A three day-old term infant borne at home, breast-fed exclusively, presented with lethargy, bulging fontanel, and bright red blood from rectum. What is the most likely etiology of his disease?

Vit K deficiency is associated with hemorrhagic disease of newborn which has manifested in this baby as Intracranial hemorrhage (bulging fontanel) and GI bleed (blood per rectum). Moreover home delivery (Vit K may not have been given at bih) and exclusive breast feeding (Vit K is deficient in breast milk) clearly point to Vit K deficiency as etiology.