A Missense Mutation in γ-Glutamyl Carboxylase Gene Causes Combined Deficiency of All Vitamin K-Dependent Blood Coagulation Factors

Abstract

To identify potential mutations in the γ-glutamyl carboxylase gene, the sequence of all exons and intron/exon borders was determined in 4 patients from a consanguineous kindred with combined deficiency of all vitamin K-dependent procoagulants and anticoagulants and results were compared with normal genomic sequence. All 4 patients were homozygous for a point mutation in exon 9 that resulted in the conversion of an arginine codon (CTG) to leucine codon (CGG) at residue 394. Screening of this mutation based on introduction of Alu I site in amplified fragment from normal allele but not from the mutated allele showed that 13 asymptomatic members of the kindred were heterozygous for the mutation. The mutation was not found in 340 unrelated normal chromosomes. The segregation pattern of the mutation which is the first reported in the γ-glutamyl carboxylase gene fits perfectly with phenotype of the disorder and confirms the suggested autosomal recessive pattern of inheritance of combined deficiency of all vitamin K-dependent procoagulants and anticoagulants in this kindred. The mutated carboxylase protein expressed in Drosophila cells was stable but demonstrated threefold reduced activity compared with WT carboxylase, confirming that the L394R mutation results in a defective carboxylase.

Guideline for the diagnosis and management of the rare coagulation disorders

“…KO then undergoes reciprocal de-epoxidation by VKOR to restore KH 2 (Presnell & Stafford, 2002). VKCDFD is caused by variations in the GGCX and VKORC1 genes, which encode GGCX and subunit 1 of the VKOR complex, respectively (Brenner et al, 1998;Rost et al, 2004a). These result in loss of carboxylase activity and the synthesis of FII, FVII, FIX and FX and other vitamin K dependent-proteins, with reduced function.…”

“…VKDCFD may present at birth with intracranial or umbilical bleeding (Oldenburg et al, 2000;Spronk et al, 2000) or in infancy or childhood with joint, mucocutaneous, soft tissue or gastrointestinal bleeding (Brenner et al, 1998). Less commonly, VKDCFD presents with bleeding in early adulthood (Lunghi et al, 2011) or is an incidental laboratory finding (Rost et al, 2004b).…”

“…Less commonly, VKDCFD presents with bleeding in early adulthood (Lunghi et al, 2011) or is an incidental laboratory finding (Rost et al, 2004b). The VKDCFD phenotype may be modified by vitamin K intake or absorption (Brenner et al, 1998). There is no close correlation between clinical phenotype and the activities of FII, FVII, FIX and FX.…”

“…VKCDFD typically manifests as prolongation of the PT and APTT and approximately parallel reductions in the activities of FII, FVII, FIX and FX. Factor activities may be <0Á1 iu/ml at presentation (Brenner et al, 1998;Spronk et al, 2000) but more typically are 0Á2-0Á6 iu/ml (Oldenburg et al, 2000;Rost et al, 2004b;Lunghi et al, 2011).…”

“…Most reported cases with VKDCFD show partial or complete long term restoration of coagulation factor activities with oral (Oldenburg et al, 2000;Spronk et al, 2000;Rost et al, 2004b) or parenteral (Brenner et al, 1998;McMahon & James, 2001;Marchetti et al, 2008) vitamin K 1 (phytomenadione). In a minority of cases, vitamin K 1 was ineffective (Lunghi et al, 2011).…”