Ggcx, also known as gamma-glutamyl carboxylase or vitamin K-dependent glutamyl carboxylase, is an enzyme that catalyzes the post-translational modification of specific glutamate residues in vitamin K-dependent proteins (VKDPs). This process, called gamma-carboxylation, is essential for activating VKDPs which are involved in multiple biological functions including blood coagulation, bone metabolism, vascular calcification, and cell proliferation [4].

Mutations in the GGCX gene are associated with multiple phenotypes. Vitamin K-dependent coagulation factor deficiency (VKCFD1) is a well-known phenotype, and patients may also have skin, eye, heart or bone manifestations [1]. Some GGCX variants that cause reduced gamma-carboxylation of Gla rich protein (GRP) are associated with skin laxity in VKCFD1 patients [2]. Different GGCX mutations show varying responses to vitamin K, determining the severity of the hemorrhagic phenotype in VKCFD1 patients, which helps in predicting the outcome and recommending appropriate treatments [3]. In a study on mice, the GgcxK325Q mutation did not affect the calcium homeostasis of the epididymis and male fertility [5]. Also, knocking out GGCX reduces the replication of Eurasian avian-like H1N1 swine influenza virus, as GGCX-mediated carboxylation modification of viral haemagglutinin (HA) contributes to the virus's receptor binding adaption [6].

In conclusion, Ggcx is crucial for the activation of VKDPs and thus for various biological functions. Research on Ggcx, especially through genetic models like the GgcxK325Q knock-in mice, has provided insights into its role in human diseases such as VKCFD1, and also in non-disease-related biological processes like male fertility and virus-host interactions.