Vitamin K deficiency

A 6-day-old boy is brought to the emergency department by his parents because of easy bruising. The infant was born at 38 weeks to a 23-year-old primigravida woman via normal vaginal delivery at home. This is his first medical evaluation. The patient’s mother took prenatal vitamins and maintained a healthy diet during pregnancy. Family history is unremarkable. Vitals are within normal limits. Physical examination reveals an alert infant. Examination shows multiple ecchymoses visible on upper and lower extremities. The remainder of the examination is unremarkable. Laboratory results are shown.
 

Laboratory features
Laboratory value	Result
Platelet count	230,000/mm3
Bleeding time	5 minutes
Prothrombin time	27 seconds
Activated partial thromboplastin time	42 seconds

Which of the following is the most likely cause of this infant’s presentation?