VKCFD2 - from clinical phenotype to molecular mechanism.

Vitamin K 2,3-epoxide reductase complex, subunit 1 (VKORC1) is an enzyme essential for the vitamin K cycle. VKORC1 catalyses the reduction of vitamin K 2,3-epoxide to the quinone form of vitamin K and further to vitamin K hydroquinone. The generated vitamin K hydroquinone serves as substrate for the enzyme γ-glutamyl-carboxylase which modifies all vitamin K-dependent proteins, allowing them to bind calcium ions necessary for physiological activity. Vitamin K-dependent proteins include the coagulation factors FII, FVII, FIX, FX, and proteins C, S und Z. Insufficient VKORC1 enzyme activity results in deficiency of the vitamin K-dependent clotting factors leading to haemorrhagic disorders. This phenotype is known as vitamin K clotting factor deficiency type 2 (VKCFD2). Worldwide, only four families of independent origin have been reported with this rare bleeding disorder. Affected family members carry the mutation VKORC1:p.Arg98Trp in homozygous form, the only mutation found so far to be associated with VKCFD2. Now, ten years after the identification of the VKORC1 gene, the molecular pathomechanism of VKCFD2 has been clarified. The Arg98Trp mutation disrupts an ER retention motif of VKORC1 leading to mislocalisation of the protein to outside the endoplasmatic reticulum. In this review, we summarize the clinical data, diagnosis, therapy and molecular pathomechanism of VKCFD2.

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

Vitamin K-dependent coagulation factors deficiency is a bleeding disorder mainly associated with mutations in γ-glutamyl carboxylase (GGCX) that often has fatal outcomes. Some patients with nonbleeding 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 nonbleeding malady caused by functional defects of matrix γ-carboxyglutamate protein (MGP). To characterize GGCX mutants in a cellular milieu, we established a cell-based assay by stably expressing 2 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 patient's 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 nonbleeding disorders in our patient. These findings provide the first evidence of a GGCX mutation resulting in 2 distinct clinical phenotypes; the established cell-based assay provides a powerful tool for studying the clinical consequences of naturally occurring GGCX mutations in vivo.

Genetic variants of the vitamin K dependent coagulation system and intraventricular hemorrhage in preterm infants.

BACKGROUND: Pathogenesis of intraventricular hemorrhage (IVH) in premature infants is multifactorial. Little is known about the impact of genetic variants in the vitamin K-dependent coagulation system on the development of IVH. METHODS: Polymorphisms in the genes encoding vitamin K epoxide reductase complex 1 (VKORC1 -1639G>A) and coagulation factor 7 (F7 -323Ins10) were examined prospectively in 90 preterm infants <32 weeks gestational age with respect to coagulation profile and IVH risk. RESULTS: F7-323Ins10 was associated with lower factor VII levels, but not with individual IVH risk. In VKORC1-wildtype infants, logistic regression analysis revealed a higher IVH risk compared to carriers of the -1639A allele. Levels of the vitamin K-dependent coagulation parameters assessed in the first hour after birth did not differ between VKORC1-wildtype infants and those carrying -1639A alleles. CONCLUSIONS: Our data support the assumption that genetic variants in the vitamin K-dependent coagulation system influence the coagulation profile and the IVH risk in preterm infants. Further studies focussing on short-term changes in vitamin K-kinetics and the coagulation profile during the first days of life are required to further understand a possible link between development of IVH and genetic variants affecting the vitamin K-metabolism.

Functional polymorphism in gamma-glutamylcarboxylase is a risk factor for severe neonatal hemorrhage.

A neonate who received vitamin K (VK) supplementation then developed severe late-onset bleeding with abnormal prothrombin time and activated partial thromboplastine time. The bleeding was corrected after intravenous VK. Molecular analysis of the gamma-glutamylcarboxylase gene revealed a heterozygous single nucleotide polymorphism, which decreases carboxylase activity and induces VK-dependent coagulation deficiency.

Polymorphisms of the factor VII gene associated with the low activities of vitamin K-dependent coagulation factors in one-month-old infants.

Despite administration of vitamin K (VK), some infants show lower activity of VK-dependent coagulation factors and they could develop intracranial hemorrhage. For preventing VK deficiency bleeding (VKDB) in infants, oral administration of VK and a screening test for VK deficiency are carried out in Japan. For the screening, the total activity of VK-dependent coagulation factors is measured using a commercial product, Normotest. This study was undertaken to clarify the importance of the following genetic and environmental factors on the coagulation status in one-month-old infants: two polymorphisms in the factor VII gene, -323P0/10 (a 10-bp insertion in the promoter region at position -323) and R353Q (the replacement of arginine [R] with glutamine [Q] at residue 353) and sex, age, gestational age, birth weight, and feeding regimen. Two hundred Japanese infants (34.6 +/- 4.0 days old) were screened for VK-dependent coagulation activity with Normotest and were genotyped for the two polymorphisms. Among the subjects screened, 18 infants (9%) carried the P10 allele and 26 (13%) carried the R353Q allele. Multiple regression analysis showed that the 10-bp inserted (P10) allele or the Q allele was associated with the lower coagulation activities. The coagulation activities for the R/Q genotype were significantly lower than those for the R/R genotype and those for the P0/P10 genotype were significantly lower than those for the P0/P0 genotype. Therefore, infants who carry the P10 allele or the Q allele show lower activity of VK-dependent coagulation factors. These infants may have a higher risk of VKDB manifestation.

Serologic and molecular genetic management of a pregnancy complicated by anti-Rh18.

Antibodies, such as anti-Rh18 (Hr/Hr(S)), that react with the common products of RHCE can cause HDN as well as severe hemolytic transfusion reactions. Individuals with anti-Rh18 antibodies can have different RHCE genetic backgrounds; therefore, sera and RBCs from these individuals may cross-react. In these situations, genotyping may be the best method to determine compatibility. We report a 26-year-old pregnant Puerto Rican woman who presented at 31 weeks' gestation with anti-E and anti-Rh18 in her serum. No potential donors were identified among family members or within the American Rare Donor Program; therefore, a unit of the patient's RBCs was collected one week before her planned caesarian section. To improve our ability to supply blood for this patient in the future, molecular testing was performed. The patient was found to be homozygous for an RH haplotype in which a variant RHD*DAR, is linked to a variant RHCE*ceAR. The DAR-ceAR haplotype has been described in Dutch-African populations, but this is the first report of an individual self-identified of Hispanic ethnicity. This case report demonstrates the clinical importance of molecular testing of patients with rare Rh phenotypes.

An AQP1 null allele in an Indian woman with Co(a-b-) phenotype and high-titer anti-Co3 associated with mild HDN.

BACKGROUND: The Colton blood group system (CO, ISBT 015) is composed of three antigens, of which Co3 (ISBT 015.003) is carried by almost all persons, except those of the extremely rare Co(a-b-) phenotype. The Colton blood group antigens are expressed by the water channel aquaporin 1 (aqp1; also known as channel-forming integral protein, CHIP-28), which is a highly conserved RBC integral membrane protein. The two most frequent alleles, CO1 and CO2, encode the antigens Co(a) and Co(b), respectively. Four null alleles have been described for the AQP1 gene to date. CASE REPORT: An Indian woman had an alloimmune antibody to an high-frequency antigen associated with mild HDN. Her RBCs were typed Co(a--b-), and the antibody was an anti-Co3. She typed CO1-positive and CO2-negative in a new genotyping method, using PCR with sequence-specific priming, for CO1 and CO2. A method for nucleotide sequencing of the four AQP1 exons from genomic DNA was developed. The patient was shown to be homozygous for a nonfunctional allele AQP1(232delG) that also carried the CO1-specific polymorphism. CONCLUSION: The kindred presented a fifth example of an AQP1 null allele, which was caused by a single nucleotide deletion leading to a shift in the reading frame beyond codon 78. A method of genotyping CO for Co(a) and Co(b) antigen phenotype prediction was presented.