Characterization of vitamin K-dependent carboxylase mutations that cause bleeding and nonbleeding disorders.

Vitamin K-dependent coagulation factors deficiency (VKCFD) is a bleeding disorder mainly associated with mutations in gamma-glutamyl carboxylase (GGCX) that often has fatal outcomes. Some patients with non-bleeding syndromes linked to GGCX mutations, however, show no coagulation abnormalities. The correlation between GGCX genotypes and their clinical phenotypes has been previously unknown. Here we report the identification and characterization of novel GGCX mutations in a patient with both severe cerebral bleeding disorder and comorbid Keutel syndrome, a non-bleeding malady caused by functional defects of matrix Gla protein (MGP). To characterize GGCX mutants in a cellular milieu, we established a cell-based assay by stably expressing two reporter proteins (a chimeric coagulation factor and MGP) in HEK293 cells. The endogenous GGCX gene in these cells was knocked out by CRISPR-Cas9-mediated genome editing. Our results show that compared with wild-type GGCX, the patient9s GGCX D153G mutant significantly decreased coagulation factor carboxylation and abolished MGP carboxylation at the physiological concentration of vitamin K. Higher vitamin K concentrations can restore up to 60% of coagulation factor carboxylation but do not ameliorate MGP carboxylation. These results are consistent with the clinical results obtained from the patient treated with vitamin K, suggesting that the D153G alteration in GGCX is the causative mutation for both the bleeding and non-bleeding disorders in our patient. These findings provide the first evidence of a GGCX mutation resulting in two distinct clinical phenotypes; the established cell-based assay provides a powerful tool for studying the clinical consequences of naturally occurring GGCX mutations in vivo .