Markedly reduced levels of γ-carboxylated MGP are crucial but not exclusive for causing facial dysmorphologies
Three VKCFD1 patients were reported with facial dysmorphologies. A Keutel syndrome-like phenotype was described for a patient that is compound heterozygous for GGCX:p.(M174R+R325Q);p.(D153G), where in addition to facial dysmorphologies, strippling of fingers was observed (Tie et al., 2016). We detected for GGCX:p.(D153G) substantially reduced levels of γ-carboxylated MGP of 38 %. Levels of γ-carboxylated GRP and BGLAP were 94% and 82%, respectively. GGCX:p.(M174R) resulted into loss-of-function for all three VKD proteins (Figure 3a, Table 2).
Another patient that was diagnosed with midfacial hypoplasia is homozygous for GGCX:p.(R83P). This pathogenic variant showed markedly reduced levels of γ-carboxylated MGP, GRP, and BGLAP with 27%, 13%, and 34%, respectively (Figure 3a, Table 2). Moreover, this patient is homozygous for the VKORC1:c.-1639 AA genotype, which corresponds to a significantly reduced ability of vitamin K recycling.
There is one patient having a midfacial hypoplasia (GGCX:p.(S284P);p.(W315X)), where the allele harboring the nonsense variant leads to monoallelic absence of GGCX protein. The other allele harboring GGCX:p.(S284P) is able to obtain same level of γ-carboxylated MGP as wt at high K doses. However, GGCX:p.(S284P) shows significantly reduced ability to γ-carboxylate MGP at low K concentrations (Figure 3b, Table 2). Notably, the mother reported a severe hyperemesis gravidarum with a weight loss of seven kg within the first trimester (Watzka et al., 2014). Interestingly, this patient is also homozygous for the VKORC1:c.-1639 AA genotype.
All types of dose-responses were detected for the above mentioned variants for PRGP1, TMG4, and GAS6 (Table S1).
Our results demonstrate that substantial reductions of γ-carboxylated MGP are associated with facial dysmorphologies in VKCFD1 patients (Figure 3a, Table 2).
Notably, not all VKCFD1 patients with severely reduced levels of γ-carboxylated MGP as patients harboring GGCX:p.(G558R);p.(F299S), GGCX:p.(V255M);p.(S300F), or GGCX:p.(R83W);p.(Q374X) have skeletal malformation at birth (Figure 3c, Table 2).
Cardiac abnormalities and the impact of γ-carboxylated GRP and MGP
Three patients with GGCX variants p.(R83P);p.(R83P), p.(S284P);p.(W315X), and p.(W157R);p.(T591K+D31N) have a congenital atrial septal defect. Another four patients with variants GGCX:p.(V255M);p.(S300F), GGCX:p.(H404P);p(R485P), GGCX:p.(R476C) and GGCX:p.(G537A);p.(Q374X) developed subclinical atherosclerosis. All these patients harbor pathogenic variants, which show reduced ability to γ-carboxylate GRP and MGP (Table S3).
All types of dose-responses were detected for BGLAP, GAS6, PRGP1, and TMG4 (Table S1).