

Correct Answer: B.  Glutamic acid γ (gamma) carboxylation

Prolonged bleeding times are commonly seen in infants who have a deficiency of Vitamin K. The sterile intestines of newborns are lacking in intestinal flora to synthesize Vitamin K, and this newborn is at particular risk, having recently undergone an antibiotic regimen. Therefore, she is likely deficient in Vitamin K. Vitamin K is necessary for the (B) γ (gamma) carboxylation of glutamic acid residues of proteins necessary for blood clotting. Vitamin K-dependent clotting factors II, VII, IX, and X are therefore deficient, resulting in prolonged PT and aPTT times. Anticoagulant Proteins C and S are also affected by the lack of Vitamin K, but the hypocoagulability is more significant in Vitamin K deficiency.