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The c.-1639G>A polymorphism of the VKORC1 gene inSerbian population: retrospective study of the variability inresponse to oral anticoagulant therapyMirjana K. Kovaca, Aleksandar R. Maslaca, Ljiljana B. Rakicevicb

and Dragica P. Radojkovicb

Background A single nucleotide polymorphism

c.-1639G>A in the promoter region of vitamin K-epoxide

reductase (VKORC1) gene has been found to account for

most of the variability in response to oral vitamin K

antagonist (VKA).

Objective Our aim was to study the effect of c.-1639G>A

polymorphism on the acenocoumarol dosage requirements

in a group of patients under stable anticoagulation, and to

estimate the variability in response to VKA.

Patients and methods We conducted a retrospective

cohort analysis of 200 stable anticoagulation patients

followed from the initiation of VKA.

Results Out of 43 low-dose patients, 40 (93%) carried the A

allele. The A allele was less frequent in the group of 30

patients requiring high VKA dose among these patients 13

(43.3%) carried the A allele in the heterozygous form and

none of them carried AA genotype. Patients with GG

genotype required 2.6 times higher dose than patients

carriers of AA genotype (P < 0.0001). Carriers of AA

genotype were more likely to be overanticoagulated during

follow up after initiation of VKA when compared with

carriers of GA and GG genotype (P < 0.0001). Patients with

GG genotype spent more time below therapeutic range

compared with patients carriers of AA (P U 0.0328) and GA

genotype (P < 0.0001).

Conclusion VKORC1 c.-1639G>A polymorphism

significantly influenced VKA dose and represented a good

predictor of individuals predisposed to unstable

anticoagulation. Pharmacogenetic testing could predict a

high risk of overdose among 28.5% of our patients, carriers

of AA genotype, before the initiation anticoagulation. Blood

Coagul Fibrinolysis 21:000–000 � 2010 Wolters Kluwer

Health | Lippincott Williams & Wilkins.

Blood Coagulation and Fibrinolysis 2010, 21:000–000

Keywords: acenocoumarol dose, c.-1639 G>A polymorphism, variability inresponse to VKA, VKORC1

aBlood Transfusion Institute of Serbia, Svetog Save 39a and bInstitute ofMolecular Genetics and Genetic Engineering, Vojvode Stepe 444a,Belgrade, Serbia

Correspondence to Ljiljana Rakicevic, Institute of Molecular Genetics andGenetic Engineering, Vojvode Stepe 444a, P.O. Box 23, 11010 Belgrade, Serbiae-mail: lilijar@eunet.rs

Received 2 February 2009 Revised 20 April 2010Accepted 27 April 2010

IntroductionOral vitamin K antagonist (VKA), including warfarin and

acenocoumarol, are the most widely prescribed drugs for

the prevention and treatment of patients with arterial and

venous thromboembolic disorders [1]. The effectiveness

and safety of VKA depend on maintaining the prothrom-

bin time, expressed as the international normalized ratio

(INR) within the therapeutic range [2]. Clinical use of

VKA is further complicated by substantial risk for hae-

morrhagic side effects, which is increased in patients with

low-dose requirements [3]. The required dose of VKA for

maintaining the prothrombin time is variable, and

depends on several acquired factors such as age, dietary

intake, interaction with other drugs and intercurrent ill-

ness [2,4]. In addition to acquired factors, it is well known

that response to VKA is genetically determined.

The first gene documented to influence VKA dose

requirement was CYP2C9. It encodes the enzyme cyto-

chrome P450 2C9 – the main enzyme responsible for the

hepatic metabolism of VKA [5]. Two common variants of

the CYP2C9 gene, �2 and �3 are associated with reduced

enzyme activity, resulted in deficient VKA clearance.

Individuals who carry deficient CYP2C9 alleles are sen-

sitive and have lower VKA dose requirements. Never-

theless, only a small part (7–10%) of the interindividual

variation could be explained by these polymorphisms [6].

Vitamin K epoxide reductase (VKORC1) is the key

enzyme of the vitamin K cycle and the molecular target

of coumarin derivates and it was found to determine up to

40% of individual coumarin dose requirement. VKORC1

recycles vitamin K 2,3-epoxide to vitamin K-hydro-

quinone. Vitamin K-hydroquinone is the cofactor for

the carboxylase that adds a molecule of carbon dioxide

to glutamic acid, producing g-carboxyglutamic acid (g-

Glu). The g-Glu residues are essential for some clotting

factors, such as factors II, VII, IX, X and protein C, S Z, to

bind phospholipids and thus be functional [5].

Mutations in VKORC1 cause two distinctive phenotypes.

Those affecting VKORC1 function lead to vitamin K

dependent coagulation factors deficiency type 2

Original article 1

0957-5235 � 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins DOI:10.1097/MBC.0b013e32833c2988

CE: Swati; MBC/200710; Total nos of Pages: 6;

MBC 200710

(VKCFD2), confirming critical role of that enzyme in

vitamin K dependent coagulation factors function [5]. On

the contrary, several genetic variations of the VKORC1

gene have been found to influence sensitivity to VKA [5,7].

Twenty-eight polymorphisms have been described, con-

stituting three main haplotypes covering almost the whole

genetic variability of VKORC1, with the following distri-

bution in Caucasians VKORC1�2, 42%, VKORC1�3, 38%

and VKORC1�4, 20% [6]. Haplotype VKORC1�2includes a single nucleotide polymorphism in the promo-

ter region (c.-1639G>A) and has been found to account for

most of the variability in response to VKA [6,7]. Several

studies clearly showed a strong association of initial varia-

bility in the INR response to VKA with VKORC1 genetic

variability. Carriers of AA genotype had decreased time to

the first INR within therapeutic range and also to the first

INR above 4 [8,9].

Our aim was to study the effect of c.-1639G>A poly-

morphism on the acenocoumarol dosage requirements in

a group of patients under stable anticoagulation. We also

aimed to estimate the rate of bleeding during initiation of

the VKA, and variability in therapeutical response, in

regard to the presence of c.-1639G>A polymorphism.

Materials and methodsData collectionA total of 200 outpatients attending the Hemostasis

Department of the Blood Transfusion Institute of Serbia,

who had maintained stable anticoagulation with aceno-

coumarol for at least 3 months, were included in the

study. We considered a patient on stable anticoagulation

whose acenocoumarol dose requirement had remained

constant for at least three previous months, and was

enough to keep the INR within therapeutic ranges,

according to the indication for VKA treatment. In order

to minimize the possible influence of hepatic, renal or

malignant disease, which could have pharmacodynamic

influence, on increased prothrombin time (INR) and

possible bleeding complications, patients with hepatic,

renal or malignancy were excluded from the study. Like-

wise, all patients treated with amiodaron, which have

synergistic influence due to pharmacokinetic mechan-

isms on increased INR were excluded. In total, 116 male

and 84 female patients were included in the study,

median age 61 years (range 20–82).

On the arrival in the laboratory, a blood sample was taken

for INR measurement and genotyping. Genotyping was

performed by polymerase chain reaction followed by

digestion with MspI (New England Biolabs) as previously

described [10].

Furthermore, a retrospective analysis of medical records

was performed to investigate the potential influence of

VKORC1 genotype on oral anticoagulants response in the

initiation phase and during a follow up from the start of

VKA administration. Complete data on acenocoumarol

doses and INR were registered from medical records, as

well as the data on age, sex, indication for treatment,

concomitant medications and medications potentially

interacting with VKA.

Patients were subjected to the VKA treatment according

to standard care without specific warfarin dosing algor-

ithms. The average initial acenocoumarol dose was 3.7 �0.6 mg. Therapeutic INR was defined as INR between

two and three irrespective of the individual target range.

A minimum of three consecutive therapeutic INR

measurements denoted stable anticoagulation. Mainten-

ance dose was defined as the mean of all doses given to a

patient during stable anticoagulation. Stable mainten-

ance dose was calculated from weekly doses that were

unchanged over a minimum of three consecutive

measurements of three therapeutic INR. INR was

checked in all patients three times in the first, twice in

the second week, and weekly during the achievement

therapeutic INR. Upon the achievement of stable antic-

oagulation dose, the INR was measured less frequently,

usually every 4 weeks. Follow up period ranged from one

to 8 years per patient, average 3.9 years.

Considering the present maintenance dose, study popu-

lation consisted of 43 consecutive patients requiring low

(7 mg per week or less), 127 consecutive patients requir-

ing medium (7–28 mg per week) and 30 consecutive

patients requiring high-acenocoumarol dose (28 mg per

week or more). Number of bleeding complications, as

well as the size and localization of bleeding recorded

during the first 3 months of VKA initiation, were

analyzed completely.

The variability of INR regarding INR more than four and

INR less than two were evaluated during follow up from

initiation of VKA. We calculated number of INR more

than four or less than two from the first stable antic-

oagulation, and took in consideration only patients who

had change of INR without change of VKA doses as well

as possible influence of dietary change, intercurrent ill-

ness or interaction with other drugs.

All individuals had signed informed consent to partici-

pate in the study and the local ethics committee approved

the study.

Statistical analysisDifferences in the acenocoumarol requirement between

patients who were carriers, and noncarriers of c.-1639G>A

polymorphism in the low-dose, medium-dose and high-

dose group were assessed with chi-squared test. Differ-

ences between homozygotes (AA) and heterozygotes (GA)

regarding the overdosed patients and the presence of

bleeding complication were assessed using chi-squared

test or Fisher’s exact test. Differences between overdosed

patients with AA and GA genotype, regarding the level of

INR and age, were assessed with Student‘s t-test. All

the statistical analyses were performed according to the

2 Blood Coagulation and Fibrinolysis 2010, Vol 00 No 00

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MBC 200710

Statistical Package for Social Science SPSS software, Inc.

Chicago, Illinois, USA). A P value of less than 0.05 was

considered as statistically significant.

ResultsCharacteristics of the studied population and the distri-

bution of the G and A alleles of c.-1639G >A polymorph-

ism are shown in Table 1. In 57 (28.5%) patients AA

genotype was present, in 90 (45%) GA and 53 (26.5%)

patients were carriers of GG genotype. The frequencies of

genotypes of the c.-1639G>A polymorphism regarding the

requirement dose of acenocoumarol are shown in Table 2.

The allelic distribution was different across the various

acenocoumarol dosage groups. In the group of 43 patients

who maintained stable anticoagulation with the low dose

of acenocoumarol, 40 patients (93%) carried the A allele.

The A allele was less frequent in the group of 30 patients

requiring a high-acenocoumarol dose among these patients

13 (43.3%) carried the A allele in the heterozygous form

and none of them carried AA genotype. In groups with low

and high dose, we observed statistically significant differ-

ence among patients with different genotypes, whereas in

the group with medium dose, statistical difference

between patients carriers of different genotypes was not

observed (Table 2). Figure 1 shows the range and mean

requirements dose of acenocoumarol for patients carrying

different alleles. In group with AA genotype, the mean

acenocoumarol dose per week for the maintenance of

stable anticoagulation was 10 mg (range 2–21), in group

with GA genotype 19 mg (range 6–49), and in group with

GG genotype 26 mg (range 8–70). The patients with GG

genotype required 2.6 times higher dose than patients

carriers of AA genotype (P< 0.0001).

Retrospective analysis showed that only patients who

carried A allele experienced problems during the

initiation of anticoagulation therapy (Table 3). The data

showed that 33 (16.5%) patients were overdosed during

the initiation of VKA and in 11 (5.5%) this was further

complicated by bleeding at different localizations (4

patients had mellena, 2 haematuria, 4 haematoma and

VKORC 1 polymorphism and response to acenocoumarol Kovac et al. 3

Table 1 Characteristics of study populationAQ5

Age (median range) 61 (20–82)Male n (%) 116 (58%)Female n (%) 84 (42%)Primary reason for anticoagulation n (%)

AF/valve replacement 157 (78%)DVT/PE 43 (22%)

Daily acenocoumarol dose (mg)Low 43 (21.5%)Medium 127 (63.5%)High 30 (15%)

VKORC1 (c.-1693G/A)Homozygous (AA) 57 (28.5%)Heterozygous (GA) 90 (45%)Wild type 53 (26.5%)

AF, atrial fibrillation; DVT, deep venous thrombosis; PE, pulmonary embolism;VKORC1, vitamin K-epoxide reductase.

Table 2 Frequency of different genotypes for the c.-1639G>Apolymorphism of the VKORC1 gene in three groups of patients withdifferent acenocoumarol dose requirements

Genotype Low dose n¼43 Medium dose n¼127 High dose n¼30

AA 25 (58.1%) 32 (25.2%) 0 (0%)GA 15 (34.9%) 62 (48.8%) 13 (43.3%)GG 3 (7%) 33 (26%) 17 (56.7%)P M0.00524 M0.158158 M0.001759

§0.000003 §0.563724 §0.000001¥0.068845 ¥0.465505 ¥0.01855

M Difference AA�GA. § Difference AA�GG. ¥ Difference GA��GG.

Table 3 The overdosed patients during initiation of accenocoumarol regarding the presence of polymorphism c.-1639G>A

Genotype

PAA (N¼57) GA (N¼90) GG (N¼53)

Overdosed patients n (%) 27 (47) 6 (7) 0 <0.000001Overdosed patients with bleeding n (%) 8 (14) 3 (3) 0 0.023325INR mean (range)

Overdosed 6.2 (4.2–12) 4.9 (4.15–6.1) NA 0.01687Overdosed with bleeding 7.5 (4.9–12) 4.5 (4.15–5) NA 0.1133

INR, international normalized ratio; NA, not applicable.

Fig. 1

80

70

60

50

40

Ace

noco

umar

ol m

aint

enan

ce d

ose

(mg

per

wee

k)

30

20

10

0AA

n = 57

Min - MaxMean ± SDMean

AA - homozygousAG - heterozygousGG - wild type

AGn = 90

GGn = 53

P < 0.01

The range of acenocoumarol dose obtained from patients with differentgenotypes for the c.-1639G>A polymorphism of the VKORC1 gene.

CE: Swati; MBC/200710; Total nos of Pages: 6;

MBC 200710

1 epistaxis). In the group of 33 overdosed patients, 27 had

AA genotype, and six carried GA genotype

(P< 0.000001). In the group of patients who carried

AA genotype, the mean value of INR level in overdosed

patients was 6.2 (4.2–12), whereas in the group with GA

genotype the mean INR was 4.9 (4.15–6.1). A statistically

significant difference (P¼ 0.01687) was observed

between groups.

The mean age of overdosed patients with bleeding

complication, was 69 years, (range 50–81) and in the

group of overdosed patients without bleeding, 59 years

(26–71) representing statistically significant difference

(P¼ 0.0312).

In the follow up period from initiation of VKA, INR more

than four was recorded 149 times in 31 (54%) carriers of

AA genotype. In 14 (16%) patients with GA genotype

INR more than four were recorded 72 times, whereas in

four (8%) patients with GG genotype INR more than four

was recorded 11 times. Patients carriers of AA genotype

were more likely to be overanticoagulated during follow

up after initiation of VKA compared with GA genotype,

P< 0.0001 and respectively with GG genotype,

P< 0.0001 (Table 4).

Patients with GG genotype spent more time below

therapeutic range compared with patients carriers of

AA (P¼ 0.0328) and GA genotype (P< 0.0001). In 11

patients (19%) with AA genotype, INR less than two was

recorded 62 times. In seven (8%) patients with GA, INR

less than two was recorded 51 times, and in 21 (40%) with

GG genotype, INR less than two was recorded 73 times

during follow up of initiation of VKA (Table 5).

DiscussionRecently, genetic variations within the gene encoding for

a subunit of the vitamin K epoxide reductase complex,

have been found to predict sensitivity to anticoagulant

therapy. The c.-1639G>A polymorphism marks the

VKORC1�2 haplotype [5], and its association with

increased response to acenocoumarol has been shown

in a group of healthy individuals [6], as well as in a group

of patients treated with warfarin or acenocoumarol [7–

15].

The aim of our study, which represents the first one ever

performed in our population, was to evaluate the effect of

the c.-1639G>A polymorphism on the acenocoumarol

dosage requirements in a group of patents under stable

anticoagulation. The rate of bleeding during the

initiation of VKA and variability in response during follow

up, considering the presence of this polymorphism, were

also evaluated.

Our study supports the importance of the role of c.-

1639G>A in the sensitivity to acenocoumarol. In the

group of patients who maintained stable anticoagulation

with low doses of acenocoumarol, 93% carried the A

allele, whereas this allelic variant was present in 43.3%

patients requiring high doses and in 74% patients in the

medium-dose group. None of the patients who carried

AA genotype was in the group requiring high-acenocou-

marol dose, and statistically significant difference was

observed only in groups with low and high dose, among

patients with different genotypes.

Similar results were demonstrated by Montes et al. [10].

They found that more than 90% of the patients required

low doses of acenocoumarol, and less than 30% of the

patients who needed a high dose carried the A allele.

Likewise, in the study performed by Geisen et al. [7], 93%

patients with the increased coumarin sensitivity and none

of the patients with partial coumarin resistance, were

found to be homozygous for the A allele (representing

VKORC 1�2).

In our study, the mean acenocoumarol dose per week in

the group with AA genotype, required for the maintenance

of stable anticoagulation was 10 mg, in the group with GA

genotype 19 mg, and in the group with GG genotype

26 mg. The data show that patients with GG genotype

required 2.6 times higher dose than patients who were

carriers of AA genotype. In a similar study by Qazim et al.[13] the mean phenprocoumon dosage per week to achieve

therapeutic VKA was 15.3 mg in patients without the

VKORC1 c.-1639G>A gene polymorphism, 10.9 mg in

patients carrying the heterozygous and 7.8 mg in patients

carrying the homozygous c.-1639G>AVKORC1 poly-

mprphism. Sonce et al. [14] also showed that the mean

warfarin dose was the highest in patients with GG geno-

type compared with the GA and AA genotype patients, and

in patients who are homozygous AQ1wild type for CYP2C9. In

order to estimate the optimum initial warfarin dose needed

to maintain stable and optimum anticoagulation they

proposed dosing algorithm that incorporate the contri-

bution of genetic (VKORC-1639, 2C9�3) and nongenetic

variables (age, height) [14].

4 Blood Coagulation and Fibrinolysis 2010, Vol 00 No 00

Table 4 Patients with INR more than four during follow upfrom initiation of VKA regarding the presence of polymorphismc.-1639G>A

AA (N¼57) GA (N¼90) GG (N¼53)

Patients n (%) 31 (54) 14 (16) 4 (8)Number of INR > 4 149 72 11Num. of INR > 4 per patient 4.8 5 2.7Patients with bleeding n (%) 1 (1.8) 1 (1) 0

P<0.0001 M, P<0.0001 §, P¼0.2571 ¥.

Table 5 Patients with INR less than two during follow upfrom initiation of VKA regarding the presence of polymorphismc.-1639G>A

AA (N¼57) GA (N¼90) GG (N¼53)

Patients n (%) 11 (19) 7 (8) 21 (40)Number of INR < 2 62 51 73Num. of INR < 2 per patient 5.6 7.2 3.5

P¼0.1139 M, P¼0.0328 §, P<0.0001 ¥.

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Oral anticoagulant therapy, particularly during the

initiation period, is associated with the overanticoagula-

ton that may result in bleeding. Therefore, we estimated

the rate of overanticoagulation patients regarding the

presence of c.-1639G>A polymorphism during the first

3 months of the initiation. Our results showed that only

patients who carried A allele were at risk of overanticoa-

gulation. In the group of 33 overdosed patients, 27 carried

AA genotype, and six carried GA genotype. From those in

the overdosed group, 11 patients (5.5%) had overanticoa-

gulation further complicated with bleeding and five of

them had to be transfused with fresh frozen plasma to

stop the bleeding and reverse the INR to therapeutic

range. Our results suggest that performing of pharmaco-

genetic testing for the presence of c.-1639G>A prior to

the initiation of VKA, could minimize the risk of over-

anticoagulation and subsequent bleeding complications

in our patients.

Regarding the mean INR in overdosed patients, a stat-

istically significant difference was observed between

carriers of AA and GA genotype (P¼ 0.01687), whereas

between carriers of AA and GA genotype who had bleed-

ing complications, no statistical difference was observed

regarding the mean INR, possible due the small number

of patients carriers of GA genotype.

Schwartz et al. [8] reported thatAQ2 patients carriers of AA

genotype, had significantly higher INR values in the first

week than non-A homozygotes. They also found that the

patients with one or two VKORC1 haplotype A alleles

had shorter times to the first INR more than four. They

reported the association of an increase in the anticoagu-

lant response in these patients, as indicated by an INR

above the therapeutic range, and an increased risk of

bleeding [8].

Contrary to our findings, Wadelius et al. [9] did not find an

association between VKORC1 polymorphism and risk of

bleeding, but they emphasized that homozygosity for

VKORC1 c.-1639G>A variant alleles increased the risk

of early INR over four. They showed the strongest

association with dose, which was observed for VKORC1,

and significantly lower for CYP2C9 [9]. The mean age of

overdosed patients with bleeding complications in our

study was 69 years, (range 50–81), whereas in overdosed

group without bleeding it was 59 years (range 26–71).

P¼ 0.0312, supports the early investigation stating that

elderly patients were at a higher risk of bleeding [16]. Our

findings were similar to study by Schwartz et al. [8] in

which patients with bleeding events older (median age,

71 years) than the ones in studied population (median

age, 61 years) were included.

In our study after initiation of VKA, INR more than 4

were recorded in 54% carriers of AA genotype, 16% with

GA genotype and in 8% with GG genotype. Patients

carriers of AA genotype were more likely to be over-

anticoagulated during follow up after initiation of VKA

compared carriers of GA genotype and GG genotype, Pless than 0.0001. Osman et al. [12] also reported more

variations in INR in patients with VKORC1�2 than those

with VKORC1�3 or VKORC1�4 haplotypes, in the

initiation phase which could be connected with an

increased risk of bleeding complications. Our patients

with GG genotype spent more time below therapeutic

range compared with patients carriers of AA (P¼ 0.0328)

and GA genotype (P< 0.0001). Similarly, Meckley et al.[17] showed in a retrospective study that patients with

GG genotype spent more time below therapeutic INR

compared with patients carriers of A allele.

In summary, even with careful monitoring, initiation of

VKA is associated with highly variable responses between

individuals and maintaining levels within the narrow

therapeutic range that can lead to adverse-drug events.

For that reason, the use of every tool that contributes to

properly estimation of VKA dosage is a considerable asset.

In planning of optimal initial and maintenance doses, in

addition to the age, height and intercurrent illness, geno-

type plays an important role, especially if the using of

computer dosing software is not available and patients are

subjected to treatment according to standard care without

specific dosing algorithm. Testing for VCKORC1 c.-

1639G>A polymorphism predicts high risk of overdose

among third of our patients. Therefore, on the basis of the

results obtained from this study, testing for VCKORC1 c.-

1639G>A may be considered as a preliminary examination

before starting anticoagulation in order to increase effec-

tiveness and safety of anticoagulation therapy.

AcknowledgementsThis work supported by grant 143051 from Ministry of

Science, Republic of Serbia.

References1 Hirsh J. Oral anticoagulant drugs. N Engl J Med 1991; 324:1865–1875.

2 Baglin TP, Keeling DM, Watson HG. Guidelines on oral anticoagulation(warfarin): third edition–2005 update. Br J Haematol 2006; 132:277–285 AQ3.

3 Dentali F, Ageno W, Crowter M. Treatment of coumarin-associatedcoagulopathy: a systemic review and proposed treatment algorithms. JThromb Haemost 2006; 4:1853–1863.

4 Wittkovsky AK. Drug interactions with oral anticoagulants. In: Colman RW,Clowes AW, Goldhaber SZ, Marder VJ, George JN, editors. Hemostasisand Thrombosis, 5th ed. Philadelphia: Lippincott Williams & Wilkins; 2006.pp. 1699–1709.

5 Oldenburg J, Watzka M, Rost S, Muller R. VKORC1: molecular target ofcoumarins. J Thromb Haemost 2007; 5 (suppl1):1–6.

6 Bodin L, Verstuyft C, Tregouet DA, Robert A, Dubert L, Funck-Brentano C,et al. Cytochrome P450 2C9 (CYP2C9) and vitamin K epoxide reductase(VKORC1) genotypes as determinants of acenocumarol sensitivity. Blood2005; 106:135–140.

7 Geisen C, Watzka M, Sittinger K, Steffens M, Daugela L, Seifried E, et al.VKORC1 haplotypes and their impact on the inter-individual and inter-ethnical variability of oral anticoagulation. Thromb Haemost 2005;94:773–779.

8 Schwartz UI, Ritchie MD, Bredford Y, Chun L, Dudec S, Frye-Anderson,et al. Genetic determinants of response to warfarin during initialanticoagulation. N Engl J Med 2008; 358:999–1008.

9 Wadelius M, Chen LY, Lindh JD, Eriksson N, Ghori M JR, Bumpstead S,et al. The largest prospective warfarin-treated cohort supports geneticforecasting. Blood 2008; 4:149070 AQ4.

VKORC 1 polymorphism and response to acenocoumarol Kovac et al. 5

CE: Swati; MBC/200710; Total nos of Pages: 6;

MBC 200710

10 Montes R, Ruiz de Gaona E, Martinez-Gonzales MA, Alberca I, Hermida J.The c.-1639G>A polymorphism of the VKORC1 gene is a majordeterminant of the response to acenocoumarol in anticoagulated patients.B J Haematol 2006; 133:183–187.

11 D‘Andrea G, D‘Ambrosio LC, Di Perna P, Chetta M, Santacroce R,Brancaccio V, et al. A polymorphism in the VKORC1 gene is associatedwith an interindividual variability in the dose-anticoagulant effect of warfarin.Blood 2005; 105:645–649.

12 Osman A, Enstrom C, Arbring K, Soderkvist P, Lindhal TL. Main haplotypesand mutational analysis of vitamin K epoxide reductase (VKORC1) in aSwedish population: retrospective analysis of case records. J ThrombHaemost 2006; 4:1723–1729.

13 Qazim B, Stollberger C, Krugluger W, Dossenbach-Glaninger A, Finsterer J.Dependency of phenprocoumon dosage on polymorphisms in the VKORC1and CYP2C9 genes. J Thromb Thrombolysis 2008; 28:211–214.

14 Sonce E, Kahn T, Wynne H, Avery P, Monkhouse L, King B, et al. The impactof CYP2C9 and VKORC1 genetic polymorphism and patientcharacteristics upon warfarin dose requirement: proposal for a new dosingregimen. Blood 2005; 106:2329–2333.

15 Quteinech L, Verstuyft C, Descot C, Dubert L, Robert A, Jaillon P, et al.Vitamin K epoxide reductase (VKORC1) genetic polymorphism isassociated to oral anticoagulant overdose. Thromb Haemost 2005;94:690–691.

16 Levine MN, Beyth R, Kearon C, Schulman S. Hemorrhagic complications ofanticoagulant treatment. Chest 2004; 126:287S–310S.

17 Meckley LM, Wittkowsky AK, Rieder MJ, Rettie AE, Veenestra DL. Ananalysis of the relative effects of VKORC1 and CYP2C9 variants onanticoagulation related outcomes in warfarin-treated patients. ThrombHaemost 2008; 100:220–239.

6 Blood Coagulation and Fibrinolysis 2010, Vol 00 No 00

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for Lippincott Williams & Wilkins Manuscript No. 200710 Dear Author, During the preparation of your manuscript for typesetting, some queries have arisen. These are listed below. Please check your typeset proof carefully and mark any corrections in the margin as neatly as possible or compile them as a separate list. This form should then be returned with your marked proof/list of corrections to the Production Editor.

QUERIES: to be answered by AUTHOR/EDITOR QUERY NO. QUERY DETAILS RESPONSE <AQ1> Please check edit in this statement for

correctness. 'Sonce et al. [14] … for CYP2C9.'

<AQ2> Please check edit in the spelling of author name in this statement for correctness. 'Schwartz et al. [8] … homozygotes.

<AQ3> Please check edits in article title of Refs. [2,11] for correctness.

<AQ4> Please check details of Ref. [9] for correctness.

<AQ5> Please check edit in Tables [1–5] for correctness.