Aim

To determine if copy number variants contribute to warfarin dose requirements, we investigated CYP2C9, VKORC1, CYP4F2, GGCX and CALU for deletions and duplications in a multiethnic patient population treated with therapeutic doses of warfarin.

Patients & methods

DNA samples from 178 patients were subjected to copy number analyses by multiplex ligation-dependent probe amplification or quantitative PCR assays. Additionally, the CYP2C9 exon 8 insertion/deletion polymorphism (rs71668942) was examined among the patient cohort and 1750 additional multiethnic healthy individuals.

Results

All patients carried two copies of CYP2C9 by multiplex ligation-dependent probe amplification and no exon 8 deletion carriers were detected. Similarly, quantitative PCR assays for VKORC1, CYP4F2, GGCX and CALU identified two copies in all populations.

Conclusion

These data indicate that copy number variants in the principal genes involved in warfarin dose variability (CYP2C9, VKORC1), including genes with lesser effect (CYP4F2, GGCX), and those that may be more relevant among certain racial groups (CALU), are rare in multiethnic populations, including African–Americans.

Background

Atrial fibrillation (AF) is common among patients with end-stage renal disease, but few data are available on its prevalence among adults with chronic kidney disease (CKD) of lesser severity.

Methods and Results

We evaluated the association of CKD with electrocardiogram-detected AF among 26,917 participants in the REasons for Geographic and Racial Differences in Stroke (REGARDS) study, a population-based cohort of African-American and white US adults ≥45 years of age. Estimated glomerular filtration rate (eGFR) was calculated using the abbreviated Modification of Diet in Renal Disease study equation and albuminuria was defined as a urinary albumin to creatinine ratio ≥30 mg/g. Participants were categorized by renal function: no CKD (eGFR ≥60 ml/min/1.73m2 without albuminuria, n=21,081), stage 1–2 CKD (eGFR ≥60 ml/min/1.73m2 with albuminuria n=2,938), stage 3 CKD (eGFR 30 to 59 ml/min/1.73m2, n=2,683) and stage 4–5 CKD (eGFR <30 ml/min/1.73m2, n=215). The prevalence of AF among participants without CKD, and with stage 1–2, stage 3, and stage 4–5 CKD was 1.0%, 2.8%, 2.7% and 4.2%, respectively. Compared to participants without CKD, the age, race, sex adjusted odds ratios for prevalent AF were 2.67 (95% CI 2.04 – 3.48), 1.68 (95% CI 1.26 – 2.24) and 3.52 (95% CI 1.73–7.15) among those with stage 1–2, stage 3 and stage 4–5 CKD. The association between CKD and prevalent AF remained statistically significant after further multivariable adjustment and was consistent across numerous subgroups.

Conclusions

- Regardless of severity, CKD is associated with an increased prevalence of AF among US adults.

Objectives

To determine whether nitrogen-containing bisphosphonate (NCBP) therapy is associated with the prevalence of cardiovascular calcification.

Background

Cardiovascular calcification correlates with atherosclerotic disease burden. Experimental data suggest that NCBP may limit cardiovascular calcification, which has implications for disease prevention.

Methods

The relationship of NCBP use to the prevalence of aortic valve, aortic valve ring, mitral annulus, thoracic aorta, and coronary artery calcification (AVC, AVRC, MAC, TAC, and CAC, respectively) detected by computed tomography was assessed in 3,636 women within the Multi-Ethnic Study of Atherosclerosis (MESA) using regression modeling.

Results

Analyses were age-stratified because of a significant interaction between age and NCBP use (interaction p-values: AVC p<0.0001; AVRC p<0.0001; MAC p=0.002; TAC p<0.0001; CAC p=0.046). After adjusting for age, body mass index, demographics, diabetes, smoking, blood pressure, cholesterol levels, and statin, hormone replacement, and renin-angiotensin inhibitor therapy, NCBP use was associated with a lower prevalence of cardiovascular calcification in women ≥65 years old (prevalence ratio [95% confidence interval]: AVC 0.68 [0.41, 1.13]; AVRC 0.65 [0.51, 0.84]; MAC 0.54 [0.33, 0.93]; TAC 0.69 [0.54, 0.88]; CAC 0.89 [0.78, 1.02]), whereas calcification was more prevalent in NCBP users among the 2,181 women <65 years old (AVC 4.00 [2.33, 6.89]; AVRC 1.92 [1.42, 2.61]; MAC 2.35 [1.12, 4.84]; TAC 2.17 [1.49, 3.15]; CAC 1.23 [0.97, 1.57]).

Conclusions

Among women in the diverse MESA cohort, NCBPs were associated with decreased prevalence of cardiovascular calcification in older subjects, but more prevalent cardiovascular calcification in younger ones. Further study is warranted to clarify these age-dependent NCBP effects.

Aims

Although the frequencies of pharmacogenetic variants differ among racial groups, most pharmacogenetic algorithms for genotype-guided warfarin dosing only include two CYP2C9 alleles (*2 and *3) and a single VKORC1 allele (g.-1639G>A or g.1173C>T) commonly found among Caucasians. Therefore, this study sought to identify other CYP2C9 and VKORC1 alleles important in warfarin dose variability and to determine their frequencies in different racial and ethnic groups.

Materials & methods

The CYP2C9 and VKORC1 genes were sequenced in selected sensitive (<21 mg/week) and resistant (>49 mg/week) individuals with discrepant therapeutic and algorithm-predicted warfarin doses based on prior CYP2C9 and VKORC1 genotyping. The CYP2C9 and VKORC1 allele frequencies were determined in healthy, racially self-identified blood donors.

Results

Sequencing identified an African–American male with a lower than predicted therapeutic warfarin dose (14.4 mg/week), previously genotyped as CYP2C9*1/*1, who was homozygous for CYP2C9*8 (c.449G>A; p.R150H). Genotyping 600 African–American alleles identified CYP2C9*8 as their most frequent variant CYP2C9 allele (0.047), and the combined allele frequency of CYP2C9*2, *3, *5, *6, *8 and *11 was 0.133. Given most warfarin pharmacogenetic dosing algorithms only include CYP2C9*2 and *3, the inclusion of CYP2C9*8 alone could reclassify the predicted metabolic phenotypes of almost 10% of African–Americans, or when combined with CYP2C9*5, *6 and *11, more than 15%. In addition, the African–American VKORC1 g.-1639A allele frequency was 0.108 and three g.1331G>A (p.V66M) carriers were identified.

Conclusions

CYP2C9*8 is prevalent among African–Americans (~1 in 11 individuals). Thus, in this racial group, the incorporation of CYP2C9*8 into genotyping panels may improve dose prediction of CYP2C9-metabolized drugs, including warfarin.