江苏地区汉族儿童多药耐药基因3个单核苷酸多态性位点的单倍型研究

目的 分析江苏汉族人群多药耐药基因-1(MDR1)的单核甘酸多态(12外显子1236 C→T突变、21外显子2677G→T/A突变、26外显子3435C→T突变)及其构成的单倍型分布.方法 通过多重单碱基延伸反应(SNaPshot SNP分型技术)对江苏地区170名健康儿童的MDR1 C1236T、G2677T/A、C3435T的SNP位点进行基因分型,统计各基因型频率.UNPHASED软件对MDR1的SNPs(C1236T-G2677T/A-C3435T)进行单倍型分析.结果 在170例儿童中,等位基因1236T、2677T、2677A、3435T频率分别为63.5%、37.4%、17.0%和35.0%.基因型频率分布符合Hardy-Weinberg平衡(HWE),差异无统计学意义(P>0.05).MDR1的1236、2677、3435三个位点间(C1236T-G2677T/A-C3435T)存在连锁不平衡性,以TTT(31.8%)、TGC(25.3%)、CGC(17.7%)和CAC(16.2%)四种单倍型为主.结论 江苏地区汉族人群MDR1的单核甘酸多态及单倍型分布具有自己的特点.在临床应用相关药物时,进行基因型及单倍型检测,将有助于指导临床个体化用药.     

CYP3A5和MDR1基因多态性对中国肝移植患者他克莫司药动学的影响

目的探讨细胞色素P450酶3A5（CYP3A5）基因和多药耐药基因（MDR1）C1236T、G2677T／A、C3435T多态性对肝移植患者口服他克莫司（TAC）后体内药动学参数的影响。方法采集28例肝移植患者手术后第1周和第3周血标本,采用LC—MS／MS法检测TAC血药浓度,计算主要药动学参数。采用聚合酶链反应结合基因测序分析28例肝移植患者CYP3A5＊3和MDR1主要基因型。结果携带MDR1 3435T基因型的肝移植患者口服TAC后,药动学参数AUC0→1和ρmax明显高于3435CC型患者,而CYP3A5＊3、MDR1 C1236T和G2677T／A基因多态性对TAC的药动学参数无明显影响。结论携带MDR1 3435T基因型肝移植患者比3435CC型患者需要较高剂量才能达到目标浓度。     

C1236T、 G2677T/A 和C3435T 基因多态性与乳腺癌分子分型的关系及意义

摘要： 目的 观察多药耐药基因 1 （MDR1） 第 12、 21 及 26 外显子 C1236T、 G2677T/A 和 C3435T 基因多态性在乳腺癌患者外周血中的分布, 分析其与分子分型的关系。方法 应用高分辨熔解曲线 （HRM） 技术检测 400 例乳腺癌患者 C1236T、 G2677T/A 及 C3435T 基因多态性。采用 Hardy-Weinberg 遗传平衡检验进行基因型分布遗传平衡吻合度检验。参照 2013 年 St.Gallen 国际专家乳腺癌分子分型共识。分析乳腺癌患者中 C1236T、 G2677T/A 和 C3435T 基因型分布特点, 并探讨其与分子分型的关系。结果 （1）400 例乳腺癌患者中 C1236T、 G2677T/A 和 C3435T 中分别有 2 例、 3 例和 2 例标本未得出基因分型结果, C1236T 位点 CC、 CT 和 TT 基因型分别占 16.08% （64/398）、 44.22% （176/398） 和 39.70% （158/398）; G2677T/A 位点 GG、 GT、 GA、 TT 和 AT 基因型分别占 16.62% （66/397）、 44.33% （176/ 397）、 7.05% （28/397）、 27.46% （109/397） 和 4.54% （18/397）; C3435T 位点 CC、 CT 和 TT 基因型分别占 21.11% （84/ 398）、 56.03% （223/398） 和 22.86% （91/398）。经 Hardy-Weinberg 遗传平衡检验, 认为 C1236T、 G2677T/A 和 C3435T 基因多态性具有群体代表性 （P > 0.05）。（2） 分子分型显示, 11例人类表皮生长因子受体2 （HER-2, 2+） 患者未行荧光原位杂交 （FISH） 检测予以剔除, 其中Luminal A型占41.90% （163/389）, Luminal B型占32.65% （127/389）, HER-2过表达型占13.62% （53/389）, 三阴型占11.83% （46/389）。（3） C3435T位点CT/TT基因型在Luminal A型患者中的频率高于其在HER-2过表达型和三阴型患者中的频率 （χ2 =12.011, P=0.001; χ2 =13.976, P < 0.001）, C1236T和G2677T/A基因多态性在不同分子分型中的分布差异无统计学意义 （P > 0.05）。结论 MDR1基因C3435T位点多态性可以为乳腺癌异质性提供更合理的补充, 不同乳腺癌分子分型患者中CT/TT基因表型可能对药物治疗更敏感。     

细胞色素 P4503 A4与 P4503 A5及多药耐药基因多态性对氨氯地平降压疗效影响研究

目的：探讨细胞色素 P450（ CYP）3A4倡1G、CYP3A5倡3及多药耐药（MDR1） C1236T、MDR1 G2677T／A和MDR1 C3435T基因多态性对氨氯地平降压疗效的影响。方法纳入159名原发性高血压患者,予氨氯地平5 mg· d－1干预4周,检测相关基因型,分析不同个体CYP3A4、3A5及MDR1相关基因型分布特征,考察不同单核苷酸多态性（ SNP）及MDR1单倍体对氨氯地平降压疗效的影响。结果 CYP3A4倡1G倡1G 基因型舒张压（ DBP）下降幅度显著低于CYP3A4倡1G倡1和CYP3A4倡1倡1（P＜0.05）;CYP3A5倡3倡3基因型DBP下降幅度显著高于CYP3A5倡1倡3和CYP3A5倡1倡1（P＜0.05）;MDR1 C1236T CC、MDR1 G2677T／A AA基因型收缩压（SBP）下降幅度显著高于其他基因型（P＜0.05）;MDR1 C3435T各基因型治疗前后SBP、DBP下降幅度差异均无统计学意义（P＞0.05）。携带MDR1 C3435T CC、MDR1 C3435T CT基因型的患者的DBP下降幅度,女性显著高于男性（ P＜0.05）。对MDR1单倍体分析,各组单倍体治疗前后 SBP、DBP 下降幅度差异均无统计学意义（ P ＞0.05）。结论CYP3A5倡3、CYP3A4倡1G基因多态性可影响氨氯地平降压疗效,MDR1各单倍体未发现与氨氯地平降压疗效相关。     

多药耐药基因单倍体对中国癫痫患者丙戊酸钠血药浓度的影响

目的：探讨多药耐药基因（MDR1）C1236T、C3435T、G26677T/A 3个SNP位点单倍型对中国汉族癫痫患者丙戊酸钠血药浓度的影响。方法：实验选择单药服用丙戊酸钠的汉族癫痫患者143例,根据临床资料分为耐药组（n=68）和控制组（n=75）,应用Pyrosequencing法测定MDR1基因C1236T、C3435T、G26677T/A多态性,同时应用荧光偏振免疫法（FPIA）测定耐药组和控制组患者丙戊酸钠的血药浓度。结果：耐药组C3435T位点CC型发生率（66.18%）高于控制组（26.03%）（P〈0.01）,而CT型发生率（19.12%）则低于控制组（60.27%）（P〈0.05）,耐药组C1236T CT型（23.53%）低于控制组（45.33%）（P〈0.05）;单倍体分析结果表明,丙戊酸钠耐药组单倍型CGC（18.38%）高于控制组（9.33%）（P〈0.05）;单倍型TTT（10.29%）低于控制组（17.33%）（P〈0.05）;血药浓度检测结果表明：CGC型的血药浓度高于控制组,两组资料间血药浓度均值的差别有统计学意义（P〈0.05）。结论：MDR1基因CGC单倍型影响癫痫患者丙戊酸钠血药浓度,可能是引起丙戊酸钠耐药的影响因素。     

肝移植中他克莫司的血药浓度与多药耐药基因多态性的关系

目的探讨肝移植术后患者的多药耐药基因（MDR1）C3435T、G2677T／A和C1236T位点的基因多态性对他克莫司（F1〈506）血药浓度的影响。方法使用荧光偏振免疫分析法（AxSYM）测定42例肝移植患者在术后1周和1个月时FK506的血药浓度,使用等位基因特异扩增法（ASA-PCR）对患者进行MDR1基因分型,比较不同基因型之间FK506的浓度／剂量比的差异。结果在42例患者中,C3435T中CC型16例（38．1％）,CT型23例（54．8％）,TT型3例（7．1％）;G2677T／A中CA;型4例（9．5％）,GT型13例（31．O％）,TT型8例（19．0％）,GA型7例（16．7％）,AT型10例（23．8％）;C1236T中CC型6例（14．3％）,CT型19例（45．2％）,TT型17例（40．5％）。根据移植术后第1周和第1个月的记录,在C1236T中CC型患者的浓度／剂量比小于CT型和TT型,且差异有统计学意义（P〈0．05）。在C3435T和G2677T／A中不同基因型之间的浓度／剂量比的差异无统计学意义（P〉0．05）。结论在肝移植患者中MDR1多态性与FK506血药浓度具有相关性,C1236TCC型患者拟取得相似的血药浓度要比CT型和TT型患者服用更高剂量的FK506。     

等位基因特异扩增法检测移植患者多药耐药基因多态性

目的：建立等位基因特异扩增法（Allele-Specific Amplification，ASA-PCR）研究移植患者多药耐药基因（multi-drugre—sistancegene，MDR1）多态性。方法：用ASA．PCR对177位肝、肾移植患者的MDR1第26外显子C3435T、第21外显子G2677T／A位点和第12外显子C1236T位点进行基因分型。结果：ASA—PCR测定结果与聚合酶链式反应一限制性片断长度多态性方法（Polymerase chain reaction-Restriction Fragment Analysis，PCR-RFLP）的测定结果一致。177例移植患者DNA标本中，C3435T：CC型69例（39.0％），CT型92例（52．0％），TT．型16例（9．0％）；G2677T／A：GG型39例（22．0％），GT型48例（27、1％），TT．型32例（18．1％），GA型30例（16．9％），AT型24例（13．6％），AA型4例（2.3％）；C1236T：CC型23例（13.0％），CT型88例（49．7％），TT型66例（37．3％）。结论：采用ASA—PCR检测移植患者MDR1多态性准确、方便，可为临床个体化用药提供理论依据。     

ABCB1基因多态性对肾移植受者环孢素血浓度的影响

目的:研究肾移植术后患者ABCB1基因多态性对环孢素（CsA）血浓度的影响。方法:采用PCR-RFLP（聚合酶链反应-限制性片段长度多态性）方法对339名服用CsA的肾移植患者进行ABCB1基因1236C>T、2677G>T/A和3435C>T多态性检测,荧光偏振免疫法检测肾移植患者CsA血浓度。结果:在339名肾移植患者中,ABCB1基因1236C>T、2677G>T/A和3435C>T突变等位基因频率分别为64.25%、51.54%和35.75%。ABCB1 1236C>T基因多态性检测显示,在移植术后1年,CC基因型个体的CsA血谷浓度明显高于CT和TT基因型个体（P<0.05）。2677G>T/A基因多态性检测提示,在移植术后7d,杂合子GA+GT基因型携带者的C₀高于GG和AA+TT+AT基因型携带者（P<0.05）。3435C>T基因多态性检测表明:在移植术后3个月,突变纯合子TT基因型携带者的C₀低于CC和CT基因型携带者（P<0.05）。其余各时间点,上述3种基因多态性对CsA血谷浓度无明显影响（P>0.05）。结论:ABCB1基因1236C>T、2677G>T/A和3435C>T多态性对极少数时间点的CsA浓度有影响,但对绝大多数时间点的环孢素浓度无影响。     

MDR1基因多态性和单倍体对肾移植术后稳定期患者他克莫司浓度/剂量比值的影响

目的 探讨MDR1 C1236T、G2677T/A和C3435T 基因多态性和单倍体对中国汉族肾移植术后稳定期患者他克莫司浓度/剂量比值的影响,为他克莫司个体化用药提供依据。方法 采用PCR-基因测序法检测104例肾移植术后稳定期患者MDR1 C1236T、G2677T/A和C3435T 的基因多态性,采用均相酶免疫测定方法(EMIT法)测定他克莫司的谷浓度,比较不同基因型患者之间他克莫司血药浓度/(剂量×体质量)(C/D)比值。结果 104例患者中,MDR1 C1236T、G2677T/A和C3435T突变频率分别为56.73%、55.77%和33.17%。MDR1 C3435T、MDR1 TTT单倍体与他克莫司C/D比值具有相关性(P<0.05)。CYP3A5*3*3患者中,MDR1 TTT单倍体与他克莫司C/D比值仍存在显著相关(P<0.05)。MDR1 C1236T、G2677T/A、CGC单倍体与他克莫司C/D比值无显著性差异(P>0.05)。结论 MDR1 C3435T、MDR1 TTT单倍体与中国汉族肾移植术后稳定期患者他克莫司C/D比值具有显著相关性,是影响肾移植患者他克莫司浓度个体化差异的重要因素。     

多药耐药基因多态性和单倍体对肾移植患者他克莫司血药浓度的影响

目的 研究多药耐药基因(MDR1)单核苷酸多态性及单倍体对中国汉族肾脏移植人群术后稳定期与他克莫司(免疫抑制剂)血药浓度的关系.方法 用基质辅助激光吸收电离子化-飞行时间质谱技术,分析63例肾移植患者的MDR1 exon12 C1236T、exon 21 G2677T/A、exon 26 C3435T的基因型,结合其口服他克莫司12 h后血药浓度,判断两者是否存在关联.结果 MDR1 C3435T基因多态性与他克莫司血药浓度/(剂量×体表面积)具有相关性,比值由小到大顺序:野生型纯合子＜杂合子＜突变型纯合子,差异具有统计学意义(P＜0.05).MDR1 C1236T、G2677T/A及单倍体型各组之间比较均无明显差异.结论 中国汉族肾移植患者稳定期,MDR1 C3435T与他克莫司血药浓度的个体差异具有相关性.     

MDR1 haplotype frequencies in Japanese and Caucasian, and in Japanese patients with colorectal cancer and esophageal cancer

The genotype frequencies of MDR1 T-129C, C1236T, G2677A,T and C3435T SNPs were compared in 154 healthy Japanese and 100 healthy Caucasians to provide basic information on the inter-ethnic differences of pharmacotherapeutic outcome. The variants were found at allelic frequencies of 5.5%, 65.6%, 16.6%, 40.6% and 40.6%, for T-129C, C1236T, G2677A, G2677T and C3435T, respectively, in Japanese, and at 5.1%, 45.9%, 3.6%, 46.4% and 56.6%, respectively, in Caucasians, with a statistically significant difference for C1236T, G2677A,T and C3435T (p<0.001). G2677A was about 5-fold more frequent in Japanese than Caucasians. These genotype frequencies were also investigated in 95 Japanese patients with colorectal cancer (CRC) and esophageal squamous cell carcinoma (ESCC), but no significant difference was detected, when compared with healthy Japanese subjects. The haplotype frequency reached a total of about 85% in Japanese with the following 4 major haplotypes; T(-129)-T1236-T2677-T3435 (36.1%), T(-129)-T1236-G2677-C3435 (22.5%), T(-129)-C1236-G2677-C3435 (14.2%) and T(-129)-C1236-A2677-C3435 (13.3%). The second and fourth haplotypes were hardly inferred in Caucasian, whereas T(-129)-C1236-G2677-T3435 (12.8%) was found to be Caucasian-specific. There was a tendency for higher frequencies of the T(-129)/C-(129)-C1236-A2677-C3435 haplotype in Japanese CRC patients and T(-129)-T1236-T2677-T3435 haplotype in Japanese ESCC patients, compared with that in healthy Japanese subjects.     

Analyses of single nucleotide polymorphisms and haplotype linkage of the humanABCB1 (MDR1) gene in Korean

Single nucleotide polymorphisms (SNPs) in theMDR1 gene that are responsible for drug efflux can cause toxicity. Therefore, this study determined the SNPs of the KoreanMDR1 gene, and analyzed the haplotypes and a linkage disequilibrium (LD) of the SNPs determined. The frequency of 9 SNPs from theMDR1 gene was determined by PCR-RFLP analyses of 100 to 500 healthy individuals. The frequcies of the SNPs were C3435T (47.7%), G2677T (37.6%), G2677A (4.4%), T1236C (21.7%), T129C (8%), A2956G (2.5%), T307C (1.5%), A41aG (9.2%), C145G (0%), and G4030C (0%). Analyses of the haplotype structure and an estimation of the LD of the combined polymorphisms demonstrated that the frequency of the 1236T-2677G-3435T haplotype is much higher in Koreans (14.1%) than in Chinese and western black Africans and the C3435T SNP in Koreans appears to have LD with T129C in Koreans for the first time. These results provide insight into the genetic variation ofMDR1 in Koreans, and demonstrated the possibility of a new LD in this gene.     

MDR1 genotypes do not influence the absorption of a single oral dose of 600 mg valacyclovir in healthy Chinese Han ethnic males

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

• The absorption of valacyclovir presents a highly negative correlation with the level of P-glycoprotein expression.
• It has been confirmed that a polymorphism of the MDR1 gene in exon 26 is related to the level of P-glycoprotein expression in intestine.
• This study was conducted to find the relationship between polymorphism of MDR1 gene and absorption of valacyclovir.

WHAT THIS STUDY ADDS

• Linkage disequilibrium exists between G2677T/A in exon 21 and C3435T in exon 26, between C1236T in exon 12 and C3435T, but not between C1236T and G2677T/A of MDR1 gene in the Chinese Han ethnic population.
• Three single nucleotide polymorphisms of MDR1 gene do not influence the absorption of valacyclovir in the healthy Chinese Han ethnic population.

AIMS

To investigate the influence of three single nucleotide polymorphisms (SNPs) in exon 12 (C1236T), exon 21 (G2677T/A) and exon 26 (C3435T) of MDR1 gene on the absorption of valacyclovir after a single oral administration in the Chinese Han ethnic population.

METHODS

Two hundred healthy Chinese subjects were genotyped for the SNPs of C1236T, G2677T/A and C3435T in the MDR1 gene using allele-specific polymerase chain reaction. Linkage disequilibrium (LD) was analysed. Twenty-four subjects derived from a large random sample (n = 200) received a single oral dose of 600 mg valacyclovir. Plasma concentrations of acyclovir were determined up to 14 h after administration to obtain a pharmacokinetic profile.

RESULTS

LD existed between G2677T/A in exon 21 and C3435T in exon 26 (P < 0.001), between C1236T in exon 12 and C3435T (P < 0.001), but not between C1236T and G2677T/A (P > 0.05). C_max, AUC_{0–1.5 h} and AUC_0–∞ were used as indices of valacyclovir absorption. AUC_0–∞ for the 2677TA genotype was 17.45 ± 2.40 µg × h/ml, which was much higher compared with the 2677GG, GA and TT genotypes of 10.44 ± 1.00, 11.84 ± 2.83, 11.34 ± 2.32 µg × h/ml, respectively (P < 0.05). Similarly, a statistically significant difference of AUC_0–∞ was also observed for different linked genotypes at position 2677 vs. 3435, and 1236 vs. 3435 (P < 0.05). However, there was no significant difference in valacyclovir absorptive pharmacokinetics between carriers and noncarriers of different haplotypes (P > 0.05).

CONCLUSIONS

Three SNPs of MDR1 gene did not influence the absorption of a single oral dose of 600 mg valacyclovir in healthy Chinese Han ethnic subjects.     

MDR1 haplotypes significantly minimize intracellular uptake and transcellular P-gp substrate transport in recombinant LLC-PK1 cells

To date, research on the effect of single nucleotide polymorphisms (SNPs) on P-glycoprotein (P-gp) expression and functionality has rendered inconsistent results. This study systematically evaluates the impact of MDR1 haplotypes (1236/2677, 1236/3435, 2677/3435, 1236/2677/3435) on P-gp functionality compared to individual SNPs (1236, 2677, and 3435) in validated stable recombinant epithelial cells. Recombinant LLC-PK1 cells expressing MDR1wt or its variants were developed and validated for this purpose. Intracellular accumulation and time-dependant efflux of a P-gp substrate, Rhodamine 123 (R123, 5 microM) were evaluated in control and recombinant cells. Additionally, the transepithelial transport of R123 (1 microM) and Vinca alkaloids (5 microM) was evaluated. Except for MDR1(2677T) and MDR1(1236T/2677T/3435T), cells expressing MDR1 variants displayed intermediate R123 intracellular accumulation (1.5-2-fold higher) and lower effluxed R123 (10-20% vs. 52%) compared to those expressing MDR1wt. Efflux ratios across MDR1wt expressing cells were significantly larger for R123 (3.95+/-1.1), Vinblastine (3.75+/-0.26), and Vincristine (2.8+/-0.29). Recombinant cells expressing MDR1 variants displayed 0%-22.7% P-gp activity (approximately 80%-100% efflux loss). Results suggest that MDR1 polymorphisms at the 1236, 2677, and/or 3435 positions significantly minimize P-gp functionality in vitro, the extent of which appears to be substrate dependant.     

MDR1 haplotypes derived from exons 21 and 26 do not affect the steady-state pharmacokinetics of tacrolimus in renal transplant patients

AIM: This retrospective study investigated the influence of MDR1 haplotypes derived from the polymorphisms 2677G > T (exon 21) and 3435C > T (exon 26) on the pharmacokinetics of the immunosuppressant drug tacrolimus in 73 renal transplant patients. METHODS: Based on both variants of SNPs 2677 and 3435, four different haplotypes and eight different genotypes were identified in the study sample. Tacrolimus trough concentrations (C(0)) were compared between different SNP variants and genotypes, as well as between carriers and noncarriers of each haplotype. Additionally, CYP3A5 genotype (6956G > A) was determined. RESULTS: No significant differences were observed between groups. Differences in mean tacrolimus C(0) values between carriers and noncarriers of each haplotype ranged from -0.04 microg/litre (95% confidence interval: -0.53 to 0.60) to -23 microg/litre (-1.07 to 1.53). No association was found between CYP3A5*1/*3 genotype and tacrolimus Co concentractions. CONCLUSION: MDR1 haplotypes derived from the SNPs 2677G > T (exon 21) and 3435C > T (exon 26) do not influence the pharmacokinetics of tacrolimus in renal transplant patients.     

MDR1 haplotypes do not affect the steady-state pharmacokinetics of cyclosporine in renal transplant patients

This retrospective study investigated the impact of MDR1 haplotypes derived from the single-nucleotide polymorphisms (SNPs) 2677G>T (exon 21) and 3435C>T (exon 26) on the pharmacokinetics of cyclosporine in 98 renal transplant patients. Based on SNPs 2677 and 3435, four different haplotypes and nine different genotypes were identified in the study sample. Frequencies of SNPs, genotypes, and haplotypes were in agreement with previously reported values. Cyclosporine pharmacokinetics were characterized using a 2-hour AUC (AUC0-12), trough concentrations (C0), and blood concentrations 2 hours after cyclosporine administration (C2). No significant differences in dose-corrected AUC0-12, C0, or C2 values were observed between carriers of different SNP variants and genotypes (Kruskal-Wallis test), as well as between carriers and noncarriers of each haplotype (Mann-Whitney U test). Carriers of haplotype 12 (2677G and 3435T), which has previously been associated with increased digoxin AUC values, had a median AUC0-12 of 18.9 micro g*h*L-1 (range: 9.0-35.2) compared to 17.5 micro g*h*L-1 (range: 7.5-37.1) in the noncarrier group. It was concluded that MDR1 haplotypes derived from the SNPs 2677G>T (exon 21) and 3435C>T (exon 26) are not associated with cyclosporine pharmacokinetics in renal transplant patients.     

Distinct haplotype profiles and strong linkage disequilibrium at the MDR1 multidrug transporter gene locus in three ethnic Asian populations

The MDR1 multidrug transporter plays a key role in determining drug bioavailability, and differences in drug response exist amongst different ethnic groups. Numerous studies have identified an association between the MDR1 single nucleotide polymorphism (SNP) exon 26 3435C>T and differences in MDR1 function. We performed a haplotype analysis of the MDR1 gene in three major ethnic groups (Chinese, Malays and Indians) by examining 10 intragenic SNPs. Four were polymorphic in all three ethnic groups: one occurring in the non-coding region and three occurring in coding exons. All three coding SNPs (exon 12 1236C>T, exon 21 2677G>T/A and exon 26 3435C>T) were present in high frequency in each ethnic group, and the derived haplotype profiles exhibited distinct differences between the groups. Fewer haplotypes were observed in the Malays (n = 6) compared to the Chinese (n = 10) and Indians (n = 9). Three major haplotypes (> 10% frequency) were observed in the Malays and Chinese; of these, two were observed in the Indians. Strong linkage disequilibrium (LD) was detected between the three SNPs in all three ethnic groups. The strongest LD was present in the Chinese, followed by Indians and Malays, with the corresponding LD blocks estimated to be approximately 80 kb, 60 kb and 40 kb, respectively. These data strongly support the hypothesis that strong LD between the neutral SNP exon 26 3435C>T and a nearby unobserved causal SNP underlies the observed associations between the neutral SNP and MDR1 functional differences. Furthermore, strong LD between exon 26 3435T and different unobserved causal SNPs in different study populations may provide a plausible explanation for conflicting reports associating the same exon 26 3435T allele with different MDR1 functional changes.     

P-glycoprotein polymorphism and levothyroxine bioavailability in hypothyroid patients

Objectives

P-glycoprotein (P-gp) contributes to the disposition of a wide variety of drugs; therefore, single nucleotide polymorphisms (SNPs) in the P-gp coding gene might affect its activity. It is well known that personalized medicine, instead of empirical treatment, is a clinically important approach for enhancing responses among patients. Indeed, there is a need to evaluate the association between SNPs of P-gp encoded multidrug resistance genes (MDR1, ABCB1), and the dosage requirements of these drugs. In the present study, we evaluated the association between the dosage of Levothyroxine (L-T4) and three common SNPs (C1236T, G2677T/A and C3435T).

Digoxin pharmacokinetics and MDR1 genetic polymorphisms

BACKGROUND: The effect of MDR1 C3435T single nucleotide polymorphism (SNP) in exon 26 on digoxin pharmacokinetics has recently been challenged. OBJECTIVE. To clarify the relationships between MDR1 genetic polymorphisms in exon 26 (C3435T) and 21 (G2677T/A) and digoxin pharmacokinetics. MATERIALS AND METHODS: MDR1 genotypes for C3435T and G2677T/A SNPs were determined in 32 healthy subjects whose single oral dose digoxin pharmacokinetics had been measured over 48 h. RESULTS: A significant relationship was observed between C3435T SNP and digoxin AUCs ( p<0,05). Homozygous TT subjects had 20% higher digoxin plasma concentrations than CT and CC subjects and a trend for higher 48 h digoxin urinary recoveries (TT>CT>CC). Similar results, although not statistically significant, were observed from the MDR1 G2677T/A SNP. CONCLUSIONS: Our results confirm that the MDR1 C3435T single nucleotide polymorphism (SNP) significantly affects digoxin disposition kinetics, with homozygous TT subjects presenting the highest plasma concentrations.