All vitamin K-dependent coagulation factors require normal function of gamma-glutamyl carboxylase and vitamin K epoxide reductase enzyme complex (VKORC1). Heritable dysfunction of gamma-glutamyl carboxylase or of the VKORC1 complex results in the secretion of poorly carboxylated vitamin K-dependent proteins that play a role in coagulation. The following review will summarize the clinical manifestations of vitamin K-dependent coagulation factors deficiency I and II and will provide a detailed explanation about the gene and protein structure, the function of the protein, and an analysis of the previously reported mutations. Laboratory assays used for diagnosis will be discussed, and treatment for various clinical settings will be recommended.