A breastfed term neonate born at home presents on day 4 of life with oozing from the umbilical stump and blood in the stool. PT and aPTT are both markedly prolonged. The underlying defect is impaired activity of which group of proteins?
- A Factors II, VII, IX and X, due to failure of gamma-carboxylation of glutamate residues ✓
- B Fibrinogen and factor XIII, due to defective fibrin cross-linking
- C Factors VIII and von Willebrand factor, due to absent hepatic glycosylation
- D Factor XI and factor XII, due to immature contact phase activation
Correct answer: A. Factors II, VII, IX and X, due to failure of gamma-carboxylation of glutamate residues
Explanation
Classic hemorrhagic disease of the newborn results from vitamin K deficiency. Vitamin K is the cofactor for gamma-glutamyl carboxylase, which activates factors II, VII, IX and X (and protein C and S). The newborn liver stores are low because vitamin K crosses the placenta poorly and breast milk contains little of it. Factors VIII and vWF are unrelated to vitamin K, so their deficiency would not prolong both PT and aPTT in this pattern.
Reference: Nelson Textbook of Pediatrics, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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